Article

Bark‐stripping by Grey squirrels (Sciurus carolinensis)

Wiley
Journal of Zoology
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Abstract

To investigate why Grey squirrels strip bark from young trees, squirrel populations and tree quality were studied at 30 English Midland woods. In young beech and sycamore woodlands, the area of bark which Grey squirrels stripped from each tree was strongly related to the phloem width (volume per unit area) of the tree, and not to the phloem sugar content. Variation in bark-stripping between woods was strongly related to average phloem widths in each plantation. The extent of bark-stripping also correlated with juvenile squirrel density, but only in years with relatively little squirrel breeding. There was a tendency for damage to recur in previously damaged areas, in a pattern suggesting that squirrels had learned the habit. The results indicate that bark-stripping can be initiated by young squirrels, perhaps through agonistic gnawing or exploratory feeding, or by older squirrels which have learned the habit, but that severe damage occurs only where the tree phloem is suitable.

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... There is some evidence that damage is more likely on dominant canopy trees and trees on edges of stands, as opposed to suppressed trees. This may be related to those trees being more actively growing, and trees with thicker phloems are more vulnerable (Gill, 1992b;Kenward and Parish, 1986). In a study of naturally regenerating oak in England, Mayle et al. (2009) found that dominant trees, and those greater than 7.5 cm DBH were at greater risk, and found damage tended to occur higher up (concentrated about 4 m high). ...
... The question as to why grey squirrels strip bark has been asked for some time and numerous hypotheses have been posed (Gill, 1992b;Kenward, 1981;Kenward and Parish, 1986). This question has a practical motivation as this knowledge may help in mitigation strategies (Kenward, 1981). ...
... It does not appear to be an issue in their native Nearctic range (Huxley, 2003;Nichols et al., 2016). Hypotheses around food shortages, water access, trace nutrient content, sugar content and territorial or agonistic behaviour have been discussed and in many cases there are reasons to doubt these explanations (Kenward and Parish, 1986). Squirrels do appear to select areas/trees with high phloem volume, and this increases the sugar intake per unit area stripped (despite thicker phloems tending to have lower sugar concentration). ...
Technical Report
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We conducted a systematic literature review as part of a Forestry Commission (FC) contract to provide good practice technical guidance to manage impacts of mammals on trees, woods, establishing woodlands and treescapes. The review examined both the positive and negative impacts of mammals and existing tree protection options and best practice. Using the PRISMA (‘Preferred Reporting Items for Systematic reviews and Meta-Analyses’) framework (Page et al., 2021), we systematically searched for relevant scientific, peer-reviewed literature. We also conducted targeted organisational searches for grey literature relevant to the objectives within an English context. We then implemented a thematic tagging process to facilitate the synthesis of findings across both types of literature, whilst building a categorised resource bank. Following exclusions, we identified and tagged 281 scientific literature sources and 218 grey literature sources. We identified eight key species or functional groups of mammals (beavers; small mammals; grey squirrels; lagomorphs; pigs and wild boar; deer; livestock including feral sheep and goats and bison; and horses and ponies) that have distinct tree protection approaches available, relating to their ecology, behaviour, type of damage caused and legal restrictions. We also developed a novel ecological framework to categorise tree protection methods according to their strategy of intervention within mammal-tree interactions and applied it to each species/functional group. Finally, we provide an extensive synthesis of the literature for each species or group, detailing literature relating to ecosystem services, damage to trees, identification of that damage, and resultant protection methods identified. This document thus provides a foundation for developing the practitioner-focussed technical guidance.
... Most authors have assumed that "bark" is a fall-back, low-quality and yearly constant resource to which primates turn to during periods of food scarcity. Almost no author mentioned the possibility that the soft inner bark of trees (particularly of pines) in plantations may constitute a seasonally profitable energy source for non-human primates (but see de Carvalho, 2007;Kenward and Parish, 1986 makes a similar argument for squirrel bark consumption). I will here argue that this may be the case. ...
... Pines planted in subtropical regions have been selected for rapid growth and may have being indirectly selected for having a particularly thick layer of phloem rich in carbohydrates. Primates having access to plantations in seasonal environments may be making use of this hyper-abundant resource, especially during the tree growing season, a hypothesis that has been proposed for and tested in other mammal groups (Kenward and Parish, 1986;Gill 1992a, b;Saint-Andrieux et al., 2009), but that has been neglected in primates, with the exception of humans (Gottesfeld, 1992;Zackrisson et al., 2000). ...
... The phloem of trees may show seasonal variation in its quality (i.e., sugar concentration) and quantity (i.e., width of phloem layer), which in temperate zones increase during the spring months (Kenward and Parish, 1986;Ziegltrum, 2004;Saint-Andrieux et al., 2009). In subtropical regions of the southern hemisphere pines may also go through a seasonal pattern of growth and higher cambium activity during the late winter and spring months (August -December), particularly North American species such as Pinus taeda (Hugo Reis pers. ...
Article
Primates bark-strip trees in forest plantations worldwide, producing large economic losses. The primate and tree species involved, the spatial and temporal patterns of this problem, the effectiveness of the methods used to mitigate damage and the causes of this behavior are not yet understood. I conducted a literature review of this topic, focusing on documents reporting primates bark-stripping trees in forest plantations and forests. The data set consisted of 51 documents of which 46 corresponded to bark-stripping of trees in forest plantations and five in managed forests. Thirteen non-human primate species have been recorded bark stripping trees of commercial value worldwide. Three of these, the chacma baboon (Papio ursinus), the black capuchin monkey (Sapajus ni-gritus) and Sykeśs monkey (Cercopithecus albogularis), are responsible for most of the damage reported in large scale plantations, affecting mostly pine (Pinus sp.) plantations in five African and two South American countries. With fewer reports, orangutans (Pongo pygmaeus) affect large scale Acacia mangium plantations in Indonesia, and yellow baboons (Papio cynocephalus) and vervets (Chlorocebus aethiops) pine plantations in Malawi and Zimbabwe respectively. The Barbary macaque (Macaca sylvanus) bark-strips Atlas cedars (Cedrus atlantica) in Moroccan forests. Eucalyptus sp. plantations, both small and large-scale, are less frequently affected by gorillas, two colobine monkeys, howler monkeys, capuchins, baboons and chimpanzees. Actions to mitigate this problem, including the massive killing of primates, had proven ineffective in the long term. Bark-stripping of pines tends to be more seasonal than that of Eucalyptus, and their damage of higher incidence and intensity. The most frequently cited hypothesis for why primates bark-strip trees in plantations is that they consume soft bark when or where their natural food is scarce. However, this hypothesis is not generally supported by empirical evidence. Eucalyptus bark may be sought after for its high sodium content. Pines are apparently bark-stripped to consume the sugary phloem during their growing season, when bark is presumably more easily peeled off. If this hypothesis were correct, a management method based on diversionary feeding could alleviate the damage produced by primates to coniferous trees of commercial value.
... Research is ongoing into the possibility of using the pine marten, Martes martes -a natural predator, as a biocontrol agent, after a grey squirrel population crash in Ireland was found to be linked to pine marten abundance (Sheehy and Lawton, 2014). In the meantime the recommended method of controlling grey squirrel damage by the Forestry Commission requires the prediction of the level of severity likely to be incurred, followed by targeted killing of grey squirrels to remove the threat in these high risk years Kenward and Parish, 1986;Mayle et al., 2007). To date, the most effective way of reducing squirrel populations, and therefore the level of damage, has been to use the anticoagulant poison warfarin (Gurnell and Pepper, 1998;Kenward et al., , 1988Pepper, 1996). ...
... At this time trees are reactivating after winter dormancy, and it is these actively growing trees that suffer the most damage (Kenward, 1982;Rowe and Gill, 1985) in addition to those that are dominant (Mayle et al., 2009). Trees with reduced competition, such as those on the edge of stands or trees remaining after thinning also have increased likelihood of damage due to active, and rapid vigorous growth (Kenward, 1983;Kenward and Parish, 1986;MacKinnon, 1976;Rowe and Gill, 1985). Increased sap volume corresponds with an increased phloem width, a factor which directly correlates with damage (Kenward, 1982;Kenward et al., 1988). ...
... Phloem vessels are the tree's sugar transport system, and it has been suggested that the root cause of squirrel damage is a fondness of sugar (Shorten, 1954). Kenward and Parish (1986) however found that damage was not correlated with phloem sugar concentration. Although they admit that whilst sugar concentration per se was not being selected for, those preferred trees with increased phloem volume, would provide the greatest weight of sugar per unit area of phloem ingested. ...
Article
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Grey squirrels, Sciurus carolinensis, damage trees in the UK by stripping bark and eating the underlying phloem; squirrel motivation for damage is, however, unknown. Damage can result in deterioration of timber quality and a significant economic toll on the forestry industry. Prediction of severe damage followed by targeted killing of squirrels is the current recommended management option. However, the use of warfarin (an anticoagulant poison) is now restricted in the UK and other more humane methods of killing are labour-intensive, so an alternative solution is needed. A better understanding of what motivates grey squirrels to strip bark may enable a preventive approach to be developed. Whilst the bark stripping literature has explored predictive factors affecting the likelihood of damage, causal understanding is lacking. The aim of this review is to introduce the Calcium Hypothesis as a possible explanation for bark stripping, with a view to informing the prevention of damage. The Calcium Hypothesis states that grey squirrels damage trees to ameliorate a calcium deficiency. The main predictive factors of bark stripping behaviour each inform and lend support to the Calcium Hypothesis. Calcium is stored in tree phloem, and damage increases with phloem width, providing squirrels with more calcium per unit area ingested. Calcium levels increase in trees as active growth resumes after winter dormancy, this occurs immediately prior to the main bark stripping season of May–July, and trees growing most vigorously are at increased risk of damage. It is likely grey squirrels also have a requirement for calcium during the bark stripping season. Adult females will be under post-parturition pressures such as lactation, and juveniles will be going through their main period of bone growth, both of which likely represent a requirement for calcium – which supports an observed positive correlation between juvenile abundance and bark stripping. A high autumnal seed crop increases juvenile recruitment the following spring, and could also induce a requirement for calcium to a population due to the high phosphorus to calcium ratio of seeds. To further investigate the hypothesis, the extent to which grey squirrels can utilise calcium oxalate, as calcium occurs in bark, should be determined, and also the extent to which grey squirrels undergo seasonal periods of calcium deficiency. Increasing our causal understanding of bark stripping could inform the future development of preventive measures to aid forest management.
... Squirrels eat the phloem tissue, which is especially voluminous during the main damage period, in June- July. The extent of fresh damage, which can be severe enough to kill most of the young trees at a site, depends mainly on the average phloem volume at the time (Kenward 1983; Kenward & Parish 1986). However, bark-stripping is also most likely to start when squirrel density is high, especially the density of spring young (Kenward & Parish 1986), probably because there are then many agonistic encounters to trigger gnawing behaviour (Taylor 1966Taylor , 1969). ...
... The extent of fresh damage, which can be severe enough to kill most of the young trees at a site, depends mainly on the average phloem volume at the time (Kenward 1983; Kenward & Parish 1986). However, bark-stripping is also most likely to start when squirrel density is high, especially the density of spring young (Kenward & Parish 1986), probably because there are then many agonistic encounters to trigger gnawing behaviour (Taylor 1966Taylor , 1969). Once triggered, damage tends to be repeated the next year, in a pattern which suggests that squirrels have learned the habit (Kenward et al. 1988). ...
... The density data from the 30 squirrel-survey sites (Table 1) indicate why. At the same sites, the strongest relationship between damage and squirrel density was also a logistic relationship, such that damage was always at level 2 or above when there were more than 0.35 young squirrels per hectare (Kenward & Parish 1986, Kenward et al. 1988). Areas with a similar density of non-juvenile squirrels can produce this many young squirrels in years with good seed crops, which are likely to occur at least once in nearby seeding trees during the vulnerable 20-30 years of a beech or sycamore crop. ...
