Wednesday, 7 February 2007

Hair trigger mouse traps with teeth

Stoats and weasels are two of our most widely distributed mammal species, familiar to most but only rarely seen well in the field. Their small size, use of available cover and energetic manner mean that the typical view is of one dashing across a quiet country lane with an arched-backed gallop, in the case of the stoat, or as if on tiny wheels, in the case of the weasel. These two carnivores are beautifully equipped for the pursuit and capture of their favoured small mammal prey. The small, almost cylindrical bodies and short legs enable them to chase small mammals into their burrow systems. The degree of efficiency associated with their ability to hunt small mammals even led one researcher to refer to them as “hair-trigger mouse-traps with teeth”, a suitably apt description.

Both species have long fascinated me. First introduced to them through a gamekeeper friend, I enjoyed many encounters with both species when I spent three years live-trapping small mammals on a north Norfolk estate. Part of my study site was well used by at least one stoat and he would sometimes stand on his back legs and stare at me intently from a short distance away. Even closer encounters were achieved with the local weasels, some of which got into the habit of entering my small mammal traps. My normal procedure for emptying these involved tipping the contents into a clear plastic bag so that the mouse, vole or shrew could be aged, sexed, weighed and marked before being released. Dropping an unexpected and angry weasel into such a bag is not something I would recommend! One such individual stood at my feet and berated me for several minutes upon release and, despite it’s tiny size, was actually rather intimidating.

Stoats may be equally intimidating and are commonly believed to mesmerise rabbits, reducing them to dithering and helpless wrecks, before delivering the killing bite. Examination of rabbits killed by stoats does reinforce the view that some of these victims have literally died from fright. Another curious behaviour associated with both stoats and weasels is the manic somersaulting and leaping about that is sometimes witnessed by observers. Some have suggested that this behaviour is either a form of play or is a trick to catch overly curious prey. However, it may actually be linked to a parasitic nematode worm that goes by the tongue-twisting name of Skrjabingylus nasicola. This bright red worm occupies the sinus cavities of a fair proportion of both species, causing damage to the skull and, potentially, the brain. It could be this that, through irritation, causes the “dancing”. Curiously, the worm spends part of its life cycle in small mammals, further strengthening the link between predator and prey.

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