The heat is on: The effect of increasing temperatures on wild and domestic animal aggregations at water sources

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Viviana J. Martinez, Environmental Studies, University of California, Santa Barbara, Malik Elkouby, Georgia C. Titcomb and Hillary Young, Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, Asher Thompson, Environmental Science, Policy and Management (ESPM), University of California, Berkeley, Naisikie Mantas, Mpala Research Centre, Kenya, Bernard Gituku, Ol Pejeta Conservancy, Kenya, Jenna Hulke, Texas A&M University

Background/Question/Methods
Earth’s climate is rapidly changing, bringing forth questions of how animals -- both domestic and wild -- will alter their behavior. With current temperature increases and dryland expansion, dwindling water availability will likely impact animal behavior and the frequency with which a species must return to a water source. While some species are well-adapted to hot, arid conditions, others with high water-dependency and thermoregulation requirements may aggregate strongly at water sources. Such aggregations are important, as they may elevate interspecies contact rates, leading to increased competition, predation, and even disease transmission.
Working at a mixed conservation and cattle ranching property in an East African tropical savanna system, we generated a two-year camera trapping dataset to measure animal activity at water sources and paired matrix sites in response to temperature fluctuations.
We combined animal identifications from more than 10,000 citizen scientists on the Zooniverse platform with interpolated hourly temperature data extracted from photographs and validated against nearby weather stations to ask: 1) Which species aggregate more strongly near water during hottest daytime temperatures? 2) Is the degree of aggregation directly related to a species’s theoretical water requirements? And 3) To what extent are interspecies contact rates at water elevated in warmer temperatures?
Results/Conclusions
We found that: 1) Elephants, cattle, and warthogs showed increased activity near water with increasing temperature, but that smaller ungulates showed much smaller effects. 2) The strength of the relationship between temperature and aggregation generally increased with a species’s estimated water requirements. However, cattle were notable outliers: cattle aggregated more strongly at water during the hottest times of the day, but to a greater extent than would be predicted based on their water requirements. 3) Interspecies contact rates were substantially higher at water sources compared to matrix sites, especially during hours of peak solar radiation during the day.
Together these results reveal the importance of temperature in influencing species aggregations and contact rates at water. Humans are rapidly altering environmental conditions that in turn affect not only wildlife behavior, but also the management of domestic animals in response to water scarcity. Given that livestock biomass is an order of magnitude greater than all wildlife on Earth, the movement and aggregation patterns of these animals near water can have important implications for wildlife water foraging amid ongoing climate changes.