Pest control will give native bats a chance
Rat numbers need to be kept low to protect bat populations in areas such as the Pureora Forest Park near Lake Taupo¯. Chris Marshall reports.
Controlling pests and conserving native bush are key in efforts to preserve native bats in areas such as the central North Island’s Pureora Forest Park, according to the Department of Conservation.
Long and short-tailed bats were once common in Aotearoa and are still present in some areas, including Hamilton, but have disappeared from many areas due to habitat loss and predation by rats, possums, stoats, and feral cats.
The tiny mammals roost together and rear their young in hollow trees, where they are especially vulnerable to attack.
As well as pest control, DOC principal science adviser Colin O’Donnell said the retention of any native bush, even regenerating shrubland, can help.
‘‘Long-tailed bats, which are the most endangered, feed out on forest edges. So the more edges you have, even little forest remnants, the better, as they are good foraging habitats.
‘‘Short-tailed bats live much more in the forest, but they do use corridors between forest patches – so a gully full of native vegetation they might use to commute between different, larger areas of forest.’’
Close monitoring of bats over many years in the Eglinton valley near Te A¯ nau and Pureora west of Lake Taupo¯ has shown a significant upswing in populations of short-tailed bats due to predator control.
Eglinton and Pureora are two of the few places where both species of bats remain. Eglinton has one of only two populations of mainland South Island shorttailed bats. The other is in the Murchison Mountains.
Pureora is a stronghold for the central sub-species of shorttailed bat, which is in decline.
Numbers of short-tailed bats in Eglinton have increased by 8 per cent a year since 1990 while in Pureora, where short-tailed bats have been tracked for the past eight years, predator control has allowed the population to grow by 10 per cent annually.
Long-tailed bats appear particularly sensitive to rat predation, requiring low rat numbers over large areas for them to thrive, O’Donnell said.
While predator control timed to cope with the beech mast has suppressed rat plagues and allowed many more to survive in Eglinton, long-tailed bats in Pureora still seemed to be in decline, he said.
Long-tailed bats can fly up to 20km a night and at Pureora range widely across farm and forestry land where they are at greater threat from predators.
‘‘Research shows that largescale predator control over at least 3500 hectares, keeping rats to very low levels, is needed to protect long-tailed bats.
‘‘Linking up forest areas and other habitats with predator control may be key to the survival of long-tailed bats at Pureora.’’
In Pureora’s warmer mixed podocarp and hardwood forest, predators tended to be consistently high rather than spiking after each beech mast.
In Pureora, bait stations are used to protect bats in an area of more than 900ha, timed for when they are raising their young. Predator control at nearby Waipapa will also help protect their wider habitat.
But landowners can also do their bit, O’Donnell said.
‘‘Individual families have their own little trapping programmes, and collectively, if you add them all together, they’re starting to make quite a difference.’’
And a benefit was that bats were a native biological control.
‘‘The long-tailed bats do like agricultural insect pests like grass grub beetles and porina moths. There have been studies in the US and in Europe which show that bats can be worth millions or billions of dollars of benefit in terms of free insecticides.’’
While still nocturnal, the long-tailed bats came out to feed earlier than the short-tailed bats, O’Donnell said, so for about 40 minutes from sunset were potentially visible against the sky, flitting around the edge of the forest catching insects.
Short-tailed bats which also feed on nectar and fruit were important pollinators and seed dispersers, he said.
‘‘Some plants really rely on bats, and a good example of that is the dactylanthus. When we look at Pureora, the short-tailed bats are their main native pollinator. If short-tailed bats disappear then probably dactylanthus would, too.’’
The unusual Dactylanthus taylorii, also known as the wood rose, is New Zealand’s only fully parasitic flowering plant and the southernmost member of its mainly tropical family.
It grows as a root-like stem attached to the root of a host tree.
While there were encouraging signs in managed sites, DOC said bat populations continued to decline at unmanaged sites.
DOC also monitors bats at other sites, including Puketı¯ Forest, Rangataua and Whirinaki in the North Island, and O¯ pa¯ rara, Te Ma¯ ruia, south Canterbury and the Murchison Mountains in the South Island.
‘‘There have been studies in the US and in Europe which show that bats can be worth millions or billions of dollars of benefit in terms of free insecticides.’’
Colin O’Donnell
DOC principal science adviser