Abstract
Most Procellariform seabirds are pelagic, breed in summer when prey availability peaks, and migrate for winter. They also display a dual foraging strategy (short and long trips) and sex-specific foraging. The Westland petrel Procellaria westlandica, a New Zealand endemic, is one of the rare seabirds breeding in winter. Preliminary findings on this large and sexually dimorphic petrel suggest a foraging behaviour with no evidence of a dual strategy, within a narrow range and with shared areas between sexes. To investigate further this unusual strategy, the present study determined the fine-scale at-sea behaviours (global positioning system and accelerometer data loggers) and trophic niches (stable isotopes in whole blood) of chick-rearing individuals (16 males and 13 females). All individuals foraged on the shelf-slope of the west coast of New Zealand's South Island with short, unimodal trips. Both sexes foraged at similar intensity without temporal, spatial or isotopic niche segregation. These findings suggest the presence of a winter prey resource close to the colony, sufficient to satisfy the nutritional needs of breeding without increasing the foraging effort or intra-specific competition avoidance during winter. Additional data are needed to assess the consistency of foraging niche between the sexes and its reproductive outcomes in view of anticipated environmental changes.
Highlights
Seabirds are mainly represented by the Procellariiforms (36%, [1]), which are responsible for their biggest consumption of marine resources worldwide
At-sea movement (GPS) data were obtained from 32 individuals, and owing to device malfunctions, atsea movements combined with behaviour data were obtained from 29 individuals (16 males/18 trips, 13 females/15 trips; table 1) totalling 1556 h in duration
Using combined global positioning system (GPS) and accelerometer data from adult males and females rearing chicks during two breeding seasons, the present study provided information on the fine-scale foraging behaviour of Westland petrels
Summary
Seabirds are mainly represented by the Procellariiforms (36%, [1]), which are responsible for their biggest consumption of marine resources worldwide (approx. 24.1 million tons yr–1, [2]). Body mass 20 g) to the largest albatross (wing span >300 cm, body mass 1200 g, [3]) While their 2 successful adaptive radiation has led Procellariiforms to occupy diverse ecological niches from tropical to polar regions [4], they still share common life-history traits linked to their pelagic lifestyle. Procellariiforms have to prospect wide areas by covering long distances within a large range [8,9]. This energetic constraint is traditionally seen as the cause of their delayed sexual maturity, low fecundity, slow growth of a single offspring and long lifespan [10]
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