[Show abstract][Hide abstract] ABSTRACT: Understanding the different factors that may influence parasite virulence is of fundamental interest to ecologists and evolutionary biologists. It has recently been demonstrated that parasite virulence may occur partly through manipulation of host competitive ability. Differences in competitive ability associated with the social status (dominant or subordinate) of a host may determine the extent of this competition-mediated parasite virulence. We proposed that differences between subordinate and dominant birds in the physiological costs of infection may change depending on the level of competition in social groups. We observed flocks of domestic canaries to determine dominant or subordinate birds, and modified competition by providing restricted (high competition) or ad libitum food (low competition). Entire flocks were then infected with either the avian malaria parasite, Plasmodium relictum or a control. Contrary to our predictions we found that the level of competition had no effect on the outcome of infection for dominant or subordinate birds. We found that dominant birds appeared to suffer greater infection mediated morbidity in both dietary treatments, with a higher and more sustained reduction in haematocrit, and higher parasitaemia, than subordinates. Our results show that dominance status in birds can certainly alter parasite virulence, though the links between food availability, competition, nutrition and virulence are likely to be complex and multifaceted.
[Show abstract][Hide abstract] ABSTRACT: In biparental systems, members of the same pair can vary substantially in the amount of parental care they provide to offspring. The extent of this asymmetry should depend on the relative costs and benefits of care. Individual variation in personality is likely to influence this trade-off, and hence is a promising candidate to explain differences in care. In addition, plasticity in parental care may also be associated with personality differences. Using exploration behaviour (EB) as a measure of personality, we investigated these possibilities using both natural and experimental data from a wild population of great tits (Parus major). Contrary to predictions, we found no association between EB and natural variation in provisioning behaviour. Nor was EB linked to responsiveness to experimentally increased brood demand. These results are initially surprising given substantial data from other studies suggesting personality should influence investment in parental care. However, they are consistent with a recent study showing selection on EB is weak and highly context-specific in the focal population. This emphasises the difficulty faced by personality studies attempting to make predictions based on previous work, given that personalities often vary among populations of the same species.
[Show abstract][Hide abstract] ABSTRACT: Oxidative stress is the unifying feature underlying the toxicity of anthropogenic pollution (e.g., heavy metals, polycyclic aromatic hydrocarbons, and nitrogen-oxides) and the ultimate culprit in the development of many diseases. Yet, there has been no attempt to summarize the published data on wild terrestrial animals to reveal general trends regarding the effects of pollution on oxidative stress. The main findings of this meta-analysis reveal that, as predicted, there is an overall increase in oxidative stress when exposed to pollution. This is mainly due to a weak overall increase of oxidative damages, although there is some variation across taxa. The reduced form of glutathione (GSH) and its associated enzymes are the most reliable biomarkers. This result is important when choosing biomarkers and when using less-invasive sampling of endangered species, or for longitudinal approaches. To be able to predict future population outcomes, possible treatments, but also evolutionary responses to a changing environment, a greater integration of biotic factors such as temperature, bioavailability of toxic elements, and species-specific responses are needed.
[Show abstract][Hide abstract] ABSTRACT: The ability of Manx shearwaters (Puffinus puffinus) to locate their nesting burrows at night was investigated using observation and experiments. Shearwaters walking to their burrows did so at random with respect to the wind direction, and did not vocalize, suggesting that visual cues are important to successful burrow homing. Experiments to test whether vision, audition or olfaction functioned in guiding birds back to burrows supported this conclusion.
[Show abstract][Hide abstract] ABSTRACT: Abstract and SummaryIn contrast to their behaviour at sea, Manx shearwaters (Puffinus puffinus) are highly-vocal at their breeding colonies during their nocturnal visits. The vocal activity shows seasonal changes that suggest the immature population is responsible for the majority of the calling. This was confirmed by catching birds in traps playing calls and also in mistnets. Male calling predominates at ground level and female calling predominates in flight. The trapping results and observations on immatures marked with small luminescent lights confirm this is due to males being responsible for establishing and defending burrows. The mistnetting also revealed a proportion of males that are comparatively silent in flight. It is argued that these represent birds as yet without burrows. As well as calling in flight, the marked birds called from within their burrows and from on the surface. Other characteristics of flighting activity are presented, which together with playback results, suggest that the process facilitates signalling, listening and assessment of breeding areas in a nocturnal species nesting in an open habitat and with poor terrestrial locomotion. The results suggest that burrow calling serves both sexual and territorial functions, and that aerial calling seems to be mainly concerned with sexual advertisement, but may also discourage intruders.
