The parameter shown is catch per trap - the number of traps has risen steadily throughout the period, so catch per trap corrects for the effect of this increase on actual numbers caught.
There is a consistent increase in numbers in mid-summer, when the female stoats come off their nests with their brood of around eight offspring. In two years (04-05 and 06-07) this produced a very large peak in December/January, but in the other two years there was a much less marked increase, spread evenly from December to February. It is not clear why there was this change in pattern - in 05-06 there was a bigger catch in the preceding Autumn, which could explain lower breeding in Spring, however 04-05 and 06-07 had similar patterns for most of the year but very different results in December/January.
Traps are checked and re-baited less often in winter and more often in summer - for most of them the frequency is two-weekly and weekly, respectively. The bait used for most is rabbit meat, with a cracked egg as well (especially important in summer, when meat rapidly deteriorates), but for some a rabbit paste is used.
All traps used are kill-traps, either Fenns or DOC 200's.