In last months SIN, I described how we were using digital recorders to look at the abundance of birds at a variety of sites. The aim was to see if areas that had received long term pest control had higher numbers of birds than other areas. It would also give an indication of the change in bird numbers that we could expect if we removed predators from around the township. The sites selected were Ackers Point, Dancing Star Foundation and Ulva Island as areas that had received long term predator control, and Port William and North Arm as sites that haven’t had this control.
The following graph really speaks for itself.
MEAN CALL COUNTS FOR NATIVE BIRD SPECIES PER 5 MINUTE SAMPLE INTERVAL. SITES: 1 = NORTH ARM, 2 = PORT WILLIAM, 3 = DANCING STAR, 4 = ACKERS POINT, AND 5 = ULVA ISLAND.
Ulva Island is setting the standard for what we would expect from an island that has been pest free for almost 20 years. The rat invasion and eradication a few years ago has obviously had little long term negative impact. The other outstanding feature is the high level of birdlife at the DSF site, with about twice as many birds as the other sites. This clearly shows the benefit of the predator fence and seven years of ensuring that any invading predators are removed.
If we set Ulva Island as the level that birds should be at in our forests, then you can see how poorly these native birds are doing in sites without any control of rats, cats and possums. Perhaps also it suggests how much we have to gain should we follow through with the predator free Stewart Island concept.