Assessing the impacts of human disturbance on wildlife: insights from wildfowl on the Exe Estuary.

Abstract

In the subject area of conservation and ecology, human disturbance is classified as any anthropogenic activity that elicits a response in an animal that would otherwise not occur under non-human related conditions. When this change in behaviour negatively impacts an animal’s energy budget it has the potential to reduce reproductive output and survival, and so ultimately, human disturbance may affect animal populations. Therefore, understanding mechanisms that lead to human disturbance and its energetic cost are vital in understanding if human disturbance may affect animal populations in the present and the future. To investigate these topics, this study looked at different aspects of human disturbance relative to two species of wildfowl, Brent goose (Branta bernicla, L.) and wigeon (Mareca penelope, L.), on the Exe Estuary, during the winters of 2017-2018 and 2018-2019. This included: identifying environmental variables that lead to overlaps in space and time between wildfowl and humans, assessing the disturbance cost within those overlaps, differentiating costs of disturbance relative to human disturbance types, understanding the compensation ability of wildfowl to deal with human disturbance, and identifying the thresholds of human disturbance wildfowl are capable of experiencing without negative impacts. Primary findings indicated that conditions associated with overlaps between wildfowl and humans were predominantly associated with food availability for wildfowl and site accessibility conditions for humans. Within these overlaps, wildfowl were found to be disturbed for a minority of the time, with Brent goose being disturbed approximately 6% of the time, and wigeon being disturbed approximately 5% of the time. Costs associated with these disturbances were found to increase if wildfowl were feeding when disturbed compared to resting. Additionally, overlaps and disturbances from different human activity types were found to vary, indicating that some human activity types may be more threatening, in terms of disturbance than others. An investigation of the literature identified that animals use their ‘spare-rest’ time to compensate for the time and energy costs associated with human disturbance. This finding, along with a calculation of energetic costs relative to energetic needs of wildfowl on the Exe Estuary, identified that time and energy costs due to human disturbance, at the time of this study, were well below any thresholds for compensation. Projections of human disturbance using an individual-based model (IBM) validated that Brent goose would need to be disturbed at least 7 times per hour and wigeon would need to be disturbed at minimum of 12 times per hour before they would be unable to compensate. These results indicate that Brent goose and wigeon populations on the Exe Estuary are currently under no immediate threat from human disturbance. Furthermore, this study has identified more widely applicable variables that lead to human disturbance in general, and mechanisms for determining if and when it is causing a problem for wildlife populations. Understanding and predicting these types of impacts will then help preserve animal populations and biodiversity richness throughout a wide variety of ecosystems.