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Exclusive core areas and intrasexual territoriality in Eurasian red squirrels (Sciurus vulgaris) revealed by incremental cluster polygon analysis

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Ecological Research

Abstract

When animal home ranges overlap extensively in species lacking overt territorial behaviours, identifying exclusive core areas within individual ranges can be difficult. By analysing the size and overlap of successively smaller core areas among individual Eurasian red squirrels (Sciurus vulgaris), we determined exclusive areas within the home ranges of resident males and females. Possible effects of habitat composition and food supplies were explored by monitoring squirrels in different conifer forests and during years with low and high tree seed production. Using outlier-exclusive cores (OEC) revealed that the total ranges consisted of large sally zones (on average, 35% of the total minimum convex polygon [MCP] range) around home ranges with multi-nucleate cores. The mean OEC home range size did not differ between the sexes but was larger with poor food availability. Home ranges (99% incremental cluster polygons [ICP]) overlapped extensively between sexes (average overlap high food–low food: males by females 21–40%, females by males 43–45%) and among males (males by males 26–44%), while intrasexual overlap among females was low (9–10%). The overlap of inner cores among females rapidly approached zero, suggesting the intrasexual territoriality of 75% core areas. This was not the case among male squirrels, for which intrasexual overlap averaged only 4% at 50% but 18% at 75% core areas. Even the smallest inner cores had some degree of intersexual overlap, indicating that complete territoriality did not occur in this species. Female home ranges were more strongly affected by annual fluctuations in food supplies than male ranges. Females reduced the size of their food-based intrasexual territories when food availability increases. Males probably benefit from using larger home ranges and core areas, which overlap with the ranges of several females, by increasing their probability of successful mating.

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Acknowledgements

We thank Peter Lurz for his help with the Ranges6 software. Constructive comments by the two anonymous reviewers helped to improve the manuscript. This study is part of the ASPER (Alpine Squirrel Population Ecology Research) project, funded by the province of Sondrio (Servizio Agricoltura, Caccia e Pesca, Settore Risorse Ambientali), the Stelvio National Park and the Parco Regionale delle Orobie Valtellinesi to Istituto Oikos NGO, Milan, Italy. Additional financial support was given by MIUR (Ministero dell’Istruzione, dell’Università della Ricerca, project COFIN 2003, number 2003053710-006) to the University of Insubria Varese, Italy. Further logistic support was provided by the province of Sondrio and the Stelvio National Park. The trapping and handling of squirrels complied with the current laws on animal research in Italy and were carried out under the permission of the Region of Lombardy. This is paper #10 of the ASPER project.

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  1. Department of Environment, Health, and Safety, University of Insubria Varese, Via J.H. Dunant 3, 21100, Varese (VA), Italy

    Erica Di Pierro, Ambrogio Molinari, Guido Tosi & Lucas A. Wauters

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  1. Erica Di Pierro
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  2. Ambrogio Molinari
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  4. Lucas A. Wauters
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Correspondence to Lucas A. Wauters.

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Pierro, E.D., Molinari, A., Tosi, G. et al. Exclusive core areas and intrasexual territoriality in Eurasian red squirrels (Sciurus vulgaris) revealed by incremental cluster polygon analysis. Ecol Res 23, 529–542 (2008). https://doi.org/10.1007/s11284-007-0401-0

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