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Red Knots (red + knot)
Selected AbstractsDifferential mortality of wintering shorebirds on the Banc d'Arguin, Mauritania, due to predation by large falconsIBIS, Issue 2008PIET J. VAN DEN HOUT Predators may influence many aspects of the daily life and seasonal movements of their prey. Here we quantify direct, and evaluate indirect effects of predation by three falcon species (Lanner Falcon Falco biarmicus, Barbary Falcon Falco pelegrinoides and Peregrine Falcon Falco peregrinus) on coastal shorebirds wintering on the Banc d'Arguin, Mauritania, an area hosting approximately 30% of the East Atlantic Flyway population of shorebirds. On the basis of 754 h of observation over five winters, 97 witnessed attacks and 585 collected prey remains, we show that shorebirds were safer in larger flocks, which tended to be attacked less often. Furthermore, species that forage relatively close to shore and in small flocks were depredated more often than expected from their relative abundance. In three species, Red Knot Calidris canutus canutus, Bar-tailed Godwit Limosa lapponica taymyrensis and Dunlin Calidris alpina, the juveniles were more vulnerable than adults. We estimated that on average 1% of the juvenile and 0.1% of the adult Red Knots present were killed by large falcons each winter. For Red Knots we simultaneously quantified annual survival on the basis of an individual colour-marking programme: mortality due to predation by falcons accounted for an estimated 6.2% (juveniles) and 0.8% (adults) of annual mortality. We suggest that juvenile Red Knots are 10 times as likely to be killed by falcons because they use riskier habitats, i.e. early and late tide foraging areas closer to shores where surprise attacks are both more common and more successful. These results indicate that the strength of indirect effects of predation operating in a shorebird population largely outweigh the effects of mortality per se. [source] Use of wetlands at the mouth of the Yangtze River by shorebirds during spring and fall migrationJOURNAL OF FIELD ORNITHOLOGY, Issue 4 2006Zhen-Ming Ge ABSTRACT The mouth of the Yangtze River is an important stopover site for migratory shorebirds using the East Asian-Australasian Flyway. From 1984 to 2004, we censused and banded shorebirds and monitored hunting activities at the mouth of the Yangtze River to understand how shorebirds used the study area. Counts and banding data revealed greater numbers of shorebirds at the mouth of the Yangtze River during northward migration (spring) than during southward migration (fall), with ratios varying from 1.5:1 to 7.2:1 at different sites from 1984 to 2005. The most common species observed during spring (northward) migration were Great Knots (Calidris tenuirostris), Red Knots (Calidris canutus), Bar-tailed Godwits (Limosa lapponica), Sharp-tailed Sandpipers (Calidris acuminata), and Red-necked Stints (Calidris ruficollis). During spring 2003,2004, 96.98% of the shorebirds observed were adults (ASY or older) and 3% were after hatching-year and second-year birds (AHY or SY). In contrast, almost all (94.73%) birds counted during the fall were hatching-year (HY) birds. These results indicate that adult shorebirds either use a different migration route during fall migration or use the same route, but do not stop at the mouth of the Yangtze River. HY birds, however, may depend on the coastal stopover sites for feeding during their first southward passage. SINOPSIS La desembocadura del Rio Yangtze es un importante punto de parada de playeros migratorios que utilizan la vía del Este-Asiático-Australásico. De 1984 to 2004 anillamos playeros y se condujeron censos para monitorear las actividades de cacería en la desembocadura del Yangtze y ademásdeterminar como los playeros utilizaban dicha área. Los conteos de aves anilladas revelaron un mayor número de playeros durante la migración hacia el norte (primaveral) que durante la migración hacia el sur (otoñal) con una tasa de 1.5:1 a 7.2:1 en diferentes localidades. Las especies que se observaron con mayor frecuencia durante la primavera (moviéndose hacia el norte) fueron Calidris tenuirostris, C. canutus, C. acuminata, C. ruficollis y Limosa lapponica. Durante la primavera del 2003,2004, el 96.98% de las aves observadas fueron adultos y el 3% fueron aves de segundo año o juveniles del primer año. En contraste el 94.73% de las aves contabilizadas durante el otoño fueron juveniles del primer año. Estos resultados indican que los adultos utilizan otra ruta durante la migración otoñal o una ruta similar pero que no paran en la desembocadura del Yangtze. Sin embargo, las aves de primer año muy bien pudieran depender de los recursos alimentarios de los puntos de parada costaneros durante su primer viaje hacia el sur. [source] Shorebird predation of horseshoe crab eggs in Delaware Bay: species contrasts and availability constraintsJOURNAL OF ANIMAL ECOLOGY, Issue 3 2007S. GILLINGS Summary 1Functional responses , the relationship between resource intake rate and resource abundance , are widely used in explaining predator,prey interactions yet many studies indicate that resource availability is crucial in dictating intake rates. 