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Abstract

Many seabird species have a long breeding-deferral period, during which individuals mature and spend most of their time at sea, making them particularly difficult to study. In some species, immatures are known to start visiting colonies before reaching adulthood, presumably to learn the behaviours required to secure a nest and mate for future breeding. However, immature colony attendance remains undocumented in many species, particularly those that are difficult to observe, such as nocturnal, cavity-nesting species and species in which immatures are indistinguishable from adults. Here, we studied the attendance patterns and behaviour of Streaked Shearwaters Calonectris leucomelas on Awashima Island, Japan, during the chick-rearing period. We logged the number and duration of visits to the colony and assessed the potential influence of moonlight on these metrics. We found a weak effect of moonlight on attendance but identified two types of nocturnal visits: one in which birds spent little time above ground and the other in which birds spent hours sitting on the surface. During the latter, birds often gathered in groups and either rested or engaged in behaviours such as allopreening, fighting, calling, and digging burrows. These longer visits sharply decreased in numbers well before the end of the chick-rearing period, and we suggest these visits are most likely undertaken by immatures, based on behaviours documented in other shearwater species. The presence of immature Streaked Shearwaters at the colony during the breeding period has implications for the population ecology of the species and highlights the potential impact of predators and other at-colony risks on an additional age class of Streaked Shearwaters, beyond adults and chicks.

DOI

http://doi.org/10.5038/2074-1235.54.1.1687

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COMPLIANT_54_1_79-86_Appendix1.pdf (48 kB)
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