Using Environmental Niche Modelling to Investigate Abiotic Predictors of Crocodilian Attacks on People

Using environmental niche modelling to investigate abiotic predictors of crocodilian attacks on people G EORGE P OWELL,THOMAS M. M. VERSLUYS,JESSICA J. WILLIAMS S ONIA T IEDT and S IMON P OOLEY Abstract Crocodilians are distributed widely through the Keywords Conservation management, crocodilian conser- tropics and subtropics, and several species pose a substan- vation, environmental niche modelling, human–crocodilian tial threat to human life. This has important implica- conflict, human–wildlife conflict, spatio-temporal modelling tions for human safety and crocodilian conservation. Un- Supplementary material for this article is available at doi.org/ derstanding the drivers of crocodilian attacks on people ./S could help minimize future attacks and inform conflict management. Crocodilian attacks follow a seasonal pattern in many regions, but there has been limited analysis of the relationship between attack occurrence and fine-scale con- Introduction temporaneous environmental conditions. We use methods from environmental niche modelling to explore the rela- anaging conflicts involving wildlife is a serious chal- tionships between attacks on people and abiotic predic- Mlenge globally, especially when the conflicts pose a tors at a daily temporal resolution for the Nile crocodile direct threat to human life (Woodroffe et al., ). Over Crocodylus niloticus in South Africa and Eswatini (formerly large regions of the tropics and subtropics crocodilians are Swaziland), and the American alligator Alligator mississip- responsible for more attacks on people per year than any piensis in Florida, USA. Our results indicate that ambient other large carnivore, with incidents reported for coun- daily temperature is the most important abiotic temporal tries (CrocBITE, ). They also attack domestic animals predictor of attack occurrence for both species, with attack such as livestock and dogs, damage fishing nets, burrow likelihood increasing markedly when mean daily tempera- through earthen dam walls, and cause general disruption tures exceed °C and peaking at °C. It is likely that this to movement and livelihoods by restricting the use of relationship is explained partially by human propensity to waterways that are required for travel, fishing and house- spend time in and around water in warmer weather but hold chores (Aust et al., ; Lamarque et al., ). also by the effect of temperature on crocodilian hunting be- Successfully mitigating harmful human–crocodilian in- haviour and physiology, especially the ability to digest food. teractions has important implications not just for human We discuss the potential of our findings to contribute to the safety but also for conservation. Negative impacts on people management of crocodilians, with benefits for both human have resulted in retaliatory killings and exacerbated issues safety and conservation, and the application of environ- such as overharvesting and habitat destruction (Fukuda mental niche modelling for understanding human–wildlife et al., ), which can have wider consequences for ecosys- conflicts involving both ectotherms and endotherms. tems. As the apex predator of the aquatic environments they inhabit, and as carnivores with varied diets, crocodilians play a key role in local food webs, affecting abundance and behaviour of prey species in ways that can influence GEORGE POWELL* Big Data Institute, Li Ka Shing Centre for Health Information the function and community structure of ecosystems (van and Discovery, Nuffield Department of Medicine, University of Oxford, Oxford, der Ploeg et al., ). They also transport nutrients from UK land to water by preying on land animals, or across ecosys- THOMAS M. M. VERSLUYS* (Corresponding author) Department of Life Sciences, tems, as in cases where they travel to feed in estuarine areas Silwood Park Campus, Imperial College London, Ascot, UK E-mail [email protected] before returning to freshwater areas. Crocodilians are also JESSICA J. WILLIAMS ( orcid.org/0000-0002-8275-7597) Department of Genetics, ecosystem engineers, modifying their environment by dig- Evolution and Environment, Centre for Biodiversity and Environment Research, ging dens, holes and tunnels, and creating nest sites. Alli- University College London, London, UK gator holes, for instance, retain water during dry seasons SONIA TIEDT School of Public Health, Imperial College London, London, UK and serve as refuges for other aquatic species (Britton, SIMON POOLEY ( orcid.org/0000-0002-0260-6159) Department of Geography, ). Birkbeck University of London, London, UK, Department of Zoology, WildCRU, University of Oxford, Oxford, UK, and School of Life Sciences, Understanding the drivers of crocodilian attacks