[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: 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.
[Show abstract][Hide abstract] ABSTRACT: Observations were made with radar from the Shetland Isles in 1960. During the late autumn a regular broad-front movement passed westwards over Shetland from Scandinavia about midnight. Its front evidently extended by dawn from the Outer Hebrides towards the Faeroe Islands. The movement consisted of fast-moving bright radar responses.During the later hours of the night the responses from the overnight passage movement generally, though not invariably, almost totally disappeared. Their disappearance seems to have been due to the birds having descended below the radar beam.The radar display always filled up again with rather faint, evenly distributed, responses in a short period around dawn, over a wide area of the south Norwegian Sea. The evidence indicates that these responses were from the same species as those observed on overnight passage, and that the sudden reappearance of responses around dawn was due to a sudden gain of altitude by these birds.The responses then assumed directions of movement which were not randomly distributed around the compass. Continuation of flight southwestwards or westwards on the overnight heading was infrequent, even in southeasterly winds. Movement in directions between W. and N.N.W. was very rare after dawn. Off Shetland three main directions of movement were recorded, E.S.E.–S.E., N.–N.N.E. and S.–S.S.W.Ascents at dawn and re-orientation behaviour have been established as taking place over both the northeastern Atlantic Ocean and the North Sea. Ascents with at least one direction of reorientation have been observed also off the Outer Hebrides, off eastern Scotland and north of East Anglia.Overnight passage was recorded from Shetland on 22 out of 48 nights and the dawn ascent was recorded on 33 mornings. Directions of movement after dawn were determined on 26 mornings, on only two of which were the directions random. On 15 of the 24 mornings when re-orientation occurred the wind at 900 m. above Lerwick was not greater than 15 knots.In 1961 ascent, without re-orientation, was recorded from Iceland Redwings and Wheatears off the Outer Hebrides by Lee (1963). The possibility that birds of Icelandic origin were responsible for any of the southeastward directions of movement observed around Shetland in 1960 could be excluded for a combination of reasons. The possibility that warblers, flycatchers, chats, or finches drifted to Fair Isle and Shetland could have been responsible for the dawn ascents and re-orientation off Shetland was also excluded. The radar responses, the detailed analysis of the radar data, the correlation of radar observations with field observations on Fair Isle and North Rona and other circumstantial evidence have strongly suggested that thrushes of the genus Turdus (especially Turdus musicus and probably T. merula and T. pilaris) were responsible for the overnight passage movements, dawn ascents and re-orientation behaviour after dawn. It is shown that Shetland falls within the regular migratory path of Scandinavian thrushes in the autumn.Neither dawn ascents nor re-orientation have yet been observed in Scandinavian thrushes in spring, but dawn ascent by Icelandic Redwings has been recorded in the spring on one occasion.The occurrence of dawn ascents was a rather better indication of the occurrence of migratory passage than the actual detection of movement during the night. On 12 mornings out of 48 a dawn ascent occurred although no overnight passage had been detected. The frequency of arrival of thrushes off Shetland was less in both moderate and strong southeasterly winds than in light winds, and the density was only very slightly higher in moderately strong, compared with light, southeasterly winds.While the immediate stimulus for the dawn ascent is undoubtedly sight of the sea beneath them, its purpose remains uncertain. The fact that it occurs not at dawn but as much as 11/2 hours before sunrise in the later part of the migration season is also unexplained.Depending on the method of analysis re-orientation took place around Shetland in 1960, E.S.E. on 11 out of 15 (or 16 out of 24) mornings, S.S.W. on 9 out of 15 (or 19 out of 24) mornings and N.N.E. on just over one-third of the mornings. Re-orientation in two or in three directions was nearly twice as common as re-orientation in only a single direction. Marked re-orientation by thrushes took place in the lightest of winds, of any direction. Re-orientation does not occur only after more or less severe drifting in easterly winds.The directions of movement after dawn were not simply down-wind or into-wind. While two-thirds of the E.–S.E. movements were more or less into-wind, most of the N.–N.E. movements, about half of those S.–S.W. and one-third of the E.–S.E. movements were across the wind. N.–N.N.E. re-orientation occurred only in light southeasterly winds and when the density of birds was high. In northeasterly winds movements were mainly down-wind S.–S.W. Unfortunately westerly winds were very infrequent in 1960.The directions of re-orientation were more regular and exact in their occurrence than the observed variations in the aspect or the strength of the wind, but the direction of the wind may play some part in determining which direction is mainly adopted.Although only one direction of re-orientation, S.S.E., appeared to have been observed in the southern North Sea it is suggested that some of the responses travelling S.S.W., apparently on a continuation of the overnight heading there, were in fact on a re-oriented S.S.W. course as off Shetland and the Outer Hebrides.In northwestern Europe the southeastward re-orientation in thrushes is evidently an adaptation enabling those of the population which find themselves out over the eastern Atlantic to regain the western seaboard of Europe. Comparison is made with the situation on the American Atlantic coast.Migratory birds generally continue flying on the same course after dawn as before it. Scandinavian thrushes are the only birds known to make marked changes in direction after sunrise, but it is not very likely that thrushes could goal-navigate after dawn while incapable of doing so during the night. It is argued that simple re-orientation is the basis of the behaviour observed. This behaviour appears to be a simple “escape” response, not directed towards a localized goal, and on average it tends to bring birds which are out of sight of land at dawn to land in the minimum time.
Ibis 04/2008; 106(1):7 - 51.
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