See bats swarm under I-80 on the Yolo Causeway
That people are fascinated by bats can be shown in the number of sold-out walk and talk tours scheduled by the Yolo Basin Foundation to watch the colony of Mexican free-tailed bats that take off from the Yolo Causeway on a hunt for insects every summer night.
Fascination could turn to frustration, however, as bat populations decline in the face of an approaching threat.
Fourteen hibernating bat species in Northern California are at risk from a fungus that causes white nose syndrome, which has been spreading westward since it originated in New York in 2006.
The cause for concern goes beyond the potential loss of the chance to spy a ribbon of bats in a summer evening sky. A paper published in the journal Science in 2011 estimated that bats in North America save at least $3 billion a year in pesticide costs by consuming insects.
Although Mexican free-tailed bats appear to be safe, researchers in California are developing plans for prevention and management of a disease that has killed between 5.7 million and 6.7 million bats.
White nose syndrome is the “most significant wildlife disease we have ever seen in North America and it has caused catastrophic mortality rates,” said Kevin Keel, a professor of veterinary medicine at UC Davis. The fungus thrives in cooler temperatures, meaning that caves where bats hibernate create the perfect conditions for its growth. When bats hibernate, they lower their body temperatures, fostering the spread of the fungus on their wings, muzzles and ears.
The fungus does not kill the bats directly, but instead alerts their immune and metabolic systems, processes that have been shut off during hibernation. An increase in metabolic activity forces bats to use stored fat reserves prematurely, and the bats ultimately starve to death or come out of hibernation early. Bats that come out of hibernation early search for food but typically die because they are weak from the depletion of their fat reserves.
The fungus has gradually migrated from New York to 26 other states and five Canadian provinces in nine years.
Only hibernating species can contract the disease. Mexican free-tailed bats do not hibernate and will not be infected with white nose syndrome. They help spread the disease, however, if they come in contact with spores and carry the fungus to caves where hibernating bats reside or caves that will act as future hibernacula for bats. Although a cave or mine will often be predominately one species, species can share caves.
Compared to the East, researchers in the West most likely will encounter a different set of challenges to manage white nose syndrome. One of these challenges will be pinpointing exactly where bats hibernate. Bats live in much smaller colonies in the West than they do in the East.
“Millions of bats are easy to find. In the West bats don’t form large aggregations, or if they do, we can’t find them,” said Scott Osborn, a senior environmental scientist with the California Department of Fish and Wildlife.
To aid bat-tracking throughout the country, the North American Bat Monitoring Program was recently established, and a pilot program has been launched in California. This program divides states into small grids and then tracks the bats in an area using acoustical software to monitor echolocation. Any significant decrease in bat population due to white nose syndrome can be observed.
Researchers working toward white nose syndrome treatment or prevention plans have other challenges.
There is no way to inoculate or vaccinate hibernating bats, “because their immune systems are turned off. … You can’t give them palliative care or supportive care to keep them alive for the rest of the winter,” said David Wyatt, a biology professor at Sacramento City College.
“If you go in and kill all the soil fungus and everything else,” Wyatt added, “then you’ve just destroyed the ecosystems of the cave. It’s the perfect storm. It’s worse than we could have imagined.”
For this reason, researchers are looking at introducing bacteria already present in the bat’s natural habitat.
Researchers from UC Santa Cruz swabbed bats hibernating in caves in Virginia and New York and isolated six bacteria that inhibited the growth of the fungus. The results were published on April 8 in the journal PLOS ONE.
The next moves would be to develop a probiotic composed of these helpful bacteria strains and test those formulations on bats that suffer from white nose syndrome – first in a lab setting and then on hibernating bats.
“Probiotics is one possible treatment. For white nose syndrome at this point we are trying as many different things as possible. It is just not some far-off East Coast issue, and it is moving westward. We don’t know how long it will take to get here, but eventually it will probably continue to march across the country as it has so far,” said Joseph R. Hoyt, a graduate student and lead author.
“Even if bats didn’t eat insects, they have value to us because they are a species that share the planet with us,” said Winifred F. Frick, professor of ecology and evoluntary biology at UC Santa Cruz said. They have intrinsic value.”
Katie L. Strong: (916) 321-1101, @katielstrong
Yolo Basin Foundation
What: A community-based nonprofit dedicated to the stewardship of the Yolo Bypass Wildlife Association. It sponsors Bat Talks & Walks, which are sold out the rest of this summer, and provides links for more information about the flying mammal. 530-757-3780; yolobasin.org