Evidence of incubation trade‐offs in Leach's Storm‐Petrel (Oceanodroma leucorhoa): ptilochronology as a measure of reproductive investment in a long‐lived seabird

Abstract

Avian incubation investment represents a trade‐off between the energetic demands of the parent and the thermal needs of the embryo. Parental energy balance and investment in somatic maintenance relative to incubation investment can be indexed by the rate of feather growth. Feather growth rates, or ptilochronology, of adult Leach's Storm‐Petrels Oceanodroma leucorhoa were used to assess parental investment to (1) determine whether individuals that invest heavily in current reproduction pay a cost for future reproduction as indicated by a cost for somatic maintenance and (2) assess whether this trade‐off is detected using ptilochronology, which may be a more direct measure of reproductive investment compared with body mass in seabirds. We found positive relationships between duration of the incubation period and both egg neglect and a mated pair's mean rate of induced feather growth, although we did not find a relationship between either egg neglect and feather growth or hatching success and feather growth. Our results suggest that during the incubation period a trade‐off exists between energy allocated to self‐maintenance and reproduction in this species, although egg neglect does not appear to be the mechanism that extends the incubation period in response to increased energetic demands of somatic maintenance. The lack of correlation between feather growth and egg neglect further suggests that some pairs may be better able to manage competing demands of self‐maintenance and incubation, possibly due to individual quality, coordination of incubation effort, burrow quality or some other factor.