Factors Affecting Incubation Patterns And Sex Roles of Black Oystercatchers in Alaska

Abstract

Studies examining the effects of human disturbance on avian parental behavior and reproductive success are fundamental to bird conservation. However, many such studies fail to also consider the influence of natural threats, a variable environment, and parental roles. Our work examines interactive relationships of cyclical (time of day, tide, temperature, seasonality) and stochastic (natural/human disturbance) processes with incubation patterns (attendance, bout lengths, recess rates) of the Black Oystercatcher (Haematopus bachmani), a shorebird of conservation concern. We used 24-hr-per-day video monitoring of 13 molecularly sexed breeding pairs to systematically examine incubation, revealing previously undocumented information that may inform conservation practices for the genus. Seven of 22 video-monitored nests failed, primarily from egg depredation by nocturnal mammals. Analyses of 3177 hr of video footage indicated a near doubling of incubation-bout lengths at night, corresponding to the increased risk of nighttime egg predation. Females had higher overall nest attendance (54% vs. 42%) and longer mean incubation bouts than did males (88 min vs. 73 min). Uninterrupted incubation bouts were over twice as long as bouts interrupted by disturbance. Incubating males departed nests substantially more frequently because of nest-area disturbances than did females in one but not both years of our study. Our findings suggest that the sexes incubate in different but complementary patterns, facilitating efficient egg care in a dynamic environment with several nest threats. We emphasize the importance of considering natural influences when human threats to shorebird reproductive behavior and success are evaluated.