[Show abstract][Hide abstract] ABSTRACT: SUMMARY1The food of nestling herons Ardea cinerea was studied at three heronries in the Thames valley in the years 1952–57. At Buscot and Wytham, Berkshire, fish of the families Cyprinidae and Percidae formed the chief food, but at Buscot many Salmo trutta were also eaten. At High Halstow, Kent, in the Thames estuary, Anguilla anguilla, Scardinius erythrophthalmus, small fish of several species, and shrimps, formed the chief food of the nestlings. It was found that herons caught fish selectively, avoiding both small and large individuals.2At Buscot and at High Halstow, but not at Wytham, there were seasonal changes in the proportion of certain prey species which suggest that the heron lays its eggs at such a time that the young are in the nest at the period of maximum availability of food.3Young herons hatch asynchronously, and in years of mortality it was always the smallest last-hatched young that died. It is shown that the adaptive value of asynchronous hatching is that when food is short the smallest young in the nest die, but when food is more plentiful all the young are raised.4The average clutch-size of the heron did not vary significantly, but the survival of young after hatching differed markedly over the six years, and also in the different heronries. These differences were due to starvation, the availability of food to the adult herons being affected by the amount of rainfall and possibly other factors. The percentage of the young surviving was higher in the smaller broods, both in the nest and after fledging.
[Show abstract][Hide abstract] ABSTRACT: Summary • Individual variation in feeding rate in the absence of competitors (absolute feeding rate) and decline in feeding rate in the presence of competitors (susceptibility to interference) are frequently used as measures of competitive ability or fitness in short-term foraging studies. They are also crucial parameters of individual-based population models that predict the distribution of animals across patches. There are, however, few data on whether absolute feeding rate and susceptibility to interference competition remain constant for individuals between years. • The hypothesis that absolute feeding rate and susceptibility to interference were similar between years was tested by observing 25 European blackbirds Turdus merula feeding in seminatural experimental patches, during January to March over a 2–4-year period 1995–98. Absolute feeding rate was measured as the feeding rates of solitary blackbirds. Susceptibility to interference was measured as the change in feeding rate of a focal bird when it fed in the presence of different numbers of competitors. • Individuals changed significantly in their feeding rate between years, but most individuals did not change in their feeding rate relative to others in the population. The absolute feeding rate of an individual was significantly positively correlated with its feeding rate in the subsequent year. • There was no significant variation in susceptibility to interference for individuals between years. Only two of 27 blackbirds showed a significant change in susceptibility to interference between years. • Relative absolute foraging rate and susceptibility to interference competition were reasonably similar between years in blackbirds. Relative fitness measures derived from short-term measures of foraging ability may therefore be valid over long periods. In ideal free models that incorporate individual competitive ability, rather than population averages, temporal changes in competitive ability can possibly be ignored.
Journal of Animal Ecology 07/2008; 70(2):218 - 227.
[Show abstract][Hide abstract] ABSTRACT: The habitat of the largest known breeding colony of Pink-footed Geese (Anser brachyrhynchus) at Thjórsárver vid Hofsjökul is described. These botanical studies were made during the Wildfowl Trust's Second Expedition to Central Iceland during July and August, 1953. The distributions and frequencies of 155 species, sub-species, varieties and hybrids of vascular plants are given; and 37 of the most common mosses and 8 most common liverworts are listed. The plant communities with which the geese are most associated are analyzed. Several of the species have rarely been recorded before from Central Iceland, Minuartia stricta and Littorella unifiora being of special interest. A collection representing all the plants described has been deposited in the British Museum (Natural History), London.
Biological Journal of the Linnean Society 06/2008; 171(1):30 - 52.
