It's spring in Tahoe. As grasses begin to emerge where there were once layers of snow and ice, so do mosquitoes carrying diseases such as West Nile virus.
Luckily, swallows arrive to help take care of the problem.
Swallows return to San Juan Capistrano Mission in Southern California, almost always on March 19 each year. Although they arrive later at Tahoe, it is just about as predictable, according to Cheryl Millham, executive director and a founder of Lake Tahoe Wildlife Care Center in South Lake Tahoe.
"They migrate here in the spring," said Millham, who has worked at the center for 26 years. "If we don't have any more bad weather, I'll probably start seeing swallows in three or four weeks.
"They always start gathering in huge flocks around the end of August and into September, and then one day they're gone."
Swallows overwinter in Brazil, Paraguay and Argentina, according to researchers at Cornell University in New York. Millham receives calls from residents along the South Shore every spring, asking what they can do about the swallows and their nests, which are commonly mistaken for wasps' nests.
The birds in the Lake Tahoe Basin are barn swallows, tree swallows and cliff swallows. Swallows make their nests of mud and need water nearby.
Barn and tree swallows make their nests of mud and twigs. Cliff swallows build their nests entirely of mud, in clusters of 20 or 30 under bridges or eaves.
Two years ago at Tahoe Keys, residents complained about swallows' nests, but once they learned the birds ate mosquitoes, they decided to put up with the mess.
"Usually when people learn how good for the environment (swallows) are, then they're fine with having them stay," said Millham.
There are at least two reasons for not destroying swallows' nests, especially during breeding season, she said.
Knocking or spraying them down is illegal. The U.S. Department of Fish and Game states in a report, "In the United States, all swallows are classified under the Migratory Swallow Treaty Act of 1918 as migratory insectivorous birds and are protected."
In fact, permits are required by Fish and Game just to remove swallow nests.
"During nesting, permits authorizing nest removal are issued only if strong compelling reasons exist," according to Fish and Game.
"I have known people who have been charged up to $1,000, plus jail time," said Millham. "When (the birds are) all done, when their babies are gone, they can knock down the nest."
Swallows, which can consume up to 1,000 mosquitoes per day during nesting season, can provide a health and safety benefit as well, said Millham.
"People should leave them alone because of the West Nile virus," she said.
The U.S. Center for Disease Control Web site says the virus, spread by mosquitoes, affects the central nervous system, especially in people age 50 and over. This year, West Nile has been detected in Los Angeles and Orange counties.
Although the disease can be fatal, less than 1 percent of people bitten by mosquitoes develop any symptoms, and few mosquitoes actually carry it, according to the Web sites.
While California has had only two cases reported in humans, four types of mosquitoes that carry the virus live in the Tahoe area, according to the health department.
The public can help prevent the disease from spreading by reporting any crows, ravens, magpies, jays, sparrows and finches that have been dead for 48 hours or less, by calling 877-WNV-BIRD. For more information, go to co.el-dorado.ca.us.
Once nesting season is over, Millham suggests, screens can be attached under eaves. Also, bookshelf brackets can be placed over a window with a board set on top to keep droppings from hitting the window.
For mosquito control in areas near water, swallow nesting structures can be built fairly simply from a post and two pieces of wood. For more information, call the Wildlife Care Center at (530) 577-CARE.
Millham stressed the importance of swallows in the Tahoe area.
"At the lake here, all people should welcome all the insect-eating animals. The biggest mosquito eaters we have are the swallows and the bats. We need to encourage them, not discourage them," she said.