Purple Martin Information and Management
Purple Martin Biology
Purple martins are our largest cavity-nesting swallow species, at approximately 7.5 inches in length. They eat nothing but insects caught on the wing. They also can bathe and drink on the wing. They have nested in man-made multi-room purple martin houses and gourd racks for hundreds of years. Native Americans were known to have hung gourds for these birds. They are almost 100% dependent on man to provide housing for them now, as natural cavities in old trees in suitable spots are rare in nature today. For more information on the history of purple martins and Native Americans, visit this page.
Contrary to popular belief, purple martins do not eat mosquitoes. They feed high in the air, above where the mosquito usually lurks. (You may wish to consider putting up a bat box to help encourage bats to eat your mosquitoes) Martins spend the winter mostly in Brazil, and come into the United States and Canada in spring and summer. They display high site fidelity; that is, they will return to the same nesting location every year if they are successful in fledging young from that site the previous year.
'Scouts' are the first adult martins back from Brazil during spring migration. These are the oldest martins (ASY, after second year) returning to established colonies to get the preferred nesting cavities. Younger martins generally follow, with subadult (SY/subbie), or 1 year-old martins coming later in the season. Martins start coming into North Carolina in late February and continue through late May and sometimes early June. See the scout report on the PMCA website for more information: http://www.purplemartin.org/scoutreport/scout.php?Y=2011&S=NC
Attracting Purple Martins and Housing Standards
You can attract martins to your new site using cd recordings of martin calls, played over a speaker. They are available commercially as the "Dawnsong" or "Daytime Chatter". Dawnsong is sung by adult males very early in the morning naturally over active housing, so it is best played anywhere from 4:30am-10:30am. After that, you can switch to Daytime Chatter. Martin decoys can be put on housing to make it look like the housing is occupied (martins are social and like to be near other martins). You can also smear some mud on the entrance holes and put pre-nests (basically a handful of pine straw) into the nest cavity to make it look like it has been used before. Sites that successfully fledged martin
young the previous year do not need to use these techniques; these
martins will return next year. Even if your site is not successful in attracting martins during the nesting season, leave the housing up until migration is complete in the summer (generally September) so that martins passing through to the south can see the site.
Housing standards and placement
Put up your martin house or gourds either when returning ASY birds are seen in your area in early spring (reference the PMCA Scout report page) or when SY martins start to arrive later in the season. Housing should be put in the proper location, which is in the most open space available. Often, well-intentioned people put housing too close to trees, which harbor predators. Try to aim for at least 40 feet between the housing and any nearby trees - the further, the better. Martins like open flyways, and trees are the biggest deterrent. Put martin housing at least 30 feet from human housing/buildings, but not more than 120 feet away - martins do like to be near people. Do not allow shrubbery or vines to grow around the base of the pole, and erect the housing 10-20 feet up on a pole. Erecting housing on a pier over the water can be successful as well. In the central area of NC, martins seem to prefer gourds over houses, whereas houses are more common at the coast.
Here is a helpful diagram from the PMCA on housing placement (click to enlarge):
House compartments should be 7"x11" (old houses with 6x6" compartment sizes should have their rooms enlarged by knocking out/cutting out an adjoining wall and closing the neighboring compartment). House compartments should open for inspection and rooms should have ventilation features and drainage or subfloors to prevent wet nests from rain, etc. Consider adding insulation to metal or thin plastic houses to protect from heat later in the season. Gourds (either plastic or natural) should be at least 9 inches in diameter. It is a myth that martins will not use plastic gourds or large natural gourds. (In some cases, natural gourds are used before plastic gourds.) All gourds should be equipped with clean-out/access ports and drainage holes, as well as ventilation features. Housing is out in the sun and it gets very hot!
How to links:
Active martin housing should have predator guards on the pole to prevent issues with climbing predators (see info below). Poles should be equipped with a pulley or winch system to make maintenance and nest checking easy. Telescoping poles, while inexpensive, can be dangerous and are prone to problems (sticking, pinched fingers, sudden drops, etc).
Keep all other bird species out of martin housing. Remember, if an investigating martin shows up, you don't want it to be chased away! (See below for more information)
Good pest-free housing in the right location will eventually attract martins! It is also perfectly possible to start a new colony with all SREH (see below)!
Martins need our help. There has been less of a trend of putting up housing for these birds in recent years, and their populations have suffered as a result of lack of managed housing and nest competition with two non-native, aggressive, invasive species. These are the English house sparrow and the European starling( aka S&S). Both will kill martins, take over their nests, and toss out eggs and young. It is important to learn to identify these pests. It is a myth that martins, starlings, and house sparrows can co-exist in the same housing. Eventually the invaders will drive out the martins.
We have spoken with some folks who believe that birds should "fight it out" for housing and "let nature take its course". Starlings and house sparrows are more aggressive than martins and will eventually take over the housing if it is left unmanaged. Here's what you need to know to give the martins a chance:
Dealing with Starlings:
European starlings can be kept out of martin housing and gourds by using SREH, or Starling Resistant Entrance Holes, rather than standard round holes. When these entrances are installed correctly (flush with or 1/8" up from the porch or floor), they will keep out almost all starlings. Click the image below to enlarge:
You can also use SREH without porches, but in some cases they are a little harder for the martins to use.
