Ten Ways to Increase the Size of Your Martin Colony

Reprinted from: Purple Martin Update 3(4): 28-29
James R. Hill, III
Purple Martin Conservation Association

Dr. Eugene S. Morton showing how he predator proofs his martin poles with 5-foot sections of slippery, 6" PVC pipe, buried in the ground. Until he did this, he was plagued by snake predation.


1. Add more housing: The easiest way to double the size of your martin colony is to double the number of compartments you offer. The problem is, most martin landlords never get around to adding a second house because they futilely wait for their first house to fill up. This is a disastrous mistake because it will never happen. Conventional martin houses (those with several compartments sharing a common porch) rarely fill beyond a 50-60% occupancy rate because of the nature of martin territoriality. Typically, male martins will defend two or more adjacent compartments, preventing all other martins from using these rooms. They are able to accomplish this by merely running up and down the contiguous porches. This phenomenon is known as "Male Porch Domination." (See recommendation #2 for a way to prevent this). Sometimes, a particularly aggressive male is able to defend an entire 12-compartment house! In such a case, the house is functionally full despite having a nest in only 1/12th of its rooms and housing only one breeding pair! Because a male martin's territory almost always includes more than one compartment, landlords severely limit the number of breeding martins they will ever attract when they offer just one house. After initially succeeding in attracting some breeding martins, all landlords should offer additional housing and/or at least 24-30 total nesting compartments. This will allow them to build their colonies to at least 12-15 breeding pairs. And don't put 'all of your eggs in one basket.' If you have only one house up and a summer storm blows it to the ground, smashing the eggs and killing the nestlings, you could be out of the martin business. Landlords with single, 12-unit houses (and thus smaller colonies) also run the risk of losing all their birds from one year to the next just from natural attrition; approximately 50% of adult martins die each year, and at least 75% of the fledglings. Give your martins a diversity of nesting choices: try adding some gourds to your set-up.

2. Add porch dividers: By adding porch dividers (i.e., wooden or metal "blinders" or "barriers" that prevent both visual and physical contact between porch-sharing neighbors), you can eliminate porch domination by males, the single biggest factor preventing higher levels of house occupancy. Currently, only one brand of commercial martin house comes with these innovative and highly-recommended devices. These are the ones manufactured by Coates Manufacturing Company. However, porch dividers are easy to make in the home workshop and can be adapted to fit any martin house, whether a commercial aluminum house or a homemade wooden one. Porch dividers have the additional benefit of preventing nestlings from wandering between compartments before they can fly. Such wanderings not only are risky for the wanderer, but can end in the starvation death of younger neighbors who are deprived of parental feedings by the hole-hogging behavior of these wandering invaders. This stealing of incoming food by larger, non-siblings is known as kleptoparasitism and is an added problem in any martin house design that has compartments connected by a common porch. Gourds eliminate this problem altogether, as do house designs with only one hole per porch, or no porch. TRIO HOUSE PORCH DIVIDERS

3. Conduct weekly nests checks: One of the best ways to increase the size of your martin colony is to know exactly what is going on in each compartment. If you are raising your martins totally 'in the dark,' you can't react in a timely fashion to all the problems that can face martins during a typical breeding season. If you don't currently use a housing system that allows for easy, vertically lowering (either a telescoping pole or a pulley and winch system), convert to such a system. Stationary poles, or poles that only tilt down, make weekly nest checking nearly impossible. Landlords who conduct weekly nest checks raise more nestlings per compartment than landlords who don't. Be sure to number your compartments and keep a written diary. And don't worry; the minor, temporary disturbance caused to parent martins by house lowerings and nest checks will not cause nest- or colony-site abandonment. Martins resume normal behavior just as soon as the house is cranked back up and the landlord walks away.

4. Control nest parasites: A five-year study conducted at the Purple Martin Conservation Association's research site in Edinboro, Pennsylvania, revealed the alarming conclusion that natural (i.e., normal) population levels of martin parasites (i.e., fleas, nest mites, blowflies, lice, blackflies, louseflies, and mosquitoes) can prevent the fledging of as many as 50% of the hatchlings! The worst martin parasites are the blowflies, nest mites and fleas. There are several ways to control these pests: First of all, you can cut No-Pest Strips (now marketed as Bio-Strips) into 1/2" chunks and place one in each compartment, out of reach of the birds. To do this, drill a hole in each piece and suspend them from a ventilation hole (in both houses and gourds), or place under the subfloor. An alternative to this technique is to sprinkle a half teaspoon of 5% Sevin powder into each compartment or gourd when you first put them up. Finally, if you would rather not use either of these pesticides in your martin nests, you have two additional options. First, you can tear out each nest when the young in it reach the age of 15 days old (they will be partially feathered). Nearly all of the nest mites, fleas and blowfly maggots will be thrown out with the nest. You should then replace the nestlings on top of a fresh, 1-inch bed of totally dried lawn clippings (i.e., grass). Don't use this technique until the young are partially feathered; they need their original nest for thermoregulation. An alternative to this method is to sprinkle a teaspoon of diatomaceous earth (DE) around each nest after the young are about a week old. This material (fossilized diatoms) "scratches" insects to death and is totally safe for martins. Use garden variety DE, not the swimming pool kind. DE is available, mail-order, from garden supply companies.

