Variation in wing and tail moult intensity in white-chinned Petrels

The cost of moult is substantial, and the timing and intensity of flight
feather moult can influence survival and fitness, especially in large,
long-winged species such as many seabirds. We explore variation in wing
and tail moult in > 2400 White-chinned Petrels Procellaria
aequinoctialis killed in fisheries off southern Africa to assess how they
integrate moult into their annual cycle and whether wing moult impacts
their behaviour at sea. All petrels showed a simple descendent primary
moult and one active moult centre, although moult of P2-3 sometimes
started before P1. The Underhill‐Zucchini moult model estimated that adult
primary moult started after breeding on 7 May (± 8 days SD) and lasted 103
days (mean end date 20 August ± 10 days). Adult moult was particularly
intense in the inner primaries, growing up to six feathers at once.
Secondary moult started two weeks after primary moult, once 3–4 primaries
had been dropped. Secondary moult typically started with the innermost
secondaries, plus inward waves from S1 and S5 in 2.7 ± 1.3 active moult
centres, replacing 4.6 ± 2.7 (1–13) secondaries at once. Adults had more
intense secondary moult than immatures. However, photographs of
non-moulting birds at sea show that 27% of birds do not replace all
secondaries each year. Tail moult usually commenced with the start of
secondary moult and was highly variable, with 1–12 rectrices growing at
once. Although adult wing moult was intense, there was no marked reduction
in flight activity among breeding adults fitted with leg-mounted activity
loggers during the moult period. Our findings largely accord with previous
studies of moult in petrels, but our large sample size reveals
considerable variation among individuals, which is surprising given the
high cost of moult. Future studies should attempt to investigate the
factors determining this variation.