2For time-stressed migrant birds refuelling at passage sites, correct decisions concerning patch use are crucial as they determine fattening rates and an individual's future survival and reproduction. Measuring availability alongside abundance is essential if spatial and temporal patterns of foraging are to be explained. 3A suite of shorebird species stage in Delaware Bay where they consume horseshoe crab Limulus polyphemus eggs. Several factors including spawning activity and weather give rise to marked spatial and temporal variation in the abundance and availability of eggs. We undertook field experiments to determine and contrast the intake rates of shorebird species pecking for surface and probing for buried eggs. 4Whether eggs were presented on the sand surface or buried, we demonstrate strong aggregative responses and rapid depletion (up to 80%). Depletion was greater at deeper depths when more eggs were present. No consistent give-up densities were found. Type II functional responses were found for surface eggs and buried eggs, with peck success twice as high in the former. Maximum intake rates of surface eggs were up to 83% higher than those of buried eggs. 5Caution is needed when applying functional responses predicted on the basis of morphology. Our expectation of a positive relationship between body size and intake rate was not fully supported. The smallest species, semipalmated sandpiper, had the lowest intake rate but the largest species, red knot, achieved only the same intake rate as the mid-sized dunlin. 6These functional responses indicate that probing is rarely more profitable than pecking. Currently, few beaches provide egg densities sufficient for efficient probing. Areas where eggs are deposited on the sand surface are critical for successful foraging and ongoing migration. This may be especially true for red knot, which have higher energetic demands owing to their larger body size yet appear to have depressed intake rates because they consume smaller prey than their body size should permit. [source] Phenotypic compromise in the face of conflicting ecological demands: an example in red knots Calidris canutusJOURNAL OF AVIAN BIOLOGY, Issue 1 2010François Vézina Phenotypic flexibility is a phenomenon where physiological functions in animals are reversibly adjusted in response to ecological constraints. Research usually focuses on effects of single constraints, but under natural conditions animals face a multitude of restrictions acting simultaneously, and potentially generating conflicting demands on the phenotype. We investigated the conflicting demands of low temperatures and a low quality diet on the phenotype of a shorebird, the red knot Calidris canutus. We tested the effects of switching diet from a high quality trout food to low quality hard-shelled bivalves in captive birds acclimated to temperatures reflecting natural winter conditions. Feeding on bivalves generated a digestive constraint forcing the birds to increase the height and width of their gizzard by 66% and 71%, respectively, over 30 days. The change in gizzard size was associated with an initial 15% loss of body mass and a reduction in size of the pectoral muscles by 11%. Because pectoral muscle size determines summit metabolic rate (Msum, an indicator of cold endurance), measured Msum declined by 9%. Therefore, although the birds were acclimated to cold, gizzard growth led to a loss of cold endurance. We propose that cold-acclimated knots facing a digestive constraint made a phenotypic compromise by giving-up cold hardiness for digestive capacity. Field studies suggest that phenotypic compromises occur in free-living red knots as well and help improve survival. [source] Gizzard and other lean mass components increase, yet Basal Metabolic Rates decrease, when red knots Calidris canutus are shifted from soft to hard-shelled foodJOURNAL OF AVIAN BIOLOGY, Issue 2 2004Theunis Piersma We measured basal metabolic rate (BMR), body mass, lean mass, and gizzard mass of captive red knots Calidriscanutusislandica maintained on a trout chow diet (soft-texture, low ash and water content) for several years and then shifted to small mussels Mytilus edulis (hard-texture, high ash and water content). During a 3-week period of feeding on mussels, body mass, lean mass, and gizzard mass increased 7.3 g (+7%), 10.5 g (+12%), and 4.9 g (+213%), respectively, yet BMR decreased from 0.96 to 0.89 W (,8%). Under the new mussel regime, red knots must have reduced the metabolic intensity of some of the tissues. This suggests that the experimental red knots experienced the transition to a mussel diet as stressful and energy limiting, resulting in an energy-saving strategy by reducing BMR in spite of hypertrophy of the gizzard and other organs. [source] | ||||||||||