Chapter
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The introduced North American grey squirrel causes problems for foresters by stripping bark from young trees, and for wildlife conservation by displacing the native British red squirrel. Trapping surveys at 30 damage-prone beech and sycamore sites showed that squirrel density was highest where tree diversity was greatest. Surveys of damage accumulated over five to nine years at 53 sites showed that bark-stripping increased with the number of seed-bearing tree species near the vulnerable crop, confirming that vulnerable trees should not be planted close to mature seed-bearing trees, or with a nurse crop of those conifer species which may provide food for squirrels in winter. Young sycamores were more prone to damage than beech, especially in plantations and where pheasants were fed in winter, but damage was reduced where there was a high percentage of ground cover and where Warfarin was used to kill squirrels. Conceptual models are presented to show how factors interact to increase the risk of bark-stripping, and of red squirrel replacement by grey squirrels through the presence of oaks in tree mixtures. Further work is needed (i) to determine how small or isolated plantations should be to minimise risk of damage (ii) to define why damage reduction is associated with extensive ground cover, (iii) to discover whether tree growth can be managed economically to reduce damage, and (iv) whether the species content of woodland can be managed to ensure the survival of red squirrels in mainland Britain.
... Population expansion and negative ecosystem effects, however, have characterized the grey squirrel introduction events in Ireland, the United Kingdom, Italy, and western areas of North America. In these regions grey squirrels have been implicated in the decline of native squirrel species and damage to forestry crops (Bertolino et al. 2014;Gurnell et al. 2004b;Kenward and Parish 1986;O'Teangana et al. 2000;Wauters et al. 2000). ...
... Annual recapture = (winter 2012(p)) 2 9 (summer 2012(p)) 5 9 (winter 2013(p)) 3 . The SE of the annual recapture estimate could not be calculated using the delta method Frontier population dynamics of an invasive squirrel species 1189 Wauters et al. (2000), e Kenward (1985), Kenward and Parish (1986), Kenward and Tonkin (1986), Fitzgibbon (1993), Kenward and Holm (1993), Gurnell (1996), , f Kyle (2009), g , , Lurz and Lloyd (2000), Bryce et al. (2001), Gurnell et al. (2004a), h Gurnell et al. (2001), i Wauters et al. (2002), j Robinson and Cowan (1954), k Hwang and Lariviére (2006), l Hibbard (1935), Longley (1963, Nixon et al. (1967), Mosby (1969), Nixon and McClain (1969), Barkalow Jr et al. (Barkalow et al. 1970), Doebel and McGinnes (1974), Montgomery et al. (1975), Nixon et al. (1975), Bouffard and Hein (1978), Thompson (1978), Nixon et al. (1980), Brown and Batzli (1985), Gorman and Roland (1989), Fischer and Holler (1991), Koprowski (1991), Tounzen et al. (2012), m Fischer and Holler (1991), Healy and Welsh (1992), n Fischer and Holler (1991) (October-March) higher than summer survival (April-September). This result is in contrast to values found for seasonal adult red squirrel survival by Wauters et al. (2008) who found summer survival rates to be C winter survival rates in Italian alpine forest. ...
... Taken together and separately, these demographic parameters each help to partly explain why the significant ecological and economic costs, such as disease transmission, rapid red squirrel decline, and bark stripping damage, inflicted by grey squirrels are higher in Britain (e.g. Kenward and Parish 1986;Gurnell et al. 2004b;Sainsbury et al. 2008) than in other regions of the invasion. Differences in demography between regions are clues that point to variability in the suitability or invasibility of each region or the invading population. ...
Article
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Several squirrel species are biological invaders and their establishment in an area is often marked by ecological and economic costs to native species and forest crops. The eastern grey squirrel (Sciurus carolinensis Gmelin 1788) has been intentionally introduced multiple times outside of its native range but its success in establishing and spreading has not been consistent. An intensive live-trapping programme was designed to investigate the demography and population dynamics of populations of this species on the invasion frontier in the Republic of Ireland, a region marked by the slow but steady invasion of the grey squirrel. Low densities and high breeding rates distinguished these frontier populations. These results were placed in context with other frontier and established grey squirrel populations throughout their introduced and native ranges. As expected, variations in invasion speed and impact severity between regions were reflected in population demography. The highest densities, survival rates and breeding rates were recorded in Britain where the grey squirrel invasion has been most damaging. Careful comparative demographic study of invading populations could improve management outcomes, indicate differential invasibility of invaded communities, and offer clues to enhance the design of conservation reintroduction projects.
... Traps were at a density of 2 ha 71 , spaced at intervals of approximately 80 m either on rough grids of 17±35 traps or, on Furzey Island, with 13 traps at regular intervals through the elongated woodland. Legg door-push traps were used to catch several grey squirrels at a time ( Rowe, 1980), whereas a treadle-operated door-fall design by the Irish Wildlife Service was suitable for single captures of red squirrels ( Tonkin, 1984;Kenward & Parish, 1986;Holm, 1990). Traps for grey squirrels were laid on the ground in southern sites, at the base of trees that showed signs of squirrel feeding or that were likely to be used as squirrel travel routes, and those for red squirrels were hung on such trees at chest height. ...
... However, for comparability with previous reviews, data are also given on peak squirrel densities that include juveniles. In this case, densities of non-juvenile squirrels were estimated by doubling the female densities, (i) because sex ratios approximated 1:1 in areas trapped completely ( Kenward & Parish, 1986;Holm, 1990), and (ii) because females have smaller, more stable ranges than males ( Kenward, 1985;Holm, 1990). When trap grids did not ®ll a wood, squirrel densities were estimated by assuming that the area trapped extended 100 m beyond the edge of the grid, because this was the average homerange radius of female grey squirrels ( Kenward & Parish, 1986). ...
... In this case, densities of non-juvenile squirrels were estimated by doubling the female densities, (i) because sex ratios approximated 1:1 in areas trapped completely ( Kenward & Parish, 1986;Holm, 1990), and (ii) because females have smaller, more stable ranges than males ( Kenward, 1985;Holm, 1990). When trap grids did not ®ll a wood, squirrel densities were estimated by assuming that the area trapped extended 100 m beyond the edge of the grid, because this was the average homerange radius of female grey squirrels ( Kenward & Parish, 1986). An edge-correction was required for red squirrels only at the 2 conifer sites trapped for single years. ...
Article
The demography of red and grey squirrels was studied by live-trapping and radio-tagging at 14 deciduous and conifer sites in southern Britain and at eight conifer sites for one year in northern England. Densities and productivity correlated with tree seed crops for both squirrel species in deciduous and conifer habitats. Productivity was reduced by high density of full-grown squirrels relative to seed abundance. In oak-hazel woods, demography of grey squirrels correlated with abundance of acorns but not of hazel-nuts, whereas density and productivity of red squirrels correlated with hazel-nut abundance. Correlations of female density and productivity with pine-cone crops did not differ between red and grey squirrels. Predators ate many radio-tagged grey squirrels in conifers, and annual survival was only 50% compared with 80-82% for both species in other habitats. Grey squirrel populations in southern conifer sites were sustained by immigration, and at northern sites female density correlated with oak abundance within 500m. Failure to exploit acorn crops puts red squirrels at a competitive disadvantage in deciduous woodland. Red squirrels had higher survival than grey squirrels in conifers, which may give them an advantage in that habitat, but could also have been explained by a lack of predators on their island study site.
... 23 Damage and death of hardwood trees caused by EGS, through bark stripping and gnawing, is a result of territorial marking or agonistic gnawing behavior in concert with higher densities. 9,13 Due to the presence of EGS in urban settings, lethal control measures are not always acceptable. ...
... 10 Functionally breeding males are usually found almost yearround. 9 In general, testicular recrudescence occurs from August to October, lasting approximately 2 mo per individual. After this, spermatogenesis occurs as early as December. ...
... 20 GonaCon use in males may help reduce or alleviate territorial marking and bark stripping, which seems to be a learned behavior in EGS males. 9 However, male-based contraception is an inadequate management strategy in most cases. Therefore, both male and female squirrels should be treated for population control. ...
Article
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Eastern gray squirrels (EGS) (Sciurus carolinensis) damage trees through bark stripping or gnawing due to territorial marking or agonistic gnawing behavior in concert with higher densities. This study was conducted to determine the effects of a contraceptive vaccine on EGS and its reproductive organ histology. Free-ranging urban EGS were vaccinated with the immunocontraceptive GonaCon. All EGS were > or = 6 mo of age as determined by a combination of pelage characteristics and body weights. The vaccine was administered by injection at a dosage rate of 0.4 ml containing 400 microg of GnRH-mollusk protein conjugate i.m. in the thigh to 33 EGS (17 male [m], 16 female [f]) in trapping session 1 (TS1), 23 (14 m, 9 f) in trapping session 2 (TS2), and 11 (8 m, 3 f) in trapping session 3 (TS3). A sham injection containing 0.4 ml saline-AdjuVac was given as control to 22 EGS (16 m, 6 f) in TS1, 20 (12 m, 8 f) in TS2, and 8 (4 m, 4 f) in TS3. In the last trapping session (TS4), 35 EGS (16 treated, 19 control) were killed for necropsy to evaluate histologic changes in testes and ovaries. Treated EGS males had testicular, prostatic, and epididymal atrophy compared with control EGS males. The tubuli seminiferi and prostatic glandular lumen of treated EGS males were atrophic, and the epididymal lumen contained no sperm cells. No histologic changes were observed in treated EGS females; however, females likely were not collected when changes due to GonaCon would have been observed. There were no observable histologic differences in the pituitary gland of treated and control EGS. There were no statistically significant differences in either testosterone or progesterone concentrations between control and treated EGS. Although there were no serious side effects to the vaccine, six EGS developed injection site abscesses. GonaCon may be a potential tool for EGS population control.
... El descortezamiento de los árboles es otro daño importante ocasionado por las ardillas, tanto en zonas urbanas como en plantaciones (Genovesi, 1997;Gurnell, 1989;Irving y Beer, 1963;Kenward y Parish, 1986;Manski, et al., 1981), además promueve infecciones de hongos o insectos (Kenward, 1989), disminuyendo la producción de los árboles y causando pérdidas económicas. Es interesante mencionar, que sólo un poco más de la quinta parte de los árboles con daño en los Viveros ha sido afectada por las ardillas. ...
... En Inglaterra, por ejemplo, el descortezamiento ocasionado por las ardillas ocurre principalmente a mediados del verano, siendo las especies más vulnerables el sicomoro (Acer pseudoplatanatus), las hayas (Fagus sylvatica) y los encinos (Quercus spp. -Kenward y Parish, 1986). ...
Article
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Resumen: La ardilla roja mexicana (Sciurus aureogaster), aunque es una especie nativa del centro de México, fue introducida en los Viveros de Coyoacán a mediados del siglo XX y desde entonces ha ido habituándose a la presencia humana. En este trabajo estimamos la densidad poblacional de ardillas grises en los Viveros de Coyoacán, describimos sus patrones de actividad a lo largo de un año y cuantificamos los daños que producen en los árboles del parque. Para estimar la densidad poblacional, se realizaron conteos visuales por transecto lineal y por cuadrantes. Los patrones de actividad fueron evaluados en los transectos lineales. El daño fue evaluado según la causa y la especie de árbol, en 12 parcelas de 400 m², y 13 puntos sobre un trayecto escogido al azar. Encontramos densidades poblacionales relativamente altas, en promedio de 5.9 a 6.5 inds./ha según los métodos de transecto y por cuadrantes, respectivamente. Con estos datos, estimamos entre 254 y 270 ardillas en todo el parque. Presentan dos picos de actividad, uno al amanecer y otro antes del anochecer. Poco más de la mitad (52%) de los árboles muestreados (346) presentaron algún tipo de daño; de éstos el 80 % fueron dañados por vandalismo y por poda, y el 20% restante por ardillas. Estos resultados revelan que es importante que se realicen campañas para no suplementar alimento a las ardillas y/o a otras especies y que exista un programa de capacitación para realizar una correcta poda de los árboles y con ello evitar daños mayores. Palabras clave: Ardillas, densidad poblacional, patrones de actividad, Viveros de Coyoacán, Distrito Federal.Abstract: The Mexican red squirrel (Sciurus aureogaster), but is a species native to central Mexico, was introduced in the Viveros de Coyoacan mid twentieth century and has since been habituated to human presence. In this paper we estimate the density of gray squirrels in the Viveros de Coyoacan, we describe patterns of activity over a year and quantify the damage occurring in the park trees. To estimate population density, visual counts were performed by transect and quadrant. Activity patterns were evaluated in the transects. The damage was assessed according to the cause and the tree species in 12 plots of 400 m² and 13 points on a path chosen at random. We found relatively high population densities, an average of 5.9 to 6.5 inds. / ha according to the methods of transect and quadrant, respectively. With these data, we estimate between 254 and 270 squirrels in the park. They have two activity peaks, one in the morning and one before sunset. Just over half (52%) of trees sampled (346) had some type of damage and of these 80% were damaged by vandalism and pruning, and the remaining 20% by squirrels. These results show that it is important that campaigns be conducted to avoid the squirrels food supplement and / or other species and that a training program to make a proper pruning of trees and thus prevent further damage.Key words: Squirrel, population density, activity patterns, Viveros de Coyoacan, Distrito Federal.
