Least Auklet (Aethia pusilla)

  • Royal Society for the Protection of Birds
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... The slight male-biased sexual dimorphism (2-9%; Table 3) in both ornamental and anatomical traits matched the pattern previously described for Least and Crested auklets (Jones and Montgomerie 1992;Jones et al. 2000). Nevertheless, in our main study population on Buldir, size dimorphism was slightly greater in the feather ornaments than in anatomical traits (Table 3), consistent with the ornaments' function in sexual and social displays as males appear to take a more active role in courtship displays than females (e.g., Hunter and Jones 1999;Bond et al. 2020;Jones 2020). ...
... While there was a large increase in feather ornament size between 1-and 2-year-olds, ornament size did not increase further with age, and there was no evidence of senescence in ornament expression even in the oldest birds ( Figure 2). Like the other Aethia auklets, average longevity in this species is about 8-9 years (Jones et al. 2007;Bond et al. 2020). We studied 28 individuals >7 years old, where senescence might be expected but we found no evidence of a decline in body condition (SMI) or ornament size (Figures 2 and 3). ...
Both sexes of Whiskered Auklets (Aethia pygmaea) display the most elaborate feather ornaments of any seabird: a slender black forehead crest, and 3 bilaterally symmetrical pairs of white facial plumes (superorbital, suborbital, and auricular). We studied patterns of ornament variation in 796 banded individuals (147 of known sex, 254 of known age from 1 to 16 years) during 1992–2009 at Buldir Island (principally), and 3 other Aleutian Islands (Davidof, Ulak, and Egg) in Alaska, USA. As expected for socially selected traits, ornaments were more variable across individuals than anatomical traits in size but with only slightly male-biased sexual dimorphism. Body condition index increased from age 1 to 3 years but changed little thereafter. Even within birds ≥4 years old, ornament size was positively related to body condition index. Subadults (one-year-olds) had smaller ornaments than adults (age 2–16 years) but there was no further change in ornament size as adults aged and no evidence of senescence even in the oldest birds (>8 years old). Nonetheless, overall ornament size varied from year-to-year at Buldir and was correlated with indices of both ocean climate and auklet productivity in the preceding 2–5 years. From Buldir to Egg Island (1,266 km), the size of both anatomical and ornamental traits increased by 5–15% except for bill depth, which was largest in birds from Buldir and Egg at opposite ends of the Aleutian breeding range. This study is one of few to examine patterns of ornament variation in a long-lived, socially monogamous bird, even though such patterns are crucial to understanding the relationship between sexual selection and life history.
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Subadult seabirds ‘prospect’, or visit breeding colonies to evaluate reproductive success, identify suitable habitats, and assess potential partners; however, prospector biology is poorly understood. I explored prospector biology to understand post-natal seabird dispersal and recruitment decisions using Least (Aethia pusilla) and Crested Auklets (A. cristatella). Here, I document auklet colony attendance, behaviour, and reproductive success and use this foundation to examine the timing of colony attendance by prospecting subadult auklets. Subadult auklets were found to spend much less time socializing than expected and their attendance at the colony appeared to be independent of reproductive success as it was restricted to the incubation period. This study is the first to document differences in adult and subadult behaviour of auklets and attempt to understand patterns of subadult colony attendance and serves as a significant first step towards understanding patterns of subadult recruitment.
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Common Murres (Uria aalge) exhibit an unusual molt sequence. Primary molt begins at a focus between P4 and P7 and progresses in two rapid concurrent waves, proximally to P1, and distally to P10. The only other birds known to have a similar molt sequence are caracaras and falcons (Falconidae), parrots (Psittaciformes), and Pied Kingfishers (Ceryle rudis). Great Auks (Pinguinus impennis) also appear to have followed the same primary-molt sequence. Phylogenies for the Alcidae indicate that Great Auks, Common Murres, Thickbilled Murres (Uria lomvia), Razorbills (Alca torda), and Dovekies (Alle alle) share a common ancestor and are more closely related to one another than to other alcids. This suggests that the unusual sequence of primary molt in Common Murres is a shared-derived character that occurs in the other four species in their clade but has been overlooked. Adult male Common Murres have significantly shorter secondaries and longer primaries, on average, than do adult females, resulting in a slightly higher aspect ratio in males. Secondary molt begins when primary molt is more than one-third completed. Secondaries are replaced rapidly but sequentially (not synchronously or simultaneously); molt appears to proceed from two foci, proximally from S1 to S4, and both proximally and distally from S8, but more data are needed to clarify this point. Rectrix molt begins when primary molt is two-thirds completed. Rectrix loss and replacement occur rapidly, possibly synchronously, and in no apparent order. Adults molt about two weeks later than nonbreeding subadults. We found no differences in the timing of molt between the sexes in adults or subadults. Duration of flight-feather molt can vary from less than 25 days to more than 80 days, possibly reflecting interyear variation in prey abundance.
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