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Cost effective drift fences for toads and newts



The construction, cost and performance of toad and newt drift fences and associated traps used at three study sites is described. Fence efficiency, in terms of the capture of animals immigrating to breeding sites, was calculated to lie between 39 and 63% of the estimated breeding population for the common toad (Bufo bufo), and between 45 and 61% for the crested newt (Triturus cristatus). Fences were consistently less efficient at intercepting emigrating animals; less than 10% of toads and between 34 and 40% of newts were captured. Cost and performance of the systems are compared with data from the literature.
Cost effective drift fences for toads and newts
J.W. Arntzen1, R.S. Oldham, D.M. Latham
Department of Biological
De Montfort University, Scraptoft Campus, Leicester
present address: School of Biological
Brambell Building,
University of Wales, Bangor LL57
Abstract. The construction,
cost and performance
of toad and newt drift fences and associated
traps used
at three study sites is described. Fence efficiency,
in terms of the capture of animals immigrating to
breeding sites, was calculated to lie between 39 and 63% of the estimated breeding population for the
common toad (Bufo bufo),
and between 45 and 61% for the crested newt (Triturus
Fences were
less efficient
at intercepting emigrating
less than 10% of toads and between 34 and
40% of newts were captured. Cost and performance of the systems
are compared with data from the
Drift fences, usually associated with pitfall traps, have been used extensively in studies of
amphibian ecology (e.g. Cummins, 1920; Storm and Pimentel, 1954; Oldham, 1966;
Gibbons and Bennett, 1974; Campbell and Christman, 1982). They are used to inter-
cept animals travelling overland and are especially suitable for species exhibiting
seasonal and directional movement to and from breeding sites. Barriers claimed to be
fully amphibian proof have been devised but these tend to be expensive both in terms of
material and labour, for example aluminium flashing (Gibbons and Semlitsch, 1981) at
3 European Community Units (ECU) per metre (1978 price) or at 2.5 ECU per m (Dodd
and Scott, 1994), "Aco" plastic drift fence at about 30 ECU per metre (installed, 1992
price; Brehm, 1989 and Aco Company, pers. comm.), vehicle crash barriers at about 20
ECU per metre (installed, 1989 price; Podloucky, 1989) and paving slabs at 15 ECU per
metre (installed, 1993 price; Oldham and Cameron, in prep.). Other materials are
mentioned (but not costed) in the literature, for example plastic fabric and 4 x 4 mm
mesh (Meinig, 1989). Economy of labour and finance normally dictate the use of
barriers that are less than totally effective, but most papers pay little attention to the
details of fence construction and the efficiency achieved. The purpose of the present
paper is to describe the fences we have used for two species, the common toad, Bufo bufo,
and the crested newt, Triturus cristatus. In particular, we will i) provide construction
details, not commonly provided elsewhere, ii) provide information on the relative
efficiency of different systems and report upon the error associated with these estimates,
and iii) provide information on the relative costs.
Fence construction and maintenance
Toad fences. In our studies we used netting of hexagonal wire mesh ("chicken wire")
which provides a highly durable, easily shaped barrier requiring relatively little support
and which comfortably survives a three year study. A gauge of 0.5 inch (1.3 cm) mesh is
suitable to obstruct all but the smallest adult toads. Toads readily scale a vertical fence
and it is necessary to bend the wire to provide an overhang of about 10 cm at the top. At
the base the wire is either dug into the ground to a depth of about 10 cm, or bent by 10 0
cm, to allow for the addition of weights which keep the wire flush with the ground. We
have no evidence of toads purposefully burrowing under fences, although they occa-
sionally bury themselves beside the fence, which could result in escape if there is no
basal extension or lip. For toads, fence height is relatively unimportant since they have a
weak jump. For economy we used chicken wire of 61 cm width, which provides an
overall fence height of about 40 cm. If interception of movement in only one direction
was of concern, then an asymmetrical fence with upper and lower overhangs pointing in
a direction opposite to the toad migration was appropriate. If two-way movement was to
be monitored then higher wire (width 76 or 91 cm) bent in the shape of an "S" in cross
section, may be used (Swan, 1986). A more effective two-way barrier was provided by
grafting additional wire on to the top of the fence to provide a "T" cross-sectional
Wooden supports (I m x 5 cm x 5 cm) were provided at 10 m centres and pitfall
traps, in the form of 10 1
plastic buckets, at approximately the same spacing. The traps
were set flush with the ground, tangential to the fence (fig. 1), and filled with water to a
depth of 5 to 10 cm. The water prevents desiccation, helps to disguise captures from
predators and hinders the escape of frogs, which might otherwise jump out. A tight fit
between the fence and trap is essential and this can be achieved by securing the wire
beneath the lip of the bucket. In dry soil, drain holes, punched in the side of the bucket
about 10 cm from the base, were used to prevent flooding, but in waterlogged soil a
small embankment was built around each trap. Alternatively, skewers or weights were
used to stop the traps floating. At 1993 prices the materials for this fence/trap system
cost approximately 1.5 ECU per metre and took about eight man-hours per 100 m to
Akwt fences. Chicken wire is unsuitable as a barrier since the smallest mesh readily
available (1.3 cm) will allow newts to pass through. Instead, chicken wire (1.3 or 2.5 cm
mesh) was used as a support and a combination of 500 gauge polythene and "Netlon"
greenhouse shading (0.3
cm mesh) as the barrier to an overall fence height of 50 cm (fig.