... In other Sciurus vulgaris preserved areas, the gray squirrel has been actively fought to prevent its establishment. However, the red squirrel population decline is still relevant today despite ongoing control efforts made since the 1950s by the British government, especially in northern England (Kenward & Parish 1986, Gurnell & Lurz 1997, Lurz et al. 1998, Bruemmer et al. 2000, Mayle et al. 2007, Signorile & Evans 2007. The gray squirrel has spread to almost all of England and Wales where its estimated population reaches 2.5 millions of individuals (Harris et al. 1995). ...
... Of course, even if squirrels eat some of the inner bark when soft (Mayle, 2004). Meanwhile, damage levels increase with the density of gray squirrels, especially with large numbers of juveniles entering the population in summer (Kenward 1983, Kenward & Parish 1986, Forestry Commission 2012. If numerous, the squirrels also have more contacts among themselves, including agonistic behaviours. ...
... The map was created with six categories, digitized as (1) two blocks of mature deciduous woodland (dominated by oak Quercus robur) totaling 27.9 ha, (2) a 1.5 ha patch of mature larch (Larix decidua), (3) a 6.3 ha plantation of young beech (Fagus sylvatica), (4) a 4.0 ha Thuja plantation and (5) surrounding fields of wheat extending for more than 75 ha. The squirrels fed mainly on acorns in autumn and winter, with tree flowers and larch cones taken in spring, and also ate ripening wheat outside the 40 ha of woodland while being tracked [48]. ...
... Results were significant for map categories that were known from independent observations to contain important resources for each species. Squirrels require woodland for seeds and nests [47,55], although gray squirrels also take foods such as wheat in summer [48]. RADA showed dependence of red squirrel range size on mature woodland (Fig 3) and more strongly significant relationships between gray squirrel ranges and wheat (Fig 4) than in either of two previous analyses that used the same data set to examine habitat preferences [22,25]. ...
Article
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An animal’s home-range can be expected to encompass the resources it requires for surviving or reproducing. Thus, animals inhabiting a heterogeneous landscape, where resource patches vary in size, shape and distribution, will naturally have home-ranges of varied sizes, so that each home-range encompasses a minimum required amount of a resource. Home-range size can be estimated from telemetry data, and often key resources, or proxies for them such as the areas of important habitat types, can be mapped. We propose a new method, Resource-Area-Dependence Analysis (RADA), which uses a sample of tracked animals and a categorical map to i) infer in which map categories important resources are accessible, ii) within which home range cores they are found, and iii) estimate the mean minimum areas of these map categories required for such resource provision. We provide three examples of applying RADA to datasets of radio-tracked animals from southern England: 15 red squirrels Sciurus vulgaris, 17 gray squirrels S. carolinensis and 114 common buzzards Buteo buteo. The analyses showed that each red squirrel required a mean (95% CL) of 0.48 ha (0.24–-0.97) of pine wood within the outermost home-range, each gray squirrel needed 0.34 ha (0.11–1.12) ha of mature deciduous woodland and 0.035–0.046 ha of wheat, also within the outermost home-range, while each buzzard required 0.54 ha (0.35–0.82) of rough ground close to the home-range center and 14 ha (11–17) of meadow within an intermediate core, with 52% of them also relying on 0.41 ha (0.29–0.59) of suburban land near the home-range center. RADA thus provides a useful tool to infer key animal resource requirements during studies of animal movement and habitat use.
... Concerning rodents, bark portions are often removed when other more preferred food resources are not available, e.g. during snow cover or during the warm season, as well as to reach the phloem sap, rich in sugary components Parish 1986, Baxter andHansson 2001). In the latter case, debarking is markedly exerted during the spring, when the sap flow increases in deciduous plants (Kenward and Parish 1986). The reasons for bark-stripping behaviors are not always clear and a number of explanations have been proposed (e.g. ...
... In autumn and winter, consistently, fruit consumption was lower than in the rest of the year (Bertolino et al. 2004). By contrast, other species have been frequently used during spring when the sap flow is greatest; in these cases, the portions of removed bark were conspicuous and many scraps were found on the ground, in analogy with the behavior of gray and red-bellied squirrels (Kuo et al. 1982, Kenward andParish 1986). ...
Article
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The Finlayson's squirrel Callosciurus finlaysonii was introduced into Italy during the 1980s and has established two viable populations. The diet of this species includes a high proportion of tree barks, suggesting an intensive debarking behavior. We reported a severe bark-stripping impact in both colonized areas, and we tested whether a preference for some tree species existed. Results of this work showed the presence of a wide spectrum of damaged species, without any strong preference, mainly with large wounds. Old deciduous plants and conifers, which presented a hard bark, were usually avoided.
... Most commonly attacked trees in the UK are beech ( Fagus sylvatica L.) and sycamore ( Acer pseudoplatanus L.), and to a lesser extent oak ( Quercus spp.), ash ( Fraxinus excelsior L.), maple ( Acer spp.), sweet chestnut ( Castanea sativa Mill.), birch ( Betula spp.) and hornbeam ( Carpinus betulus L.) ( Rowe and Gill, 1985 ). Damage by grey squirrels is reported on conifers, too, although it is defi nitely less common. The size and position of the wound are extremely variable and depend on the age and species of the tree ( Kenward and Parish, 1986 ). The fi rst mention of damage by grey squirrels in Italy dates back to 1984, when Currado et al. (1987) reported damage in Stupinigi Park on a poplar ( Populus × euroamericana ) plantation and on a few young hornbeams ( C. betulus ) damaged in 1983. ...
... L. Signorile personal observation) and by the comparison with bark stripping in England, where damage in plantations is patchy even in uniform stands, and the number of mature seed-bearing tree species with in 200 m from each plantation is also important ( Kenward et al. , 1996 ). Bark stripping is strongly correlated with phloem volume per unit of area ( Kenward and Parish, 1986 ). The bias observed in poplar plantations, therefore, could be a consequence of a larger phloem width in trees close to the streams, but young trees growing close to the hedgerow may suffer from competition and shading stress. ...
... The peak summer densities of red squirrels in oak-hazel woods on the Isle of Wight, and of grey squirrels in similar woods in Dorset and Hampshire. Squirrel densities were from trapping(Holm, unpublished;Kenward & Parish, 1986) ...
... The peak summer densities of red squirrels in Scots pine woodland on Furzey Island, and of grey squirrels in similar woodland in Wareham Forest, 12 km to the west, in relation to cone crops. Squirrel densities were from trapping (Holm, unpublished;Kenward & Parish, 1986). Fallen cones from the previous crop, either whole or cores stripped by squirrels, were counted in 0.25 m quadrats under the closed canopy at each site ...
Article
The geographic range of red squirrels contracted sharply in Britain during the 1940s arid 1950s, as increasingly large areas were colonized by the congeneric North American grey squirrel. Red squirrels remain common only on offshore islands, and in the large conifer forests of northern England and Scotland. The initial replacement of red squirrels was in arras dominated by oak woodland, probably because acorn crops are exploited less efficiently by red squirrels than by grey squirrels. Dirt studies have shown that acorns are digested less efficiently by the red squirrel, which occurs in conifers through most of its Eurasian range, than by the introduced grey squirrel, which is primarily a native of deciduous woodland. The red squirrel will probably be replaced in deciduous and mixed woodland throughout mainland Britain, and may eventually persist only in large areas of conifers which arc far from oak trees. The conservation of red squirrels on islands is therefore particularly important for their survival, perhaps making it worthwhile to create new island populations where they do not at present exist.
... It is more common for Grey Squirrels Sciurus carolinensis, than Red Squirrels Sciurus vulgaris, to be reported for causing damage to trees to in Britain. At least 10 hypotheses have been proposed to explain why squirrels bark strip (Kenward, 1983;Kenward &Parish, 1986). Two of the more probable causes of bark stripping behaviour are: (i) limited food availability leading to exploratory bark stripping that is reinforced by a liking for the sugary sap or, (ii) social pressures inducing bark stripping as a displacement activity. ...
... Social pressures may trigger agonistic interactions as a result of either the dispersal of young, or due to the effects of overcrowding. There is evidence in favour of both these suggestions (Davidson & Adams, 1973;Kenward, 1982;Mercer, 1984;Kenward & Parish, 1986). A positive correlation between squirrel numbers and the extent of damage would be expected for both hypotheses. ...
Article
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The relation between population density and the extent of damage incurred by bark stripping behaviour was investigated in a Scots Pine plantation known to have suffered considerable damage. Population density was estimated by three non-interventionist methods that could potentially be applied elsewhere: line surveys, drey counts and cone counts. The different methods of estimating the population size proved to be consistent and produced an unusually high value of four Red Squirrels per hectare. Within the study area, fresh damage was related to local population densities.
... At Magod squirrels consumed only the ripe fruit pulp and seeds of Vitex altissima (Verbenaceae) and avoided its bark, leaves and flowers which contain the flavonoid vitexin (Rao, 1965). Squirrels did not eat the seeds of Olea dioica (Oleaceae) which are intensely bitter (Kirtikar & Basu, 1935). The wood of Terminalia paniculata (Combretaceae) is reported to contain ellagic acid-3,3'dimethyl ether, the corresponding glucoside and flavellagic acid-3,3',4-trimethyl ether (Lowry, 1968) and squirrels did not consume any part of this species although it was fairly common in the core study area at Magod (6.8% of trees). ...
... Since gross energy was correlated with protein, fat and TNC contents (Table 4), squirrels consuming items with a high rate of energy intake automatically ingested items rich in positive nutrients. Similarly, Kenward (1982Kenward ( , 1983 and Kenward & Parish (1986) reported that the extent of bark stripping of beech, sycamores and maples by grey squirrels, S. carolinensis, in the British Isles was positively correlated with the volume of sap flow or phloem width per unit area and not with sugar concentration. ...
Article
The effect of nutrients and their availability on the diet of the herbivorous Malabar giant squirrel Ratufa indica (Sciuridae) was investigated at Magod and Bhimashankar in western India. The daily consumption of food items (percent wet diet) and the intake rates of these items and the contained nutrients (wet g s-1) were determined by continuous observation of focal animals. Water content was a significant positive predictor of relative food item consumption while mineral contents in general had the opposite effect. The intake rates of water and more digestible nutrients such as nonstructural carbohydrates, as well as the intake rate of minerals such as zinc (at Magod), were significant positive predictors of the relative contribution of an item to the daily diet, thus indicating considerations of feeding costs versus benefits. Tannins, some alkaloids, and other secondary metabolites may negatively influence food choice. Protein content, relative to digestibility reducers, influenced food item consumption only at Bhimashankar. There was seasonal variation in daily biomass consumption. At Bhimashankar, daily biomass consumption increased with the proportion of fruit in the diet while this did not occur at Magod. This is perhaps a result of the higher water content and the lower content of some soluble nutrients within fruit at Bhimashankar relative to Magod. There was also intra-month variation between individual squirrels in daily biomass of food consumed. Squirrels consumed ephemeral food items opportunistically and non-ephemeral items such as mature leaves and bark on a regular daily basis. Squirrels probably obtained minerals and nitrogen from both fruit (especially seeds) and non-fruit sources (mature leaves and bark in the case of minerals, young and mature leaves in the case of nitrogen). However, they obtained lipid and non-structural carbohydrates mostly from fruit. Squirrels were selective in their utilization of tree species on a monthly basis, but this selectivity was not evident over a longer time period because individuals were constrained to use different phenological stages of tree species present within their territories. Large body size in this squirrel permits dietary flexibility and enables an overall generalist feeding strategy.
... It was introduced at various locations from America around the start of the 20th century and has since spread widely (see Shorten, 1954;Lloyd, 1983;Huxley, 2003). It has also become a serious pest, as it frequently debarks pole-sized trees: young stands with fast growing beech Fagus sylvatica L. and sycamore Acer pseudoplatanus L. are especially vulnerable, especially if they contain a high density of juvenile squirrels, some mature seed-bearing trees, and have a history of squirrel debarking (see Shorten, 1954Shorten, , 1957Kenward, 1982Kenward, , 1983Kenward, , 1989Rowe, 1984;Rowe and Gill, 1985;Kenward and Parish, 1986;Gurnell, 1987;Kenward et al., 1988aKenward et al., ,b, 1992Mountford, 1997Mountford, , 2004). Debarking can be observed widely in southern Britain. ...
