Predator control started early in 2003. The reduction in rat numbers has been spectacular - since 2007 the usual result of monitoring immediately after the Spring baiting is such that we would expect to find only one or two visited tunnels out of the 150 placed throughout the Ark. In March, around six months after the last baiting, and at the time of the natural peak for rat populations, the numbers are about 3 times higher, but still generally only 5 -8%.
The initial increase in mouse numbers was attributed to them flourishing in the absence of rats, but since 2006 their numbers have also dropped sharply - this was unexpected, but has been sustained and it now seems clear that the combination of broudifacoum and a 100m by 50m grid of bait stations is sufficient to significantly reduce mouse numbers. Click the forward arrow above to see the results for after baiting, only, which allows a more sensitive vertical axis.