2). Newts are good climbers and some trouble was taken to provide a lip on each side of
Figure 1. Schematic
of a chicken wire fence/pitfall system
for toads.
the barrier. These lips were supported by rot-proof twine. The posts, at 5 or 6 m centres,
were set closer together than for the toad barrier and a span of metal wire between the
posts carried the additional load of the sandwich of materials. Netlon was preferred to
polythene on the lower part of the barrier because of: (i) its greater durability (it easily
withstood a three year project and was not damaged by burying); (ii) it allows air
circulation; this reduces the possibility of interference with the newts' olfactory migra-
tory cues and also makes the fence less prone to wind damage. Polythene was used for
the upper part of the barrier because it would be harder for the newts to climb if they did
succeed in passing the lip. The fence might be further improved by the addition of two-
sided ':\verhang in the polythene at the top of the fence (fig. 2). If damaged the fence was
repaired using strong adhesive "Post Office packing tape". In places exposed to wind
and sunshine the polythene did not last the three year study period and had to be
replaced. The use of UV-resistant polythene, at twice the normal price, might be
recommended. Pitfall traps were as described for the toad fence. At 1993 prices the
materials for this fence/trap system cost approximately 3.5 ECU per metre and took
about 30 man-hours per 100 m to install.
An alternative material used on some occasions was "Netlon cladding". This was self
supporting, very durable, easier to erect (except on uneven ground) and less easily
damaged by the growth of vegetation. Again the base of the fence was buried by about
10 cm and the top was provided with a two-sided polythene overhang of 10 cm each
side. The cost of this system was about 6 ECU per metre.
Figure 2. Schematic
of a fence/pitfall
for newts. The actual fence
consists of a sandwich
of polythene
and "Netlon" greenhouse
and is supported by chicken
wire (see
text for details).
Fence maintenance. Both kinds of fence require frequent checks, both to ensure their
efficacy (to remove debris which might fall into the traps and enable escape, top up
water in the pitfall traps or bale it out, etc.) and the well-being of the trapped animals. A
disadvantage of the method is that rodents, insects and other small animals sometimes
drown in the traps. This can be avoided by using bottomless containers as traps
(Oldham 1966), especially appropriate where desiccation is not a problem, as in moist
Fences and pitfall traps decline in efficiency as vegetation grows around them during
the spring and summer. They can also be damaged by extreme wet and dry conditions
as a result of flooding and cracked soil respectively. Furthermore, as with any field
equipment they may be damaged by animals, vandals or thieves. Each of these condi-
tions was countered by appropriate maintenance. We have found "Stockholm tar"
(available from agricultural suppliers) to be a useful deterrent against theft.
Fences were susceptible to damage by the growth of vegetation adjacent to the fence,
especially the newt fences. This was cleared manually when necessary. An alternative to
mechanical removal of encroaching vegetation are herbicides such as "Round up" (P.S.
Franklin pers. comm.).
Study sites and monitoring.
Fences, as described, were constructed in 1990 at three sites in
Leicestershire to monitor amphibian movements during three successive breeding sea-
sons. At study site A (Charnwood) a 800 m long fence was set around a 1.2 hectare lake.