... These findings concur with a number of other studies (e.g. MacKinnon, 1976;Rowe and Gill, 1985;Kenward and Parish, 1986;Kenward et al., 1988aKenward et al., ,b, 1992Kenward, 1989;Rayden and Savill, 2004), which have also found that vigorous beech individuals of similar sizes/ages are particularly susceptible to debarking, especially if they are growing in stands with high average phloem levels, that have been recently thinned, contain a high density of juvenile squirrels and a mixture of seed-bearing trees. Records made in the old-growth stands within Lady Park Wood support these findings: vulnerable sized beech trees here have suffered little debarking because they are suppressed and growing slowly ( Mountford, 1997). ...
Article
Debarking of trees by American grey squirrels Sciurus carolinensis can be observed widely in British woodland. In this study, squirrel debarking and associated damage and mortality were assessed from 1977 to 2002 in mixed-deciduous stands in Lady Park Wood. Debarking mainly affected beech Fagus sylvatica stems sized 7.5–35 cm dbh, particularly those that were located in the upper stratum and growing most rapidly. Damage escalated during the study period: by 1983 24% of live beech stems in the vulnerable size-range had been badly damaged; this climbed to 48% by 1993, but reached only 54% in 2002, though a substantial number of beech had also been killed by debarking by 2002. Long-term mortality rates ranged from 2.3% to 5.4% per year and population half-life values from 13 to 30 years. The trigger for the initial debarking outbreak seemed to have been a severe drought in 1976. This opened the canopy and thereby released many, previously suppressed, beech trees. Debarking declined after 1993 as the canopy re-closed and beech growth generally declined. Over the same period, however, debarking to other species increased, suggesting it may have become habitual. Not all beech trees or stands where beech was prominent were seriously affected, and some badly damaged beech showed signs of recovery. Nonetheless, debarking had strongly impeded beech and thereby increased the long-term prospects for ash Fraxinus excelsior, lime Tilia cordata/platyphyllos and other tree species.
... Regional extinctions and frequent reduction in red squirrel population numbers elsewhere in Britain are due mainly to the range expansion of invasive eastern grey squirrels, Sciurus carolinensis, introduced in the late 1800s [26,27]. Ecologically, red squirrels are important for forest tree regeneration due to seed caching and are less impactful to forestry and tree growth due to reduced stripping of native tree bark compared to grey squirrels [28,29]. Economically, red squirrels are the key flagship species that is able to promote reintroductions and conservation schemes and generate ecotourism due to the positive social impact red squirrels provide as a species that is well-loved by the public [30]. ...
Article
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Conservation translocations, including reintroductions, are practices that are vital to restoring biodiversity and ecosystem function within conservation schemes globally. Sadly, population translocations have had a poor success rate historically. At a time where biodiversity is constantly decreasing, improving translocation success is vital for future conservation schemes. Often, to improve success, the selection of individuals is based on genetic characteristics and behaviours linked directly to survival. Further development to improve selection is proposed within this paper using animal personality. The study took place opportunistically to test how personality, in particular an animal’s boldness/timidness, may influence a population restoration of red squirrels into the Ogwen Valley, North Wales. Despite frequent translocations, data on how boldness and timidness may affect the establishment of this species are low. Testing was performed on key survival behaviours and boldness/timidness pre-release. This was performed via video data collection and identification of key behaviours that could be used to identify boldness or behaviours that could be linked to reduced fitness once released. Encounters at different distance intervals were monitored post-release via camera trapping to identify if boldness/timidness may change the furthest encounter distance of focal animals away from their release site. Relationships between the period for an individual to reappear post-threat was significantly linked to boldness, with other behavioural results and the encounter distance also showing trends of a potential relationship. Our results indicate that bolder individuals have a higher chance of expressing behavioural traits that will increase exposure to risks and, therefore, reduce the likelihood of successfully establishing populations. However, the small sample size of this study means that further research is needed. We suggest that during early stages of conservation translocation programmes, personality testing for boldness should become common practice, and we recommend selecting timid individuals for an initial release to improve population establishment, with bolder individuals utilised later to expand population distribution.
... The recovery of the native pine marten Martes martes in the United Kingdom and Ireland, after an extended period of decline and near-absence (Langley & Yalden, 1977;Sainsbury et al., 2019), has been hailed as an advance in controlling invasive non-native grey squirrel Sciurus carolinensis populations (Sheehy & Lawton, 2014;Sheehy, Sutherland, O'Reilly, & Lambin, 2018). Grey squirrels are classified as a pest in the United Kingdom due to the damage they cause to timber through bark stripping (Kenward & Parish, 1986), as well as competing with, and spreading infection to, native red squirrels Sciurus vulgaris (Rushton et al., 2006). In regions of Ireland (Sheehy & Lawton, 2014) and Scotland (Sheehy et al., 2018) where pine martens have been recovering for a substantial period and are living at high, medium and even low densities, grey squirrel populations have been negatively affected. ...
Article
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Predators can shape the distributions and dynamics of their prey through direct and indirect mechanisms. Where prey animals are regarded as pests, the augmentation of predator populations might offer a potential tool in their management. Declines in invasive non‐native grey squirrel Sciurus carolinensis populations in Ireland and Scotland have been related to an increase in range and density of native pine marten Martes martes populations. These reductions in grey squirrel abundance have, in turn, been linked to recovery of native red squirrels Sciurus vulgaris. Taking the opportunity presented by a conservation translocation of pine martens from Scotland to Wales, we investigated the short‐term effects of exposure to translocated martens on the space use and survival of resident grey squirrels. Grey squirrel range size and daily distance travelled increased significantly with increasing exposure to martens but we found no effect of marten exposure on the recapture probability (i.e. apparent survival) of the sampled squirrels within the study time frame. This is suggestive of contemporary, non‐lethal effects changing the ranging or foraging regimes of squirrels, due either to predator avoidance and/or earlier lethal effects associated with a reduction in intraspecific competition. Synthesis and applications. Our evaluation mimics the conditions experienced by grey squirrels at the front edge of naturally recovering pine marten populations and presents direct evidence that pine marten translocations could play an influential role in the behaviour and dynamics of invasive non‐native grey squirrel populations. Translocations of native predators, undertaken primarily for biodiversity conservation, could therefore find additional application in managing the ecological and economic impacts of invasive non‐native prey.
... Many studies have attempted to determine what triggers the grey squirrel to damage trees (Kenward & Parish, 1986;Kenward et al., 1996), with a view to informing preventive approaches; however, the underlying causal mechanism is still unknown. It has been suggested that bark stripping represents an attempt to utilise inner bark as a source of carbohydrate when other food resources are lacking (Kenward, 1983;Kenward, Parish, Holm, & Harris, 1988;MacKinnon, 1976); however, bark stripping still occurs in semi-wild enclosures when food is provided ad libitum, and bark is of low calorific value (Kenward, 1982). ...
Article
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The damage caused when grey squirrels strip the outer bark off trees and ingest the underlying phloem can result in reduced timber quality or tree death. This is extremely costly to the UK forestry industry and can alter woodland composition, hampering conservation efforts. The calcium hypothesis proposes that grey squirrels ingest phloem to ameliorate a seasonal calcium deficiency. Calcium in the phloem predominantly takes the form of calcium oxalate (CaOx), however not all mammals can utilise CaOx as a source of calcium. Here, we present the results of a small-scale study to determine the extent to which grey squirrels can utilise CaOx. One of three custom-made diets containing calcium in varying forms and quantities (CaOx diet, Low-calcium carbonate (CaCO3 ) diet and Control diet) were fed to three treatment groups of six squirrels for 8 weeks. Bone densitometric properties were measured at the end of this time using peripheral quantitative computed tomography and micro-computed tomography. Pyridinoline-a serum marker of bone resorption-was measured regularly throughout the study. Bone mineral density and cortical mineralisation were lower in squirrels fed the CaOx diet compared to the Control group but similar to that of those on the Low-calcium diet, suggesting that calcium from calcium oxalate was not effectively utilised to maintain bone mineralisation. Whilst no differences were observed in serum pyridinoline levels between individuals on different diets, females had on average higher levels than males throughout the study. Future work should seek to determine if this apparent lack of ability to utilise CaOx is common to a large sample of grey squirrels and if so, whether it is consistent across all areas and seasons.
... Based on the 2012 distribution survey ) and a mean rate of spread of 1.94 kilometres (km) per year (O'Teangana et al. 2000a), grey squirrels could reach the more remote areas on Ireland's western seaboard within 50 years (Flaherty 2016;Goldstein et al. 2016). Much research has revealed that, once established, the grey squirrel populations displace native red squirrel (S. vulgaris) populations (Kenward & Holm 1993;Wauters et al. 2000;Gurnell et al. 2004;Bertolino et al. 2014) and cause economic loss to the forestry industry through bark stripping (Kenward & Parish 1986, Lawton et al. 2010. It is reasonable to expect that all suitable habitats within Ireland will be eventually colonized by grey squirrels (Di Febbraro et al. 2013). ...
Chapter
The invasive grey squirrel (Sciurus carolinensis) has successfully spread to cover the eastern half of Ireland since its introduction to the Irish midlands in 1911, but it has so far failed to spread west of the River Shannon. The species has declined in parts of its former range but the south, southwest and northwest of the island remain vulnerable to grey squirrel invasion. Managers and ecologists can use spatial tools to devise a strategic approach to invasive species management to minimise costs and maximise success. We demonstrate how these tools can be employed to devise a management approach to control the continuing expansion of this non-native species. Suitable habitat beyond the current grey squirrel range has been identified using a species distribution model. Predicted grey squirrel dispersal routes were highlighted using least cost pathway analysis. A spatially explicit population model examined grey squirrel expansion in the south and southwest of the island, where the species continues to spread. Results from discriminant analysis suggested the failure of grey squirrels to expand into certain areas and the recent decline or disappearance in part of their former range were correlated with pine marten (Martes martes) presence and habitat fragmentation. Through these spatial analyses, we identified future monitoring locations and effective control strategies to inform a more strategic management approach to limit the spread of the grey squirrel in Ireland.
... Why grey squirrels strip bark is not fully understood, but the behaviour is correlated with high juvenile density where agonistic gnawing and exploratory feeding occur (Kenward & Parish 1986). Grey squirrels also strip and gnaw bark associated with scent marking activities (Taylor 1977;Koprowski 1993), however, marking points are typically found only on mature to over-mature timber and areas are generally small (~300 cm 2 ) unlike the large scale damage that appears unrelated to marking at traditional sites (Koprowski 1991). ...
Chapter
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Invasive alien species (IAS) comprise a global threat to biodiversity and may also cause economic harm by damaging natural resources and property. Indirect costs associated with IAS control and protection of native species add further economic burdens. The eastern grey squirrel (Sciurus carolinensis) is a successful invader in Europe, and this chapter reviews the current knowledge on the types and scale of damage it has inflicted on the continent’s economies.
... A similar behaviour was reported for C. erythraeus which was also introduced into Japan besides in France (Kuo et al. 19 c : Setoguchi 1990 ;Zhu et al. 1990;Jouanin 1992). The amount of damage varies between areas and is often correlated to squirrel density, tre e quality, and sap produc- '00 uo et al. 1982;Kenward and Parish 1986;Dagnall et al. 1998). At Acqui Tenne bark-stripping occurs especially in winter, when other food resources are scarce. ...
... Szacuje się, że zamiera do 5% uszkodzonych drzew (Mayle et al. 2007). Największe uszkodzenia powstają w rejonach o dużym zagęszczeniu młodych osobników, a spałowanie może wynikać z zachowań antagonistycznych lub poszukiwania nowych źródeł pokarmu (Kenward, Parish 1986). Najczęściej uszkadzane są drzewa w wieku 10-40 lat, szczególnie w okresie od maja do lipca (przegląd w: Bruemmer et al. 1999). ...
