New Zealand has only three native terrestrial mammals, and all three are bats. One, the greater short-tailed bat, hasn’t been seen since 1965 and is considered extinct. The other two – the lesser short-tailed bat and the long-tailed bat – are in serious decline.
Isolated for more than 80 million years, the plants and animals of New Zealand evolved on islands completely free of mammalian predators – until the arrival of humans. The first predators, rats, arrived with the Maori people about 1,000 years ago. Since then, about 65 non-native mammal species have been introduced, most unintentionally. Native species, especially bats and birds, have paid a high price.
The decline of the long-tailed bat has been blamed, in part, on the loss of roosting and foraging habitat because of logging and land-clearing. But sharp declines have been documented in areas of with little forest modification, suggesting something else is the prime culprit.
The rugged wilderness of the Eglinton Valley has been the hub for long-tailed bat research – led by Department of Conservation scientists Colin O’Donnell and Jane Sedgeley – since 1993. Moira Pryde joined the team in 2001, charged with analyzing the incredible abundance of data.
A total of 1,026 individual bats were captured, fitted with numbered tags and released. Most were recaptured several times over a decade of netting in the valley. Computer analysis of the 5,286 captures and recaptures strongly suggests that introduced predators were the main villains in the species’ decline.
Pryde also found unusually low survival rates in 1996, 2000 and 2001. That corresponds to “mast years,” when beech trees that dominate local forests produce bumper crops of seeds, which in turn allow a sudden increase in predator populations. Mast years occur at irregular intervals.
Pryde’s analysis indicated that, if current trends continue, the long-tailed bat population in the valley will decline by an average of 5 percent per year, with extinction probable within 50 years.
The good news is that she found a likely solution: predicting the mast years and aggressively controlling predators during those periods. That strategy, the data suggest, could not only stop the bats’ decline but also allow their numbers to grow once again.
For this crucial research, Moira Pryde won Bat Conservation International’s award for Best Conservation Paper at the 2006 biennial Australasian Bat Society Conference in Aukland, New Zealand.
Members of Bat Conservation International can read the whole story about the bats and introduced predators in New Zealand in the Winter 2006 issue of BATS magazine.