Porch Dividers: A Way to Improve the Productivity
of House-nesting Purple Martins

Reprinted from: Purple Martin Update 2(1): 6-7
Carlyle Rogillio
4913 Dreyfous Avenue
Metairie, LA

With the present interest in improving martin colonies, landlords can very likely increase the number of martins attracted to their housing with the use of porch dividers. For four years now, I have used porch dividers to significantly increase both the occupancy and productivity rates of my martin houses. During one of these years in one house, I attributed a 50% increase to the use of porch dividers.

Jennifer Outlaw installing a set of home-made wooden porch dividers on a hexagonal martin house in order to increase the occupancy rate and to prevent nestling crossover.

Within the North American breeding range of the Purple Martin, there are probably more rectangular, 12-compartment, martin houses than any other type. And have you noticed that the middle compartments in these 12-unit houses are almost never used? This is because of the conflict of territory and space. Let me explain: in the Purple Martin, it is usually the older, adult birds that arrive back from migration first and they seem to claim and defend the outer compartments and adjacent areas. This is their "territory" and it usually includes the porch area of the nearby compartments as well. Sometimes a particularly domineering couple will attempt to claim an entire house, but typically, after a few scuffles with other martins, they will settle into just an outer compartment. However, as is usually the case, their territory will include their own compartment and will also extend next door to the center compartment on that same porch. The end result is that most center compartments in 12-unit rectangular boxes become an unused "no-bird's land." Should a pair of martins move into and claim a center compartment before the outer compartments are taken, then the two outer compartments adjacent to it often lie unused.

Actually, in the bird world, there are two types of private space. Besides its territorial space, each bird has its own individual "private" space. There is an unwritten, but well understood, law that a bird shouldn't infringe on another's territory, nor should it sit too close to another bird so as to infringe on its "private" space.

While the two types of space are similar, they are different in that the territorial space is a fixed area and stays when the bird leaves, but its individual, private space travels with it wherever it goes. This is noticeable when a group of birds perches on a power line. Each bird will maintain a certain perching distance, about one-half a wing span, from any adjoining birds. This minimal space that the birds maintain between themselves is known as the species "individual distance". If one bird lands too close to another, so as to invade its private space, the less dominant bird will fly or sidle down the wire. If it sidles down the wire, it sometimes causes a chain reaction, with each bird down the line moving to maintain its private space.
For these two reasons (i.e., because a bird wants to maintain both its territorial and private space), the center rooms of 12-compartment rectangular houses often end up not being used for nesting. It is pretty hard for a newly-arrived bird, often younger and more easily intimidated, to move into a middle compartment and sit shoulder to shoulder with a dominant, adult bird. But, porch dividers help better define territories and also provide a barrier that prevents an individual's private space from being violated. A 12-compartment house equipped with porch dividers can attract nesting birds to every compartment. Even though the twelve-compartment type house seems to be the most prevalent, the same principle applies to all other types of martin houses that have adjoining compartments sharing a common porch.

Increased occupancy was a beneficial result from my having installed porch dividers on my martin houses, but the primary reason I put up the dividers was for the benefit of the baby martins. I wanted to prevent nestling "crossover." What is nestling crossover? Well ....... every year, prior to installing the dividers, I would find several dead baby birds that a short time earlier had been healthy. I knew they were healthy because I had previously banded and weighed them (I am a federally licensed bird bander and rehabilitator). Some of the dead babies were in their compartment, but some had ventured (or "crossed-over") into other compartments.

One year, I took the time to watch more closely what was happening as the young approached the fledging stage. It appears that quite often, the hungriest or most adventurous nestlings will either exit from, or be pushed out of, their compartment and will crawl along the common porch into another compartment. If they go into an adjoining compartment, and it is empty, usually the parents will continue to feed them there. But, if these wandering nestlings move several compartments away, the parents will neglect them - especially if they go completely around the house, as is possible in houses where the porches go all the way around the house. Dr. Tom Dellinger of Duncanville, Texas, and Dr. Eugene Morton of the Smithsonian Museum in Washington, D.C., both of whom band and monitor their martins closely, have noticed the same problem of wandering pre-fledglings in their houses.

Sometimes these wandering martin nestlings will find their way back to their home cavity, but more often than not, they don't. Those that do get back are usually in a hungry and weakened state and aren't strong enough to compete with their siblings for their share of the incoming food. Sometimes the crossovers will find their way into a compartment with smaller nestlings and either trample or peck them, or commandeer most of their incoming food.

I had one compartment where all of the babies except one had just fledged. While the parents were out tending to the just-fledged babies, the remaining youngster apparently got hungry, got out of his compartment, then crossed-over to the opposite side of the house. He got into a compartment with three smaller babies. The parents of the smaller babies refused to feed the larger bird. Later, I saw him in still another compartment. I took the house down, and found all three of the smaller babies dead. I gave the offender several good feedings and put up some makeshift dividers to contain him in his compartment. His parents resumed feeding him, and he fledged the following morning.

Between seasons, I made some simple porch dividers from one-inch boards, dressed to 3/4 inches. Not only did they stop the problem of nestling crossover, but they also increased the occupancy rate of the adult birds. There are aluminum houses that come with porch dividers. But lacking these, they are easy to make yourself. You owe it to your birds to give porch dividers a try.

A 12-compartment house equipped with homemade wooden porch dividers. Even though this picture was taken early in the martin season, one couple has already claimed a center compartment. Note the dividers on the ends of the house. They prevent nestlings from wandering around to the opposite side of the house.



Carlyle Rogillio is founder of Helping Hands, Inc., a nonprofit organization that operates a wildlife rehabilitation center in Metairie, Louisiana.

Copyright 1989 by Purple Martin Conservation Association. All Rights Reserved.

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