Article
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Abstrakt. Wiewiórka szara po raz pierwszy została sprowadzona do Europy pod koniec XIX wieku. Obecnie występuje na Wyspach Brytyjskich i we Włoszech, gdzie. jej liczebność stale rośnie, a zasięg występowania zwięk-sza się. W konsekwencji konkurencji o zasoby, a także w wyniku transmi-sji wirusa ospy przez wiewiórkę szarą, rodzimy gatunek, wiewiórka ruda ustępuje. W rejonach, gdzie wiewiórka szara występuje w dużych zagęsz-czeniach wyrządza również istotne ekonomicznie szkody w drzewostanach. Kolonizacja reszty Europy wydaje się nieunikniona, choć odległa o kilka-dziesiąt lat. Realnym i aktualnym zagrożeniem jest ryzyko nielegalnej intro-dukcji osobników pochodzących z hodowli, ponieważ prawdopodobieństwo utworzenia żywotnej populacji przez dwa osobniki tego gatunku wynosi co najmniej 50%. Słowa kluczowe: wiewiórka ruda, wiewiórka szara, gatunek inwazyjny, kon-kurencja międzygatunkowa, przenoszenie chorób, szkody w leśnictwie Abstract. Grey squirrel Sciurus carolinensis in Poland: science fiction or an actual threat? Grey squirrel was first introduced to Europe in the end of XIX century. Currently it is present in the British Islands and in Italy and everywhere its abundance and distribution range increase. Due to the interspe-cific competition and squirrel pox transmission, red squirrel, indigenous species , declines. In areas of high abundance of grey squirrel, serious economic damages to forests are also registered. Arrival of grey squirrel to the rest of Europe from Italy within a few decades seems unavoidable. The likelihood that the release of one pair of the species would establish a new population is higher than 50% and it means that an actual and real threat is now the risk of illegal voluntary or involuntary introduction of pet squirrels.
... The majority of city dwellers in the UK have favourable attitudes to the grey squirrel (64 %), but a large minority have less favourable views (Rotherham and Boardman 2006). This is partly because the species imposes economic and social costs, by damaging human dwellings by gnawing insulation and electrical wiring (DEFRA 2001), damaging trees through bark stripping (Kenward and Parish 1986), damaging supplementary bird feeders and removing large quantities of food from them (Hewson et al. 2004), and reducing food intake rates of many bird species that use these feeders (Bonnington et al. 2013). Negative attitudes towards grey squirrels also arise because they typically lead to the local extinction of the native red squirrel Sciurus vulgaris (Linnaeus 1758) through competition and increasing disease risk (Wauters and Gurnell 1999; Tompkins et al. 2003; Gurnell et al. 2004a). ...
Article
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Urbanisation is widely considered to promote the establishment of non-native species, but there is limited empirical evidence of the ecological factors driving their responses. The grey squirrel Sciurus carolinensis (Gmelin 1788) is native to North America, but is widespread in the UK and is starting to spread across Europe. It is regarded as one of the world's worst invasive animals due to its adverse impacts on native biodiversity. We use the non-native grey squirrel population in Sheffield (UK) as a case study to assess which factors limit its distribution and abundance in urban environments. In 2010 the city-wide population of adult squirrels peaked at an estimated 6539 in autumn (0.46 squirrels/ha), with maximum local densities of 8.29/ha. These densities appear to be slightly lower than those recorded in urban environments in the species' native range. Grey squirrels occurred more frequently at urban sites with larger amounts of green-space in the surrounding region. Local habitat characteristics were, however, more powerful predictors of urban grey squirrel occurrence and abundance than regional availability of green space. Canopy cover, seed bearing trees and supplementary feeders, provided for garden birds, positively influenced grey squirrels. The potential for grey squirrels to connect city dwellers with nature thus appears to be highest in urban locations that have considerable capacity to support native biodiversity. The beneficial impacts of supplementary feeding on grey squirrel populations is notable given concerns that squirrels can adversely influence bird populations. These habitat associations also imply that grey squirrels typically respond negatively to urbanisation, which challenges arguments that urbanisation favours exotic species.
... Red and grey squirrels overlap in their food preferences (Wauters et al. 2002), so replacement of red with grey squirrels may or may not lead to any substantive change in forest composition in the longer term. Although grey squirrels in the UK are known to debark and kill forest trees (Rowe and Gill 1985;Kenward and Parish 1986;Dagnall et al. 1998), this behaviour has not been observed in Italy (Signorile and Evans 2006). We have focussed here on the importance of the grey squirrel expansion in Perugia as derived from the threat the grey squirrel represents for S. v. italicus and S. v. meridionalis because that threat is very clear based on past observed interactions between grey and red squirrels elsewhere in Europe, whereas wider effects of the species replacement on southern Italian ecosystems may also be important but require further study. ...
Article
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A new population of the invasive American Eastern grey squirrel (Sciurus carolinensis) has recently settled in central Italy from an accidental release in Perugia, Umbria in the early 2000s. The grey squirrel is known to compete with and exclude native red squirrels (S. vulgaris) in the British Isles and Northern Italy, so it represents a potentially important new conservation threat to the red squirrel subspecies of south and central Italy, S. vulgaris italicus and S. v. meridionalis, which are endemic to peninsular Italy. The grey squirrel population range in Perugia is currently expanding at a rate of about 0.29 km/year (SD 0.19), slower than grey squirrel invasions elsewhere in Europe. Nuclear DNA analysed at 12 different microsatellite loci revealed that the grey squirrels in Perugia have extremely low genetic diversity, consistent with a small founder size. Genetic assignment tests indicate that the Perugia population was founded by translocations from an established population in Piedmont, Italy. No genetic substructure is evident yet in the Perugia population. These results together have serious consequences for the management of the grey squirrel invasion in Perugia and the conservation of the red squirrel subspecies: the Perugia grey squirrel population should be eradicated if politically feasible; otherwise new releases of grey squirrels, especially from sources other than the Piedmont population, should be prevented because such introductions could increase genetic diversity, thereby potentially increasing population range expansion rate to the much higher levels seen for more diverse grey squirrel populations elsewhere in Europe.
... Kenward & Holm 1993, Gurnell et al. 2004, are implicated in the decline of some woodland bird populations (Newson et al. 2010) and are a significant forest pest in Italy and the UK. Grey squirrels are subject to ongoing control efforts in the UK (Kenward & Parish 1986, Mayle et al. 2007, Signorile & Evans 2007. ...
Article
Rodents are traded as pet species, a practice that frequently results in new introduced populations. This is particularly true for tree squirrels where, often, only a few founders can establish viable colonies. Here, we review the worldwide introductions, ecology and impacts of two tree squirrel species, C allosciurus erythraeus and C allosciurus finlaysonii , and discuss the elements of a strategy to reduce squirrel introductions and settlements. C . erythraeus has established viable populations in A rgentina, F rance, The N etherlands, H ong K ong and J apan. An introduction to B elgium may have been stopped successfully. C . finlaysonii has been introduced to I taly, S ingapore and J apan. After 1950, the mean number of introduction events was one every two years. The most evident damage caused by these species is bark stripping that can be severe and may significantly impact trees and timber plantations. Data on negative impacts to native species are reported but have not yet been formally quantified. Both squirrel species carried with them parasites from the native range into the new habitats, leading to the introduction of other species. The ability of tree squirrels to establish themselves successfully, often from only a few founders, combined with their human appeal make them high‐risk species, and the pet trade should be considered as a high‐risk pathway for new introductions. A proactive approach to preventing new introductions should therefore include trade restrictions, and should be combined with public education initiatives at national and European scales. Tree squirrels represent an ‘alien species conundrum’. Experience from the UK and I taly has shown that if action is delayed until introductions are recognized as a problem, it is generally too late to control populations effectively, due to logistic, legal or economic reasons, or due to lack of public support. In the case of new populations, a rapid response mechanism is therefore critical. Once established, populations may become invasive and difficult or impossible to control.
... Most tree squirrels can damage forests and commercial tree plantations by bark-stripping (Dagnall et al. 1998; Pulliainen and Salonen 1963; Zhu et al. 1990), inflicting wounds that degrade timber quality severely and favor the penetration of insects and fungi (Kenward 1989; Dagnall et al. 1998). The amount of damage varies from site to site and is often correlated with squirrel density, tree quality, and sap production (Dagnall et al. 1998; Kenward and Parish 1986; Kuo et al. 1982). Several hypotheses have been advanced to explain bark-stripping: displaced aggression at high population densities, selection for sugar-rich sap, and/or soft phloem-tissue as an alternative food in times of food shortage (Gill 1992; Kenward and Parish 1986). ...
Article
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We studied seasonal activity patterns and feeding behavior of a population of Finlayson's squirrel (Callosciurus finlaysonii) native to Indochina and introduced into Italy. Squirrels spent the majority of active time foraging, switching between resources according to availability. In winter, they fed mainly on buds or stripped bark, shifting to flowers when plants bloomed in spring, and to mature seeds and fruits from June to October. By November–December, bark-stripping became progressively more important. This activity accounted for 36.5% of the yearly feeding time. The flexibility to exploit a wide range of foods, the ability to change food habits throughout the year, and hoarding behavior are factors that could indicate a proclivity to use different habitats successfully.
... Plantations of these species aged between 15 and 40 years with high average stem phloem volume contents in June/July, and in particular large and vigorous individuals, appear most susceptible to attack (Mackinnon, 1976; Kenward, 1983; Rowe and Gill, 1985; Kenward and Parish, 1986; Kenward et al., 1988). Outbreaks of bark-stripping are most likely to occur when squirrel densities are high (Kenward and Parish, 1986), when stands have a diversity of seeding tree species (Kenward et al., 1992), and once damage is triggered ...
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The scale and distribution of American grey squirrel (Sciurus carolinensis) bark-stripping damage to beech (Fagus sylvatica) stems was monitored in a mixed broadleaved woodland retained as a Research Natural Area through the use of permanent transects. During an initial outbreak of de-barking damage in 1983 almost one-third of beech individuals ≤4 cm d.b.h. in stands of 40 years' growth were badly damaged and by 1993 this level of damage had risen dramatically to over 50 per cent. One-third of badly damaged individuals in 1983, including a number of potential canopy dominants, died during the decade, but some that survived grew very vigorously. Throughout squirrels preferentially debarked intermediate sized (10-25 cm d.b.h.) stems in particular parts of the stands aged 40-50 years, apparently tending to select stems that were growing rapidly. Other species and stand areas of >100 years' growth remained largely unscathed. Within the 10-year period squirrels had critically affected the successional development of the wood.
... However, the risk of invasion of the squirrel was deemed to be relatively low according to horizon scanning (Total Risk= 2.4, Annex D). The apple snail typically colonizes rice fields (Halwart, 1994), but it could potentially spread to natural wetlands and estuaries and feed on aquatic vegetation if provided with the opportunity of invasion (Carlsson et al., 2004), 1985; Kenward & Parish, 1986). Considering the ecological and economic damage caused by this species in Great Britain, it is fundamental to prevent its spread towards suitable areas in the continent. ...
