Variation in Age Ratio of Midcontinent Greater White-Fronted Geese During Fall Migration

Annual productivity is an important parameter for the management of waterfowl populations. Fall age ratio (juveniles:total birds) is an index of productivity of the preceding breeding season. However, differences in the timing of migration between family groups and nonbreeding birds may bias age-ratio estimates. We examined temporal variation in age ratios of midcontinent greater white-fronted geese Anser albifrons frontalis from interior and northwestern Alaska at a northern autumn staging area near Delta Junction, Alaska. Photographic sampling conducted near Delta Junction resulted in an annual age ratio of 0.388 ± 0.004 (mean ± SE) in 2010 and 0.390 ± 0.001 in 2011. Our study demonstrated temporal variation in age ratios over the duration of the migration period during August and September. We recommend that sampling be conducted for 3-d periods at the beginning, middle, and end of the migration period to account for temporal variation in migration of family groups.

Relatedness and Nesting Dispersion within Breeding Populations of Greater White-Fronted Geese

We studied patterns of relatedness and nesting dispersion in female Pacific Greater White-fronted Geese (Anser albifrons frontalis) in Alaska. Female Greater White-fronted Geese are thought to be strongly philopatric and are often observed nesting in close association with other females. Analysis of the distribution of nests on the Yukon-Kuskokwim Delta in 1998 indicated that nests were significantly clumped. We tested the hypothesis that females in the same nest cluster would be closely related using estimates of genetic relatedness based on six microsatellite DNA loci. There was no difference in the mean relatedness of females in the same cluster compared to females found in different clusters. However, relatedness among females was negatively correlated with distance between their nests, and geese nesting within 50 m of one another tended to be more closely related than those nesting farther apart. Randomization tests revealed that pairs of related individuals (R > 0.45) were more likely to occur in the same cluster when analyzed at the scale of the entire study site. However, the pattern did not hold when restricted to pairs found within 500 m of each other. Our results indicate that nest clusters are not composed primarily of closely related females, but Greater White-fronted Geese appear to be sufficiently philopatric to promote nonrandom patterns of relatedness at a local scale. Parentesco y Dispersión de Nidos en Poblaciones Reproductivas de Anser albifrons frontalis Resumen. Estudiamos los patrones de parentesco y la dispersión de nidos en hembras de Anser albifrons frontalis en Alaska. Se piensa que las hembras de A. a. frontalis son fuertemente filopátricas y frecuentemente se las observa nidificando asociadas de modo cercano con otras hembras. El análisis de la distribución de los nidos en el Delta de Yukon-Kuskokwim en 1998 indicó que los nidos estuvieron significativamente agrupados. Evaluamos la hipótesis de que las hembras en el mismo grupo de nidos estarían cercanamente emparentadas usando estimaciones de parentesco genético basadas en seis loci de ADN microsatelital. No hubo diferencias en el promedio de parentesco de hembras en el mismo grupo comparado con hembras que se encontraron en grupos diferentes. Sin embargo, el parentesco entre las hembras se correlacionó negativamente con la distancia entre los nidos, y los gansos que se encontraban nidificando a menos de 50 m unos de otros tendieron a estar más cercanamente emparentadas que aquellos nidificando más lejos. Análisis de aleatorización revelaron que parejas de individuos emparentados (R > 0.45) presentaron mayor probabilidad de encontrarse en el mismo grupo cuando los análisis se hicieron a la escala de todo el sitio de estudio. Sin embargo, el patrón no se mantuvo cuando los análisis se restringieron a pares ubicados dentro de 500 m uno de otro. Nuestros resultados indican que los grupos de nidos no están primariamente compuestos por hembras cercanamente emparentadas, pero que A. a. frontalis parece ser suficientemente filopátrica como para promover patrones no aleatorios de parentesco a escala local.

Functional and numerical responses of predators to cyclic lemming abundance: effects on loss of goose nests

The alternative-prey hypothesis predicts that predation on goose eggs will be most severe the year following a lemming peak. We tested this by investigating how predators of goose eggs responded to lemming abundance on the Kent Peninsula, Nunavut, Canada, where nest success of white-fronted geese (Anser albifrons frontalis) and Canada geese (Branta canadensis hutchinsii) fluctuates widely. The main predators of both goose eggs and lemmings are arctic foxes (Alopex lagopus), glaucous gulls (Larus hyperboreus), and parasitic jaegers (Stercorarius parasiticus). Foxes responded functionally to lemming density: in prime goose-nesting areas they spent less time foraging during the peak lemming year than during the increase, and were seen foraging in prime nesting areas less often during the peak than during the decline. However, numbers of fox sightings in the study area during the nesting period did not differ significantly among years. The total response (functional × numerical) of gulls was lowest at the lemming peak and highest during the increase. The total response of parasitic jaegers did not vary significantly among years. Hence, we predicted that the number of nests lost to all predators combined should be lowest at the peak and possibly highest during the increase. During the 3 years of this study, loss of Canada goose nests was lowest at the peak but highest during the decline, and annual losses of white-fronted goose nests varied little. In cycles prior to this study, nest loss was high in declines but not particularly low during peaks. Several factors may alter the functional and numerical responses of predators, obscuring the simple pattern of nest loss predicted by the alternative-prey hypothesis.