Savannah and forest elephants in Uganda 193


to the savannah phenotype. The three groups obtained from the K-means analysis partially match the three groups (for- est, savannah and intermediate) obtained from the species assignment key analysis, with Group 1 being the intermedi- ate phenotype, Group 2 being the savannah phenotype and Group 3 being the forest phenotype. Sex and age biases were taken into account (Supplementary Material 2).


Discussion


We first validated, using a K-nearest neighbours algorithm, the relevance of the six morphological criteria for discrim- inating between the savannah and forest phenotypes by testing them on 296 individuals whose geographical origins were known. When applied to a set of 1,408 videos recorded in Sebitoli, in the hybridization area in Uganda, these cri- teria produced three groups of phenotypes using an un- supervised K-means approach (the expected savannah and forest phenotypes and a third group, present in 51.1% of the videos). This third group could correspond to hybrid indi- viduals, whose presence had been noted previously in the south of our study area (Mondol et al., 2015; Bonnald et al., 2021). To date, there has been no genetic study of individuals


whose phenotypes are known. As hybrids are fertile (Mondol et al., 2015; Bonnald et al., 2021), we assume there are several hybrid phenotypes depending on the level of hybridization. Moreover, the dominant pattern (savannah state or forest state) of each morphological criterion is unknown, which in- creases the uncertainty regarding the phenotypes of hybrids. In our survey we defined the main and secondary criteria


and assumed that intermediate states were less informative than the features of forest or savannah elephants, leading to a lower weight being given to the intermediate states in the species assignment key.Wemade this assumption based on the fact that the intermediate states could be found in both forest and savannah phenotypes and were not restricted to hybrids. When we compared the results obtained from the species


assignment key with those from the K-means analysis, we only obtained a partialmatch. Although the choice of mor- phological criteria effectively discriminates between the two elephant species, in all three groups there are individuals with the intermediate phenotype. Our analysis potentially reveals a continuous gradient of phenotypes ranging from the savannah to the forest phenotype via intermediate phe- notypes corresponding to hybrid individuals. The species assignment key could be biased by the ages of


individuals. As the forest elephant is a paedomorphic form of the savannah elephant (Debruyne, 2003), young savan- nah elephants resemble forest elephants and old forest ele- phants could be confused with savannah elephants (using features such as ear length and back curvature; Bedetti


et al., 2020). Moreover, criteria based on tusks and temporal fossae, which are not yet developed in young individuals (Laws, 1966; Sikes, 1966; van der Merwe et al., 1995), make the assignment of young individuals difficult. Although females have shorter and thinner tusks than males (Elder, 1970; Layser & Buss, 1985), sex does not represent a bias here because we did not consider the length and circumfer- ence of the tusks. The IUCN decision to recognize the African elephant as


two species aims to reinforce conservation actions, especial- ly for forest elephants, which are Critically Endangered. It also means that we need to gather more information related to hybrids, including number, behaviour and ecology. To be able to carry out effective conservation actions, precise in- formation on the biology, behaviour and reproduction of each species is necessary, which requires being able to dis- tinguish the species of the individuals being studied in areas where the home ranges of forest and savannah elephants overlap. Genetic determination of elephant species is pre- cise, but this process is costly and time consuming. The species assignment key presented here is a simple tool for distinguishing between forest and savannah elephants in environments where both species can be found. However, more studies on the morphology of hybrids are necessary to make the species assignment key more accurate for application in hybridization areas.


Acknowledgements We thank the Uganda Wildlife Authority and the Uganda National Council for Science and Technology for permis- sion to conduct research in Kibale National Park, Uganda; Jean-Michel Krief, co-director of the Great Ape Conservation Project; Camille Lacroux for the initial checking of the camera trap videos; and all field assistants of the Sebitoli Chimpanzee Project, especially Daniela Zainabu Birungi, Robert Asimwe and Robert Nyakahuma, for the collection and the initial checking of camera trap videos. Financial support for Sebitoli Chimpanzee Project came from Projet pour la Conservation desGrands Singes, Fonds Françaispourl’Environnement Mondial, Fondation Prince Albert II, Fondation Nicolas Hulot and Muséum National d’Histoire Naturelle, and the Fondation Ensemble. Julie Bonnald thanks the Muséum National d’Histoire Naturelle, Great ApeConservationProject andKinoméfor thefinancial supportof her PhD studies and Nicolas Métro and Yohann Fare for the supervision of her work. We thank Frédéric Baer, Jean-François Poudron, Muriel Caslant, Gian-Marco Gesulfo, Camille Lacroux, Nelly Ménard, Sylvie Le Bomin, Shelly Masi, Malenoh Sewuh Ndimbe and Bethan Morgan for providing photographs of elephants; Marion Taylor Baer for editing help; and Régis Debruyne, Martin Fisher and two anonymous reviewers for their insightful comments.


Author contributions Designing the field programme in Uganda, obtaining the field site, team and authorizations to conduct research: SK, EA; data analysis: JB, RC, MP; analysis, writing: JB, RC, SK; interpretation of results, editing: all authors.


Conflicts of interest None.


Ethical standards This research abided by the Oryx guidelines on ethical standards.


Oryx, 2023, 57(2), 188–195 © The Author(s), 2022. Published by Cambridge University Press on behalf of Fauna & Flora International doi:10.1017/S0030605321001605


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