[Show abstract][Hide abstract] ABSTRACT: SUMMARY1 This paper describes a five-year study in the pine plantations of Thetford Chase, East Anglia, to test the hypothesis that populations of tits (Paridae) and Goldcrests Regulus regulus are controlled by food shortage; and secondarily to assess the impact of bird predation on populations of forest insects.2 In winter, tits spend most of the day feeding; each bird examines some 1100 trees daily, and must find about 5 mg. dry weight of food, or 24 average-sized insects, every minute of the day to maintain itself. Coal Tits Parus ater and Willow Tits P. montanus stored much food in spring and autumn; but stored foods formed a very small part of their diet. Interspecific segregation among the feeding birds was less marked than among the same species in broad-leaved woods.3 The stock of invertebrate food in the pine foliage in winter ranged from 15–500 mg. dry weight per m2 of forest. The stock declined steeply during the winter, but increased again slightly in early spring. The level to which it fell in late winter was closely correlated with the mean air temperature at the time.4 In winter, the birds sometimes ate a substantial proportion of the available stock of food; in particular, they regularly ate about 50% of the stock of the eucosmid Ernarmonia conicolana (Heyl.), which was an important food of Blue Tits (Gibb 1958). The birds probably ate similar proportions of other suitable foods. Intraspecific competition for food was judged to be often severe.5 In winter, the birds' density was closely related to their stock of food. Coal Tits' survival from the end of the breeding season to the end of September was nearly constant from year to year, and was not correlated with the stock of food; but their survival from October to March was extremely variable and was closely correlated with the stock of food. This confirms that the population of tits was controlled by food shortage; nevertheless their territorial behaviour in autumn was probably also important.6 The paper ends with a discussion on the impact of bird predation on forest insects. It is concluded that as the birds eat a substantial proportion of the invertebrate stock in winter, they are at least a force to be reckoned with; also, if they help to stablise forest insect populations stepi should be taken to increase their numbers, perhaps most profitably by planting a variety of tree species to provide them with additional winter food.
[Show abstract][Hide abstract] ABSTRACT: Most information on the distribution, movements and ecology of cetaceans in the N.E. Atlantic have come from whale catches mainly in the early part of this century, and from strandings records collected by the British Museum (Nat. Hist.). With the formation of the Cetacean Group in 1973, a scheme for recording live cetaceans at sea was started. This paper summarizes the results of about two thousand sightings involving nearly 25,000 individual animals between the years 1958– 1978 (but mainly from the last 10 years), and relates them to existing information collected from other sources. Difficulties of identification and potential sources of bias are discussed.Most large cetaceans are present in British waters as part of a latitudinal feeding migration whereas smaller species may be present in the N.E. Atlantic throughout the year with movements being mainly of an offshore-inshore nature. Some species are clearly very rare probably as a result of over-exploitation in the last century and early part of this century. These include the Right whale, Blue whale and probably Humpback whale. Other species are rarely recorded because their usual range is some distance from British waters. These include narwhal and White whale (from Arctic waters), Pygmy sperm whale, smaller beaked whales and Euphrosyne dolphin (from warm temperate to tropical waters). The Harbour porpoise is by far the most common and widespread species in British waters, occurring mainly in inshore waters, although it has apparently declined in certain regions (e.g. Southern North Sea, English Channel, Irish Sea) in recent years probably as a result of pollution, disturbance and/or over-exploitation of food resources. Bottle-nosed and Risso's dolphins are also widely distributed close to the coast, although the latter is restricted to the west and south coasts and the former is associated particularly with some large estuaries. Common dolphins are relatively abundant and widespread, and are more pelagic than the previous three species. White-sided dolphins have a mainly pelagic distribution centred on the Northern North Sea whilst the White-sided dolphin has a wider distribution which includes all the western seaboard.Of larger cetaceans, the Killer whale is relatively common particularly on the west coasts and the Pilot whale is locally and seasonally abundant at the north and south ends of Britain and Ireland where they probably represent distinct populations. The Bottlenose whale, Minke, Fin and Sei whales are confined to the west and north coasts, all but the Minke whale having a primarily pelagic distribution. Sperm whales although increasingly commonly stranded on British coasts, are rarely sighted in inshore waters.The west coast of Britain and Ireland are the most important regions for cetaceans whereas the Southern North Sea has the smallest number although in previous decades numbers were probably higher. Most cetacean species occur mainly in the summer months, particularly August and September, although some species, e.g. White-sided Dolphin, Pilot whale and Minke whale show peaks later in the year. A number of species show secondary spring peaks, e.g. Bottle-nosed and Common dolphins, Risso's dolphins, and Pilot whales. Present evidence suggests that only the large whales exhibit definite latitudinal migrations, all other species being resident at high latitudes although they may show offshore-inshore or possibly small latitudinal movements. Many of the movements indicated from the present analysis can be linked to the seasonal changes in food availability and to the timing and geographical location of breeding, and these are described in detail. Many concentrations of a particular cetacean species occur regularly in the same area year after year and these may often be related to spawning concentrations of a particular fish species.Variations in herd size are noted between species and within species at different times of the year. These are related to aggregations associated with feeding, breeding, and long-distance movements winch will vary according to the biology and ecology of different cetacean species.
Mammal Review 04/2008; 10(1):1 - 52.
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