Attracting & Managing Purple Martins

Attracting & Managing Purple Martins
Over one million North Americans put up housing for Purple Martins. Unfortunately, many of these folks are unable to attract breeding martins. The advice given here will increase your chances of attracting martins. Once martins nest at your location, they will come back every year, if you manage the site properly.

Landlords who lose their entire colony from one year to the next often suspect their ‘flock’ died in a storm during migration or was poisoned by pesticides on their wintering grounds. These scenarios are unlikely; the martins that share a breeding site do not migrate or overwinter as a colony. The reason for total colony loss is most often the result of something that happened in the landlord’s own back yard, during the nesting season. Good management practices can prevent or minimize most of these problems.

Location
The major reason people fail to attract martins is that martin housing is not placed correctly, or their site is inappropriate martin habitat to begin with. Martins have very specific aerial space requirements. Housing should be placed in the center of the most open spot available, about 30-120 feet from human housing. There should be no trees taller than the martin housing within 40 feet, preferably 60 feet. In the southern half of their breeding range, martins are less particular about house placement. Southern landlords can sometimes place housing within 15-20 feet of trees, and still attract martins. Generally, the farther housing is placed from trees, the better. Height of the housing can be anywhere from 10-20 feet. Keep tall bushes, shrubs, and vines away from the pole. Do not attach wires to a martin house, especially if they lead to trees, buildings, or to the ground. If your yard has too many trees near the martin housing, relocate the housing to a more open area, mount the housing higher, or prune (or remove) trees to create a more open site.

Timing
Most ‘would-be’ martin landlords rush to get their martin housing opened up for the arrival of martin “scouts” in their particular area. This is 4-5 weeks too early for new sites, and decreases chances for success. Contrary to popular folklore, “scouts” are not looking for new breeding sites for their flocks. “Scouts” are simply the first martins to arrive in, or pass through, an area on their way back to their previous year's nesting sites. These martins aren't likely to switch to new housing. Prospective landlords should not open their housing until about four weeks after the first martins are scheduled to return to their area (see map). No matter where you live, keep your housing open through June. Martins may arrive and begin nesting as late as the end of June, anywhere in North America. Landlords of active sites can leave their housing completely closed up until the martins return and land on the housing. Purple Martins exhibit a very high level of site fidelity — once they have bred successfully at a specific location, the same individuals return to breed there year after year.

Competition
If any other species is allowed to claim unoccupied martin housing, martins are not likely to stay. All birds set up territories around their nest sites and defend them against other birds. When House Sparrows or European Starlings lay first claim to martin housing, they fill the compartments with their nests, chase off investigating martins, fight with nesting martins, kill nestlings, and break eggs. Allowing House Sparrows and starlings to nest in martin housing will significantly reduce martin occupancy and productivity. Controlling nest-site competitors may require repeated lowerings of the house for nest tear-outs, and in the case of the nonnative House Sparrow and European Starling, trapping and/or shooting. The starling-proof entrance hole can be used to keep starlings from claiming martin housing. Should native bird species (e.g., Tree Swallow, Eastern Bluebird, Great Crested Flycatcher, etc.) try to take over your empty martin housing, temporarily plug all the entrance holes with door stops or paper cups, then put up appropriate, single-unit housing elsewhere on your property. Once they have accepted the new housing, reopen the martin housing. Housing should be stored inside for the winter, or closed up, to keep paper wasps, squirrels, and other birds from claiming the house before the martins return.

Housing
Houses and gourds should be painted white, or a light pastel color; trim can be any color. White housing seems to attract martins best. White housing reflects the heat of the sun, keeping nestlings cooler. Compartment floor dimensions should measure at least 6" x 6," but 7" x 12" offers better protection against predators and weather, if starlings are controlled. Compartment height can be from 4&1/2" to 6" or 7." Place entrance holes about 1" above the floor. Hole size can range from 1&3/4" up to 2&1/4." Many published plans for martin housing, and some manufactured houses, are made to improper dimensions, so if your housing is unsuccessful, check the dimensions, and modify where needed. Look for housing designed to raise and lower vertically, and with easy access to compartments. Landlords may need to lower housing daily to evict nest-site competitors, or to check on martin nestlings. Systems that telescope up and down, or raise and lower with a pulley and winch, are the most practical. Nest checks will not cause martins to abandon their nests or their colony site; number the compartments and keep written records.

Replacing Active Housing
The same martins return each year, and may abandon the site if the housing they are used to is gone, or drastically altered. To safely replace a single active house, place the new housing near the housing you plan to remove, and give the martins an entire season to get used to it. Do not remove the active housing until some of the martins have accepted and bred in the new housing for at least one season. Once martins have nested in the new housing, you can remove the old house, or put an additional new house in its place. Landlords with several active houses can replace a house between seasons without risk of colony loss.

Predation
The most common reason martins abandon their colony site is because predators have raided their nests. It only takes one foray up a martin pole by a snake, raccoon, or squirrel, or a few visits by an owl, hawk or crow, to cause all the surviving birds to abandon the site. Landlords who don't conduct weekly nest checks may never know their martins, nestlings, or eggs are disappearing. All martin poles (wooden or metal) can easily be climbed by predators and should be equipped with pole-guards. Martin houses that have become regular targets for hawks, owls, or crows should be equipped with external cage-type guards. Landlords should be alert for evidence of predation (e.g., dropped owl feathers, plucked martin feathers, chewed-off martin wings, etc.) under martin housing.

Weather extremes
Since martins feed solely on flying insects, they are extremely vulnerable to weather conditions that affect insect availability. Prolonged bad weather, such as rain, snow, cool temperatures, and/or heavy winds, all reduce or eliminate insect flight. If poor weather persists for more than 4 or 5 days, martins begin to die of starvation. Heat waves and droughts can also be a problem. When air temperatures go above 100o F. for many days, nestlings can perish from overheating. Prolonged drought can also adversely affect insect numbers. Some weather conditions may contribute to a population explosion of some external parasites normally found in martin nests, including fleas, nest mites, and blowfly larvae. Never use pesticides in bird nests or boxes. The safe way to reduce numbers of nest parasites is to remove nest material (and nestlings), sprinkle 1 or 2 two teaspoons of freshwater diatomaceous earth over the floor, then replace the old nest material with clean, dry wood shavings, pine straw (dried pine needles), or dry straw. Shape a shallow bowl in the material, and place the nestlings back in the nest.