101,587 research outputs found
Age and environment affect constitutive immune function in Red Knots (Calidris canutus)
Full text linkWe studied subspecies, age and environmental effects on constitutive immune function (natural antibody and complement titres, haptoglobin activity and leukocyte concentrations) in Red Knots (Calidris canutus). We compared C. c. islandica and C. c. canutus in the Wadden Sea and found no difference in immune function between subspecies. However, C. c. canutus on their wintering grounds in Banc d’Arguin had higher natural antibody and lower complement levels than C. c. canutus or C. c. islandica in the Wadden Sea. This suggests that immune function is determined more by the surrounding environment than by subspecies. We also compared age classes in the Wadden Sea and found that first year birds had significantly lower natural antibody levels than adults, but that second year birds no longer differed from adults. Finally, we examined the interaction of age and environment in Banc d’Arguin. We found that first year birds (but not adults) in a low quality habitat had higher leukocyte concentrations than first year birds or adults in a high quality habitat. Differences in available resources and defence needs between environments, and differences among individuals differentially distributed between sites, are likely important contributors to the variation in immune function we report. Future studies, which examine these factors on wild birds, will be important for our understanding of how animals function in their natural environment.
Seasonal body mass changes in Eurasian Golden Plovers Pluvialis apricaria staging in the Netherlands: decline in late autumn mass peak correlates with increase in raptor numbers
Full text linkEurasian Golden Plovers Pluvialis apricaria staging in the Netherlands during the non-breeding season show strikingly constant seasonal changes in body mass with a first mass peak in late November and December and a second peak in late April and May. Despite huge sample sizes, variations in this pattern over successive years in the 1990s and among age classes were minuscule. However, in contrast to the body mass levels at other times of the year, there was a marked decline in the winter peak mass of Golden Plovers from the 1970s/early 1980s to 1989–2000. The decrease, by an average of 29 g, was about half the extra mass previously stored in autumn. This additional mass is known to consist of fat and may be interpreted as an energy store − insurance − for sudden cold spells when a negative energy balance forces the birds to move south and stay in front of the frostline. As the rate of the mass increase in September–October showed no change from the 1980s to the 1990s, changes in food availability are unlikely to explain the long-term mass decline. Also, there were no differences in two factors known to influence energy expenditure and feeding rate, air temperature and rainfall. The one striking environmental change relevant to plovers was the steep increase in the occurrence of raptors in the northern Netherlands in the 1980s, notably Peregrine Falcons Falco peregrinus and Goshawks Accipter gentilis. We argue that the halving of the winter mass peak over a decade is consistent with the hypothesis that under increased risk of predation, birds lower their body mass in order to reduce individual vulnerability, a reduction that may be traded off against an increased risk of starvation.
“Coastal” versus “inland” shorebird species: interlinked fundamental dichotomies between their life- and demographic histories?
Full text linkIn this contribution I present an extended but testable hypothesis (or “evolutionary scenario”) to explain how and why many life-history features of latitudinal migrant shorebirds, basically characterised by the correlation between habitat choice in the winter and the breeding season, may be functionally and causally intertwined. The most novel (and contentious) aspect of the hypothesis is that historical restrictions in suitable habitat may generate further restriction of suitable habitat with the causal chain consisting of population bottlenecks, leading to reduced adaptive genetic variation, leading to reduced ability to fight diseases, thus affecting potential habitat choice.
Blood parameter changes during stopover in a long-distance migratory shorebird, the bar-tailed godwit Limosa lapponica taymyrensis
Full text linkBar-tailed godwits migrate from West African wintering sites to breeding areas in northern Russia with only one stopover. We compared hematocrit (Hct), blood hemoglobin concentration (Hb), and mean cell hemoglobin concentration (MCHb; a measure of the relative proportion of Hb in the cellular blood fraction) between arriving godwits lured to land 60 km short of the stopover site and godwits during subsequent refueling. The Hct and Hb of arriving godwits was low when compared to that of refueling birds. On the stopover site, Hct and Hb correlated positively with size-corrected body mass. In addition, Hb and MCHb reached peak levels in the last days of stopover. We explored the possibility of regenerative anemia in arriving godwits by comparing the fraction of reticulocytes (young red blood cells) between arriving and refueling birds. No differences were found. Therefore, we suggest that the increase in Hct, Hb, and MCHb during refueling is not in response to a severe anemic state at arrival. Rather, we suggest that the increase in blood parameters may anticipate the increased aerobic requirements of impending migratory flight and possibly satisfy heightened oxygen demands of the larger body mass of fattened birds. The Hct increase on the stopover site may also serve to buffer the red blood cell population against possible red blood cell breakdown during long-distance flight.