Technical Report
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 The European project RINSE (Reducing the Impacts of Non-native Species in Europe) investigates the best strategies for managing invasive non-native species across the Two Seas Programme area (i.e. area comprising the British Channel and the southern part of the North Sea).  The RINSE project specifically aims to develop cross-border tools to improve the prioritisation and targeting of invasive non-native species, so that resources can be directed towards the species and sites of greatest concern.  As part of RINSE, the main objective of this project is to audit the current state of biological invasions in the RINSE study area and to provide a prioritised list of INS that may pose a threat to local ecosystems in the future. This will be achieved in a series of three inter-related stages:  Registry of Non-Native Species (NNS) in the four RINSE countries (Great Britain, France, Belgium and The Netherlands) with information on their taxonomic classification, current distribution and environment inhabited.  Horizon scanning of Invasive Non-native Species (INS). Screening of the ‘worst’ invaders according to national and international organizations. Species will be divided into two groups depending on their presence (Black List) or absence (Alert List) in any of the four RINSE countries. Expert consultation will be used to rank species in each list according to their actual or potential impacts in the region.  Distribution modelling of INS. Species distribution Models (SDM) will be developed for a representative number of Black and Alert INS, using a combination of environmental and socio-economic predictors. The non-native species registry  The RINSE Registry compiled information from 3,454 non-native species, representing approximately 30% of all known non-native species (NNS) in Europe.  Great Britain features the largest number of reported non-native species, followed by France, The Netherlands and finally, Belgium.  The largest number of NNS in the Registry belongs to the phylum of Arthropoda, accounting for about three times as many NNS as Chordata, and four times as many as Angiospermae.  Over three quarters of NNS reported in the RINSE countries inhabit terrestrial habitats.  Almost all Anseriformes (e.g. geese, ducks, and swans), mammals, bony fish and flowering plants were deliberately introduced into RINSE countries, and mostly for ornamental reasons or leisure activities such as fishing. Horizon scanning of invasive non-native species  Most of the species identified as the world’s worst invaders were already present in at least one of the RINSE countries (77%) and were therefore assigned to the Black List of INS. The remaining 23% of species formed the Alert List of INS, being absent from all the RINSE areas.  The top 12 Alert INS with highest risk scores according to the consulted experts included a mix of primary producers: blady grass (Imperata cylindrica), melaleuca (Melaleuca quinquenervia) and Kudzu (Pueraria montana lobata); herbivores: emerald ash borer (Agrilus plannipenis), Canadian castor (C. Canadensis) and apple snail (P. canaliculata); predators: Japanese sea star (Asterias amurensis), racer goby (Neogobius gymnotrachelus), Amur sleeper (Perccottus glenii), nomad jellyfish (Rhopilema nomadica) and red fire ant (Solenopsis invicta); and the filter-feeding Amur clam (Potamocorbula amurensis).  Most of the Black List INS (56%) were present in the four RINSE countries, which exemplify the high level of biological interchange among them resulting from the intensive trade, transport and travel.  From The Netherlands, several aquatic inland species may pose a threat to Great Britain: Chattonella (Chattonella verruculosa), two Ponto-Caspian amphipods (Chelicorophium robustum and Dikerogammarus bispinosus), marmokrebs crayfish (Procambarus fallax) and tubenose goby (Proterorhinus marmoratus). From Belgium, an amphibian (Bufo marinus) and two insects (Latrodectus geometricus and L. hasselti) may affect other RINSE countries.  The top 12 Black INS raising the greatest concern amongst RINSE experts were dominated by primary producers such as the New Zealand pigmyweed (Crassula helmsii), floating pennywort (Hydrocotyle ranunculoides), killer algae (Caulerpa taxifolia), green sea fingers (Codium fragile), Japanese knotweed (Fallopia japonica) and giant hogweed (Heracleum mantegazzianum). Other type of organisms in the list included predators: harlequin ladybird (Harmonia axyridis), American mink (Mustela vison); herbivores: Canada goose (Branta canadensis) and grey squirrel (Sciurus carolinensis); and the omnivorous killer shrimp (Dikerogammarus villosus). Distribution modelling of invasive non-native species  Species distribution models displayed high performance for all Alert and Black INS modelled, and allowed investigation of the partial influence of environmental and socio-economic drivers on the current global distribution of the worst INS.  The permutation importance of environmental variables ranged between 70 and 82% for inland species (i.e. terrestrial plus freshwater species), and reached 99% for marine organisms.  Temperature-related variables were the most important driver of inland species distribution since it affects the body size, reproduction, growth, ecological role and survival of species, as well as determining the context for establishment (e.g. habitat and resources available, pool of interacting species).  In the marine environment, water temperature was also a primary driver of biological invasions, followed in importance by nitrate and chlorophyll-a concentration, which reflect the availability of resources and can also indicate human disturbance (eutrophication).  Several of the INS modelled featured distributions clearly influenced by the location of transport routes. This included invasive plants such as the water hyacinth (Eichhornia crassipes), Kudzu (P. montana lobata) and Kahili ginger (Hedychium gardnerianum).  Insects were predominantly affected by the Human Influence Index, including the silverleaf whitefly (Bemisia tabaci), Mediterranean fruitfly (Ceratitis capitata), Argentine ant (Linophitema humile) and oak processionary (Thaumetopoea processionea).  Closeness to ports was identified as an important predictor for aquatic inland species (e.g. Aphanius dispar, Clarias batrachus, Gammarus fasciatus, Dreissena r. bugensis, Myriophyllum heterophyllum, P. marmoratus, Anguillicola crassus), which are involuntarily transported as contaminants or stowaways.  The SE of England and NE of Belgium and the Netherlands (urban areas adjacent to major ports like London, Portsmouth, Calais, Oostende, Zeebrudge, Rotterdam and Antwerp) are under the highest risk of multiple invasions. Risk progressively decreases outwards, i.e. north and westwards in Great Britain, and south and eastwards in the continent. Recommendations  Halting the pathways of introduction:  The ornamental/pet trade is one of the most important vectors of invasive species into the RINSE region and could be controlled by a better enforcement of existing laws and coordination of neighbouring countries. Especial attention should be paid to Internet commerce that has facilitated the import of plants and animals.  Unintentional introduction as ship foulants or contaminant of commodities is the second major pathway of invasion. INS prevention may improve through continued ballast water control, ship inspections and control of imports (especially forest products). Educational outreach programs are needed to raise awareness amongst the general public and to promote the early detection of newcomers.  Strengthen cross-border communication and cooperation in sharing, linking and integrating INS databases and management strategies.  Species of special concern:  Four of the top Alert INS are present in countries as close as Germany and Poland: the racer goby (N. gymnotrachelus), Amur sleeper (P. glenii), Canadian beaver (C. canadensis) and blady grass (I. cylindrica).  Amongst Alert plants, the Asian wild raspberry (Rubus ellipticus), South-American Brazilian holly (Schinus terebinthifolius) and Asian salt cedar (Tamarix ramossisima) feature high invasive potential and a high suitability scores across RINSE.  In Great Britain, Black aquatic inland species present in The Netherlands and Belgium are of special concern: Chattonella (C. verruculosai), two Ponto-Caspian amphipods (C. robustum and D. bispinosus), marmokrebs (P. fallax), tubenose goby (P. marmoratus) and cane toad (B. marinus).  Three of the modelled Black terrestrial animals matched high suitability scores across RINSE while at the same time being flagged as one of the worst existing invaders in the region: the grey squirrel (S. carolinensis), Asian hornet (Vespa velutina) and oak processionary (T. procesionea)  Amongst aquatic inland INS showing high suitability scores in RINSE, high risk species include the racer goby (N. gymnotrachelus), water milfoil (M. heterophyllum) and quagga mussel (D. r. bugensis)  The importance of minimum annual temperature in our models suggests that global warming could expand the potential distribution of some of the assessed species northwards by increasing minimum winter records. The interaction of climate change and invasive species should be considered when developing long-term strategies of environmental management.  Given the importance of the Human Influence Index in our insect models, future studies of invasive insects’ potential distribution should consider using this or other similar indicators of the intensity of human disturbance to improve their predictions.  The Alert and Black lists of INS are not fixed and require continuous update through a wider screening of published lists of INS combined with expert consultation.  Likewise, distribution models need to be updated should the species expand their distribution towards new areas. In addition, modelling the potential distribution of a larger set of Alert species would provide environmental practitioners with a more complete scenario to inform decisions.
... That body mass in tree squirrels increases with body length (Kenward & Parish 1986; Wauters & Dhondt 1989a, b; Wauters et al. 2007a), was confirmed in this study with body mass of subadult and adult red squirrels increasing with foot length. Among males, foot length was the only variable that significantly affected body mass: on average, body mass of male squirrels increased by 14.4 g with each mm increase of foot length. ...
... This increases the total number of sciurids known to occur in Nova Scotia from 5 to 6-i.e., S. caro-linensis (Eastern Gray Squirrel), Tamiasciurus hudsonicus Exleben (American Red Squirrel), Tamias striatus L. (Eastern Chipmunk), Glaucomys volans L. (Southern Flying Squirrel), G. sabrinus Shaw (Northern Flying Squirrel), and Marmota monax L. (Woodchuck) (Scott and Hebda 2004). Eastern Gray Squirrels are known to damage crops and personal property (Flyger 1999), injure and kill young trees via bark stripping (Kenward and Parish 1986), prohibit the natural regeneration of hardwood forests (Pigott et al. 1991), prey on eggs and nestlings of tree-nesting birds (Flyger 1999), and competitively displace and exclude native sciurids and other granivorous species (Bruemmer et al. 2000, but see Gonzales et al. 2008). Although the future ecological impact of the Eastern Gray Squirrel in Nova Scotia is unknown, it seems likely that this highly adaptable species can be expected to expand its range and increase in abundance in the province in the decades ahead. ...
Article
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Sciurus carolinensis (Eastern Gray Squirrel) is one of the most recognized sciurids in North America. Since 1930, apparently isolated Nova Scotia sightings of Eastern Gray Squirrel have been believed to result from captive releases or escapes. However, the species was not believed to have become established in the province. Here we report first evidence that the Eastern Gray Squirrel is now present as a breeding mammal in Nova Scotia.
... The species richness and structural diversity in hedgerow flora is reflected in the diversity of other groups associated with hedgerows such as birds (Hinsley and Bellamy, 2000), small mammals (Kotzageorgis and Mason, 1997), butterflies (Dover and Sparks, 2000) and other invertebrates (Maudsley, 2000; Maudsley et al., 2002). The presence of mammals such as muntjac deer Muntiacus reevesi (Ogilby), hares Lepus europaeus (Pallas), rabbits Oryctolagus cuniculus (L), and grey squirrel Sciurus carolinensis (Gmelin) however, may have detrimental effects on the floristic diversity and structure of hedgerows if there is excessive pressure through the browsing, grazing and bark stripping activities that has been shown to occur in woodlands (Kenward and Parish, 1986; Cooke, 1995; Gill, 2000). If hedgerows are to retain their structural integrity then some management is required (Barr and Gillespie, 2000; Baudry et al., 2000), with a lack of management appearing to be as detrimental as the over-management of hedges (Garbutt and Sparks, 2002). ...
Article
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Little information exists on appropriate techniques for restoring degraded hedges. In this study different hedgerow types were subject to coppicing at ground level and pollarding at 60 cm to compare treatments most suitable for returning neglected hedges to a manageable dense structure. Survivorship of the treated stools, the number of new shoots produced and the length of shoots were measured. Analysis of the results showed that, for most species, the pollarding treatment produced better survivorship with both longer shoots and a greater number of shoots per stool than coppiced stools. From these results it is clear that a blanket management prescription of coppicing to restore hedgerows is not sufficient due to the varying responses shown by the different species; beech Fagus sylvatica L and hornbeam Carpinus betulus L for example showed a poor response to coppicing. It is recommended that other measures, including the planting up of gaps and hedge laying, may need to be incorporated into an overall restoration and maintenance programme in order to optimize the structure and function of hedgerows.
... In Great Britain, juvenile recruitment levels are believed to be a major factor influencing the risk of barkstripping damage. Kenward and Parish (1986) demonstrate that damage occurs when juvenile density is high (0.25 per ha). Contraception offers a potential nonlethal option for reducing the rate of spread of the grey squirrel, limiting the risk of Squirrelpox virus disease transmission, and reducing damage to woodlands. ...
Article
Background: The grey squirrel, Sciurus carolinensis Gmelin, is an invasive alien species introduced into Great Britain in the late nineteenth century and into Northern Italy during the early twentieth century. Grey squirrels have displaced the native European red squirrel, Sciurus vulgaris L., throughout much of Great Britain and have a significant impact on trees and woodlands through bark-stripping activity. In Britain, eradication is no longer an option at a regional scale, but fertility control offers a non-lethal approach to reducing negative impacts. The cholesterol mimic DiazaCon™ has been successfully used to inhibit reproduction in some species. These studies aimed to evaluate whether DiazaCon™ is effective in inhibiting reproduction in grey squirrels. Results: DiazaCon™ reduced serum cholesterol levels in female grey squirrels at a range of doses. The period of effect increased with increasing dose. Reproduction rate was not significantly different between treatment and control groups owing to a lack of breeding in controls. Conclusions: DiazaCon™ has potential to reduce serum cholesterol levels enough and for a sufficient period to reduce fertility in female grey squirrels. Information on baseline physiology and blood chemistry of grey squirrels is required to inform interpretation of the level of significance of the effect.
... High densities and behavioural differences in response to fragmentation of habitat may have unforeseen and negative community-level consequences. Damage to trees, such as bark stripping and girdling, increases with increasing density of eastern grey squirrels in the United Kingdom ( Kenward & Parish, 1986). Sciurus and Tamiasciurus are known predators of avian eggs and nestlings ( Gurnell, 1987;Steele, 1998;Koprowski, 1994a,b). ...
