Power line risk to Cape (Gyps coprotheres) and white-backed (G. africanus) vultures in Southern Africa
Date
2016
Authors
Howes, Caroline G.
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Abstract
This study examined the movements of white-backed (Gyps africanus) and Cape vultures (G. coprotheres) to assess their habitat preferences, measure seasonal changes in foraging behaviour, and examine where vultures are at risk of electrocution by and collision with power lines. White-backed and Cape vultures are two Old World vulture species found in southern Africa. They are listed as Critically Endangered and Endangered respectively, with massive population declines over the past three decades. These declines are due to poisoning, habitat loss, lack of food, use in traditional medicine, and electrical infrastructure mortality. Vultures provide key ecosystem services such as reducing disease transmission, cycling nutrients, and attracting tourists and therefore, a loss of vultures could cost the continent millions of US dollars.
Thirteen vultures (five white-backed and eight Cape vultures) were tracked using either DUCK-4A or BUBO-4A GPS-GSM trackers (Ecotone Telemetry, Sopot, Poland). Birds were tracked between April 2013 and October 2014. These data were used to examine the habitat suitability of both species using MaxEnt habitat suitability modelling. Key drivers of country-wide habitat suitability for white-backed vultures were mean temperature (30.9% contribution), precipitation seasonality (22.0% contribution), and biome (19.5% contribution), while key drivers for Cape vultures were distance to artificial feeding station (24.8% contribution), and precipitation seasonality (50.5% contribution). Anthropological variables (land use, cattle density, and population density) contributed very little to the models.
Using the same tracking data, seasonal changes in foraging movements were examined, particularly in relation to hypothetical food availability. Data were categorised by seasons (winter, spring, summer, and autumn) using weather data over the past decade. There was little evidence for seasonal movement in white-backed or Cape vultures which may be because food availability is not the limiting factor regardless of time of year.
Lastly, a model was constructed in MaxEnt using the Endangered Wildlife Trust’s Wildlife and Energy Programme dataset of white-backed and Cape vulture electrocutions by and collisions with power lines. Voltage was a major contributor to risk in every model for both collision and electrocution. This is likely to be related to the type and height of the power line structures rather than actual voltage. Either land use or population density also contributed to all four models. Slope contributed to white-backed vulture models while
feeding station and elevation contributed to Cape vulture models. Each of these variables probably relates not only to the likelihood of vulture presence but also how vultures behave in the area (e.g. flying lower in natural or low population areas to forage more effectively therefore putting them at higher risk of collision).
This study suggests that management initiatives should include carefully placing vulture feeding stations to change foraging patterns and provide safe, uncontaminated carrion, and proactive retrofitting of high risk power lines to reduce the high unnatural mortality in white-backed and Cape vultures in South Africa. It is important to continue to improve these models using more tracking data from more populations of white-backed and Cape vultures, and more electrocution and collision data gathered from regular, randomly selected power line surveys.
Description
A dissertation submitted to the Faculty of Science,
University of Witwatersrand,
in fulfilment of the requirements for the degree of Master of Science
Johannesburg, South Africa
March 2016
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Citation
Howes, Caroline (2016) Power line risk to Cape (Gyps coprotheres) and white-backed (G. africanus) vultures in Southern Africa, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21046>