Wandering Vultures: Understanding behaviour and space-use for conservation

Vultures travel over large distances; identifying where they are most at risk is imperative to effective conservation work. Vultures are most at risk from illegal poisoning when they are foraging and feeding. Using telemetry data from tagged vultures, we identified these risky behaviours from GPS data and the spaces vultures choose to do them to target interventions and mitigate human-wildlife conflict to reduce poisoning events.

Above: White-backed vulture (Gyps africanus) flying overhead in southern Tanzania.

Vultures are some of the widest ranging species in the world thanks to their soaring flight, which allows them to range over 100,000km² in a year and travel over 200km in a single day with no regard for protected areas or national boundaries. Telemetry studies through GPS tagging offer a unique opportunity to understand where vultures go and how behaviours may vary across the landscape. GPS transmitter studies can provide insights into individual movements, range size, habitat use, foraging behaviour, and mortality. North Carolina Zoo began studying vultures in southern Tanzania in 2015, and though the typical home range sizes of vultures in this area turned out to be small they also discovered the potential of white-backed vultures for huge dispersal events: one juvenile travelled over 1800km visiting multiple countries and going all the way to South Africa before returning home. In addition, the project has helped to identify two distinct populations in east and west Tanzania that do not overlap and seemingly have very different behaviours. Due to their vast ranges, protection of vultures requires safe landscapes both inside and outside protected areas. Our project sought to identify priority areas where conservation efforts could be focused; where vultures are both actively foraging or feeding and thus likely to encounter threats.

Cover article: (open access)
Peters, N. M., Beale, C. M., Bracebridge, C., Mgumba, M. P., & Kendall, C. J. (2022). Combining models for animal tracking: Defining behavioural states to understand space use for conservation. Journal of Biogeography, 49, 2016– 2027. https://doi.org/10.1111/jbi.14483

The current greatest threat to vulture populations in East Africa is direct and indirect poisoning, with many vulture species suffering associated population declines across their range. This is usually the result of human-wildlife conflict, where humans will put out poisoned meat targeted at lions, hyenas, or leopards which pose a threat to their livestock. Because it is an efficient and silent method, most poisoning incidents are likely never found or reported making the true impact on populations substantially higher and difficult to quantify. In addition, poisoning events are often discovered days or weeks after they occur, making the full scale of the mortalities hard to quantify.

Above: White-backed vulture (Gyps africanus) being released after trapping and GPS tagging in Tanzania.

Poisoning is a secretive and illegal activity, but using GPS tagged vultures we have been able to identify several problem areas. In addition, we know that poisoning is only a risk while vultures are foraging and feeding, so keeping those areas safe for vultures is critical.  Modelling techniques, such as Hidden Markov models, allow for the identification of behaviours based on telemetry data. When combined with a spatial model such as a Point Process Model, this allows us to discover the preferred foraging and feeding areas for vultures. Using this two-step process we were able to refine space-use analysis by specific behaviours to identify areas to focus human-wildlife conflict community work.

We found that vultures in general prefer areas alongside rivers and open habitats, which may be in part due to their nesting alongside rivers and preference for open areas due to their reliance on eyesight. We also found that vultures spend most of their time stationary (75.5%) which as a large, soaring scavenger is a good evolutionary trait to conserve energy when relying on sparse and unpredictable food source (carrion). Perhaps most surprisingly, we found that vultures when foraging and feeding do not select for areas of high livestock density. Despite this, livestock carcasses laced with poison are fed on by vultures.

Feeding events usually include multiple different vulture species: here the Lappet-faced (Torgos tracheliotos), Rüppell’s (Gyps rueppelli), and White-backed (Gyps africanus) vulture can all be seen. White-backed vultures are the most social species and usually dominate the carcass based on numbers alone.

Animal behaviour and movement intertwines with human landscapes to create complex conservation issues. With the constant expansion of the human population and our activities, risks to wildlife such as habitat loss, poaching, and conflict will continue to increase where humans and wildlife overlap. Our findings provide a fascinating insight into the vast distances covered by vultures and how habitat use varies with different behaviours, and is a reminder of the interconnected nature of animals and landscapes. Our paper aims to provide additional tools to scientists to help create effective species conservation and prioritise community-led conservation work.

Written by:
Natasha M. Peters
PhD Student, Department of Biology, University of York, York, UK

Additional information:
Colin Beale: https://www.york.ac.uk/biology/research/ecology-evolution/colin-beale/

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

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