The base of a crescent, seen above, is 3 inches wide, and 1 3/16" high at the middle. Any smaller, and martins cannot get in. Any larger, and starlings will get in. Take the time to measure the entrance to make sure it is correct. The other entrance holes seen below can be purchased as entrance plates from various vendors (See links page). Click on the image below to enlarge it.
Dealing with house sparrows:
House sparrows must be removed via trapping, shooting, and with nest tear-outs, since they can fit in any hole a martin can. There are several commercial sparrow traps available, both as baited traps (bait with cracked corn, white bread, popcorn or torn-out nest material) or as compartment or gourd traps for certain brands of housing.
For more info on trapping and shooting S&S, including the why and how, see this page. Starlings and house sparrows are not considered to be migratory protected species. (For more info on this subject, see this page and go to p.40 in the pdf document.)
Dealing with wasps:
Sometimes paper wasps attempt to build nests in martin housing, often from the ceilings of house compartments, attics, or access ports of gourds/inside top of gourds. you can prevent them from hanging a nest by rubbing the affected area with unscented bar soap, or spraying a layer of Pam onto the area. Just make sure the Pam isn't going to be in an area where feathers might contact it.
Uh oh, another native bird is trying to nest in my martin housing!
If native bird species such as bluebirds, wrens, great-crested flycatchers, or titmice try to move into the martin housing, provide separate houses for them. Do not allow them to nest in martin housing or they may drive off all investigating martins. Close off the martin housing until the native bird in question has established a nest somewhere else, then re-open the martin housing. It has been suggested to move the native bird housing at least 30 feet away from martin housing to prevent it from defending both the martin housing and its own housing.
Why don't I have martins yet?
Make sure your site doesn't have any tree encroachment or nest competition problems. Sometimes it takes years to get martins to
move into new housing. Try something new - if you only have a house up, try hanging gourds underneath. Patience and perseverance is key. Playing the
dawnsong (early morning recordings of male martins singing - available
from the PMCA) and putting up decoys can help lure martins into checking
out your site. Some new colonies are started with ASY birds, but most
are started with SY birds, which arrive later in the season.
Why do I need a predator guard? I don't have snakes/raccoons/etc:
Snakes and raccoons are out there, you just haven't seen them - even in the city. If you have active martin housing without a predator guard and have not yet had a problem, you are on borrowed time. Rat snakes can climb wood or metal poles, even if they are greased. Raccoons are also excellent climbers. Predator guards can be constructed out of stovepipe material or even an old inverted trashcan, or they can be purchased commercially (see links page). Generally, the wider and longer the guard, the more effective it is against the big snakes. You can also use an electric fence. Here are some links to help you build your own predator guard:
Hawks and owls can also be an issue for martins at established sites. Torn-off house doors or torn entrance holes to gourds can be a sign of owl issues. Sharp-shinned and Cooper's hawks specialize in eating birds and can attack martin colonies. Consider putting wire caging around the housing to protect from hawks and owls. Here is a photo of hawk/owl caging around a house (click to enlarge):
Managed housing is a term that describes martin housing maintained for the sole purpose of successfully hosting breeding pairs of martins, and no other bird. Well-managed housing is roomy, ventilated, sturdy, accessible for nest checks, and easily raised and lowered for maintenance. It has predator guards and starling resistant entrance holes aka SREH, or a human presence that is constantly on alert for starlings. It is not infested with house sparrows. Owls, hawks, snakes, raccoons, squirrels, and other poorly-informed people can all be viable threats to nesting martins and should be considered when housing is erected for martins.
Nest Checks: Why do them?
Doing nest checks will not cause martins to abandon the nest. Nest checks enable the caretaker to check for problems and fix them, as well as to keep tabs on the health of the colony. Encapsulated eggs can be rescued if caught in time (hatched eggshell gets stuck over unhatched egg). Dead young or adults can be removed before the nest gets messy. Parasite problems can be minimized with the use of a pinch of sevin dust under the nest material, or a pyrethrin-based spray (there are some made for aviaries). Nest checking helps the caretaker determine the age of the young, so that their approximate fledge age can be determined. If the young "disappear" before that time, you will know you had a problem (predation: snakes, raccoons, owls, or even unmated SY males, which can sometimes drag out young and eggs). If the caretaker is frequently in the habit of walking around the base of the housing or within site of the martins, the birds will get used to his or her presence and feel more relaxed when nest check time arrives.
One of the best ways to conserve the purple martin is to help bring others into the hobby. Let that curious kid on his/her bike help you with a nest check, or with raising and lowering the housing. We have encountered elderly landlords who are too weak to do regular maintenance on the housing, and the martins suffer as a result. Let your legacy be the continuation of the martins for the next generation so that when you're gone, someone else can care for the colony. That legacy starts with involvement of the next generation in the hobby.