Natal and breeding dispersal in American Avocets

Abstract

We banded 811 nestling and 478 adult American Avocets (Recurvirostra americana) at a breeding site in northeastern California and observed their occupancy of space over the next one to two breeding seasons. Of the fledged young, 12% were seen after their hatching year, and 4.6% bred within one to two years after hatching. Twelve birds returned and bred at age two, and one individual bred at age one. Only 21 to 25% of avocets estimated to have survived to age two returned and bred; the rest presumably dispersed elsewhere, Females dispersed farther from their hatching site than did males. Overall, 53.6% of banded adults were seen one or two years following banding, but only 24.3% were known to have bred within 20 km of the banding site. There was a significant tendency for adults to avoid returning or to disperse greater distances in the year after they were banded. Approximately 72 to 78% of the adults estimated to have survived for two years after they were banded were seen subsequently; 56% of these birds returned and bred. There were no significant differences between males and females in dispersal distances or breeding return rates. Males responded to nesting failure by dispersing farther the next year, but females did not. There were no relationships between mate retention, dispersal distance, or subsequent success, Avocets were paired upon arrival at their breeding sites, which led to mate changes between years. We suggest that avocet dispersal patterns are life-history adaptations to unpredictable breeding habitats that yield few benefits from site familiarity.