Ardea
Official journal of the Netherlands Ornithologists' Union

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Bluso-Demers J.D., Ackerman J.T. & Takekawa J.Y. (2010) Colony attendance patterns by mated Forsterís Terns Sterna forsteri using an automated data-logging receiver system. ARDEA 98 (1): 59-65
In order to examine 24-hour colony attendance patterns by mated Forsterís Terns Sterna forsteri in South San Francisco Bay, California, during incubation and chick-rearing stages, we radio-marked 10 individuals consisting of five pairs and recorded colony attendance using an automated data-logging receiver system. We calculated and analyzed five variables: the total attendance time by pairs and individuals, the duration of individual attendance bouts, and the duration both members of a pair either overlapped in colony attendance or were both absent from the colony. The percentage of time spent on the colony by at least one individual of a pair was highest during incubation and declined during chick rearing. Overall, male terns spent a greater proportion of time diurnally attending the colony than females. Females spent a greater proportion of time on colony at night, and without these nocturnal records, we would have reported overall female colony attendance rates as being much lower. Despite sex-specific differences in attendance rates, the length of attendance bouts did not differ between the sexes. Simultaneous colony attendance by both members of a pair was high at night, but during the day, pairs infrequently overlapped in their colony attendance and both members were frequently absent. Our data-logging system functioned well, and our data illustrates the importance of collecting 24-hour records when considering attendance rates.


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