A New Technique for Establishing a Purple Martin Colony Site
Purple Martin Preservation Alliance
For centuries, we have longed for the company of Purple Martins. I suspect the Native American Indians enjoyed hosting them for much the same reasons that European colonists later did, and for the same reasons we do today - they are graceful, cheerful, and entertaining.
And for centuries getting martins was a relatively uncomplicated affair. Landlords simply put up a martin house or strung some gourds and sat back! Unfortunately, that's now the recipe for attracting European Starlings and House Sparrows, two nonnative nest-site competitors introduced into this continent in the late 1800's by well-meaning, but misguided individuals.
For the past 50 years, convincing martins to share our backyards has become increasingly difficult. Several factors have combined to make martins scarce in many areas of their breeding range: habitat loss, harsh spring weather, loss of interest in the hobby from an increasingly urbanized culture, and the depredations of starlings and House Sparrows are just a few. With the resurgence of interest in the martin hobby over the past few decades came a clamoring for ways to fill all those empty Purple Martin houses. But the scarcity of martins created by decades of neglect is not easily undone. The gradual rebuilding of the martin population that is needed for natural recolonization leaves many wanting faster ways to reestablish former colony sites.
Several methods of artificially establishing Purple Martin colony sites have been attempted over the course of the half-century. Each of these techniques, although successful with other species of birds, has failed for Purple Martins. These methods include hacking, trap & transfer, and cross-species fostering.
Cross-species fostering involves placing the eggs or nestlings of one bird species into the nests of closely-related species already established in a particular area, with the hope that the foster-parents will successfully rear and fledge the "adopted" nestlings, which hopefully will return to the site the following year and breed. When tried with martins, this technique failed because the foster parents had a breeding cycle that was too different from the martin's. The martin's closest North American cousins - Barn and Tree Swallows - each have fledging ages of 14-16 days, whereas Purple Martin nestlings require about 26-30 days in the nest to reach fledging age. Therefore, the foster-parents abandoned the fledglings after about two weeks, leaving them to perish.
Trap and transfer involves capturing wild adults of a species and transporting them to a release site where it is hoped they will become established and breed. This technique also failed with Purple Martins because all swallows have a very strong homing instinct. When released, the martins immediately flew back to the exact site from which they were captured. Even when the adults are captured in the martin housing with their young, at night, and transported to the release site, they would return to the site from which they were "kidnapped," abandoning their young in the process.
Hacking involves hand-rearing and releasing the young of a particular species at a site and hoping they stay or return to breed at that site. The Pennsylvania Game Commission once conducted a two year hacking project in Ligonier, PA. Just like Trap & Transfer and Cross-Species Fostering, Hacking attempts have also failed with Purple Martins because of the high mortality and dispersion rates of juveniles. Only 3 or 4 out of 10 martins survive their first year of life and return to North America to attempt breeding. Of those that survive and return to breed, only 25% (or 1 out of 4) return to the natal colony site. Most disperse to other sites within about a 50-mile radius. Therefore, for every 10 martins successfully "hacked out," only one can be counted upon to return to the hacking site. And these numbers may be optimistic, since hand-reared martins probably have a lower survival rate than those with parents to teach them survival skills. Theoretically, hacking would work if carried out on a large enough scale, perhaps 100 or more martin nestlings. However, this would be a waste of resources since it has been shown that breeding martins can attracted using a technique known as Social Attraction.
Social Attraction relies upon a species' social nature to succeed. Most bird species are solitary breeders and will defend a large territory around their nest site, preventing others of their own kind from breeding nearby. Colonial birds, on the other hand, strongly prefer to nest in close proximity to each other. The social attraction method was developed by Dr. Steven Kress, a Cornell University biologist trying to reestablish Atlantic Puffin (Fratercula arctica) colonies lost to overhunting and overfishing. Kress reasoned that if he could trick migrating puffins into believing that former colony sites were again active, they would stay and attempt to breed. His technique involves the use of decoys, vocalizations, fake nests, and mirrors. Social Attraction is ultimately the art of deception, trickery, and manipulation, and, it will work for Purple Martins, too.
