Divergent foraging strategies during incubation of an unusually wide-ranging seabird, the Murphy’s petrel

Abstract

Divergent foraging strategies may emerge within a population due to a combination of physiological and environmental factors; yet to persist, neither strategy should offer a consistent selective advantage over the alternative in the long term. Murphy’s petrels Pterodroma ultima from Henderson Island (24°20′S, 128°20′W) in the South Pacific Ocean are highly vagile, and exhibit two distinct foraging trip types during incubation; similar proportions of birds undertake either looping trips around the South Pacific Gyre to waters off Peru (hereafter “East”) or trips south-west of the colony towards the Subtropical Front (“South”) (mean maximum ranges of c. 3800 or 2000 km from the colony, respectively). However, the relative benefits of the distinct trip types remain unclear. Through tracking birds with GPS and salt-water immersion loggers in 2015, the fine-scale foraging behaviour was examined for East (trip durations: 14.1–19.8 days, maximum ranges 2387–4823 km) and South trips (12.9–25.8 days, 1565–1991 km). Data on behaviour classified from GPS tracks, the number of wet bouts per hour (a proxy for landing rates) and wind speeds, were used to distinguish two distinct foraging modes: birds on East trips spent more time in directed movement, whereas those on South trips spent a greater proportion of time in area-restricted search (ARS) behaviour. East trips were associated with higher overall mass gain, and wet bouts occurred in equal proportions during directed movement and ARS behaviour. This suggests that in unproductive marine environments, it may be more profitable to maximise area covered to increase the chances of encountering prey. Analysis of lower-resolution geolocator data (collected from 2011 to 2014) indicated that individuals were largely consistent in trip type between years. Since birds that conducted East trips were 19% lighter on departure from the colony and experienced more frequent tailwinds on foraging trips, we speculate that these birds may benefit from reduced movement costs, whilst also experiencing reduced competition for foraging opportunities.Electronic supplementary materialThe online version of this article (10.1007/s00227-018-3451-7) contains supplementary material, which is available to authorized users.

At-sea movements of wedge-tailed shearwaters during and outside the breeding season from four colonies in New Caledonia

“…We considered intensive and extensive search modes represented small-and large- ). This method required few prior assumptions and it has been used to interpret ecologically meaningful behaviours from movement data for a range of seabird species including procellariiforms , Mendez et al 2017, Bennison et al 2018, Clay et al 2019).…”

Gadfly petrels use knowledge of the windscape, not memorized foraging patches, to optimize foraging trips on ocean-wide scales

“…Optimal foraging theory predicts that animals looking for food adopt mechanisms to maximize their energy acquisition per unit time and minimize their energy loss [1][2][3]. The constraints faced by breeding oceanic seabirds-patchily distributed resources and having to return to their colony to alternate incubation shifts with the partner-result in sometimes spectacular foraging trips, many thousands of kilometres from the colony [4][5][6][7]. Seabirds thus have morphology and flight behaviour adapted to glean energy for these long commutes from the wind.…”

“…As predicted by aerodynamic theory-and as suggested by their genus name (from the Greek words 'Pteron', wing, and 'dromos', run)-the high aspect ratio per wing loading (the highest of all seabirds) makes them especially anatomically adapted for efficient flight: a fast, gliding flight with low profile drag [20]. Gadfly petrels are highly mobile, capable of undertaking exceptionally long foraging trips [4][5][6][7] by spending a large proportion of time in direct flight, actively looking for prey [4,7]. For example, Murphy's petrels (Pterodroma ultima) tracked from Henderson Island did not consistently target specific areas and foraged both during directed movement and area restricted search [6], and the higher mass gains were associated with the most wide-ranging trips [6].…”

“…Gadfly petrels are highly mobile, capable of undertaking exceptionally long foraging trips [4][5][6][7] by spending a large proportion of time in direct flight, actively looking for prey [4,7]. For example, Murphy's petrels (Pterodroma ultima) tracked from Henderson Island did not consistently target specific areas and foraged both during directed movement and area restricted search [6], and the higher mass gains were associated with the most wide-ranging trips [6]. Despite being the largest genus of pelagic seabirds, with several threatened species, many aspects of gadfly petrels' ecology have never been investigated and, at present, the flight behaviour and the wind use of the long distance flyers par excellence remain largely unknown.…”

“…Previous studies have shown that travelling seabirds follow prevailing favourable winds [6,8], but little is known about the mechanisms with which they manage to do so. Here, we examine whether long distance fliers such as gadfly petrels are capable not only of planning their route based on a priori knowledge of the regional wind regimes, but also of refining their route based on the local wind conditions.…”