How to Manage Pests
Pests of Homes, Structures, People, and Pets
Swallows, particularly cliff swallows, Hirundo pyrrhonota, often live in close proximity to people. While enjoyable to watch, cliff swallows nesting in colonies on buildings and other structures can become a nuisance. Their droppings can foul machinery, create aesthetic problems, and cause potential health hazards by contaminating foodstuffs. Their mud nests eventually fall to the ground and can cause similar problems. In addition, swallow nests frequently contain mites and insects such as swallow bugs (Oeciacus vicarius); swallow bugs are related to bed bugs and will bite humans, although humans are not their usual host.
Seven members of the swallow family breed in California: the tree swallow (Tachycineta bicolor), violet-green swallow (Tachycineta thalassina), purple martin (Progne subis), bank swallow (Riparia riparia), rough-winged swallow (Stelgidopteryx serripennis), barn swallow (Hirundo rustica), and cliff swallow. The first three nest in cavities such as woodpecker holes or birdhouses. Bank and rough-winged swallows nest in natural crevices or burrows dug in earthen banks. Barn and cliff swallows build mud nests attached to buildings and other structures, a habit that sometimes puts them into conflict with people. This is particularly true of the cliff swallow—the swallow of San Juan Capistrano—which nests in large colonies of up to several hundred pairs. In contrast, barn swallows tend to nest as single pairs and, consequently, do not cause many problems.
Swallows feed on insects and spend a large part of each day in the air catching flies, beetles, and mosquitoes. Their long, pointed wings give them great speed and maneuverability. Normally, swallows are not seen on the ground except when collecting mud for their nests. Most do not have musical voices but only twitter or squeak.
The cliff swallow is 5 to 6 inches in length and is the only square-tailed swallow in California. In contrast, the barn swallow is distinguished by its long, deeply forked tail. The cliff swallow is also recognized by its pale, orange-brown rump, white forehead, dark rust-colored throat, and steel blue crown and back.
Distribution and Habitat
Cliff swallows are found throughout California, except in high mountains and the dry southeastern desert. Four basic conditions are found at all cliff swallow colonies: (1) an open habitat for foraging; (2) a vertical surface beneath an overhang for attaching the nest; (3) a supply of mud that has the proper consistency for nest building; and (4) a body of fresh water for drinking.
The original nesting sites of cliff swallows were cliffs and walls of canyons. Structures, such as buildings, bridges, and overpasses, and agricultural activities have increased the number and distribution of suitable nesting sites, and cliff swallow populations have increased accordingly. In general, wherever irrigation water and buildings or other structures are found, suitable breeding conditions may exist.
Cliff swallows spend the winter months in South America. In late winter and early spring, they begin a northward migration through Central America and Mexico. Arrival dates can vary greatly because of weather conditions. The first migrants usually appear in southern California by late February or early March. Two or three weeks later cliff swallows begin arriving in northern California. Cliff swallows migrate during the day and catch flying insects en route. Swallows will not penetrate regions unless flying insects are available for food, which usually occurs after a few days of relatively warm weather (70°F or more).
Cliff swallows arrive at nest colonies in successive waves. A definite homing tendency exists among adults that previously nested at a colony. These birds are the first to return, followed by adults who bred at other colonies in previous years and by young birds who have not yet bred. The younger birds include individuals not born at the selected colony.
In addition to their homing tendency, breeding swallows are attracted to old nests. Under suitable conditions, a nest is quite durable and can be used in successive years. Old nests are usually claimed on the first day of arrival, although probably not by the original makers. Dilapidated nests are quickly occupied and repaired.
Cliff swallow nests are gourd-shaped enclosed structures built of mud pellets, consisting primarily of sand with smaller amounts of silt and clay. (In contrast, barn swallow nests are cup shaped and the pellets contain coarse organic matter such as grass stems, horsehairs, and feathers.) The cliff swallow nest chamber is globular and extends forward into an entrance tunnel that opens downward. The tunnel may be absent from some nests. Nest dimensions vary from 5-1/2 to 10-1/2 inches in length and 5-1/2 to 8 inches in basal width, and the opening averages 1-3/4 inches in diameter. The nest is cemented with mud under the eave of a building, bridge, or other vertical surface. Usually the first nests are located at the highest point possible with subsequent nests attached below it, forming a dense cluster.
