Incubation patterns, parental roles, and nest survival of black oystercatchers (Haematopus bachmani) : influences of environmental processes and potential disturbance stimuli Public Deposited


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  • Shorebirds display great variation in mating systems and breed in dynamic environments that are increasingly subject to human threats worldwide. In order to adequately assess productivity and demography of shorebird populations, it is important to understand factors that influence patterns of parental care and reproductive success. The Black Oystercatcher (Haematopus bachmani) is a shorebird species of concern and an indicator of the health of intertidal ecosystems. Much information on breeding biology is lacking for the species, though it is reported to regularly experience low reproductive success and may be vulnerable to human disturbance during nesting. This thesis examines relationships among natural and human processes related to incubation and nest success of Black Oystercatchers in a high density breeding area of Alaska, experiencing increasing human recreational activity. In 2005 and 2006, oystercatcher nests were continuously monitored with video cameras to investigate the association of cyclical (time of day, tide, ambient temperature, seasonality) and stochastic (natural/human disturbance) processes with incubation patterns (nest attendance, incubation bout length, incubation recess rate) and sex roles. Review of over 3,000 hours of footage from 13 molecularly sexed nesting pairs revealed complimentary bi-parental care with differing roles between sexes. Females allocated more to nest attendance and had longer incubation bout lengths, indicating a greater investment in incubation compared to males. Males responded more frequently to nest area disturbance stimuli compared to females, indicating that males invest more in nest defense. Incubation patterns were also influenced by tide stage and height, ambient temperature, and disturbance stimuli. Incubation bout lengths nearly doubled at night, independent of sex. Longer nocturnal bouts may minimize parental activity near the nest during periods of increased predation risk when incubation duty changes could reveal the presence of nests to nocturnal predators. Video footage was also used to document the types and frequencies of human and predator stimuli, and extreme weather and tide episodes encountered near oystercatcher nests, and the effect of these potential disturbance stimuli on incubation behavior and nest success. Nearly 800 potential disturbance stimulus events were documented within 25 m of video monitored nests. Other bird species were the most frequently observed type of potential disturbance, but were largely ignored by incubating oystercatchers. Oystercatchers were most frequently disturbed (as evidenced by displacement from a nest) by conspecifics and humans, with nests left unattended for longer periods following human disturbance than any other disturbance type. Although infrequent, a high proportion of mammal observations also resulted in oystercatchers flushing from their nests. Changes in incubation behavior due to disturbance were not found to affect nest success, nor did nest success decrease with proximity to areas of frequent human recreational activity. Nocturnal nest predation by mustelids and nighttime flood tides accounted for six of seven nest failures recorded on video, even though nights were disproportionately short during the study. Thus, future shorebird breeding studies should assess causes of nest failure from latent nocturnal causes, rather than just obvious diurnal causes. With the analysis of extensive nest observation data this study identified natural and anthropogenic processes that affected incubation patterns of an uncommon shorebird species, specially adapted to a dynamic nesting environment. Results elucidate factors influencing oystercatcher life history and lay the groundwork for further investigation into the effects of human disturbance on nest success and demography of the Black Oystercatcher. Future research should investigate nest success in breeding areas experiencing higher levels of disturbance, include post-hatching breeding stages, and be conducted over multiple breeding seasons.
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