The reproductive behaviour of an urban population of red fox Vulpes vulpes

A completed PhD study by Graziella Iossa. Partially funded by Rotary Foundation of Rotary International, Newby Trust Ltd. and The Sir Richard Stapley Educational Trust.

Supervised by Stephen Harris and Phil Baker.

collared fox
© Mammal Research Unit
Photo by George Havens


Species mating systems are a fundamental component, together with social and spacing systems, of a species' ecology. Mating systems are the result of complex interactions reflecting taxonomic constraints, individual choices according to environmental limitations and conflicts between sexes, within sexes and between parents and offspring.

The red fox Vulpes vulpes is considered to be monogamous on the basis of indirect evidence such as males guarding their mate during the mating season, the presence of a pair of foxes defending a territory and one oestrous event per year. However, genetic studies in Bristol have shown polygyny (one male pairing with more than one female) and polgynandry (two or more males pairing with two or more females in the same group) at high population density.


In this project the reproductive behaviour of an urban red fox population was examined through behavioural observations and genetic analyses of parentage, and the results compared to the same population at higher density. I also examined canid reproductive biology in an evolutionary perspective with regard to the evolution of carnivore mating systems.

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Foxes actively defend from other foxes the area in which they live throughout the year thus being territorial animals. Territories were positively correlated to male quality such as body size, as well as to the pressure exerted by neighbouring males, a finding never demonstrated before for a canid. Body size was also correlated to male reproductive behaviour: only large males were unfaithful and mated with their next-door neighbour's female, gaining extrapair copulations. Contrary to a previous study, no multiple paternities or incest were recorded and male subordinate reproduction was negligible.

Canid species, as well as carnivore species, have evolved in a context of high sperm competition as exemplified by their relative testes size, which is larger than expected in species accruing multiple partners. In many other taxa it has been shown that when male competition for mates is high, the relative expenditure in the testes is also high.

In conclusion, red fox mating behaviour is much more complex than what was previously believed on the basis of behavioural observations alone.


This study is concluded but research on foxes in the Mammal Research Group is ongoing. I would like to thank the many members of the public who have cooperated with me during the course of my study.

If you live in Bristol and in particular from northwest Bristol (Stoke Bishop, Henleaze, Coombe Dingle, Sea Mills, Westbury-on-Trym and Sneyd Park) please report sightings of collared and uncollared foxes, dead foxes (tagged or untagged) and cubs (contact details below).

Part of this research has recently been published:

Iossa, G., Soulsbury, C.D., Baker, P.J. & Harris, S. (2008) Body mass, territory size and life-history tactics in a socially monogamous canid. Journal of Mammalogy: in press.

Iossa, G., Soulsbury, C.D., Baker, P.J. & Harris, S. (2008) Sperm competition and the evolution of testes size in terrestrial mammalian carnivores. Functional Ecology 22: 655-662.
doi: 10.1111/j.1365-2435.2008.01409.x

Soulsbury, CD, Iossa, G, Baker, PJ &a,p; Harris, S. (2008) Environmental variation at the onset of independent foraging affects full-grown body mass in the red fox. Proceedings of the Royal Society B: Biological Sciences: in press.

Soulsbury, C.D., Iossa, G., Edwards, K.J., Baker, P.J. & Harris, S. (2007) Allelic dropout from a high-quality DNA source. Conservation Genetics 8: 733-738.
doi: 10.1007/s10592-006-9194-x

Soulsbury, C.D., Iossa, G., Baker, P.J., Cole, N.C., Funk, S.M. & Harris, S. (2007) The impact of sarcoptic mange Sarcoptes scabiei on the British fox Vulpes vulpes population. Mammal Review 37: 278-296.
doi: 10.1111/j.1365-2907.2007.00101.x

Please email me for pdf files

Contact details

Dr Graziella Iossa
Mammal Research Unit
School of Biological Sciences
University of Bristol
Woodland Road
Bristol BS8 1UG, U.K.

Telephone: 0117 9288918
Email: Dr Graziella Iossa