With the help of the PMPA, its members, and many devoted martin enthusiasts, both amateur and professional, I have employed, adapted, and refined this technique to work for Purple Martins. After 10 years of effort, I successfully attracted one pair of subadult martins and two bachelor males to a site north of Pittsburgh, PA, an area of martin scarcity. In 1999, Purple Martins bred in Natrona Heights, Pennsylvania, for the first time in over 30 years!
This article is geared towards martin enthusiasts in areas where martins are scarce or where the local habitat is marginal. If you live in an area of Purple Martin abundance, or in prime martin habitat, you probably won't need to employ Social Attraction techniques to "bring down" your first pair of martins.
Cavity-hunting martins are reluctant to colonize new sites because the absence of breeding martins creates uncertainty about the quality of the site. The goal of Social Attraction is to convince investigating subadults that Purple Martins are already established, giving them the confidence to make a breeding attempt themselves. Creating and maintaining a convincing illusion of colony activity is the key.
It is important to understand that no single item is intended to "fool" investigating martins entirely. After all, a martin soon discovers that a decoy is unreal after it inspects it. Rather, the key is to bombard investigating martins' senses with multiple stimuli, the combination of which is overwhelming and just convincing enough to "click off the switch" of disbelief in a sort of subconscious way. The more diverse and numerous the attraction stimuli, the more convincing and successful the overall deception is likely to be.
Martin vocalizations are, perhaps, the most important component of the Social Attraction technique. Properly broadcast, martin vocalizations can "advertise" your site to migrating and investigating martins over a broad area and at high altitudes (see Fig. 1). "Dawnsong" is particularly powerful because it is used by adult male Purple Martins specifically for the purpose of attracting other martins to established breeding sites. Dawnsong is most effectively played through an outdoor horn speaker attached to an audio system, controlled by a timer that automatically starts the tape or CD at 4:00 AM and stops it at 6:00 AM. A Purple Martin decoy can also be attached to the speaker. An article detailing how to effectively play the dawnsong appeared in Purple Martin Update Vol. 8(3):8-10.
Fig. 2. A Purple Martin decoy (top) and a real martin (bottom) on a house with a speaker mounted in the bottom, center compartment. The combination of decoys and dawnsong creates an illusion of colony-site activity.
A daytime vocalization
tape or CD can also be played intermittently throughout the day from 6:00 AM to
8:00 PM. The dawnsong tape may be substituted. I also mounted a small speaker
inside the martin house (see Fig. 2). Using the balance control knob on my
receiver, I was able to switch from the large outdoor horn speaker to this
smaller speaker, enticing martins inside the house. This second speaker is not
necessary if your main speaker is close to the housing. In any case, be sure to
lower the volume when martins arrive at your site; otherwise, they might be
alarmed or disoriented.
Decoys: At least two life-size Purple Martin decoys should be deployed on clearly visible perches at the colony site to provide a visual stimulus (see Figs. 2, 3, and 4). In addition, consider positioning other decoys creatively, such as perched in entrance holes, clinging to gourds, tail sticking out of cavities, perched on an eggshell feeder, or sitting on the ground next to an artificial mud puddle. Move them around once or twice a day, if possible, especially after you see martins visiting the site. Always wait until investigating martins have left before moving the decoys around; otherwise, your handling of the decoys could cause alarm. By mounting several decoys on a perching tree (a pole with several symmetrical perching arms), you can spin/rotate the pole from time to time, creating the illusion that the decoys have moved by themselves. (Caution: never spin poles supporting martin housing.)
Fig. 3. A subadult male Purple Martin investigating a Trio Castle that is equipped with decoys, mirrors, and mud splatters, all intended to simulate nesting activity. Note the 3" x 3" mirrors taped to two of the flip-up doors.