Publisher Correction: Fuelling conditions at staging sites can mitigate Arctic warming effects in a migratory bird (Nature Communications, (2018), 9, 1, (4263), 10.1038/s41467-018-06673-5)
Full text linkIn the original HTML version of this Article, the order of authors within the author list was incorrect. The consortium VRS Castricum was incorrectly listed after Theunis Piersma and should have been listed after Cornelis J. Camphuysen. This error has been corrected in the HTML version of the Article; the PDF version was correct at the time of publication
Plasma metabolites reflect seasonally changing metabolic processes in a long-distance migrant shorebird (Calidris canutus)
Full text linkMigrant birds have tightly scheduled annual cycles consisting of several distinct life cycle (sub-)stages such as reproduction, migration, moult and overwintering, each of which have specific metabolic requirements (e.g., fattening during migration, protein build-up during moult). This study examines changes in fat and protein metabolism during the annual cycle of body mass and moult over 1.5 years in a captive flock of an arctic-breeding shorebird, the red knot Calidris canutus islandica. 2–5 h after food withdrawal, plasma uric acid levels were still decreasing and β-hydroxy-butyrate levels were low, indicating prolonged catabolism of dietary protein, probably linked with a conversion into lipids. Such a late-resorptive state is achieved much earlier in passerines, but only after several days in penguins and, thus, seems to depend on meal size or mass-specific metabolic rate. Substages of body mass gain and high body mass were characterized by increased plasma triglyceride levels reflecting increased turnover of lipids, and low levels of the ketone body β-hydroxy-butyrate, indicating that the bird is not short of glucose. The high uric acid levels during these substages indicated an increased breakdown of nutritional protein. During moult, plasma triglyceride levels were low, suggesting that lipids were less available than at other times of the year. It is concluded that plasma metabolite levels indicate the metabolic processes related to migratory fuelling and moult and the influence of exogeneous factors.
Scale and intensity of intertidal habitat use by knots Calidris canutus in the Western Wadden Sea in relation to food, friends and foes
Full text linkIn August-October 1988-1992 we studied the distribution and abundance of knots Calidris canutus around Griend in the western Wadden Sea, and the extent to which these can be explained by benthic prey availability and presence of avian predators. Numbers in the nonbreeding season showed monthly averages of 10000 to 25000 birds. Over 100000 knots were recorded on three occasions. Knots feed in large flocks, individual birds usually experiencing 4000 to 15000 flock-mates. The Siberian-breeding/west-African wintering canutus subspecies passed through in late July and early August. Otherwise the Greenlandic/Canadian breeding islandica subspecies was present. Over the period 1964-1992 there were no clear trends in the number of knots, but canutus-knots were particularly abundant in July-August 1991, whereas in 1992 both subspecies were absent.
Macoma balthica was the preferred prey of both subspecies. Hydrobia ulvae, Mytilus edulis and Cerastoderma edule were eaten when Macoma was absent close to the surface of the sediment. As Macoma buried deeper from July onwards, canutus faced better average feeding conditions than islandica later in the year. The spatial distribution of knots feeding on the intertidal flats around Griend was best explained by the harvestable biomass of the prevalent prey species in a particular year and season, i.e. Macoma (main prey when their harvestable biomass densities were greater than ca 0.8 g AFDM per m2) and Cerastoderma, and by the avoidance of situations where they run the risk of attack by bird-eating birds. Flocks of knots covered most of the intertidal flats in the western Dutch Wadden Sea in a couple of tidal cycles. This is about 800 km2, much larger than the equivalent area used by knots on their wintering grounds in Mauritania (10-15 km2), a difference that is correlated with prey spectrum, prey availability and predictability.
