Short-term exposure to unmanned aerial vehicles does not alter stress responses in breeding tree swallows.

Bradley D Scholten,Hyeryeong Choi,Dena M Baker,Margaret E Caulfield,Darren S Proppe,Abigail R Beard,Steven Cooke

doi:10.1093/conphys/coaa080

Abstract

Recent studies suggest that visual and acoustic anthropogenic disturbances can cause physiological stress in animals. Human-induced stress may be particularly problematic for birds as new technologies, such as drones, increasingly invade their low-altitude air space. Although professional and recreational drone usage is increasing rapidly, there is little information on how drones affect avian behavior and physiology. We examined the effects of drone activity on behavior and physiology in adult, box-nesting tree swallows (Tachycineta bicolor). Specifically, we monitored bird behavior during drone flights and in response to a control object and measured telomere lengths and corticosterone levels as indicators of longer-term physiological stress. We predicted that drone-exposed tree swallows would habituate behaviorally after multiple flights, but that telomeres would shorten more quickly and that baseline corticosterone levels would be altered. One significant and two strong, non-significant trends in behavioral assays indicated that adult swallows acted more aggressively towards drone presence compared to a control object, but were slower to approach the drone initially. Swallows were also more reluctant to use nest boxes during drone activity. Tree swallows habituated to drone presence as expected, although the rate of habituation often did not differ between drone-exposed and control groups. Contrary to our prediction, drone activity did not affect telomere length, corticosterone levels, body mass or fledging rates. Overall, our results indicate that a small number of short, targeted, drone flights do not impact tree swallow health or productivity differently than a non-invasive control object. Minor behavioral differences suggest that increasing the frequency of drone use could impact this species. We provide some of the first results addressing how drone activity alters behavioral, physiological and molecular responses to stress in songbirds. A better understanding of these impacts will allow ecologists to make more informed decisions on the use and regulation of new drone technologies.

Highlights

We examined the effects of drone activity on behavior and physiology in adult, box-nesting tree swallows (Tachycineta bicolor)
We provide some of the first results addressing how drone activity alters behavioral, physiological and molecular responses to stress in songbirds
When tree swallows responded to drone exposure, they swooped at the object significantly more often than towards a control object (X 2 = 3.91, df = 1, 200, P = 0.048; Fig. 1A and B)

Summary

Introduction

Natural landscapes are changing quickly, largely due to a growing human population and rapid urbanization. In addition to habitat loss, urbanization increases the exposure of wildlife to humans, roads, vehicles and their corresponding sounds (De Gregorio et al, 2014; Haddad et al, 2015; French et al, 2017; Hunt and Vargas, 2018; Injaian et al, 2018, 2019). Increased human exposure leads to decreased flight responses in sea turtles and changes in immune response and baseline corticosterone levels (CORT) in marine iguanas (French et al, 2017; Hunt and Vargas, 2018). Anthropogenic noise, a side-effect of human development, alters physiology and behavior in animals (Wright et al, 2007; Injaian et al, 2018). In some cases, CORT has been found to increase (Injaian et al, 2019), decrease (Kleist et al, 2018) and not change (Flores et al, 2019) in response to noise

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