Article
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Habitat fragmentation is often considered a major threat to biodiversity; however, our understanding of how fragmentation impacts populations is poor. Identifying appropriate models for such studies is difficult. Tree squirrels are dependent on mature forests for food, cover and nests; these are habitats that are being fragmented rapidly and that are easily defined by humans. Squirrels represent excellent models for study of fragmentation. The literature on tree squirrels was reviewed to glean data on density and home-range size in forest fragments. Sufficient data were available on four species (Sciurus carolinensis, S. niger, S. vulgaris, Tamiasciurus hudsonicus). Density was negatively related to fragment size for S. carolinensis and S. niger and marginally so for T. hudsonicus. Sciurus vulgaris did not exhibit this relationship. Home-range size was analysed for three species of Sciurus and was positively related to forest fragment size for S. carolinensis and S. niger. Again, only S. vulgaris did not to show this relationship. Sciurus vulgaris is rarely found in small forest fragments and is believed to be especially sensitive to fragmentation; other tree squirrels appear to be sensitive to fragmentation in more subtle ways. Home range compaction provides a mechanism by which densities may increase in small fragments. The demographic consequences resultant from the high densities of squirrels found in small woodlots are not known but may explain the forest damage, avian nest predation and reduced diversity often cited to occur in woodland fragments.
... Okubo et al. 1989; Lurz et al. 2001; Verbeylen et al. 2003). Expensive yet unsuccessful control programs have been implemented in Europe (Sheail 1999) as grey squirrels damage trees (Kenward and Parish 1986; Mountford 1997) and displace Eurasian red squirrels (Sciurus vulgaris) (Gurnell et al. 2004). Over 200 papers on grey squirrels in Europe have been published, however, despite being introduced in 1909, little is known about eastern grey squirrels in western Canada (Robinson and McTaggart-Cowan 1954; Gonzales 2005; Hwang 2005). ...
Article
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Applied ecology could benefit from new tools that identify potential movement pathways of invasive species, particularly where data are sparse. Cost surface analysis (CSA) estimates the permeability (friction) across a landscape and can be applied to dispersal modelling. Increasingly used in a diversity of applications, several fundamental assumptions that might influence the outputs of CSA (cost surfaces and least-cost pathways) have yet to be systematically examined. Thus, we explore two issues: the presumed relationship between habitat preferences and dispersal behaviour as well as the degree of landscape fragmentation through which an organism moves by modelling a total of 18 sensitivity and dispersal scenarios. We explored the effect of fragmentation by altering the friction values (generally assigned using expert opinion) associated with patch and linear features. We compared these sensitivity scenarios in two sites that differed in fragmentation. We also used eastern grey squirrels (Sciurus carolinensis) as an example invading species and compared diffusion models and two contrasting cost surface dispersal scenarios. The diffusion model underestimated spread because squirrels did not move randomly through the landscape. Despite contrasting assumptions regarding dispersal behaviour, the two cost surfaces were strikingly similar while the least-cost paths differed. Furthermore, while the cost surfaces were insensitive to changes in friction values for linear features, they were sensitive to assumptions made for patch features. Our results suggest that movement in fragmented landscapes may be more sensitive to assumptions regarding friction values than contiguous landscapes. Thus, the reliability of CSA may depend not only on the range of friction values used for patches but also the degree of contiguity in the landscape.
... In Great Britain, juvenile recruitment levels are believed to be a major factor influencing the risk of barkstripping damage. Kenward and Parish (1986) demonstrate that damage occurs when juvenile density is high (0.25 per ha). Contraception offers a potential nonlethal option for reducing the rate of spread of the grey squirrel, limiting the risk of Squirrelpox virus disease transmission, and reducing damage to woodlands. ...
Article
Grey squirrels (Sciurus carolinensis) are an invasive species in Britain and Italy. They have replaced native red squirrels (Sciurus vulgaris) throughout most of Britain, and cause damage to trees. Currently, lethal control is used to manage grey squirrel populations in Britain, but nonlethal methods might be more acceptable to the public. One such method is contraception with 20,25-diazacholesterol dihydrochloride (DiazaCon™). DiazaCon™ inhibits the conversion of desmosterol to cholesterol, resulting in increasing desmosterol concentrations and decreasing cholesterol concentrations. Because cholesterol is needed for the synthesis of steroid reproductive hormones, such as progesterone and testosterone, inhibition of cholesterol synthesis indirectly inhibits reproduction. Desmosterol is used as a marker of efficacy in laboratory studies with species that do not reproduce readily in captivity. Grey squirrels were gavaged with a DiazaCon™ solution for 2 days, and then fed DiazaCon™-coated peanuts for an additional 8 days at target doses of 50 and 100 mg DiazaCon™ per kg body weight. There was a significant difference in cholesterol concentrations in the treatment groups compared to the control group. Cholesterol was reduced by ≥ 40% for 2 months in both treatment groups. There were no differences among groups with respect to blood chemistry and hematology parameters, and mean values are reported. The mean overall dose of DiazaCon™ received was 29.0 ± 1.6 and 55.3 ± 4.3 mg/kg in the low (50 mg/kg) and high dose (100 mg/kg) groups, respectively. DiazaCon™ might provide an effective, acceptable alternative to lethal control.
... Across the northern hemisphere, many large mammalian species engage in bark stripping (browsers and mixed-feeders mainly ; Gill 2006). Moose Alces alces (Faber & Edenius 1998), sika deer Cervus nippon (Yokoyama et al. 2001, Ando et al. 2003), white-tailed deer Odocoileus virginianus (Michael 1987), sheep Ovis aries (Anderson et al. 1985), horse Equus caballus (Kuiters et al. 2006), goat Capra hircus (Scogings & Macanda 2005) and red deer Cervus elaphus (Putman & Moore 1998) were shown to consume bark; however, this behaviour is not limited to ungulates (Lutz 1951, Kenward & Parish 1986, Me´nard & Qarro 1998). Numerous hypotheses have been proposed to explain bark stripping by herbivores and although many studies investigated the underlying causes of this behaviour (DeCrombrugghe & Louis 1981, Husak 1985, Reimoser & Gossow 1996, Putman & Moore 1998, Ando et al. 2003, Kuiters et al. 2006), it remains poorly understood (Verheyden et al. 2006). ...
Article
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Bark stripping by large herbivores is widespread, yet poorly understood. Our study was carried out in a 2000-ha area situated in the Vosges Mountains, France, where beech Fagus sylvatica bark is heavily bark stripped by red deer Cervus elaphus. We tested whether the seasonal variation in the frequency of beech bark stripping by red deer was correlated with bark nutritive value or bark mechanical properties (using an index of bark detachability). We also evaluated whether red deer selected beech trees based on the chemical composition of their bark (e.g. carbohydrates and minerals). Bark-stripped trees had slightly higher carbohydrate contents than non-stripped trees, but this difference resulted from a physiological reaction of the tree to bark stripping. Bark composition was similar between stripped and non-stripped trees spring and summer, but was easier to detach during these periods than during autumn and winter. Therefore, beech bark stripping by red deer in the Vosges Mountains does not appear to be driven by nutritional needs, but it may help deer in improving digestion efficiency.
... However, no repellent is likely to provide total protection. Nevertheless, red fox and raccoon scents could reduce damage by gray squirrels during periods when trees are most vulnerable, e.g., May to July in England (seeKenward and Parish 1986) and between mid-February and April in Oregon (seeBaldwin et al. 1986). Preventing gray squirrels from raiding gardens and bird feeders may also be possible, at least for a short period when it is most necessary. ...
Article
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The ability of gray squirrels (Sciurus carolinensis) to discriminate between different predator odors and the use of predator odors to deter gray squirrels from foraging on plants have not been previously investigated. To test the hypothesis that predator scent decreases foraging, I investigated the effect of such scent on consumption of butternuts (Juglans cinerea) in the field. Results showed that (i) red fox (Vulpes vulpes) scent was significantly more effective than either a control or human scent; (ii) raccoon (Procyon lotor) scent was significantly more effective than white-tailed deer (Odocoileus virginianus) scent (but only after 7–9 h); (iii) red fox scent was not significantly more effective than raccoon scent; and (iv) human scent was not significantly more effective than the control. The utility of predator odors in controlling damage by gray squirrels should be explored.
Article
Red squirrel (Sciurus vulgaris) range within the United Kingdom (UK) has retracted significantly due to the spread of an Invasive Alien Species, the North American Eastern grey squirrel (Sciurus carolinensis). Where grey squirrels are sympatric, red squirrel populations decline through inter-specific competition and squirrelpox virus (SQPV) infection. Grey squirrel eradication from the island of Anglesey facilitated the complete restoration of native red squirrels. Although native species recovery delivered significant ecological and economic benefits, the eradication extended only to a narrow sea-channel boundary, across which grey squirrel dispersal continues to occur. Hence, the long-term sustainability of Anglesey's red squirrel population is vulnerable to grey squirrel re-establishment without continuous intervention. Recent research has demonstrated that as pine marten (Martes martes) landscape use intensity increases, so too does red squirrel occupancy, likely linked to parallel declines in grey squirrel occupancy. Restoration of this mustelid predator is a potential tool to deliver sustainable grey squirrel control by restoring a missing trophic component, depressing grey squirrel incursion rates onto Anglesey, reducing red squirrel exposure to SQPV. Recent UK pine marten translocations have sourced animals under licence from wild Scottish populations. We explore the alternative use of captive-bred founders, simultaneously introducing new genetic variability against a limited diversity within extant populations. A current conservation translocation is paired with an ongoing assessment of founder behaviour and ‘personality’ measured before release. We then highlight the multi-disciplinary approach to delivering applied red squirrel conservation programmes in the face of invasive species.
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Grey squirrels (Sciurus carolinensis) are common inhabitants of wooded urban and suburban parks throughout their native and introduced range. The ecology of grey squirrels in rural environments has been the focus of considerable research, yet the ecology, behaviours, economic impact, and conservation implications of urban grey squirrels continue to gain increasing attention. In this chapter, we summarise key ecological characteristics of grey squirrels (Sciurus carolinensis) within an urban/suburban environment and how these differ from those observed in rural environments, the ecological role grey squirrels play in an urban ecosystem, and associated management challenges. Whilst urban and rural grey squirrels select similar habitats, urban populations can occur at much higher densities than their rural counterparts, from which they exhibit behavioural differences. Urban grey squirrels provide a wide range of ecosystem services, including cultural services that result in many urban dwellers having positive attitudes towards grey squirrels. This presents challenges for managing conflicts that can arise due to the damage that grey squirrels can cause to infrastructure, vegetation and other wildlife. Understanding basic ecology and population dynamics of urban grey squirrels, particularly in their introduced range, is essential for predicting their risk of invasion and spread, impacts on native wildlife, and for designing control programmes.
Article
The grey squirrel is an invasive pest species in the United Kingdom and populations are controlled to protect timber crops and native fauna. Although animals are culled using a variety of methods, there are few data available on the relative efficiency of different trap designs, and in particular spring traps. We compared grey squirrel captures in Magnum 116 spring-traps set within Fineren boxes against captures in a single entry live capture trap design. Trapping was conducted in mature mixed woodland in North Wales. No significant difference in the frequency of grey squirrel captures or body mass of trapped individuals between trap designs was observed. Despite the Fineren box design limiting access by non-target species, by-catch was recorded. We make recommendations for future research to minimise this and also compare our results for Magnum 116 traps with data available on captures in Fenn IV spring traps. The findings have broad relevance to the control of grey squirrels across their wider international invasive range.
Article
This study was designed to test the hypothesis that large-scale provision of diversionary food (sunflower seeds) would reduce red squirrel (Tamiasciurus hudsonicus) feeding damage to lodgepole pine (Pinus contorta) crop trees. Study areas with managed lodgepole pine stands were located near Vernon and Quesnel in south-central British Columbia, Canada. Large-scale applications of sunflower seeds were conducted on a manual basis in 1989, and by manual and aerial means in 1990, and an operational level by aerial means in 1991. Feeding damage to crop trees was assessed in control and treatment blocks. Populations of the red squirrel, northwestern chipmunk (Eutamias amoenus), and Columbian ground squirrel (Spermophilus columbianus) were sampled intensively by live-trapping on control and treatment blocks in 1990. Manual application of seed (clumped distribution) significantly reduced damage in the treatment block (11.3% of trees damaged) compared with the control (57.5% of trees damaged). Aerial application of seed (uniform distribution) also significantly reduced damage in replicated treatment vs. control blocks. Provision of diversionary food resulted in a temporary increase in the overall number of red squirrels caught on the treatment areas followed by a return to control levels within 6 wk. This increase was primarily the result of an increased number of transients in the trapped sample. The population density of resident (transients excluded) red squirrels did not increase when diversionary food was added. Similarly, we could not detect differences in reproduction, body masses, or survival of squirrels between control and food-supplemented areas. Northwestern chipmunks and Columbian ground squirrels also showed a temporary increase in density when food was added. Application of sunflower seed on an operational basis significantly reduced damage by squirrels in replicated study areas covering three different forest ecological zones. Provision of diversionary food is an effective strategy to protect intensively managed stands of lodgepole pine from red squirrel feeding damage.