Both sexes construct the nest, proceeding slowly to allow the mud to dry and harden. Depending on mud supply and weather, nest construction takes 1 to 2 weeks. Mud is collected at ponds, puddles, ditches, and other sites up to one-half mile away, with many birds using the same mud source. A typical nest contains 1,000 to 1,400 mud pellets, each representing one trip to and from the nest. Cliff swallows sometimes build two or three nests per season; not all nests are used, however.
Egg laying usually begins before the nest is completely finished. Each day one egg is laid until the clutch of three to four eggs is completed. In central California, egg laying generally occurs between late April and the end of May. In southern California nesting can begin during late March and in the extreme northeastern part of the state as late as June. Within a colony the date of egg laying varies because of the staggered arrival dates of the birds.
Renesting will occur if nests or eggs are destroyed. For example, nests may fall because they were built too rapidly or they may crumble because of prolonged humid weather. House sparrows (Passer domesticus) sometimes take over empty swallow nests and have been known to drive off swallows from new nests. A cliff swallow nest taken over by house sparrows is identified by the abundant nest lining (grasses, weeds, and feathers) protruding from the entrance.
Hatching and Feeding
Both sexes incubate the eggs, which hatch in 15 or 16 days. The adults are kept busy feeding the nestlings by foraging over an area sometimes 2 to 4 miles from the nest. Occasionally, long periods of continuous rainfall make it difficult for the adults to find food and they may abandon the nestlings. A sign of a successful nest is white excrement rimming the nest entrance, indicating the presence inside of young swallows.
Fledging and Post-nesting Period
In mid-May to mid-June, 20 to 25 days after hatching, the young birds fledge (take their first flight). They look similar to adults but are dull colored and have less sharply defined color patterns. The young will return to the nest for 2 to 3 days to be fed before leaving it permanently. They remain near the colony for about a week.
In California most cliff swallows raise one brood each year, although some may raise two. The time required from the start of nest building to departure after raising one brood is 47 to 64 days. Swallows are usually present at the colony for up to 100 days.
After leaving the nesting colony, cliff swallows will remain in the general area for several weeks. By mid-August there is a general southward movement, and by the end of September few swallows remain, except in southern California where a few linger into October.
Actions to solve problems with swallows should be started as soon as they are identified. Cliff swallows are colonial and the number of nesting birds can increase significantly from year to year. They are best managed by nest removal and exclusion techniques. There are no chemical toxicants registered for cliff swallow control, and shooting, trapping, or harming swallows is not permitted.
Legal Status and Permit Requirements
All swallows are included under the Migratory Bird Treaty Act of 1918 as migratory insectivorous birds and as such are protected by state and federal regulations. It is illegal for any person to take, possess, transport, sell, or purchase them or their parts, such as feathers, nests, or eggs, without a permit. As a result, certain activities affecting swallows are subject to legal restrictions.
The California Department of Fish and Game, the enforcement agency, considers February 15 to September 1 to be the swallow nesting season. Completed nests during this breeding season cannot be touched without a permit from the U.S. Fish and Wildlife Service. Outside of these dates, the nests can be removed without a permit. During nesting, a permit authorizing nest removal will be issued only if it can be justified by strong, compelling reasons. For example, such justification might include a health or safety hazard posed by a nesting colony situated over a doorway/entrance, near a loading area of a warehouse or a food processing facility, or at an airport if aircraft and maintenance safety are impaired.
If eggs or young are in the nest when a permit is requested, the application will probably be denied. It is best to request the permit during the nonbreeding season and well before spring nest construction begins. Past history and problems will be taken into consideration. The permit is issued for one season only. The permit will authorize the permittee or the permittee's employee(s) to use specified methods to remove the nests. The number of nests removed must be reported within 10 days after the permit expires.
For all permit requirements, contact the main office of USDA-APHIS Wildlife Services in your state. In California the address is 3419A Arden Way, Sacramento, CA 95825; phone (916) 979-2675. You will be referred to a district biologist who will assess the problem and make control recommendations. If lethal control is recommended, then a permit application must be completed and sent to the U.S. Fish and Wildlife Service regional office along with a fee.
In areas where a permit is required, the nest removal method will be specified by the permit. In California, old nests or nests under construction may be washed down with water or knocked down with a pole. Swallows are strongly attracted to old nests or to the remnants of deteriorated nests, so all traces of mud should be removed. During nest building, nest removal will require many days because cliff swallows persistently rebuild nests for most of the breeding season. They usually return the following year and the whole process must be repeated.
