Factors influencing prey capture success and profitability in Australasian gannets (Morus serrator).

Thomas Cansse,Melanie R Wells,John P Y Arnould,Louarn Fauchet

doi:10.1242/bio.047514

Abstract

ABSTRACTKnowledge of the factors influencing foraging efficiency in top predators can provide insights into the effects of environmental variability on their populations. Seabirds are important marine predators foraging in a highly temporally and spatially variable environment. While numerous studies have focussed on search time and its effects on foraging energetics in seabirds, relatively little is known about the factors influencing capture success and prey profitability in these predators. In the present study, animal-borne cameras were used to investigate the chase durations, capture success, handling durations and profitability of prey consumed by Australasian gannets (Morus serrator) (n=95) from two breeding colonies in south-eastern Australia exposed to different oceanographic conditions. Capture success was generally lower when individuals foraged alone. However, foraging in multi-species groups and in high prey densities increased chase time, while larger prey elicited longer handling times. While prey type influenced profitability, high prey density and foraging in multi-species groups was found to lower prey profitability due to increased time expenditure. While previous studies have found group foraging reduces search time, the increased profitability explains why some animals may favour solitary foraging. Therefore, future studies should combine search time and the currently found factors.

Highlights

Foraging is a key aspect in the life history of all heterotrophic organisms
Previous research has suggested that individuals maximize their energy intake per time unit (Krebs et al, 1978) by reducing prey handling time and/or reducing search time (MacArthur and Pianka, 1966)
While search time in foraging seabirds has been studied extensively (Garthe et al, 2014; Patrick et al, 2014; Weimerskirch et al, 1997), little is known about the factors influencing capture success and prey profitability

Summary

Introduction

Efficient foragers aim to maximize energy intake while keeping the cost of obtaining food to a minimum (Schoener, 1971; Stephens et al, 2008). Foragers have to make choices such as where and when to forage, how long to spend in a food patch and the time spent on handling food. The energy gained by consuming food should be higher than the energy and time spent on finding, handling and consuming food (MacArthur and Pianka, 1966). Profitability can be calculated as the net energy gain divided by the time spent on handling the food and can be used as a measure of foraging efficiency. A higher profitability leads to a higher foraging efficiency and, more efficient foragers

Methods

Results

Conclusion