A Revolutionary New Entrance Hole Design:
Duke Snyder's Starling Excluder

Ken Kostka
Purple Martin Preservation


Duke Snyder of Butler, PA, in front of one of his homemade aluminum martin houses fitted with his starling-excluder entrance holes. Duke has never had a starling gain entry through one of his revolutionary new doors.

If you've ever driven the country roads outside of Butler, PA and come across a couple of martin houses with rather unusual-looking entrance holes, consider yourself lucky, because you may have witnessed martin management history in the making. You've stumbled across the "Area 51" of SREH (starling resistant entrance hole) experimentation - the home of John "Duke" Snyder.

Duke's interest in martins began nearly thirty years ago, when he learned about them through his boss who had a 9-pair colony site. Impressed with the gregarious nature of the birds, Duke first tried establishing his own colony site in 1972, in Lyndora, PA. His efforts were bound to fail that year - Tropical Storm Agnes stalled over western Pennsylvania in June, causing constant rain for over three weeks during the peak of the breeding season and killing almost all of the martins in southwestern PA. His efforts to attract martins from 1972-1978 were unsuccessful.

In 1979, Duke moved to his present home about 7 miles west of Butler, and again tried to attract martins. 1979 passed with only visitors, but on May 24th, 1980, one subadult pair arrived and eventually nested in an unmodified 12-room aluminum house. Tragically, the nestlings disappeared when they were only 1-2 weeks old; they were probably taken by a raccoon, snake, owl, or hawk. The pair did not return the following year, and 7 long years would pass before Duke hosted nesting martins again.

Then on May 16th, 1987, Duke attracted a "pair and a spare" - one subadult pair and an unmated subadult male that stayed for the entire breeding season. The pair bred successfully and raised three young. The following year, on April 23rd, 1988, two adult pairs returned and nested successfully. By 1996, Duke's colony site had grown to over 30 pairs.

Like many other landlords, Duke controlled European Starlings, but in 1977, after countless hours spent shooting and trapping these destructive, nonnative pests, he decided to try Charles McEwen's crescent SREH's. These holes, which are 1&3/16" high by 2&7/8" wide, exclude most starlings. The crescent SREH's in Duke's houses proved slightly less effective, however, because they were cut in aluminum (a thin material) rather than wood (which is much thicker). Additionally, Duke made his McEwen SREH's slightly larger than recommended since he had one or two Purple Martins that appeared to have gotten stuck.

Three Purple Martin nestlings stick their heads out of the excluder door begging for food, while the upstairs neighbor is feeding his nestlings.

One advantage of the excluder is the ability of three or more nestlings to access the entrance hole simultaneously for feeding. This gives runts a better chance to compete for food.

Then something happened that spurred Duke to take on a new challenge. On April 7th, 1997, his first Purple Martin pair returned and roosted nightly in the same compartment. On April 14th, at 7:00 A.M., as Duke was watching and drinking coffee, he saw two starlings fly onto the porch of this active compartment. One starling remained outside while the other entered. Seconds later, the female martin emerged and was attacked by the starling on the porch. The starling viciously stabbed at the female martin's head with its dagger-like beak, and she escaped by diving off of the side of the porch. Moments later, the other starling exited, and both starlings flew after the female martin. Duke checked the compartment and found the male martin dead inside. His eyes had been gouged and there were several lacerations elsewhere on his body. Later that morning, the female martin returned, circled the martin box, and left. She did not return.

Shocked, saddened, and outraged by seeing his first returning male martin killed by starlings and the female martin chased away, Duke resolved to design an entrance hole that was not only starling-resistant, but starling-proof.

Through careful observation, Duke discovered that the starlings which managed to enter the crescent entrances usually did so by rotating their torso to the right or the left in order to allow slightly more clearance for their deep, thick sternum. To prevent this twisting behavior of the starling, Duke came up with an ingenious idea. He incorporated two 1/2" tall peg-like triangular protuberances into the bottom of his new "excluder" entrance hole, about 1&1/4" apart. These pegs would allow the slender torso of a martin enough room to go straight through, but would be too narrow for the starling's bulkier torso. The starlings would be unable to enter by rotating or twisting their hefty frame. But the new "cookie-cutter" design of the hole would also require the martins to hold their wings away from their bodies in order to enter. There was no guarantee that Purple Martins would be willing to do so.

In 1999, Duke added excluders doors to one of the two houses in his front yard before the martins returned. Seven pair nested in cavities with the excluder holes! They entered, exited, and went about their business without difficulty. He was further encouraged to see the parents and fledglings returning to their natal cavities night after night at the end of the season. Duke also erected a new aluminum house fitted with excluders in his backyard, away from his established colony site. Two pair of subadult martins nested successfully in cavities with excluder holes. One pair fledged five young; the other pair fledged two.

To test the effectiveness of these entrance holes against starlings, Duke built a starling test facility in his backyard, out of sight of his martin houses. He constructed 15 natural cavity-type boxes out of hollow logs, which starlings love (see top photo). Duke designed these starling "nestboxes" so that the excluder plates could be easily substituted for the 2" round hole. He gave the starlings a free pass for several weeks, allowing them to go about nestbuilding. Then he added the excluders. Every starling pair abandoned their nesting attempt. To date, not a single starling has ever been seen entering a cavity with one of the starling excluder entrance holes. Duke said, "When I removed the excluder holes from the logs, the starlings moved in. When I placed the excluder holes in the logs, the starlings moved on."

For the 2000 season, Duke retrofitted all of the entrance holes on one of his two homemade aluminum houses with excluder entrances. About 20 pairs of martins nested in this house (see bottom photo). The other house had about 10 pairs of martins nesting in cavities with excluders.

I have watched martins using these entrance holes on many occasions and they are very promising. They may even prove to be starling-proof. Although it does take a split second longer for martins to enter and exit (as is true with the crescent SREH), this slight delay is offset by the tremendous advantage martins gain by being protected from starlings. Starlings are notorious for attempting to take over martin nests by killing or injuring martins, and by despoiling their nests. Of course, at unestablished sites, nesting starlings will chase off investigating martins, ruining the chance of colony-site establishment.

Several starling test cavities; excluders were substituted for round holes after starlings had built nests. In every case, the starlings abandoned the nesting attempt.

Twenty pairs of Purple Martins bred in this house fitted with excluders in the year 2000.

An additional advantage of the excluder entrance is that as many as three (and perhaps four) older nestlings can be fed at one time (see photos on previous page). With conventional round entrance holes, only one or two martins can comfortably access the entrance hole while waiting to be fed by food-bringing parents. With the excluder, smaller nestlings are more likely to gain access to incoming food because there are 3 distinct "feeding holes." Also, they are less likely to get pushed out to the ground while jockeying for position, as is sometimes the case with traditional 2" round holes.

During field-testing, the excluder holes were mounted about 1/2" above the porch and inside floor. This is the standard height when the door is placed on Trio houses. European Starlings are a serious threat to Purple Martins nesting in regular 2" round entrance holes, especially at colony sites where they are not, or can not, be rigorously controlled by trapping or shooting. It is also recommended that a small piece of friction/traction tape be placed on the porch directly in front of the hole, in order to allow for easier entry.