can help University of KwaZulu-Natal, Pietermaritzburg, South Africa minimize future incidents and inform conflict management. *Contributed equally Previous analysis of crocodilian attack patterns has focused Received March . Revision requested May . on identifying high-risk human demographics and beha- Accepted June . First published online June . viours; there has been limited analysis of potential abiotic Oryx, 2020, 54(5), 639–647 © The Author(s), 2020. Published by Cambridge University Press on behalf of Fauna & Flora International. doi:10.1017/S0030605319000681 Downloaded from https://www.cambridge.org/core. IP address: 170.106.35.234, on 30 Sep 2021 at 08:09:15, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605319000681 640 G. Powell et al. environmental predictors of attack patterns, such as tem- for human safety and conservation arising from this study, perature and rainfall (Fukuda et al., ; Brien et al., ; as well as the potential application of environmental niche Das & Jana, ). There are, however, strong theoretical modelling to the analysis of conflict with other species, both grounds for the importance of abiotic conditions because ectothermic and endothermic. temperature constrains crocodilian hunting behaviour via effects on ectotherm physiology, especially metabolic function (Hutton, ; Lance, ; Seebacher & Franklin, Methods ). Similarly, people’s propensity to expose themselves to crocodilian-inhabited waterways is probably correlated Attack and biophysical data with environmental conditions. Accordingly, despite crocodilian attacks occurring year-round in many tropical regions Information on attacks by Nile crocodiles in South Africa (e.g. India and Bangladesh), documented attack patterns are and Eswatini (–) was obtained from archival highly seasonal across Australia (Brien et al., ) and are searches including the personal archive of Tony (A.C.) correlated with mean monthly rainfall and temperature in Pooley (conservation warden responsible for monitoring South Africa, Eswatini and the southern USA (Woodward crocodile attacks in Natal Province, –, who was ac- et al., ; Pooley, ). To date, studies have only explored tive in investigations until ), attack records kept at the the contribution of abiotic factors at a coarse temporal and St Lucia Crocodile Centre, Mtubatuba, South Africa, provin- spatial resolution. In particular, they have exclusively used cial and national newspapers (print and online) in KwaZulu- average monthly or seasonal data, which do not capture Natal and South Africa, and the Times of Swaziland archive in the impact of climatic changes across days. Furthermore, Mbabane, Eswatini. Online searches used the search term these data have been used to represent regional environ- ‘crocodile’ paired with ‘attack’, ‘bite’ or ‘victim’,inEnglish mental conditions, but have typically been sourced from andAfrikaans.InformationonAmericanalligatorattacksin single weather stations, limiting the ability to capture vari- Florida (–) was provided by the Fish & Wildlife ation across space. Conservation Commission (FWC, ). Incidents involving Here, we use environmental niche modelling methods to a bite were reported to the Commission by telephone, by vic- examine the relationships between abiotic and biotic vari- tims or their families, medical caregivers, or law enforcement ables and the occurrence of crocodilian attacks on people agencies. In most instances post , the Commission’slaw at a greater spatial and temporal resolution than in previous enforcement officers conducted investigations and inter- studies. Environmental niche modelling describes methods viewed victims and witnesses. Attacks by crocodilians were for inferring the occurrence of biological phenomena in en- excluded if they were not witnessed or lacked forensic sup- vironmentally heterogeneous areas and has previously been port, if spatial or temporal data were lacking, or if they were utilized to analyse human conflict with jaguars in Brazil classified as provoked. and Mexico (Zarco-González et al., ; Carvalho et al., The attack records had different spatial resolutions: geo- ), wolves in Iran (Behdarvand et al., ), leopards graphical coordinates were available for the Nile crocodile in Pakistan (Kabir et al., ) and monkeys in India attacks (Fig. ), whereas for the American alligator attacks (Beisner et al., ). Crocodilian attacks can theoretically the Florida county in which the attack occurred was re- be thought of as an entity that can only occupy a specific en- corded (Fig. ). ArcGIS . (Esri, Redlands, USA) was vironmental niche defined by particular biophysical limits; used to ensure Nile crocodile attack coordinates fell within thus, it is possible to use environmental niche modelling to the IUCN

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