What do you do when some of the best habitat on your refuge isnt actually on your refuge? You find a way to partner. What do you do when people are bothering bats in a mine? You put a gate on the entrance.
Kofa National Wildlife Refuge has done both.
The abandoned Hull Mine on a 130acre private inholding within the southwestern Arizona refuge is home to a maternal colony of 400plus California leaf-nosed bats. The landowner always has been generous about allowing biologists access to the mine, so refuge staff members have known for years that it is one of the largest roosts in the region.
The mine was established in the early 1900s as a gold and silver mine. During World War II, it yielded lead for ammunition. Today, it is well known on the Internet to collectors of leadbased crystals such as wulfenite and vanadinite, which are valued for their interesting shapes and rich redorange colors. Because the abandoned mine is easily accessible from a nearby highway, human disturbance is a big concern.
Visitors to the mine invariably disturb the bats, causing them to leave their roost and fly around, sometimes out of the mine into what may be an inhospitably hot day, says refuge manager Susanna Henry. This is especially concerning if the bats are using the mine as a maternity roost.
The California leafnosed bat has an average weight of half an ounce and wingspan of 13 inches. It lives an average of 20 to 30 years and has such acute hearing that it can detect the footsteps of a cricket. The bat is a federal species of concern and wildlife of special concern (threatened) in Arizona. Human disturbance has contributed to its decline.
So, refuge staff approached the landowner about placing a bat gate at the primary mine entrance. He was willing, both to protect the bats and prevent trespassing. Because the entrance is big enough to accommodate a truck, a tamperresistant bat gate would be expensive and the refuge would need help.
Biologist Jason Corbett of Bat Conservation International (BCI) visited Kofa Refuge to survey several mines in April 2008. He was impressed by the bats at Hull Mine and agreed it should be gated. He spent two years helping the refuge pursue funding sources, with little success. Refuge staff was about to despair when Dominic Barrett from the Partners for Fish and Wildlife Program offered help.
The Partners program provided financial assistance. Funding was matched with inkind services from the landowner and BCI, which agreed to administer the funds and coordinate logistics. Tom Gilliland from Mine Gates Inc. of Tucson arrived in July 2010 to take measurements. In September, Gilliland and his crew returned to install the customized gate, which is 15 feet wide, 10 feet high, weighs about 300 pounds and is made of superstrong Manganal steel. After days of heavy lifting, welding and retrofitting, the installation was done.
The gate even includes an opening known as an owl window so that larger birdsmostly barn owlscan continue to roost in the entrance. And its padlocks can be opened to allow researchers, students and others to enter with permission from the landowner.
A December 2010 survey found 336 bats exiting through the gate in one evening. So, the gate does not appear to hinder the bats. With the help of the landowner and BCI, Kofa Refuge will continue to monitor the mine and track progress of the bat population.
Lindsay Smythe is a biologist at Kofa National Wildlife Refuge.