Patterns of year-round colony attendance by VHF radio-tagged Crested Auklets (Aethia cristatella) at their prototypical Aleutian breeding site

Abstract

Seabird colony attendance during their breeding seasons is driven by reproductive obligations of incubation and chick rearing, resulting in relatively predictable attendance patterns near breeding sites. Less is understood about patterns and function of activity ashore at colony sites outside the breeding season. We attempted to quantify year-round activity of crevice-nesting Crested Auklets (Aethia cristatella) at Gareloi Island, Alaska, a site with some of their largest colonies. In June and July 2013 and 2014, 94 Crested Auklets (92 adults and 2 subadults) were fitted with uniquely coded 1.0 g VHF radio-tags (0.6% of body mass) at 2 inland study plots in the southeast colony. Radio receiver–loggers remotely detected and recorded individuals present on the nearby colony site surface 24 h/d from date of tagging through autumn, winter, spring, and summer 2013–2015. Notably, we found Crested Auklets present in all months of the year, with half of our radio-tagged auklets (n = 47, 29 females, 10 males, 8 unknown sex) detected inland at the colony site during nonbreeding months (Sep–Mar). Visit duration for these individuals comprised about 0.4% of their total annual colony site activity; this is the first evidence of year-round Crested Auklet colony attendance that may be unique to Gareloi. Other findings included extreme individual variability and intersexual differences in colony attendance frequency, differences in attendance between breeding and nonbreeding birds, a lapse in surface activity prior to laying in May, and frequent nocturnal activity on the colony surface. Enhanced circannual patterns of Crested Auklet colony attendance at this island may relate to defense of nesting site and other social advantages, permitted by a nearby highly productive sea area with year-round foraging opportunities.