The barrier crossed several streams and habitats. The fence, with an overhang pointing
outwards, was intended primarily to intercept immigrating toads. Newt barriers were
constructed around ponds at site B (C?addesby, 300 m2) and site C (Corn Close, 800 m2)
respectively 100 m and 150 m in circumference. They were intended to intercept
animals on both inward and outward migration. Inspection of the traps at sites was daily
or twice daily during periods of peak movement. In off-peak periods inspection was
carried out every third day at a minimum. It appeared that most pitfall captures
occurred at night so that morning collection minimised exposure to predators. We
report on the functioning of the fences in the first year they were operational.
Fence efficiency
Population size has been estimated using a single capture-mark-recapture determina-
tion (Lincoln Index). All captures at the outside pitfalls and fence during the breeding
season were marked and released over the fence. The sum of these animals provided the
first sample. All captures at the inside pitfalls, after breeding, provided the second
sample. The recaptures were toads and newts caught on both occasions. This method
does not take into account animals present within the perimeter before the fence was
erected or mortality during the breeding season. It also assumes that animals are not
deterred by the fence into retreating from the site and that their behaviour is the same
on approach and exodus. Fence efficiency (FE) is defined as the percentage of the
population approaching the fence which was caught in the pitfalls.
at breeding
sites. The results obtained with both target species are shown in
table 1. A clear distinction was observed between the proportions of the populations
caught immigrating (FEi) and emigrating (FEo). This was expected for the toads since
the overhang of the fence pointed outwards and could be easily scaled from the inside.
The marked difference at the newt sites cannot be explained in the same way. Imperfec-
tions in the fence and pitfall traps, which increase later in the season as vegetation
grows, may account for some of the difference. Other contributory factors could be a
tendency for newts to remain inside the pond perimeter until late in the season, or
changes in newt behaviour, such as a reduced tendency to rush headlong into the traps
after the breeding season or greater persistence in attempting to pass the barrier. Fence
efficiency results were similar at sites B and C, and, at site B, higher for females than for
males (table 1).
For toads there was a marked sexual difference in FEi, the value for females being
estimated at more than 1.6 times the value for males. The, on average, substantially
larger females may find climbing more difficult, especially if in amplexus, or the smaller
males may have been better able to penetrate the fence. Again, there may be behav-
ioural differences, such as a greater imperative on the part of the females to achieve the
pond whereas males are known to spend time on the approach searching for females.
Fence efficiencies
recorded in the literature. Swan (1986) recorded toad immigration efficien-
cies similar or marginally higher than ours. She worked on three fenced ponds (table 1), ),
each of the two smaller ones for two succesive years each. FEi varied between 62 and
%, FEo between 21 and 31 %. Her values for FEo are higher than ours, probably the
result of using wire bent in the shape of an "S" in an attempt to prevent toads passing
the barrier ('fence trespassing') in either direction. Gittins (1983) used a plastic barrier
and recorded relatively high values for both FEi and FEo, with little difference between
the sexes. The difference between the values for FEi and FEo was ascribed to mortality
within the enclosure. The high efficiencies recorded by Oldham (1966) for Bufo ameri-
canus were obtained by visiting the fence three times in each 24 hours. Two of these visits
were made during the hours of darkness and about half the captures were made at the
fence itself, rather than in the traps. This suggests that the lower efficiencies in the other
studies, which usually involved only one collection per day, during daylight, may, in
part, have been caused by failure of toads to enter the pitfall traps.
For newt the estimated values revolve around 50% for FEi. Outlying values at 23%
were obtained for an incomplete fence constructed for studing T. carnifex (Andreone and
Giacoma, 1989) and for a low fence (Amtkjaer, 1981). The implied significance of fence
height is not supported by Verrell's (1985) result (69%) using a relatively low fence. The
only fence approaching full efficiency in intercepting migrating T. dobrogicus,
height and depth with an especially solid construction (Schramm, 1992). Values for FEo
are mostly 10 to 20% lower than FEi. The outlying (low) value for FEo obtained by
Bouton (1986) for T. marmoratus is probably due to finishing observations early in the
year. The two studies (Swan, 1986 and Franklin, 1993) involving the same ponds in
successive years showed wide variations in fence efficiency changes from one year to the
next. For FEi the change ranged from a 9% increase to a 29% decrease and for FEo
from a 9% increase to a 9% decrease.
