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Plumage-based Ageing Criteria for the Black-footed Albatross Phoebastria Nigripes
| Content Provider | Semantic Scholar |
|---|---|
| Author | Hyrenbach, K. David |
| Copyright Year | 2002 |
| Abstract | SUMMARY I describe plumage-based ageing criteria for the Black-footed Albatross Phoebastria nigripes and assess the utility of this technique using known-age museum specimens and at-sea observations. First, I quantify the repeatability of the plumage assessments and document that 95%, 95%, and 100% of the inspected specimens were reliably scored into one of three standardised plumage classes. Next, I assess the correspondence between the three plumage classes described here and three age groups: juvenile (0.5 years), immature (0.5–4.5 years), and mature (>4.5 years) birds. Overall, 82%, 68%, and 100% of age class 1, 2, and 3 specimens inspected were juvenile, immature, and mature birds, respectively. Finally, to illustrate the applicability of the ageing criteria, I characterise the monthly age-class composition of the Black-footed Albatross population off southern California (29–35°N, 117–124°W) from February through to December. I surveyed albatross population structure during 19 cruises between August 1996 and April 2000. Overall, 97% of the 294 birds sighted during surveys were aged using the plumage-based criteria. I used hierarchical clustering to identify time periods with similar age-class population composition. This analysis revealed four distinct stages: (1) the incubation period (November–December), characterised by the absence of white-rumped (breeding age) individuals; (2) the chick-brooding period (February– March), characterized by the numerical dominance of juvenile birds; (3) the chick-rearing (April–June) and postbreeding (August–October) period, characterised by the presence of all three age classes with mature birds being numerically dominant; and (4) the period of dispersal from breeding colonies (July), characterised by the absence of juvenile birds and the numerical dominance of mature individuals. These observations are in agreement with previous studies of Black-footed Albatross distributions off the west coast of North America. Despite substantial individual variability in moulting and bursa involution patterns, this study suggests that plumage characteristics can be effectively used to discriminate between different albatross age classes at sea. |
| Starting Page | 85 |
| Ending Page | 93 |
| Page Count | 9 |
| File Format | PDF HTM / HTML |
| Volume Number | 30 |
| Alternate Webpage(s) | http://www.marineornithology.org/PDF/30_2/5_hyrenbach.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