Do not place decoys so that they block the best cavities, such as perched inside the biggest gourd or in front of the cavity facing the most open direction. Leave these prime areas available for the real martins. Place decoys in marginal areas, such as the side of the housing with the least open flyway.
Fig. 4. A martin on an eggshell feeder "socializing" with several decoys. Decoys can be used to get martins to investigate eggshell feeders stocked with crickets for emergency, cold-weather survival.
It's only necessary to display adult male (all blue-black) decoys, because young females gauge the quality of breeding sites based primarily on the presence of adult males. Any site with adult males is bound to have resident females incubating eggs. Also, decoys need not be highly detailed; although I recommend they be accurate in size, posture, and profile. Decoys are available on E-bay
I have observed investigating martins perch next to, peck at, and inspect decoys, going so far as to mount them in an apparent attempt to copulate. One morning in mid-June, the subadult male of my pair began repeatedly dive-bombing and scolding the two adult male decoys positioned on the house nearby! These decoys had not been moved in weeks and surely he "knew" they were not real. Perhaps he was showing off for his mate (who was incubating eggs) by challenging these two "wood-be" martins.
Mirrors. Mirrors provide another visual stimulus and should be mounted to the entrance holes of several cavities or to the rear walls inside several compartments, so that investigating martins peering into empty cavities see what appear to be other martins. Strategically placed, I believe mirrors can be a very powerful stimulus. Small pieces of mirror can be cut with a glass cutter and duct-taped in place (see Fig. 3).
Artificial Nests and Eggs. Artificial martin nests, complete with mud dams, green leaves, and clutches of fake eggs, are signals to investigating martins that breeding has or is taking place at the site. Decoys could even be positioned inside cavities to simulate incubating females. Fake nests are easily fashioned from small twigs, soft, dried pine needles, or wood shavings. Martins build a rather flat nest with a mud "dam" at the entrance hole. Eggs can be made from clay and painted white. Finally, martins line their nests with fresh green leaves, so you should do the same to your fake nests.
Starling/House Sparrow control. Using the Social Attraction technique doesn't mean getting out of the chore of having to control starlings and House Sparrows. It is essential that you create a starling-free and House Sparrow-free zone at your site. Both of these destructive nest-site competitors can chase off investigating martins, and must therefore be humanely eliminated by trapping or shooting. It is now possible to minimize starling problems by equipping deep-compartmented houses and big gourds with starling-resistant entrance holes (SREH's). Given a choice, starlings prefer deep wooden cavities over very large gourds, but will use either.
Offering the ideal type of housing is the best first step you can take in attempting to attract martins. Martins strongly prefer 10-12" deep (front to back) cavities in wooden houses and large (10-14") gourds. While they will nest in all types and sizes of housing, if you live in an area where martins are scarce, ideal housing is critical since there are fewer martins to go around, and they can afford to be choosier.
I also recommend offering the type of housing used at the nearest active site. If the closest breeding martins are in a Trio Musselman, make sure you offer one of those! If they're in natural gourds, offer those. You never know what a cavity-hunting martin is going to prefer. The pair of martins attracted to my Pittsburgh site were initially attracted to (and slept in) the T-14 wooden house, perhaps because wooden houses predominate in my area. However, they eventually chose to nest in a 13" natural gourd hung under the T-14. The martins may have chosen the gourd to avoid harassment by starlings, or they may have preferred the gourd once they had a chance to become familiar with it. I also recommend leaving a few shallow (6 in. deep), round-holed cavities since most martins are familiar with round holes (see Fig. 3). Eventually, you can switch to all deep cavities with SREH's.
The key to establishing a colony of martins is attracting the first breeding pair, which acts as a strong magnet, drawing in visitors from colony sites many miles away, as well as wandering martins. There were as many as four additional martins present at my site at one time, mainly in the morning. It was surreal to see so much activity after so many years of empty martin houses. The Social Attraction method can require a substantial amount of time and money, but it can be used to attract that critical first pair and to reestablish martins in areas they've absented for decades.
This article is dedicated to my parents, Victor and Mildred Kostka, who made these efforts possible.