Baseline and stress-induced corticosterone levels across birds and reptiles do not reflect urbanization levels.

Allison S Injaian,Maren N Vitousek,Tony D Williams,Lynn B Martin,Jerry F Husak,Bonnie K Kircher,Michaela Hau,Matthew J Fuxjager,Clinton D Francis,Eliot T Miller,Jeremy W Donald,Rosemary Knapp,Jenny Q Ouyang,Michele A Johnson,Laura A Schoenle,Wolfgang Goymann,Davide M Dominoni,Steven Cooke

doi:10.1093/conphys/coz110

Abstract

Rates of human-induced environmental change continue increasing with human population size, potentially altering animal physiology and negatively affecting wildlife. Researchers often use glucocorticoid concentrations (hormones that can be associated with stressors) to gauge the impact of anthropogenic factors (e.g. urbanization, noise and light pollution). Yet, no general relationships between human-induced environmental change and glucocorticoids have emerged. Given the number of recent studies reporting baseline and stress-induced corticosterone (the primary glucocorticoid in birds and reptiles) concentrations worldwide, it is now possible to conduct large-scale comparative analyses to test for general associations between disturbance and baseline and stress-induced corticosterone across species. Additionally, we can control for factors that may influence context, such as life history stage, environmental conditions and urban adaptability of a species. Here, we take a phylogenetically informed approach and use data from HormoneBase to test if baseline and stress-induced corticosterone are valid indicators of exposure to human footprint index, human population density, anthropogenic noise and artificial light at night in birds and reptiles. Our results show a negative relationship between anthropogenic noise and baseline corticosterone for birds characterized as urban avoiders. While our results potentially indicate that urban avoiders are more sensitive to noise than other species, overall our study suggests that the relationship between human-induced environmental change and corticosterone varies across species and contexts; we found no general relationship between human impacts and baseline and stress-induced corticosterone in birds, nor baseline corticosterone in reptiles. Therefore, it should not be assumed that high or low levels of exposure to human-induced environmental change are associated with high or low corticosterone levels, respectively, or that closely related species, or even individuals, will respond similarly. Moving forward, measuring alternative physiological traits alongside reproductive success, health and survival may provide context to better understand the potential negative effects of human-induced environmental change.

Highlights

Over the past decade, much research has focused on human impacts on wildlife due to rates of human population growth and increased infrastructure (Benítez-López et al, 2010)
There was a negative relationship between baseline cort and anthropogenic noise levels for urban avoiders, and, to a lesser extent, urban exploiters
We found no general patterns in the association between human-induced environmental change and baseline or stressinduced cort in birds or baseline cort in reptiles

Summary

Introduction

Much research has focused on human impacts on wildlife due to rates of human population growth and increased infrastructure (Benítez-López et al, 2010). 83% of the USA is within 1 km of a road (Riitters and Wickham, 2003), and anthropogenic noise sources have doubled ambient sound levels even in the most protected habitats in the USA (Buxton et al, 2017) Fields such as conservation physiology can help predict animals’ responses to human-induced environmental change and increase the effectiveness of conservation management (Madliger et al, 2018). Baseline glucocorticoid levels reflect concentrations prior to the disturbance of sampling; whereas stress-induced glucocorticoid levels reflect the response to an acute stressor, such as standardized capture and restraint protocols. Both baseline and stressinduced glucocorticoid levels can be taken with relative ease in the field and have enabled conservation practitioners to take preventative action in certain cases (Tarlow and Blumstein, 2007; Busch and Hayward, 2009). Using glucocorticoids to diagnose populations that are negatively affected by human-induced environmental change remains generally challenging for two main reasons: (i) studies within and between species have found varying results with regards to the effects of human-induced environmental change on glucocorticoid levels (Table 1) and (ii) interpretations of increased baseline and/or stressinduced glucocorticoid levels differ throughout the literature (Wingfield and Kitaysky, 2002; MacDougall-Shackleton et al, 2019)

Methods

Results

Conclusion