The early year movements of mink

 Most of the Rivers around Scarborough contain populations of American Mink, an invasive non-native species which escaped and in some cases was released from fur farms around the 1950s/60s in Britain. This species has been linked to the decline of water voles in some areas including locally. Populations appear to be particularly strong along the River Derwent, Scalby Sea Cut/Beck and along the River Hertford. 

Along the Derwent stretches this species is routinely controlled by the local Angling Club and in other areas on a more ad hoc basis by gamekeepers, farmers and conservationists. However as the species is so well established occurring away from main channels along ditches, drains and streams casual control only serves to create a continual void for animals from unmanaged stretches to fill and at best suppresses population size and recruitment.

The American Mink on the Carrs, an area of lowland agricultural land associated with the River Hertford to the south of Scarborough, are well established and appear not to be subjected to any intense or regular management. This means territories are relatively fixed geographically and easy to study. As with other predators like foxes I find regular control results in territories being more flexible and occurring in ever changing areas, also resulting in a higher turnover of individuals diversifying activity and behaviour patterns. 

Mink as with similar mustelid species like Otters and Stoats are territorial with very little intrasex overlap, but lots of overlap of the opposite sex. So a typical territory will include a male territory which contains 2-3 female territories within it. Territories are usually less linear than Otters and are also smaller usually around 2-3 miles in length at average population density. Where habitat quality is high territories are smaller and visa versa. 

Territoriality will really kick off towards the end of next month (February) with the onset of the breeding season. This time period sees males moving around much more widely  in search of females and subsequently results in increased levels of male vs male encounters. This results in a lot of fighting and the formation of loose, temporary dominance of hierarchies governing access to receptive females. This chaotic period last around 3-4 weeks in which mating takes place, the presence of males results in ovulation being induced in females.

It is at this stage where mated females establishing a breeding den and giving birth can be particularly problematic to native wildlife like Water Voles. Females are small and flexible, unlike the large bulky males, and can easily enter and manoeuvre within water vole burrows. A female Mink in need of extra food for its young which establishes itself near a Water Vole colony is very bad news and in most cases will significantly reduce or eradicate the local population. 

Water Voles interestingly persist on the Carrs even with the presence of Mink, albeit at lower densities and away from main water channels. Water Voles are found higher up ditch sections especially in association with dense Phragmites beds.