Survival of Western Sandpiper Broods on the Yukon-Kuskokwim Delta, Alaska

The rate of chick growth in high-latitude breeding shorebirds is rapid, but little is known about the effect of chick mass, growth, and brood movements on subsequent brood survival. To address these topics, we monitored chick growth patterns, daily brood movements, and survival of Western Sandpipers (Calidris mauri) on the Yukon-Kuskokwim Delta, Alaska. We assessed the effect of chick age, mass, and hatch date on brood survival using Program MARK. We mapped brood locations daily, and compared brood movement patterns between successful and unsuccessful broods. Younger chicks survived at lower rates and moved shorter distances than older chicks. The overall probability of one or more chicks from a brood surviving to 15 days of age was 0.73 ± 0.05 SE. Brood survival declined seasonally, and broods with heavier chicks survived at higher rates than those with lighter chicks. On average, successful broods fledged 1.7 ± 0.1 SE chicks. Rate of chick growth was intermediate between those of high arctic and temperate-breeding shorebirds, and chick mass at hatching declined seasonally. Western Sandpiper brood survival was lowest when chicks were young, spatially clumped, and unable to maintain homeothermy, probably because young chicks were more vulnerable to both complete depredation events and extreme weather. Our data suggest that larger, older chicks are able to avoid predators by being spatially dispersed and highly mobile; thermal independence, achieved after approximately day five, enables chicks to better endure prolonged periods of cold and low food availability. Supervivencia de Nidadas de Calidris mauri en el Delta Yukon-Kuskokwim, Alaska Resumen. La tasa de crecimiento de polluelos en aves que se reproducen a latitudes altas es rápida, pero se conoce poco sobre el efecto del peso y el crecimiento de los polluelos y de los movimientos de las crías sobre la supervivencia de las nidadas. Para evaluar estos tópicos, monitoreamos los patrones de crecimiento de polluelos, el movimiento diario de las crías, y la sobrevivencia de Calidris mauri en el Delta Yukon-Kuskokwim, Alaska. Determinamos el efecto de la edad, el peso y la fecha de eclosión de los polluelos sobre la supervivencia de la nidada utilizando el programa MARK. Mapeamos la localización de las crías diariamente, y comparamos los patrones de movimientos entre nidadas exitosas y no exitosas. Los polluelos más jóvenes tuvieron tasas de supervivencia menores y se movieron distancias más cortas que los polluelos de más edad. La probabilidad general de que uno o más polluelos de una nidada sobreviviera hasta 15 días de edad fue 0.73 ± 0.05 EE. La supervivencia de las nidadas disminuyó estacionalmente y las nidadas con polluelos de mayor peso tuvieron tasas de supervivencia mayores que las nidadas con polluelos más livianos. En promedio, las nidadas exitosas produjeron 1.7 ± 0.1 EE polluelos. La tasa de crecimiento de los polluelos fue intermedia con respecto a las aves playeras que se reproducen en el ártico y las que lo hacen en zonas templadas. El peso de los polluelos al momento de eclosionar disminuyó estacionalmente. La supervivencia de las nidadas de C. mauri fue mínima cuando los polluelos eran jóvenes, estaban agrupados y no eran capaces de mantener la homeotermia, probablemente debido a que los polluelos jóvenes eran más vulnerables a eventos de depredación completa y al clima extremo. Nuestros datos sugieren que los polluelos más grandes y de mayor edad son capaces de evitar a los depredadores al encontrarse espacialmente dispersos y ser altamente móviles; la independencia térmica que es alcanzada aproximadamente luego del día cinco permite a los polluelos soportar periodos prolongados de frío y de baja disponibilidad de alimento.

Influence of Female Age and Body Mass on Brood and Duckling Survival, Number of Surviving Ducklings, and Brood Movements in Redheads

I documented brood and duckling survival, the number of surviving ducklings, and brood movements of Redheads, and examined the association between these variables and female age and body mass. Redhead brood success was 55% and duckling daily survival rates averaged 0.868. Female body mass, but not age, was related to brood and duckling survival and the number of surviving ducklings. Successful females were heavier and produced more ducklings. All brood-movement measures differed between successful and unsuccessful females, however, the distance of the first move between wetlands accounted for the most variability in brood success. Increased body mass, but not age, was associated with longer first brood movements.

Habitat-related variation in movements and fledging success of American black duck broods in northeastern Nova Scotia

Female American black ducks (Anas rubripes) are known to move their broods from low- to high-nutrient rearing sites. We studied the extent of brood movement and fledging success in a northeastern Nova Scotia watershed. Annually, about half the broods moved either overland or along three rivers from small, widely dispersed oligotrophic–mesotrophic wetlands to a large hypertrophic tidal marsh. Mean brood size at fledging was 3.50 in the tidal marsh but 7.05 at the dispersed freshwater wetlands. Females that remained at dispersed sites fledged more ducklings than females that moved to the marsh. Attrition occurred predominantly in the marsh or in transit. Females fledged fewer young when they raised broods at the marsh than when the same females raised broods at inland sites. Females were as successful at nutrient-poor sites as at nutrient-rich sites. The study suggests that concentrating birds in nutrient-rich sites may be counterproductive in terms of female reproductive fitness and population recruitment.