Exclusion refers to any control method that denies physical access to the nest site area. Exclusion represents a relatively permanent, long-term solution to the problem. In California, a permit is not required for this method if it is done before the birds arrive, during nest building when there are no eggs or young in the nest, or after the birds have left for the winter. If swallows have eggs or young in the nest, exclusion may not be used without a permit.
Netting can provide a physical barrier between the birds and the nest site. The mesh size should be 1/2 to 3/4 inch; however, 1 inch has been used successfully. If a plastic net is used, it should be attached so that it can be pulled taut. This prevents flapping in the wind, which looks unsightly and results in tangles or breakage at mounting points. The net should not have any loose pockets or wrinkles that could trap and entangle birds.
Attach netting to buildings before the birds arrive and leave it up permanently or remove it after the nesting season. Netting can be attached using tape, staples, or hooks on the eaves and the side of the building. An advantage of hooks is that the net can be taken down during the nonbreeding period or for maintenance of light fixtures, painting, etc. If staples are used, they should be rust-resistant to avoid unsightly rust stains on the building. For netting, a supporting framework of wooden dowels, wood laths, or metal rods along the edges will ease attachment to the hooks and create more even tension on the net. Netting may also be wrapped once or twice around wood laths and nailed directly to the building. It should extend from the outer edge of eaves down to the side of the building where protection from the elements given by the eaves is lost. Be sure there are no openings in the net where swallows might enter.
Some individuals have reported that hanging a curtain of netting from the eave will prevent nesting. The curtain should be 3 to 4 inches from the wall and extend down from the eave 18 inches or more.
Blocking the entrance will prevent cliff swallows from nesting inside buildings. Hang netting or strip doors of vinyl plastic or similar material across the entrance like a curtain, allowing passage of vehicles, materials, or people. Weighting the bottom of the netting will help keep it reasonably taut and in position during windy weather. Cliff swallows have been known to abandon nests inside a barn loft when the entrance was partially closed, reducing it to less than 8 x 8 feet.
Usually, swallows will not fly into a net but will stop and hover in front of it. If only that section of a building where swallows have nested is netted, the swallows will often choose alternative sites on the same structure. Therefore, any part of a building suitable for nesting must be netted. After the netting or wire mesh is installed, monitor the area for entry points and make necessary adjustments.
Nesting is sometimes discouraged through the use of metal projectors.These are sharp, needlelike wire or plastic devices generally installed along building ledges and windowsills to discourage birds from roosting. This method is not always successful in preventing swallows from nesting. In one instance cliff swallows learned to land on the metal spines and eventually built nests attached to them. Attach the sharp projectors to cover the area where swallows prefer to build nests, especially horizontally along walls protected by eaves. Additional projectors running vertically should be attached along interior corners. Once installed, projectors are left in place permanently.
Fiberglass panels that are 6 inches wide have been used to prevent nesting in some situations. The panels are installed between the eave and wall forming a smooth, concave surface that makes nest attachment difficult.
Modification of the surface where swallow nests would be attached sometimes effectively discourages nesting. Swallows prefer rough, uneven surfaces that provide a good foothold and suitable surface for nest attachment. Removing the rough surface of the wall and overhang can make the site less attractive to swallows. Attaching glass, sheet metal, or other very smooth-surfaced materials to the potential nest site can inhibit swallow nesting. A fresh coat of paint producing a slick surface may discourage nesting. Removing old nests and painting the area may discourage nesting the following year.
Other methods have shown little success or are unproven against cliff swallows. These include employing hawk, owl, or snake models or using taped alarm calls, noisemakers, revolving lights, and chemical roost repellents.
A partial list of sources of supply for netting and metal or plastic projectors is given below. Netting is also available at many hardware and farm supply stores.
HEALTH AND ENVIRONMENTAL IMPACTS OF MANAGEMENT ALTERNATIVES—from California Department of Pesticide Regulation
Pest Notes: Cliff Swallows
Authors: T. P. Salmon, UC Cooperative Extension, San Diego Co.; and W. P. Gorenzel, Wildlife, Fisheries, and Conservation Biology, UC Davis
Produced by University of California Statewide IPM Program
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