Courtship and copulation constitute crucial elements of avian reproduction and fitness. Despite the potential impact of environmental perturbations and long-term climate change on avian reproduction, few studies provide quantitative information on courtship and copulation behaviors and their responses to proximate environmental factors. We provide the first quantitative description of courtship and copulation behavior in Glaucous-winged Gulls (Larus glaucescens), an important indicator species of marine environmental quality in North America's Pacific Northwest. Male and female Glaucous-winged Gulls exhibited similar frequencies of most pre- and post-mount behaviors, which closely resemble those used by other larids. Mounts were more frequent than expected during the pre-egg-laying and egg-laying stages of the breeding season and less frequent than expected during the incubation stage. In 2008, numbers of successful copulations vs. unsuccessful copulations, numbers of cloacal contacts per successful copulation, and copulation duration did not differ by reproductive stage. In 2012, copulation duration increased with day of the year and decreased with wind speed, and the number of cloacal contacts per copulation decreased with wind speed. The odds of paired head toss increased with tide height and decreased with solar elevation. The odds of female courtship beg increased with the number of days from its peak occurrence, and also with solar elevation, tide height, and Bald Eagle (Haliaeetus leucocephalus) disturbances. Mount interval, the time from the start of one mount in the study area to that of another, was positively related to time of day, barometric pressure, and solar elevation but was negatively related to solar radiation and colony occupancy. Both the temporal and spatial occurrence of copulation were socially facilitated by the behavior of neighboring birds in the colony. Our results suggest that changes in environmental variables due to climate change could affect reproductive behaviors and reproductive success in this species.

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