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VOLUME 30, NO. 3 Fall 2012


Bats in the Backyard
Learning to protect urban bats in New Zealand
Darren Le Roux

New Zealand is home to only two bat species, and they account for 100 percent of the nation's native terrestrial mammals. New Zealand long-tailed bats (Chalinolobus tuberculatus) and New Zealand lesser short-tailed bats (Mystacina tuberculata) are found nowhere else on Earth, and both are listed nationally as threatened, largely because of habitat loss, plus predation by rats, feral cats and other non-native pests.

My work toward a master's degree from the University of Waikato in Hamilton, New Zealand, focused on long-tailed bats – small (less than a half-ounce [14 grams]) insect-eating bats that often roost in colonies of 10 to 50 individuals. They typically roost in cavities of large, old trees. But the old-growth forests that provide such homes have been disappearing since the arrival of Europeans 1,000 years ago; such forests now cover less than 14 percent of the country. The IUCN reports that long-tailed bat populations declined some 30 percent in a decade.

Supported in part by a BCI Global Grassroots Conservation Fund grant and a range of partners, I used arrays of automated bat detectors to assess the presence and activity of long-tailed bats in and around the city of Hamilton, New Zealand's fourth-largest urban area with some 150,000 people.

Hamilton is a growing city with many proposed land-development projects planned, especially for its less-developed southern fringes and rural outskirts. The threats facing these urban bats are immediate and serious.

And these conservation challenges are compounded by a paucity of conclusive information about long-tailed bat populations in and around Hamilton. Without knowing where the bats are, little can be done to protect them. A primary objective of this research was to develop specific recommendations for the long-term conservation of these bats in Hamilton and, at least eventually, throughout New Zealand.

Meanwhile, public support is essential for long-term conservation, but only an estimated 5 percent of New Zealanders are even aware that they share their islands with native bats. Public education about the value of bats and the need to maintain old-growth vegetation was and remains a critical part of our work. Among other efforts, I cofounded (with Environment Waikato) Project Echo, a multi-organization program to combine community education and involvement with continued monitoring of bat populations. We are also experimenting with bat houses, which were not being used in New Zealand.

Bats had previously been confirmed in only two sites in Hamilton: a rural oak-forest fragment and the Hammond Bush urban parkland. Both sites are flanked by the Waikato River, New Zealand's longest river, which bisects the city. Our initial study, designed to develop monitoring strategies while learning more about bat-activity patterns, was limited to those two habitats.

We chose 16 trees in four microhabitats of the forest and four in Hammond Bush, then randomly rotated five pairs of automated bat detectors among the trees. Using ropes and pulleys at each selected tree, we set one detector 13 to 23 feet (4 to 7 meters) above the ground and another at 65 to 100 feet (20 to 30 meters). In that first year, we monitored bat activity for a total of 217 days over a period of 10 months.

We recorded 23,000 echolocation calls. Ninety-four percent of the passes were classified as search-phase calls (the slow, steady pulses used to locate prey), while 6 percent were feeding buzzes (the very rapid hum of bats closing on their prey).

Based on these and other data, my recommendations for efficient acoustic monitoring of this species include: monitor bats from one to three hours after sunset on warm nights during warmer months; use bat detectors secured at the lower height; and concentrate on open spaces and/or near artificial and natural water bodies.

The next step was to apply the recommendations at multiple urban and rural sites that seemed suitable for New Zealand long-tailed bats. I suspected bats might well be more widely distributed around Hamilton than previously thought. The first such effort confirmed the presence of bats at 8 of 11 monitored sites. Subsequent surveys with colleagues expanded that number to 16 habitats used by bats, all of them on the southern urban/rural fringe of the city.

Distance (or corridor access) to the Waikato River or its major tributaries proved the most important variable in our study. Pass rates also fell sharply with increasing proximity to houses, roads and streetlights. These results confirm the importance of maintaining and restoring well-connected, less-developed habitats for urban bats. If New Zealand long-tailed bats are to remain within Hamilton City in the face of continuing urban expansion, critical conservation decisions and their implementation are absolutely required.

We clearly found that bat roosting and foraging behavior is more concentrated in rural environments (primarily forest fragments) than within city boundaries. It is important to note that a failure to detect bats at a specific site does not necessarily mean that bats are entirely absent or that they will remain absent in the future. Continued research and monitoring are needed.

Project Echo is one approach to gathering critical information on the urban bats. Among other things, the project solicits reports of bat sightings in the city and loans bat detectors, without charge, to interested residents. The program also works with citizens to protect standing old and dead trees as habitat for bats and other wildlife.

During my study, I worked with partners to conduct bat talks and walks at the Waikato Museum. We are also developing an education program that can be incorporated into school curricula.

Meanwhile, we are testing the feasibility of bat houses for Hamilton's long-tailed bats. With support from the Hamilton City Council as well as BCI, we have so far installed 25 bat boxes of four different designs. These include the BCI-developed single-chamber bat house, plus some unusual options that are carved with chain saws out of wood stumps so they retain such rugged features as split bark.

Unfortunately, no bats have moved in as yet, but we remain hopeful. One of our major objectives is to have Hamilton residents inspecting the boxes for occupancy. And already these bat boxes are proving to be powerful education tools, as many people seem fascinated by the construction and installation process. A recent Bat Fun Day, the first of its kind in New Zealand, saw more than 100 people turn out to watch the installation of several bat boxes and to enjoy "bat biscuits."

More New Zealanders are learning that there are bats in their backyards – and that bodes well for the New Zealand long-tailed bats of Hamilton.

DARREN LE ROUX earned his Master of Science Degree from the University of Waikato and is now working toward a Ph.D. at the Australian National University in Canberra, Australia.

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All articles in this issue:
BCI Highlights
Living Inside a Deadly Trap
The Memo from Our Executive Director
News & Notes
Bats in the Backyard
Nicaragua: Now the Land of 100 Bat Species
Searching Texas Caves for Signs of WNS

Unless otherwise noted, all images are copyright ©Merlin D. Tuttle and/or ©Bat Conservation International