5. Eliminate nest-site competitors: Conscientious martin landlords never allow any other species of bird to nest in housing intended for martins. This is extremely important when it comes to the non-native English House Sparrow and the European Starling. Most martin landlords don't monitor their martins closely enough to discover just how detrimental these two foreigners are to a typical colony. To the casual observer, it may appear they coexist relatively peacefully with martins. This is deceptive. Their depredations and cavity-clogging behaviors are so insidious that they reduce martin occupancy and nesting success by at least 50%. They bludgeon martins to death in battles over compartment ownership, puncture and eat their eggs, throw out their nestlings, transmit blood diseases to them, build nests on top of their nestlings, and clog so many compartments with their nest material that they render them unusable by martins. If a landlord does not have the time or inclination to wage war against these two introduced niche snitchers, he/she should take their martin housing down. Raising House Sparrows or starlings anywhere on your property hurts all of our native cavity-nesting species. Successful martin landlords control these pests using a triple strategy: First, they trap House Sparrows and starlings with both nest-box and bait traps. Secondly, they tear out their nests during each weekly nest check. And finally, they invest in a good pellet rifle (it helps if the martin housing is placed within pellet range of a house window). To minimize the attraction of starlings, use starling-proof entrance holes in your homemade houses (refer to the McEwen interview printed elsewhere in this issue for details), or you can use martin houses that have compartments measuring exactly 6" x 6" x 6." Starlings will try these 6-inch cubes on for size, but will typically reject them as too cramped. (Despite this advantage, the PMCA still recommends compartments with floors measuring 7" x 12" because they are owl proof and the nests stay far drier.) Gourds, hung so they can swing in the wind, are also less attractive to House Sparrows and starlings, and tend to be owl proof.

6. Predator proof your houses and poles: The Purple Martin Conservation Association believes that Great Horned Owls visit nearly every active martin house each summer to feast on baby martins. Unfortunately, the majority of these predatory visits go undetected because most landlords don't conduct weekly nest checks. If they did, they would realize their nestlings were disappearing long before fledging age and could put owl guards on their houses. In addition, every martin pole should be equipped with a climbing animal barrier. Rat snakes, squirrels, and raccoons can easily negotiate all martin poles, including the common metal ones. Predation is one of the major causes of colony loss and/or decline.

7. Halt or reverse the trend of tree encroachment: With the passage of time, plant succession and tree growth act to enclose most people's yards. Unfortunately, as the trees in your yard grow larger and closer to your martin housing, the less attractive your site will be to martins. It is less attractive because it forces martins to fly at steeper angles (and thus, at slower speeds) to clear the tops of the trees, a situation making them more vulnerable to aerial predators. Because tree-enclosed yards are so unattractive to martins, it will gradually become more and more difficult for adult male martins to recruit migrating subadults to the colony site to breed. As a result, the number of martins using your yard will gradually decrease each year until you no longer will be able to attract any. The solution is to keep the area around the housing as open as possible. Don't allow shrubs and bushes to grow up in the vicinity of the housing, and keep all nearby trees pruned. If you must, consider cutting down any trees that are slowly enclosing your martin housing. This is only necessary if you begin recording a consistent, annual decline in the number of breeding pairs you attract. Obviously, the best way to document a true decline is through weekly nest checks, year after year, combined with keeping a permanent martin diary. Another option is to transfer your colony to a more open spot on your property by placing some new housing there. Don't move the old housing to the new location until martins have bred in the new housing for at least a year - you could lose your entire colony. Obviously, the more open your yard, the more acceptable it will be to martins.

8. Offer crushed eggshell: Purple Martins have a physiological need for both calcium and grit. For this reason, martins absolutely relish crushed, chicken eggshell because it is high in calcium and has excellent grit properties. Research has shown that martins without a readily-available calcium source often have nestlings that suffer fatal calcium deficiencies. Because of this requirement, all martin landlords should supply their martins with crushed chicken eggshells to safeguard against this form of nestling mortality. You can save your eggshells all winter long, or ask the manager of your local McDonald's restaurant to save them for you on one or two mornings. Just soak the shells in water to wash the gooey albumen off, then spread them in the sun to dry. Once dry, crush them into quarter inch pieces between your hands, then store them in a ventilated bucket. The best way to offer eggshells to your martins is in an elevated eggshell feeder, but they will also take them from the ground if spread in an open, bare location near their housing. However, ground-feeding martins are very vulnerable to cat predation.

9. Recycle your electronic bug zappers: The deceptive advertisers of Madison Avenue have fooled us again! They've learned you only have to put the phrase "kills mosquitoes," (or "Purple Martins can eat 2000 mosquitoes a day!") on their products and they will sell thousands of additional units. Truth be damned! Bug zappers - those hideous, ecologically disastrous, electrical devices that attract insects with the use of an ultraviolet light, then electrocute them - should be outlawed. They do not attract mosquitoes as their manufacturers imply. (Only exhaled carbon dioxide attracts mosquitoes.) What they do attract (and thus kill) are beneficial insects, mainly moths, that lay the eggs that turn into the caterpillars that fuel a huge section of the bird food chain. So, indirectly, bug zappers actually "kill" birds! By eliminating insects, they "compete" with a colony of martins for food, possibly reducing the number of martins your neighborhood can support. And finally, by killing moths and other beneficial insects, they also can prevent the pollination of your night-blooming garden plants, preventing fruit formation. If you were suckered into buying one of these destructive, misleading products, complain to the manufacturer, then disassemble it and recycle its parts!

10. Join the Purple Martin Conservation Association: If you are not already a member, join! You'll receive four, quarterly issues of the Purple Martin Update, an outstanding 32-page, color magazine devoted entirely to martin information. The tips and knowledge you will glean from this fine publication not only will help you become a more successful martin landlord, but it will also help you derive more pleasure from this very rewarding hobby. To join, just send a check for $16.00 (individual), or $20.00 (family) to the PMCA. Canadians send $20.00 U.S. Do it today!


Copyright 1992 by Purple Martin Conservation Association. All Rights Reserved.

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