The Sub-Annual Breeding Cycle of a Tropical Seabird

S James Reynolds,Alistair Dawson,B John Hughes,Colin P Wearn,Graham R Martin,Petra Quillfeldt

doi:10.1371/journal.pone.0093582

S James Reynolds, Alistair Dawson + Show 4 more

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https://doi.org/10.1371/journal.pone.0093582

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Abstract

Breeding periodicity allows organisms to synchronise breeding attempts with the most favourable ecological conditions under which to raise offspring. For most animal species, ecological conditions vary seasonally and usually impose an annual breeding schedule on their populations; sub-annual breeding schedules will be rare. We use a 16-year dataset of breeding attempts by a tropical seabird, the sooty tern (Onychoprion fuscatus), on Ascension Island to provide new insights about this classical example of a population of sub-annually breeding birds that was first documented in studies 60 years previously on the same island. We confirm that the breeding interval of this population has remained consistently sub-annual. By ringing >17000 birds and re-capturing a large sample of them at equivalent breeding stages in subsequent seasons, we reveal for the first time that many individual birds also consistently breed sub-annually (i.e. that sub-annual breeding is an individual as well as a population breeding strategy). Ascension Island sooty terns appear to reduce their courtship phase markedly compared with conspecifics breeding elsewhere. Our results provide rare insights into the ecological and physiological drivers of breeding periodicity, indicating that reduction of the annual cycle to just two life-history stages, breeding and moult, is a viable life-history strategy and that moult may determine the minimum time between breeding attempts.

Highlights

The periodicity of animal breeding has long fascinated biologists who have often invoked ecological explanations of within and between-species variation in the timing of breeding and its evolution (e.g. [1,2])
The mean breeding interval of the Ascension Island population was shorter by 76.168.7 days than that of annually breeding conspecifics elsewhere in the species’ range
Despite having studied the Ascension Island population of birds since 1990, we still know little about the physiological constraints on birds of this population in relation to the breeding cycle

Summary

Introduction

The periodicity of animal breeding has long fascinated biologists who have often invoked ecological explanations of within and between-species variation in the timing of breeding and its evolution (e.g. [1,2]). Of all life-history stages, reproduction is probably most sensitive to an organism’s ecology This is true for almost all animal taxa that combat unpredictability of resources by interrupting breeding at different reproductive thresholds (e.g. some insects) and delaying implantation of embryos (e.g. some mammals). Such plasticity in the timing of breeding is not exhibited by birds [5], many of which undergo extensive physiological and behavioural preparations for breeding with its timing modulated by proximate factors such as temperature and photoperiod [4,6]. These include species whose populations breed every six months such as swift terns (Sterna bergii) on Aldabra Atoll [10] and white terns (Gygis alba) on Christmas Island (Pacific) [11], every seven to eight months such as white-tailed tropicbirds (Phaethon lepturus) on Ascension Island [12] and Aldabra Atoll [13], and bridled terns (Sterna anaethetus) on Aldabra Atoll [10], and every nine to 10 months such as Christmas shearwaters (Puffinus nativitatis) on the Pitcairn Islands [14], and Audubon’s shearwaters (Puffinus lherminieri) and swallow-tailed gulls (Creagrus furcatus) on The Galapagos Islands [15,16]

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