Ecological Archives E090-077-A1

Lauren A. Harrington, Andrew L. Harrington, Nobuyuki Yamaguchi, Michael D. Thom, Pablo Ferreras, Thomas R. Windham, and David W. Macdonald. 2009. The impact of native competitors on an alien invasive: temporal niche shifts to avoid interspecific aggression? Ecology 90:1207–1216.

Appendix A. Presence of otters and polecats at the River Thames study site.

Detailed field sign surveys for riparian mammals (including otters) were carried out along the banks of the R. Thames study site twice per year (in spring and autumn) between 1995 and 1999. No otter sign was found at the study site during this period (R. Strachan et al., unpublished data), with the exception of a single otter track found in the winter of 1997/98. The national otter survey, utilizing the same field sign survey methods (searches for faeces – spraints - and tracks along the riverbank), in 1991–1994, also revealed otter presence in the Thames region as a whole to be only sporadic: four of 170 500-m survey sites were found to contain otter spraints. This was the first time that otter sign had been detected in the Thames region since the national otter survey began in 1977 (Strachan and Jefferies 1996). Otter sign was detected in the study site itself in 2000 (R. Strachan, personal communication) following the release, in 1999, of 17 otters c.10 km upstream from the study site (Bonesi and Macdonald 2004), and the rate of spread (based on signs) in the Thames region, immediately following the release, was high: 18 of 225 survey sites in the Thames region, in 2000–2002, were found to contain otter spraint (Crawford 2003). Our own field sign surveys (see also Appendix C) of the R. Thames study site, in the mid-2000s, revealed otter sign, at this time, to be widespread (Table A1). A similar abundance of otter sign was found in several of the R. Thames tributaries surveyed between 2004 and 2006 (Table A1). Although we cannot estimate otter density in the mid-2000s, we infer widespread presence of otters at the study site, and in the surrounding Upper Thames valley, based on the presence of otter spraint.

Polecats were first recorded as returning to Oxfordshire in 1993 (Birks and Kitchener 1999). A single transient male was trapped c. 2.5 km from the R. Thames study site in December 1996 (A. Grogan, personal communication) but no polecats were caught on the river itself during live-trapping for mink between 1995 and 2000 (N. Yamaguchi, M. Thom, and L. Bonesi, unpublished data). Live-trapping in 2004–2005, however, resulted in the capture of seven individuals on the river and 17 within 1 km of the river, seven of which occupied stable home ranges bordering the river in 2004-05 (L. A. Harrington and D. W. Macdonald, in press).

TABLE A1. Index of otter presence at four river sites in the Upper Thames valley (Oxfordshire, UK), 2004–2006. Index is based on presence of otter spraint and quantified as the % contiguous 500-m sections of riverbank within which at least one spraint was found (both banks were included within one river section). See mink survey methods in Appendix C.


500-m river sections with ≥ 1 otter spraint (%)




N (surveys)

R. Thames





R. Windrush





R. Evenlode





R. Cherwell






Birks, J. D. S., and A. C. Kitchener. 1999. The distribution and status of the polecat Mustela putorius in Britain in the 1990s. The Vincent Wildlife Trust, London, UK.

Bonesi, L., and D. W. Macdonald. 2004. Impact of released Eurasian otters on a population of American mink: a test using an experimental approach. Oikos 106:9–18.

Crawford, A. 2003. Fourth otter survey of England 2000-02. Environment Agency, Bristol, UK.

Harrington, L. A., and D. W. Macdonald. 2008. Spatial and temporal relationships between invasive American mink and native European polecats in the southern United Kingdom. Journal of Mammalogy 89:991–1000.

Strachan, R., and D. J. Jefferies. 1996. Otter survey of England 1991–1994: A report on the decline and recovery of the otter in England and on its distribution, status and conservation in 1991–1994. The Vincent Wildlife Trust, London, UK.

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