Predator escape tactics in birds: linking ecology and aerodynamics
Full text linkIn most birds, flight is the most important means of escape from predators. Impaired flight abilities due to increased wing loading may increase vulnerability to predation. To compensate for an increase in wing loading, birds are able to independently decrease body mass (BM) or increase pectoral muscle mass (PMM). Comparing nearshore and farshore foraging shorebird species, we develop a theory as to which of these responses should be the most appropriate. We hypothesize that nearshore foragers should respond to increased predation by increasing their PMM in order to promote speed-based escape. Instead, farshore foragers should decrease BM in order to improve agility for maneuvering escape. Experiments on 2 shorebird species are consistent with these predictions, but on the basis of the theoretical framework for evaluating effect size and biological significance developed here, more experiments are clearly needed. Copyright 2009, Oxford University Press.
Red Knot diet reconstruction revisited:context dependence revealed by experiments at Banc d'Arguin, Mauritania
Full text link<p>Capsule Context-specific equations are needed to reconstruct diet composition and intake rate of Red Knots by the use of shell fragments retrieved from droppings.</p><p>Aims To explore whether the method to reconstruct Red Knot diet described by Dekinga & Piersma [Dekinga, A. & Piersma, T. 1993. Reconstructing diet composition on the basis of faeces in a mollusc-eating wader, the Knot Calidris canutus. Bird Study 40: 144-156] accurately predicts the diet of Red Knots Calidris canutus canutus outside Northwest Europe, at Banc d'Arguin, Mauritania.</p><p>Methods Feeding experiments with captive Red Knots on the bivalves Dosinia isocardia or Loripes lucinalis were carried out at Banc d'Arguin, the main wintering area of Red Knot subspecies C. c. canutus. Ingested diets were compared with the reconstructed diets derived from the general method developed by Dekinga & Piersma (1993). Droppings collected over multiple years were also analysed to evaluate the calibration method from this study.</p><p>Results Of the total ingested shell mass (DMshell) in both bivalves, approximately 65% of the shell mass was retrieved in the droppings (DMdrop). Therefore, dry mass of droppings in the field (DMdrop) has to be multiplied by 1.547 to calculate the ingested dry mass (DMshell). For size estimations of ingested shells from droppings, hinges should be used for D. isocardia and hinges including tops for L. lucinalis.</p><p>Conclusion The correction factor of 1.547 found here is 50% larger than the factor 0.993 for heterodont bivalves from Europe established by Dekinga & Piersma (1993). Application of the published factor would lead to serious underestimation of energy intake rates based on dropping frequencies and dropping content (by as much as 35%), although it would have small effects on the relative species composition of the diet. Having shown that such correction factors can differ among sites and prey we recommend their determination in new ecological contexts.</p>
Spatially structured genetic variation in a broadcast spawning bivalve: quantitative vs. molecular traits
Full text linkUnderstanding the origin, maintenance and significance of phenotypic variation is one of the central issues in evolutionary biology. An ongoing discussion focuses on the relative roles of isolation and selection as being at the heart of genetically based spatial variation. We address this issue in a representative of a taxon group in which isolation is unlikely: a marine broadcast spawning invertebrate. During the free-swimming larval phase, dispersal is potentially very large. For such taxa, small-scale population genetic structuring in neutral molecular markers tends to be limited, conform expectations. Small-scale differentiation of selective traits is expected to be hindered by the putatively high gene flow. We determined the geographical distribution of molecular markers and of variation in a shell shape measure, globosity, for the bivalve Macoma balthica (L.) in the western Dutch Wadden Sea and adjacent North Sea in three subsequent years, and found that shells of this clam are more globose in the Wadden Sea. By rearing clams in a common garden in the laboratory starting from the gamete phase, we show that the ecotypes are genetically different; heritability is estimated at 23%. The proportion of total genetic variation that is between sites is much larger for the morphological additive genetic variation (QST = 0.416) than for allozyme (FST = 0.000–0.022) and mitochondrial DNA cytochrome-c-oxidase-1 sequence variation (ΦST = 0.017). Divergent selection must be involved and intraspecific spatial genetic differentiation in marine broadcast spawners is apparently not constrained by low levels of isolation.
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