Environmental influences on Adelie penguin breeding schedules, endocrinology, and chick survival C.E. Ninnes a,⇑ , J.R. Waas a , N. Ling a , S. Nakagawa a,b , J.C. Banks a , D.G. Bell a , A. Bright a , P.W. Carey c , J. Chandler a , Q.J. Hudson a , J.R. Ingram a , K. Lyall a , D.K.J. Morgan a , M.I. Stevens d,e , J. Wallace a , E. Möstl f a Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand b Department of Zoology, University of Otago, P.O. Box 56, Dunedin, New Zealand c Sub-Antarctic Foundation for Ecosystems Research, 8 Estuary Road, Christchurch 8061, New Zealand d South Australian Museum, G.P.O. Box 234, Adelaide SA 5000, Australia e School of Earth and Environmental Sciences, University of Adelaide, SA 5005, Adelaide, Australia f Institute of Biochemistry, Department of Natural Sciences, University of Veterinary Medicine, A-1210 Vienna, Austria article info Article history: Received 18 October 2010 Revised 9 April 2011 Accepted 16 May 2011 Available online 23 May 2011 Keywords: Adelie penguin Breeding schedules Corticosterone Testosterone Oestrogens Sea ice abstract To understand how the social and physical environment influences behaviour, reproduction and survival, studies of underlying hormonal processes are crucial; in particular, interactions between stress and reproductive responses may have critical influences on breeding schedules. Several authors have exam- ined the timing of breeding in relation to environmental stimuli, while others have independently described endocrine profiles. However, few studies have simultaneously measured endocrine profiles, breeding behaviour, and offspring survival across seasons. We measured sex and stress hormone concen- trations (oestrogens, testosterone, and corticosterone), timing of breeding, and chick survival, in Adelie penguins (Pygoscelis adeliae) at two colonies in two different years. Clutch initiation at Cape Bird South (CBS; year 1, 14,000 pairs) occurred later than at Cape Crozier East (CCE; year 2, 25,000 pairs); how- ever, breeding was more synchronous at CBS. This pattern was probably generated by the persistence of extensive sea ice at CBS (year 1). Higher corticosterone metabolite and lower sex hormone concentrations at CBS correlated with later breeding and lower chick survival compared to at CCE – again, a likely con- sequence of sea ice conditions. Within colonies, sub-colony size (S, 50–100; M, 200–300; L, 500–600; XL, >1000 pairs) did not influence the onset or synchrony of breeding, chick survival, or hormone concentra- tions. We showed that the endocrine profiles of breeding Adelie penguins can differ markedly between years and/or colonies, and that combining measures of endocrinology, behaviour, and offspring survival can reveal the mechanisms and consequences that different environmental conditions can have on breed- ing ecology. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Penguins and many other species initiate breeding synchro- nously because individuals respond similarly to seasonal environ- mental cues, like increasing photoperiod ([24], see also [49]) or rainfall [50,67]. For example, differences in the annual cycle of Adelie penguins, such as time of arrival at breeding grounds, are largely driven by photoperiod, and change along a latitudinal gra- dient [1]. Studies of Adelie penguins at Cape Bird [51] and at Cape Crozier [3] (very close in latitude) show the timing of the occupa- tion period (averaged across seasons for each study) to be identical [1]. However, inter-annual variation of other environmental condi- tions may interrupt the initiation of breeding following the primary cue. For example, divergences from the usual timing of breeding of Adelie penguins at either Cape Crozier or Cape Bird have been attributed to seasonal differences in the extent of sea ice [1]. Additionally, following arrival at breeding grounds, reproduc- tion is often more synchronous than would be expected based so- lely on environmental cues [28]. Darling [18], who was working with herring gulls (Larus argentatus) and lesser black-backed gulls (L. fuscus), proposed that social stimulation, derived from the pres- ence or activities of conspecifics, synchronised and hastened egg- laying in colonial birds by influencing the reproductive state of fe- males. This phenomenon became known as the ‘Darling Effect’ [25]. One obvious way to examine this effect was to measure reproductive schedules in breeding assemblages of differing size [18]. Darling suggested that, mediated via endocrine pathways (though he never measured these), individuals in larger 0016-6480/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.ygcen.2011.05.006 ⇑ Corresponding author. Fax: +64 7 838 4324. E-mail address: calum.ninnes@gmail.com (C.E. Ninnes). General and Comparative Endocrinology 173 (2011) 139–147 Contents lists available at ScienceDirect General and Comparative Endocrinology journal homepage: www.elsevier.com/locate/ygcen