Age-related Physiological Change and Population Stress Variability in Grey-faced Petrels

Abstract

To improve conservation management of at-risk populations, studies of avian physiology can provide insights into the sub-lethal impacts of stress and indicate potential underlying causes. Grey-faced petrels (Pterodroma gouldi) breeding on the east coast of Auckland, New Zealand, exhibit poor reproductive success and slow chick development compared to west coast conspecifics. This offers a rare opportunity to map physiological traits indicative of sub-lethal stress in a Procellariiform species. Corticosterone stress hormones and haematological parameters can identify nutritional stress and shifts in energetic demands. As such, these were quantified to understand how these populations vary throughout key stages of the breeding cycle. Compared to west coast birds, east coast Grey-faced petrels had higher initial and response (peak – initial) levels of corticosterone during the incubation stage, weighed less, and had haematological profiles indicative of poor body condition and higher energy expenditure. Their chicks also had higher levels of feather corticosterone, and weighed less near fledging. Combined, these results suggest that east coast birds are under greater nutritional stress. Determining whether age-related physiological changes exist is crucial to studying stress physiology. This is the first study to compare physiological indices of breeding Grey-faced petrels aged between 5 and 29. Contrary to previous seabird studies, there were no differences in corticosterone secretion with age. Moreover, there were no changes in haematology with age except a slight decline in haemoglobin concentration. Age, therefore, is not a confounding factor in studies of Grey-faced petrel physiology; and birds are proposed to have haematological minima that must be met for them to attempt breeding. This work provides novel insight into the physiology of known-age Grey-faced petrels and chicks. Regarding life history trade-offs, parents appear to transfer the costs of poor foraging to their chick to preserve their own condition, consequently increasing chick developmental stress. This appears to be exacerbated in the sub-quality foraging environment off the east coast of Auckland. Future studies should identify the underlying causes of these divergent stresses by examining habitat, foraging, and dietary patterns from each population.