A wide variation in fence efficiencies is illustrated in table 1, but it is clear that most
systems do not achieve the complete sampling suggested as possible in some studies (e.g.
Bell, 1979, for the crested newt). As pointed out by Dodd (1991) few amphibian studies
address the importance of fence trespass and his observations suggest that many species
are able to circumvent a drift-fence pitfall trap enclosure, partly by using holes beneath
the fence made by invertebrates or mammals. On the other hand, a 100% proof fence
may not result in a maximum FE score due to mortality and other factors referred to
Most systems involve a compromise between the rival requirements of cost reduction
and efficiency. It must be admitted, in the present study, that the pains taken to improve
the design of newt fences were not clearly rewarded by improved catch efficiencies (table
1) in comparison with other systems. Anything less than 100% efficiency carries with it
the likelihood of sampling bias. Bias in terms of sex and size are illustrated in the present
work. A species bias and increased mortality are also possible. Potentially even more
significant, and harder to control for, is temporal bias. Estimated efficiencies during
emigration were consistently and significantly lower than during immigration, both in
our studies and in the literature.
Acknowledgements. Our gratitude goes
to those people-too many to name individually-who helped
in the construction and removal of the fences, to the Leicestershire and Rutland Trust for Nature
Conservation (M. Walpole),
the Co-operative
Society Ltd. (K. Preston), N. Whait and G.F.
Collings for access to their land and to Chr. Arntzen for drawing the figures. Financial support was
provided by NERC through its Joint Agricultural
and Environment
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... If during construction the fences were buried a few centimetres too deep, while fence height above ground was maintained, bending the top of the fence resulted in a too short overhang. In addition, the author reported that 78.2% of inspected fences, even recently built fences, showed signs of deterioration, such as broken mesh, too high vegetation (allowing animals to climb over the fence; Arntzen et al. 1995), as well as deteriorated or absent overhang. These results are especially troubling, since such a state will also reduce the effectiveness of fences for their second role, namely to guide animals to wildlife passages (Clevenger et al. 2001;Beebee 2013;Testud and Miaud 2018). ...
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Transport infrastructures, such as highways, disrupt animal migrations and cause roadkill. To mitigate the latter problem, fences have been built but their effectiveness has rarely been tested under controlled conditions. Here, we tested the effectiveness of the most commonly used fence in France and probably in Europe (wire netting fence) to block animals. We tested the wire netting fence, with and without a structural modification (i.e. an overhang), with three small mammalian species (the European hamster: Cricetus cricetus Linnaeus, 1758; the common vole: Microtus arvalis Pallas, 1778 & the wood mouse: Apodemus sylvaticus Linnaeus, 1758) and two amphibian species (the marsh frog: Pelophylax ridibundus Pallas, 1771 & the European green toad: Bufotes viridis Laurenti, 1768). During testing, all small vertebrate species tested were placed into an arena, from which they could only escape by crossing the wire netting fence. Without an overhang, almost all adult individuals of all tested species were able to climb over a 30 to 40 cm high wire netting fence. Furthermore, the addition of an 8 cm long overhang at the top of the fence stopped the amphibian species tested but not the most agile mammalian species, such as the hamster and the wood mouse. Based on these results, we do not support the construction of wire netting fences along roads as a measure to stop small animals from crossing. We recommend the use of more effective and durable fences, which, in addition, can be associated with wildlife passages to reconnect isolated populations.
... The Municipality of Örebro conducted the second translocation during spring and early summer of 2007 and 2008. They used a drift fence, located at a maximum of 2 m from the pond margin, with pit-fall traps (10 L buckets) around the outer margin of the fence to catch newts at the Marieberg pond during spring migration in April (Griffiths and Raper 1994;Arntzen et al. 1995). Migrating newts approaching their aquatic habi-tat were hindered by the fence and caught in the traps. ...
