outdoorcentral.com
Barn swallows and Cliff swallows build mud nests on man-made structures, but their insect-eating abilities make them a welcome summer visitor.
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Colorado is fortunate to be the summer home for many species of migratory birds, including several species of swallows, notably the barn swallow and cliff swallow. These small, industrious birds are chiefly known for two things: eating millions of insects each summer and building mud nests on the sides of buildings, bridges and man-made overhangs.
Swallows typically winter in southern climates, as far south as Central and South America. They return to Colorado and other northern states and provinces in spring – although legend of San Juan Capistrano states they return punctually in March, in Colorado it can be as early as February or as late as June, depending on the weather.
Particularly in Colorado’s resort areas, there are many buildings, condominiums, and vacation properties that often go unused between winter ski season and summer outdoor recreation season. During the mud season between April and June, the birds are often busy building and repairing nests. When the humans return from their annual migration for Colorado’s glorious summer weather, many management companies and homeowners spruce up their properties.
Barn swallows and cliff swallows can be differentiated by their distinct tails: the barn swallow has a sharply forked tail, while the cliff swallow has a square-shaped tail. Both barn swallows and cliff swallows build nests out of mud pellets that they carry in their mouths to a nest site protected by an overhang.
Barn swallows build open, cup-shaped nests. Cliff swallows build enclosed, gourd-shaped nests with a slightly downward facing entrance. It is easy to distinguish the species based on the nests alone: Barn swallows do prefer to have their nests several feet apart. However, Cliff Swallows tend to form large colonies and nests are often packed very close together.
The male begins the nest as a shelf adhered to a vertical surface. The pair continues the construction by building up the sides and bringing them together to form a roof. The typical nest, which contains as many as 1,000 mud pellets when finished, is lined with grasses and feathers.
Some people find mud-based swallow nests an unattractive decoration on the sides of buildings, but destroying an active nest and/or the young in the nest is illegal. Swallows, their nests and eggs are all protected by the federal Migratory Bird Treaty Act of 1918 and may not be destroyed while active. The U.S. Fish and Wildlife Service allows vacant nests to be destroyed, but nests with active birds, their young or the presence of eggs must be left alone. Otherwise, it is a violation.
“One building complex with the most swallow issues is immediately adjacent to the Dillon Reservoir. I have seen well in excess of 100 nests at one time on the building. This is quite a few swallows helping us with the mosquito population,” said Kirk Oldham, wildlife manager for the Colorado Division of Wildlife. “But, there are two sides to the problem here. One side feels that the swallows are not being given a chance and would like to see citations written. The other side feels that they are simply pests, make a mess, and ruin the siding.”
Swallows are one of the most acrobatic of birds, but they eat insects almost constantly while in flight. For this reason, attracting swallows to a property may be one more positive step to managing insect pests. Oldham pointed out that Swallows’ tiny but gaping mouths capture hundreds of insects, including flying ants, termites, aphids, mosquitoes, crane flies and moths.
Insects make up, on average, 99.8 percent of the swallow’s diet.
“We’ve been doing a lot of work to educate the community about the benefits of the swallows, especially in the wake of West Nile Virus, which can be carried by mosquitoes. I can’t help but think that any species that feeds as voraciously on mosquitoes as swallows helps reduce the risk in addition to many other benefits,” Oldham said. “I have suggested that if the property managers need to remove old nests that they only remove those that are immediately above doorways, walkways, and places where visitors spend time.
It does not make sense to take down nests that are on the backsides and between the buildings. The birds can still nest, but may be encouraged to find places that are less visible to human visitors.” When nests are vacated, existing nests can be removed and swallows can be dissuaded from reusing areas by hanging netting where they are not welcome.
Some property managers have found a peaceful solution by creating specific areas where swallows are “allowed” to nest, adding a shelf, eaves or overhangs in an area that is away from main doors may encourage the birds to nest on locations where they are less of a nuisance.
“People who find a swallow nest near their front door or otherwise causing a problem may find that placing an artificial nest off to one side of the door or even on a different wall may be the surest way to coax the swallows to move,” Oldham said. Experts who have studied swallow relocation said the birds seem to prefer building on a vertical wall of rough wood, often on a small projection such as a protruding knot or nail.
Placing a piece of wood, particularly rough wood such as weathered barn wood, approximately 1 ½” from the building’s eave or overhang, appeals to swallows. The swallows seem to prefer to build right up near the ceiling. This likely helps them avoid predators and protects nests from wind and rain. Mud nests plastered on a wall cannot get wet or they will soon fail.
Swallows do not like continuous ledges or shelves, probably because predators, such as rats and mice, can easily reach the nest by crawling along such horizontal surfaces. Although barn swallows seem to prefer a distance of several feet between nests, they do tend to build nests near other swallows and birds will interact with others of their species. Since swallows tend to raise two to three broods each year and generally change to a new nearby nest with each brood, empty nests can be removed carefully once they are vacant. Creating a nearby shelf acceptable for nesting may encourage the birds to move towards a more agreeable location.
For more information on the International Migratory Bird Treaty Act (MTBA) of 1918, see
http://laws.fws.gov/lawsdigest/migtrea.html
including range of fines and penalties for violations of the Act.
Photos on the web: for an unusual photo of a Barn swallow nest on a light bulb, go to
http://dnr.state.co.us/imagedb/images/1020.jpg
To see photos of Cliff swallow nests, go to
http://dnr.state.co.us/imagedb/images/1054.jpg and
http://dnr.state.co.us/imagedb/images/1055.jpg
