Volume 170, April 2025, 105724Author links open overlay panel, , , , , Highlights•

City-dwelling wildlife face weekday/weekend fluctuations in human foot traffic

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Fluctuating exposure to people may affect stress levels of urban animals

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Adrenocorticotropic hormone (ACTH) challenge conducted on urban red-winged starlings

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Starling faecal glucocorticoid metabolites (fGCMs) track circulating glucocorticoids

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High human foot traffic correlates with low fGCM concentrations in urban starlings

Abstract

Urban wildlife must cope with diverse challenges and stressors, including human presence. However, in addition to being a disturbance, humans can provide energy-rich food and protection from predators. We evaluated the impact of human presence on red-winged starlings (Onychognathus morio) in a highly urbanised environment using faecal glucocorticoid metabolite (fGCM) concentrations as a stress-related biomarker. We performed an adrenocorticotropic hormone (ACTH) challenge to validate a non-invasive method for quantifying glucocorticoids in red-winged starlings. Using this method, we quantified fGCMs in excreta collected from free-living starlings during weekdays (high human presence) and weekends (low human presence) to determine the birds' responses to fluctuating human numbers. Following the ACTH challenge, starlings' circulating glucocorticoid (GC) concentrations increased by 127 % within 30 min and the corresponding fGCM concentrations increased within 1 h of injection. Of the four enzyme immunoassays (EIA) tested, an 11-oxoaetiocholanolone EIA, performed best, detecting a 310 % increase in fGCM concentrations post-ACTH challenge and suggested a 1-h lag between injection and peak fGCM excretion in this species. Human foot-traffic was significantly higher on weekdays compared to weekends, yet free-living red-winged starlings showed overall 30.4 % lower fGCM concentrations on weekdays compared to weekends. Red-winged starlings consume a higher proportion of anthropogenic food on weekdays than weekends and we cannot rule out the possibility that diet-related alteration in gut passage time affect fGCM concentrations. However, the correlation between fGCMs and human foot traffic may also suggest urban red-winged starlings benefit from human presence. Our results raise the possibility that, under certain conditions, the benefits associated with human presence outweigh potential negative effects associated with human activity, at least during the non-breeding season.

Keywords

Avian urban ecology

Adrenocorticotropic hormone (ACTH) challenge

Faecal glucocorticoid metabolites

Weekend effect

Data availabilityThe datasets generated and analysed during the study titled “High human presence is correlated with lower faecal glucocorticoid metabolite levels in an urban bird population.” are available as electronic material on UCT’s ZivaHub: https://doi.org/10.25375/uct.28643384.v1.

© 2025 The Authors. Published by Elsevier Inc.