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The Great Crested Newt (Triturus cristatus) is considered threatened throughout Europe; consequently, the species and its breeding habitat are protected in many countries. Translocation of a population is a conservation tool used when habitat occupied by a species is scheduled to be destroyed by human development. The outcome of these translocations is rarely monitored. This study describes and discusses a translocation of T. cristatus in south-central Sweden (Örebro), which occurred because of planned destruction of breeding habitat associated with development of a shopping and industrial area. We provide quantitative data concerning numbers of relocated amphibians and subsequent monitoring in both the pond being destroyed, which is serving as the source of newts to be translocated, and the pond that received the translocated newts. The translocation exemplifies how difficult it is to determine size and conservation value of a population without thorough initial investigations. A large part of the translocated population seemed to disappear at the receiving area, which initially indicated that the translocation was ineffective. Nevertheless, longer term monitoring indicated that a population was established and reproduced in the new habitat. We argue that translocation should never be a first choice to make human development possible but one should always strive for preservation of an existing habitat. However, if a translocation is unavoidable, an appriopriate assessment of the affected population should be performed and a detailed analysis of habitats in the potential receiving areas should be carried out to select an area best fitted for the species in question.
... Im Zuge der Einstufung der Arten in das Konzept der FFH-Richtlinie wurden auch verschiedene Amphibienarten unter Anhang II und IV gelistet. Amphibien gehören weltweit zu der am stärksten bedrohten und am schnellsten schwindenden Wirbeltierklasse überhaupt (Stuart et al. 2004, Wake & Vredenburg 2008 Pounds 2001, Skelly et al. 2003, Pounds et al. 2006, Sodhi et al. 2008 Arntzen et al. 1995, Kneitz 1998, Hachtel et al. 2006, wurde die Kammmolch-Subpopulation im Greiffenhorstpark auf über 8 000 Individuen geschätzt (Ortmann 2009 (Drechsler et al. 2015). Die Fang-und Wiederfang-Ereignisse wurden mit Hilfe des Lincoln-Petersen-Index zur Größenabschätzung der einzelnen Subpopulationen verwendet (Begon 1979 In den dieser Studie zugrunde liegenden acht Jahren konnten Kammmolche in folgenden Gewässern nachgewiesen werden: 1, 2, C, A, B, B2, 17, 18, 20, 8, 9, 10, 11, 12, 13b, 14, 15 und ...
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Among European amphibians, the great crested newt (Triturus cristatus) is an endangered species and listed in the Habitats Directive of the European Union on appendix II and IV. Irrespective of its high protection status, a population of crested newts in the Greiffenhorstpark in Krefeld (Germany) representing one of the species' so far largest single subpopulation with an estimated census size of 8,000 newts, has been heavily disturbed by human-induced reconstruction measures. In order to re-establish the historical character of the Greiffenhorstpark betonit-layers were inserted on the ground of the main water body so that a year-round permanent water level without desiccation could be achieved. In the course of these reconstruction measures 4,390 crested newts were trapped with an amphibian drift fence and relocated into a smaller man-made pond inside a golf course nearby. By applying an individual based capture-mark-recapture approach we estimated sizes of 27 sites of crested newts in the Greiffenhorstpark and the area of the Latumer Bruch over a period of 7 years (2004-2011) and determined for each monitored water body also the habitat-suitability for crested newts. Altogether, 5,424 crested newts could be trapped and individually recognised using the program Amphident. Additionally, we analysed the genetic population structure of crested newts for 17 polymorphic microsatellite loci on the basis of 2,500 individuals. Our monitoring demonstrated the devastating effects of the construction measures on the crested newt population. The population of the main water body in the Greiffenhorstpark crashed from initially 8,000 individuals before the construction measures to less than 10 individuals in 2011. The main reason for this die off is the establishment of stable fish populations due to the lack of periodicity with desiccation events of the water body. With few exceptions, almost all 26 monitored sites showed strong declines in estimated population size. Though stable – with estimated population sizes between 200–300 individuals – the water body on the golf course only houses a small subset of the individuals that were translocated from the main water body. As a result, the translocation of thousands of crested newts obviously failed. Our data are alarming and indicate that almost all measures undertaken to stabilise the population of the crested newt in the Latumer Bruch has so far failed. In order to prevent a complete die off of the whole population of crested newts in the near future in this area, we strongly suggest to undertake measures that effectively mimic the periodicity of the water level so that the fish populations are decimated effectively to enable the return of the crested newts to this important central water body that functions as a source population for the whole Latumer Bruch. Key words: Amphibia, Triturus cristatus, Habitats Directive, HSI, predatory fishes, mark-recapture, genetic analysis, population monitoring, population crash, bottleneck, management measures.