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Large declines in the breeding populations and contractions of breeding range have occurred in several woodland birds in Britain in recent decades. Data from the BTO's Common Birds Census indicate that 10 out of 32 woodland species declined by more than 50% between 1966 and 1999, while 5 species increased by more than 50% over the same period. The declining species differ substantially in their ecology and life-history patterns. No single general explanation can be identified for the declines and it is likely that multiple factors have exerted a combined effect on several of the species. Seven factors emerge from this review as especially relevant and worthy of further study: (i) pressures on migrants during migration or in winter; (ii) climate change on the breeding grounds; (iii) general reduction in invertebrate food supplies; (iv) impacts of land use on woodland edges, habitats adjacent to woodland and hedgerows; (v) reduced management of lowland woodland; (vi) intensified habitat modification by deer; and (vii) increased predation pressure from Grey Squirrels Sciurus carolinensis, Great Spotted Woodpeckers Dendrocopos major and corvids.
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Survival was positively correlated with body weight in the 2nd winter of life, independent of body length. Females weighing <300 g did not come into oestrus. Female body weight and dominance were the best predictors of fertility. In coniferous habitat, body weight when lactating and the difference in weight over the lactation period predicted success in raising offspring. In deciduous habitat body weight was the best predictor, while the probability of having young was negatively influenced by body length and age. In coniferous woodland, both body weight and longevity were significantly correlated with lifetime reproductive success of females. In deciduous woodland, only body weight had a significant effect due to early breeding in some females with poor survival. Body length was weakly correlated with habitat quality, but there was a strong effect of habitat quality on body weight. Large squirrels settled in areas with the best seed-crop, and gained more weight than those that settled in areas with a poorer seed-crop. -from Authors
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Introduced species are a most serious threat to biodiversity, second only to habitat degradation. The eastern gray squirrel (Sciurus carolinensis) is native to eastern North America, but has been introduced to several countries outside its natural range. In Europe, it has been introduced to Britain, Ireland, and Italy, and in all 3 countries it has spread and replaced the native European red squirrel (S. vulgaris). There are several possible explanations for the replacement of the European red squirrel by eastern gray squirrels, but the main hypotheses involve exploitation competition between the 2 species, although a disease that is fatal to red squirrels and possibly spread by the gray squirrel also may have contributed. Gray squirrels cause economic damage to forests by removing bark from trees, particularly broadleafed types such as oak and beech, and have the potential to suppress natural forest regeneration. In North America, eastern gray squirrels have been introduced into many areas in the Pacific Northwest, and throughout the southern part of Vancouver Island. They appear to be increasing their range and population densities. This paper outlines the history of eastern gray squirrel introductions to Britain and Italy, the effects on native species, and the management options currently in use and under evaluation. From this knowledge, we predict that gray squirrels on Vancouver Island may have detrimental impacts on the native North American red squirrel (Tamiasciurus hudsonicus) and the endangered Garry oak (Quercus garryana) ecosystem.
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The introduction of the eastern grey squirrel (native to America) in Europe is causing a dramatic decline in the range of the native European red squirrel, due to competition. Grey squirrels compete with the native species mainly for food; furthermore, they can maintain and spread a poxvirus, which causes a lethal disease in red squirrels in Britain. According to some modelling scenarios, grey squirrels will spread from Italy to France and Switzerland in the next 20-30 years, and to a large part of Eurasia in the long term. This would represent a serious threat for the survival of the red squirrel throughout its range. This case study of bio- logical invasion suggests that the risks posed by the in- troduced species may be minimized with a reduction in animal trade between countries and using a proce- dure of risk-assessment for every imported species.
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The demography of red and grey squirrels was studied by live-trapping and radio-tagging at 14 deciduous and conifer sites in southern Britain and at eight conifer sites for one year in northern England. Densities and productivity correlated with tree seed crops for both squirrel species in deciduous and conifer habitats. Productivity was reduced by high density of full-grown squirrels relative to seed abundance. In oak±hazel woods, demography of grey squirrels correlated with abundance of acorns but not of hazelnuts , whereas density and productivity of red squirrels correlated with hazelnut abundance. Correlations of female density and productivity with pine-cone crops did not differ between red and grey squirrels. Predators ate many radio-tagged grey squirrels in conifers, and annual survival was only 50% compared with 80±82% for both species in other habitats. Grey squirrel populations in southern conifer sites were sustained by immigration, and at northern sites female density correlated with oak abundance within 500 m. Failure to exploit acorn crops puts red squirrels at a competitive disadvantage in deciduous woodland. Red squirrels had higher survival than grey squirrels in conifers, which may give them an advantage in that habitat, but could also have been explained by a lack of predators on their island study site.
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Body measurements of squirrel populations are described. The relation between body length and body weight was examined and factors causing individual or seasonal variation in body weight were studied.
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The literature on bark‐stripping by red deer Cervus elaphus in Europe is reviewed to reveal quantitative variation in this behaviour and relate it to deer density and local characteristics such as dominant tree species, occurrence of artificial feeding, altitude, region and size of the study site. We also review the importance of bark in red deer diets over the seasons and discuss the causes of bark‐stripping, focusing on the significance of bark as food. Over the 36 sites examined, the rate of bark‐stripping was highly variable (from 0 to 84% of susceptible trees debarked), with less damage in Scotland than in other European sites for which bark‐stripping rates were higher at high red deer density. Altitude, the size of the study site, the number of dominant tree species and the occurrence of artificial feeding do not significantly relate to the rate of bark‐stripping. Bark sometimes made up a large proportion of red deer diet (> 10%), especially in areas with severe winters (high levels of snow), whereas in study sites with mild winters, bark was practically not eaten at all. These results suggest that severe bark‐stripping could be related to a reduction in food resource availability. This food availability hypothesis needs to be better documented, dealing particularly with the possible interaction between food availability and red deer density.
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The social system of the grey squirrel (Sciurus carolinensis) was investigated. The area used by males and females expands after weaning, then stabilizes and remains the same in location and extent for life. The home range of an established individual is broadly overlapped by the home ranges of several other animals. Each established individual is regularly in contact with only a limited number of recognized neighbours with which it has well-established dominance relationships. Individual recognition promotes lowered aggressive levels between neighbours which allows each squirrel to use its entire home range evenly. Aggressive behaviour is directed toward strange squirrels, either young or immigrants, which attempt to enter this system. Thus, the established individuals hinder the settlement of new animals. Young squirrels born in a given locality have a greater chance of establishing than do immigrants. The relevance of the findings to population regulation is discussed.
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Squirrels cause damage by competing with man for nuts, fruit or grain crops, by competing for food with animals favoured by man, by gnawing human constructions and by stripping bark from trees grown for timber. Competition for food with man, game or livestock can best be prevented by excluding or destroying squirrels. Competition between Grey and Red squirrels in Britain is not yet understood, but the Grey squirrel may be more successful in deciduous woodland because it is better adapted to foraging there and for surviving food shortage than its congener. Gnawing power cables can be prevented by coating with glass beads as a repellant. The reasons for bark-stripping are not clear, but it may well be triggered by food shortage, or possibly by agonistic behaviour, and the extent of damage may then be influenced by variation in the sap quality of the trees. Habitat management, to reduce the winter food supply for squirrels, and perhaps also to increase food availability during the summer damage period, may provide less costly control measures than killing squirrels.
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Red squirrels occur most commonly in conifer habitats where their basic year round diet is conifer seed, supplemented by seed, berries and fruits of deciduous species when available. Conifer buds and shoots are important foods in winter and spring, as are flowers in late spring and early summer. Fungi are eaten throughout the year but mostly in autumn. Grey squirrels occur most commonly in hardwood forests where their primary food is nuts and samaras of deciduous trees and shrubs. Buds, shoots and flowers are substituted in spring and early summer, along with a variety of coarse plant and animal foods in summer. Both species prefer seed, so other plant foods predominate in the diet only in places or times when seed crops are small. Seeds of the same species are used by both Red and Grey squirrels when and where available but there have been no quantitative studies of diet of both species in closely similar habitats, so food preferences within the range of foods used by both species are unknown. Squirrels have strong preferences for particular food species, trees within a species and even between individual seeds and buds within each tree. Diet varies between individuals and between sex and age groups within squirrel populations. The determinants of these food preferences remain unknown, despite natural advantages of squirrels for testing foraging models.
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The response of rhesus monkeys to new foods was measured in two ways—by measuring the amount of food consumed on repeated exposure, and the latency of an instrumental response made with respect to the food. The following results were obtained:1.Using the consumption measure, the amount of food consumed may be quite small on the first few days (even though the food is promptly sampled after being offered to the animal) and then rise to a large value after a period of weeks.2.The visual experience of the animal in watching other animals consume the food can be important in determining whether it will subsequently accept the food. It is possible to convert a “non-consumer” into a “consumer” by arranging for such visual experience to take place.3.Mere passage of time does not appear to be sufficient in reversing an initial rejection of a food, or an acquired acceptance of a food.4.Using an instrumental response measure, it appears that the important change that occurs is that the rate at which the animal becomes satiated with the food decreases with repeated experience.5.It is difficult, if not impossible, to predict the ultimate status of a food from the animal's first 20 or so instrumental responses made with respect to it.6.Familiarity of environment can be an important variable in acceptance of a new food.These and other points are discussed, and the general notion of a “food repertoire” is developed.
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Home range patterns of squirrels in the genera Sciurus and Tamiasciurus are reviewed. Emphasis is placed on the need to use analytical techniques which are appropriate to the questions of interest, and certain weaknesses in published studies are outlined. Variation in home range size between different species, populations of the same species and individuals of the same population is discussed in relation to ecological theory and the biology of tree squirrels. Larger species do not necessarily have larger home ranges. There is an inverse relationship between home range size and population density, but its interpretation is not clear in the absence of experimental studies. Differential utilization of space within the home range is considered to be a common pattern, although it is rarely explicitly described in tree squirrel studies. In general, species of the genus Tamiasciurus defend exclusive territories, whilst those of the genus Sciurus do not. Explanations for these patterns are discussed in terms of ‘economic defendability’ and resource heterogeneity. Problems for future study are suggested.
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The relationships between volumetric soil water content (), in situ soil water potential (soil) and predawn xylem pressure potential (predawn) were quantified in four contrasting lodgepole pine ecosystems in Wyoming, USA. On three of the sites, changes in soil correlated closely with predawn, but on a porous soil derived from coarse granitic parent material, predawn declines occurred much sooner than corresponding declines in soil, possibly because of local depletion of rhizosphere moisture and low molecular diffusivity of water in that soil. Exptrapolation of laboratory-derived characteristic curves for soil moisture to field conditions yielded different relationships between and soil than curves derived from in situ measurements, probably because of disruption of soil structure and porosity during sample collection and handling in laboratory studies. Although a close correlation between and predawn was observed, future efforts at modelling the soil-plant-atmosphere continuum should be directed towards a more detailed understanding of the complex relationships between soil at varying depths and plant water stress.
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It is proposed that for many if not most animals — both herbivore and carnivore, vertebrate and invertebrate — the single most important factor limiting their abundance is a relative shortage of nitrogenous food for the very young. Any component of the environment of a plant, by varying the amount of adequately nutritious plant tissue available to herbivores, may consequently affect the abundance of food through all subsequent trophic levels; in this regard weather may be important more often than is immediately obvious. The hypothesis proposes that animals live in a variably inadequate environment wherein many are born but few survive, and leads to a concept of populations being “limited from below” rather than “controlled from above”. And it may lead to a reappraisal of the role of predation, competition and social and territorial behaviour as factors likely to influence the numbers of animals in the environment, the response of “pests” to manipulation of populations of their food plants by Man, and the likely effectiveness of agents of biological control.
The ecology and behaviour of Blue Monkeys (C. m. myasae) on the Zomba Plateau Malawi in relation to bark-stripping of exotic softwoods
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