Forced Dispersal Instrumental in Establishing 3-5 New Colonies
Ken Kostka
 Purple Martin Preservation Alliance
Pittsburgh, PA

             The Purple Martin Preservation Association employed the Forced Dispersal management technique again in 2010 with excellent results. Three new colonies were established in Westmoreland Co., PA, thanks to the efforts of Jeff Hunt, the PMPA’s Executive Director. And one new colony was established in Armstrong County, PA (only the second known colony in that county), thanks to Duke Snyder, a hard-working PMPA volunteer. One of the three new colonies in Westmoreland Co. consisted of four breeding pair, and the other two consisted of one breeding pair. (One nesting pair is no guarantee that breeding will occur at a site the following season, but there was an abundant amount of martin activity at both “one-pair colonies” - increasing the chances of success next season.) The new colony in Armstrong Co. consisted of three breeding pairs, all of which fledged nestlings. The new colony in Slippery Rock (Butler Co.) had two subadult pair.

         In hopes of forcing martins to start new colonies in the western Pennsylvania area, over 120 total pairs of martins were displaced (or prevented from breeding) at 11 established colonies between May 24th and May 29th. The entrance to their nesting cavity was closed after significant nest-building (but before egg-laying) had begun. The martins were displaced after nest-building in hopes that established pairs would stay together when seeking out a new nest site.  In addition, all unused cavities were closed to prevent the martins from simply moving into another compartment at the same colony and starting over. In many cases, the martins would not leave the colony for several days, and squabbling over cavities would occur at dusk when it was time to roost. In the end, however, breeding success of the remaining pairs was not significantly affected.

         It should be noted that none of the nesting martins at the newly-established colonies had bands that could prove they were from a colony where martins had been displaced. There was simply not enough time to capture and band all the martins whose nesting cavities were eventually closed. But in all cases, the activity at the new sites began shortly after the compartments at established colonies were closed (and the martins were forced to disperse). The Forced Dispersal Technique has been proven to work through banding studies in the past, however; see the end of this article for more information.

 The Lois Noonan Colony, Slickville, PA. Lois Noonan ended up with 5 nesting pairs in 2010, all of which showed up after the displacement, and four of which fledged young. Her property borders the Phil Cain Memorial Airfield, so there’s a lot of open space. Photo on right is Lois Noonan.

 Murraysville Community Park.  While Jeff has been unable to attract martins to his own residence, which is only a few hundred yards from Beaver Run Reservoir, a huge lake, he has successfully started a colony only 2 miles away in a small municipal park bordered on one side by woods and on the other side by cornfields. Photo at left is Jeff Hunt.

 Hempfield Industrial Park. When the PMPA was first started in 2003, Jeff erected a series of 12 compartment aluminum houses in an open area around an industrial park near Greensburg, PA.. The houses are modified to have deep compartments and Excluder entrance holes. Three pairs bred or attempted to breed there in 2010. One pair failed when the male died of wing entrapment. One pair failed to fledge its nestlings, and one pair successfully fledged four young.

 One possible reason for Jeff’s success in starting three new colonies using the Forced Dispersal technique is the large number of martins he displaced. Jeff has worked tirelessly over the past 10 years to build up three formerly small and sparrow-infested colonies into three large (50-60 pair) robust colonies in Westmoreland Co. These colonies include The Zeglin Dairy Farm colony, the Youghiogheny Country Club colony, and the Butlers Golf Course colony. The larger the colony, the more pairs that can be displaced while still keeping the colony robust. Jeff displaced 20 pair from each of the three colonies he manages, accounting for half of all pairs displaced in the project.

R. Miller. Slippery Rock. Two subadult pairs nested at this site. Various factors indicated they were pairs made homeless by the project.  First, both pair showed up shortly after May 25th, the date of the displacement. Second, they arrived at about the same time.  Third, the site was within 10 miles of four other colonies from which martins were displaced. And fourth, they moved into a house that was already occupied by a pair of nesting Tree Swallows. Tree Swallows are usually quite aggressive towards investigating martins, suggesting these pairs may have had to fight their way into this site. The housing consisted of a Trio Castle with two Snyder Excluder gourds hung under it. One pair of martins nested in one of the Snyder Excluder gourds.  The other pair of martins nested in a Castle compartment. The Tree Swallows were already nestin in the other Excluder gourd. 

West Shamokin Jr./Sr. High School. Rural Valley. As noted earlier, none of the martins were banded, but perhaps the best evidence that a colony was started as a result of forced dispersal is this one. On May 25th, 15 nesting pairs were displaced from the Richard Wood Horse Track colony in Shelocta (Gastown), PA, and within a week, three pairs began nesting at West Shamokin High School, 6.25 miles NNE. The male of all three pairs was ASY! It is extremely unlikely that these three pairs began nesting normally this late in the season at an unestablished site; they must have been martins displaced by the forced dispersal project! All three pairs fledged young. Two nested in Excluder gourds and one in a 12 unit metal house.