A population of great crested newts (Triturus cristatus) in central England was monitored from 1988-1995. Recognition of individuals was used to quantify population dynamics. Adult annual survival varied from 31-100%. Long-term members of the breeding population had a significantly higher rate of annual survival (65%) than individuals breeding for the first time (57%). The population showed variable patterns of recruitment. A period of six years with little recruitment was followed by a rapid increase in population size, more than three-fold, over two years. The change in the population characteristics coincided with a crash in the population of predatory three-spined sticklebacks (Gasterosteus aculeatus), raising the possibility that newt recruitment was held in check by predation. Juveniles were rarely captured, but their recapture rate between years (49%) indicated that the rate of annual survival for juveniles in this population could be relatively high (estimated as 59%). Most juveniles matured at two years of age. The study population thus consisted of long-lived adults, showing variable survival, and erratic recruitment. The longevity of adults enabled the population to persist under adverse conditions until beneficial circumstances could be exploited by rapidly increasing the population size. These demographic traits may be common in T. cristatus populations.
A modification of the Habitat Evaluation Procedure (USFWS, 1976) applied to crested newt habitats is described, using ten key habitat criteria, based upon the assumption that habitat quality determines population size. Seven of these criteria (pond area, permanence, shading and density, macrophyte density, number of waterfowl and terrestrial habitat quality) are assessed using objective habitat measurements, the other three (site geography, water quality and fish occurrence) using qualitative rule-bases, to produce a Habitat Suitability Index for each site. Preliminary validation of the method for a set of 72 sites provides a significant rank correlation between indices of population size and of habitat. The procedure has the potential to provide a simple method of habitat assessment, for site surveying or selection of host sites for translocation, and can be upgraded easily as knowledge of crested newt habitat requirements improves. There was an incidental indication from the validation exercise that the number of newts caught by bottle trapping was affected negatively by the presence of macrophytes.
Published evidence from 178 great crested newt population translocations in the UK carried out between 1985 and 1994 emphasizes the need for continued monitoring following translocation. In more than half the cases, there was insufficient evidence for judging success, mainly due to lack of monitoring. Using the liberal criterion of the presence ora population one-year following translocation, 37% of all cases were successful and 10% unsuccessful. Most of the failures were predictable from existing knowledge of great crested newt requirements. Conflict between development objectives and great crested newt conservation at a site in northern England prompted a large-scale translocation of over 1000 individually photographed adults to a conservation area immediately adjacent to the development site. During the first year following translocation, adult newts showed a strong tendency to move towards their previous breeding site, some travelling 500 m in doing so, but none reaching home ponds 900 m away. At least 60% of the translocated newt population either escaped from - or attempted to leave - the conservation area. The remainder accepted the ponds in the conservation area, some of which were less than one year old, and bred successfully. Population sizes were extrapolated from the results of trapping both outside and within the conservation area. The estimated density of adults in the conservation area, at 150 ha-1 was high compared to that in the proposed development site (about 5 ha-1). Nevertheless, in the first year the population in the conservation area showed good production of metamorphs, and mortality consistent with that found in previous studies. Furthermore, most recaptured adults had grown (median of 18% gain in mass) during the season. This was probably the result of the increased habitat diversity in the conservation area, especially the aquatic habitat. It must be recognised that this translocation procedure can be applied only to the adult component of the population.
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A population of the Italian crested newt (Triturus carnifex) was studied in 1984 at a pond near Druento (Turin, Piedmont, northwestern Italy). Animals entering and leaving the pond fell into paired pit-fall traps during both spring and autumn migrations. A positive correlation found between rainfall and migration, a shortening of migration periods and summer inactivity suggest that, in the Mediterranean region, air moisture may be a limiting factor for newt activity. During their aquatic period adults showed strong individual differences in weight changes that cannot be explained on the basis of initial body weight or length. High variability in crested newt life history traits may be the result of repeated bottlenecks caused by environmental stress and high population isolation.
