Thursday, 18 November 2010
Stoatally obvious, or is it?
As days shorten and field work becomes less attractive, we tend to find more time for thinking about the big issues in reserve management. Predation is one such issue.
Reserves that have high numbers of ground-nesting birds often seem to have poor productivity. Over recent decades, birds and their predators have been increasingly squeezed into smaller areas of good 'honey-pot' habitat. Predation by Foxes has been shown to account for a high percentage of nest losses in several species eg Lapwing.
So, trying to prevent Fox predation may seem to be the obvious answer on sites where it is proven to be a problem, and this may be attempted by lethal (shooting) or ideally non-lethal measures (such as electric fencing or habitat manipulation). However, the results do not always seem to be clear-cut. The productivity of the target species may not recover, or other species may unexpectedly decline.
The complicating factor may be 'meso-predator release'. Top predators tend to suppress numbers of smaller, less dominant (meso) predators, such that when the top predator is removed, the meso-predator increases in abundance. So, in Finland, the removal of Lynx can allow Foxes to increase, causing a decline in a key prey species, the Mountain Hare. In the UK, the removal of Foxes may allow mustellids (generally Stoats and Weasels) to increase, and this may impact on species more vulnerable to mustellid predation. So things begin to get complicated, and answers are not always obvious.
And then there's the inter-action of Badgers with Foxes to consider.....and the effect of fluctuating small mammal populations. Hmmm, more thinking time required.