    Starting a martin colony is difficult and requires constant vigilance until it is well-established. Many things can go wrong. For example, one pair at  Hempfield Industrial. Park failed due to wing entrapment. At Noonan’s colony, one pair’s eggs were destroyed by a House Sparrow before the landlord was convinced that they needed to be controlled. Had this been her only nesting pair, years of effort would have been thwarted.

    At all colonies, there was a lot of activity in addition to the pairs which bred. This could be explained not only by the usual bunch of surplus subadult males, but by martins that did not re-nest and spent the rest of the summer visiting the newly-established colonies. But if over 100 pairs were displaced, and only a handful of  pairs can be accounted for, what about the dozens of other martins made homeless?

The following possibilities remain: 

  1. They squeezed into existing colonies where cavities were available. Some landlords were either unwilling to close cavities or unaware of the project. While we asked landlords to displace up to 25% of their breeding pairs, or at least block all cavities that were not yet being used, some landlords had no interest in participating or were unaware of the project. For example, many Amish living in rural areas outside of the project area had housing available. Part of our strategy in waiting until late May to displace the martins was the hope that they would not have enough time to roam outside the project area to find established colonies to squeeze into. However, martins are very flighted birds. They can easily travel long distances in short amounts of time. Many displaced breeders may have already been familiar with established colonies “far” from the project area due to past late-summer, post-breeding wanderings. Probably 50-60% of the martins bred at established colonies, either within or outside the project area.
  1. They nested at housing/sites that were unknown to the PMPA. The landscape is dotted with uncolonized Martin housing. Most of this housing is already occupied by European Starlings, House Sparrows, Eastern Bluebirds, or Tree Swallows – all aggressive nest site competitors that will usually repel investigating martins. Nonetheless, some displaced martins may have discovered and bred in housing that was available but unknown to the PMPA. I would guess that 10-15% nested at unestablished but unknown sites.
  1. They did not renest and spent the rest of the season as “floaters” wandering around and visiting established sites. During the displacement project of 2005 I was able to document that a significant number of displaced breeders from one colony did not re-nest, and a spent a great deal of time visiting the lone pair that did renest at a new colony site 7 miles away. However, the displacement occurred about two weeks later in the season, on June 10th , and it was thought this may not have left the martins enough time to re-nest. I would estimate that 20-30% of the martins displaced in this year's project did not renest.   

        Make no mistake – the Forced Dispersal technique does work. During the 2005 displacement project, a banded male from the Saxon Golf Course colony near Saxonburg was displaced and bred at an uncolonized site 7 miles south in Natrona, PA. That colony grew to 20 breeding pairs in 2009, and would have had close to 30 pairs in 2010 had we not displaced 10 pairs!  In 2008, Bob Allnock was on the brink of giving up in his attempt to establish a colony. After years of trying, he had two breeding pairs in 2007, and they both fledged young, but none returned the following season. I instructed him to displace about half of the 30 or so breeding pairs at Moraine State Park, three miles distant, which he did, and a bunch of martins showed up at his site within several days; he ended up with 13 breeding pairs that season! But there are no guarantees. Of the 10 pairs displaced from the Natrona colony in 2010, none bred at a targeted site 1.5 miles away in my backyard! (I was able to band about half of the birds displaced from the Natrona colony in 2010, and it will be interesting to see if any attempt to breed there again in 2011.)

     Many factors could have affected whether or not displaced martins decided to nest or not nest at a targeted site. The biggest factor is whether the site is being managed to prevent nest site competitors from using the housing. If House Sparrows, European Starlings, Eastern Bluebirds, or Tree Swallows are being allowed to nest in the housing, they will usually chase off investigating martins. The second factor is habitat quality. An open area near water will be almost always be chosen over a tree-encroached backyard. Thirdly, the quality of the housing is important. Martins prefer big gourds and houses with deep cavities, and they seem to prefer wood over plastic or aluminum. And finally, martins seem more likely to choose a site where the Social Attraction Technique is being employed, because those sites already appear to have nesting martins.

     This forced dispersal project also resulted in martin activity at many sites that did not result in nesting martins. For example, at the property of Patrick Kopnicky in Fawn Township PA, (only 2 miles from the Lock 4, Natrona colony), an adult male (ASY-M) and several other (non-ASY martins) showed up at his Trio 12 unit house on May 30th, one day after the displacement at Lock 4.  The male was present every morning for about a week, although the other martins disappeared after a day. At Crooked Creek Park, about 10 miles from the Gastown colony near Shelocta, several pairs (both males were ASY) showed up on June 2 and were present  for several days. One pair seemed to have chosen a compartment and began to gather nesting material, but neither pair stayed and bred.

Thanks to all those landlords who selflessly gave up some of their hard-earned breeding pairs in the effort to establish new colonies!