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Five years of field observations suggest that amphibians inhabiting a sandhills community are able to circumvent a drift fence-pitfall trap enclosure as they move toward and away from an ephemeral pond. Trespass rates varied depending on species and showed no tendency to increase or decrease as the study progressed. Laboratory trials confirmed that frogs easily crossed the fence by walking up the side or hopping over it. Frogs crossed the fence readily regardless of sex or whether the frog was an adult or juvenile. Although striped newts did not climb over the fence in the laboratory, they may use tunnels to go under fences under field conditions. Other species may burrow directly under the fence. A priori assumptions about a species' ability to climb a fence, or that trespass rates do not vary temporally or among sites, are unwarranted and may lead to misinterpretations of the results from studies using drift fences and pitfall traps.
Terrestrial activity of 16 species of frogs in South Carolina was correlated with season, environmental temperatures and the incidence and amount of precipitation. Terrestrial drift fences and pitfall traps encircling two aquatic habitats were used to monitor movements to and from local habitats. Ranidae (primarily Rana pipiens) were most abundant at a permanently aquatic habitat whereas Bufonidae and Pelobatidae (mainly Bufo terrestris and Scaphiopus holbrooki) were captured more frequently at a temporary pond. Numbers of individuals captured during each month showed fairly consistent progressions from highs in spring to lows in autumn. Activity was positively correlated with the incidence of precipitation, and the number of captures increased with the amount of rainfall. Anuran activity decreased noticeably during periods of low temperature. The use of a complete enclosure system in conjunction with pitfall traps is discussed and considered to be a valuable method for studying population dynamics of species which migrate to localized habitats.
Populations of Bufo americanus were studied in London, Ontario, from 1958 to 1962 to determine how they locate their breeding sites.Toads were capable of rapid, well-oriented movement to the breeding site, some moving at least 650 yd.Population turnover at breeding pools was high. There was a continuous influx and exodus of toads during the breeding season.Only 15% of 5937 captured toads were female. This disproportion might have resulted from later sexual maturation of females.Experiments showed that toads in breeding condition, within at least 80 yd of their breeding site, did not move at random but oriented towards the site. After translocation, individuals demonstrated homing behavior, returning over 100 yd to a particular breeding site, even when other active sites were available. Moreover, toads showed annual fidelity to a pool. Homing behavior evidently depended on familiarity with the characteristics of the breeding sites or the routes of influx to them.Experiments were performed on the significance to orientation of auditory, olfactory, hygrotactic, geotactic, and visual cues. Toad populations were capable of orienting towards a pool in the absence of a chorus, but were also able to orient towards the recording of a chorus broadcast from a position on land. Experiments involving surgery indicated that olfaction was not essential to orientation. Similarly, neither humidity nor topographic gradients appeared to be indispensable. Evidence on vision was inconclusive. Toads are probably able to utilize several characteristics of the breeding site, or its surroundings, during orientation. The relative significance of these characteristics probably depends on the nature of the environment.
The population dynamics of a population of crested newts Triturus cristatus were studied in 1983 at a pond in southern England, Three length classes of individuals were distinguished. Adult newts between 67 and 84 mm snout-vent length migrated to the pond in spring, on days when the temperature approached 5°C. Males tended to arrive earlier than females and to remain in the pond for longer. A second period of immigration of smaller adults, between 57 and 70 mm in length, took place in the autumn; these newts overwintered in the water and may have been about to breed for the first time. Juvenile newts measuring between 40 and 51 mm in length also visited the pond during the spring and summer. Immigrant male and juvenile crested newts were significantly higher in weight than emigrants: there was no significant difference between the weights of immigrating and emigrating females.
A pond was completely enclosed by a clear polythene barrier and all toads entering and leaving were recorded over an entire year. The inward breeding migration lasted one month, and the outward migration about one month for females and two months for males. Interruptions in the numbers arriving during the inward migration could be explained by low air temperature. Large males and females arrived before smaller individuals, and males arrived before females, staying about a month, four times longer than females. During the breeding season 865 individuals were captured; the male: female ratio was 4.7: 1. Relatively few toads visited the pond during the summer, but at this time the imbalance in the adult sex ratio was not so great as during the breeding season. Juvenile toads also visited the pond during the summer. It appears that females suffer a mortality rate of about 4.7% per week during their stay in the pond and males a rate of 2.6% per week.