Linking foraging and breeding strategies in tropical seabirds

Submitted by Johan on 21 May 2021.

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In this study we challenged the widespread view that tropical seabirds forage more unpredictably than temperate and polar species, and we tested the hypothesis that the foraging behaviour of a species is associated with its breeding strategy.

By deploying GPS trackers on two sympatric species, we found that while the asynchronously breeding brown boobies foraged unpredictably, considered typical breeding and foraging behaviour for tropical seabirds, the seasonally breeding masked boobies foraged more predictably, adopting a foraging strategy like that expected of a temperate/polar breeding species.

Background to this research

In temperate and polar regions, seasonal fluctuations in marine productivity cause seabirds to congregate and breed at specific times of the year. The typical foraging strategy that seabirds breeding in these regions adopt is to repeatedly visit similar locations at sea throughout a breeding season.

By contrast, in tropical environments where marine productivity is less seasonal it may not be profitable for seabirds to consistently frequent the same areas at sea, nor for them to be constrained to a particular season to breed.

Diagram highlighting the differences in foraging behaviour of tropical and temperate seabirds.

Using the Important Bird and Biodiversity Area (IBA) of Dog Island, Anguilla in the Caribbean as our study site and via the deployment of GPS data loggers, we examined the foraging behaviour of two closely related tropical seabird species that colonise the same island yet exhibit markedly different breeding strategies: the asynchronously breeding brown booby Sula leucogaster and the seasonal breeding masked booby Sula dactylatra. We obtained tracks for 251 birds over 5 years.

We hypothesised that while some tropical species breed asynchronously in response to unpredictable fluctuations in prey availability, others adopt a seasonal breeding strategy for the same reasons that temperate and polar species do.

Our results support this hypothesis and suggest that the predictability of seabird foraging behaviour in the tropics may be related to breeding strategy, with populations that breed seasonally exhibiting more predictable foraging behaviour than those that breed aseasonally.

By: Dr Louise Soanes, University of Roehampton

Read more in the Open Access paper here: