Assessing the effects of repeated handling on the physiology and condition of semi-precocial nestlings.

Hannah Watson,Mark Bolton,Winnie Boner,Britt J Heidinger,Pat Monaghan

doi:10.1111/ibi.12402

Abstract

Repeated exposure to elevated levels of glucocorticoids during development can have long‐term detrimental effects on survival and fitness, potentially associated with increased telomere attrition. Nestling birds are regularly handled for ecological research, yet few authors have considered the potential for handling‐induced stress to influence hormonally mediated phenotypic development or bias interpretations of subsequent focal measurements. We experimentally manipulated the handling experience of the semi‐precocial nestlings of European Storm Petrel Hydrobates pelagicus to simulate handling in a typical field study and examined cumulative effects on physiology and condition in late postnatal development. Neither baseline corticosterone (the primary glucocorticoid in birds), telomere length nor body condition varied with the number of handling episodes. The absence of a response could be explained if Storm Petrels did not perceive handling to be stressful or if there is dissociation of the hypothalamic–pituitary–adrenal axis from stressful stimuli in early life. Eliciting a response to a stressor may be maladaptive for cavity‐dwelling young that are unable to escape or defend themselves. Furthermore, avoiding elevated overall glucocorticoid exposure may be particularly important in a long‐lived species, in which accelerated early‐life telomere erosion could impact negatively upon longevity. We propose that the level of colony‐wide disturbance induced by investigator handling of young could be important in underlining species‐specific responses. Storm Petrel nestlings appear unresponsive to investigator handling within the limits of handling in a typical field study and handling at this level should not bias physiological and morphological measurements.

Highlights

Wild birds are routinely handled for the purposes of recording morphological, physiological and behavioural metrics, the collection of samples for molecular analyses and the deployment of trackingDespite evidence of both acute and chronic effects of handling, few avian studies have considered the possibility for repeated capture and handling to bias subsequent interpretations of physiological or demographic data
There was no effect of either treatment period, age at first handling, hatching date or days not handled on baseline CORT, Telomere length (TL) or body condition
Our results demonstrate that Storm Petrel nestlings were robust to handling as frequently as every 5 days and up to a maximum of seven times during postnatal development

Summary

Introduction

Wild birds are routinely handled for the purposes of recording morphological, physiological and behavioural metrics, the collection of samples for molecular analyses and the deployment of tracking. Despite evidence of both acute and chronic effects of handling, few avian studies have considered the possibility for repeated capture and handling to bias subsequent interpretations of physiological or demographic data (see mammalian studies by Haydon et al 1999, Clinchy et al 2001). Repeated activation of the HPA axis (as a result of persistent or repeated exposure to a stressor) can lead to chronic elevation of GCs and life-long changes in the functioning of the HPA axis, possibly via the disruption of negative feedback mechanisms (Meaney et al 1988, Romero 2004). The costs of eliciting an adrenocortical response are more likely to outweigh the benefits

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