The Pros and Cons
Reprinted from: Purple Martin Update 3(2):12-15
James R. Hill, III
Purple Martin Conservation Association
|Author, and Purple Martin Conservation Association founder, James R. Hill, III, looking into a natural gourd at the PMCA's research site in Edinboro, Pennsylvania. At this location, over 50% of the 125 martin pairs nest in gourds.|
Martins have been nesting in human-supplied gourds for hundreds of years. Long before Europeans first arrived on the North American continent, native American Indians were attracting these purple swallows to their villages using hollowed-out calabash gourds. The tradition of putting up gourds for martins continues to this day.
Unfortunately, many people have misconceptions about gourds. They will tell you that using gourds for martin housing is: unsafe, unhygienic, old-fashioned, etc. Nothing could be farther from the truth. Some of the people who repeat these misleading statements are simply not knowledgeable about gourds, others are just repeating misinformation they have heard or read elsewhere.
The purpose of this article is not to promote gourds as being "better than" martin houses, but to counter this misinformation about gourds. Gourds can only be said to be "better" than houses when the gourds are of the correct size and type, are properly prepared and well-maintained, and when the house in question is inadequate due to incorrect design features, poor maintenance, etc. Knowing the facts about both types of housing will enable martin landlords to make informed choices and increase their chances of attracting a healthy, successful colony. Listed below are some of the strengths and weaknesses of gourds.
Gourds offer larger nesting compartments: A 12-inch diameter gourd has about three times the floor area of your standard 6" x 6" martin house compartment. Research has shown that martins prefer nesting compartments larger than those offered by commercial martin house manufacturers (see Update 2(4): 6-9.) Larger compartments mean less crowding, less defecating and walking on top of siblings, less feather damage, less predation, drier nests, and perhaps, less premature fledging of nestlings. Research has also shown that cavity-nesting birds lay larger clutches of eggs in larger nesting compartments. For all these reasons, martins probably have higher reproductive success in gourds than they do in houses, but this remains to be tested.
Gourds have range-wide acceptability: Martins are easily attracted to gourds everywhere within their breeding range, not just in the southern United States where they were originally and traditionally used. Unlike metal, plastic, or wooden houses, gourds have range-wide acceptability to martins, even among the west-coast population, which do not have the tradition of colonizing multi-compartment houses. At the extreme northern limit of the martins' breeding range, in Canada, martins tend to avoid metal houses, probably because they are such poor cold-weather insulators.
Gourds have a higher R-value: Gourds keep nestlings cooler in hot weather and warmer in cold weather than conventional aluminum houses. This is because the fibrous walls of gourds are better insulators than aluminum, as long as the gourds are painted white and are adequately thick shelled. Research has shown that gourds are equal to wooden houses in this beneficial regard. Overheated nest compartments are one of the leading causes of nestling death, either through heat stroke or premature fledging.
Gourds discourage the nesting of English House Sparrows and European Starlings: Because a properly-hung gourd swings in the wind, gourds are far less attractive to starlings and House Sparrows, the martins' worst nest-site competitors. In conventional martin houses, a single pair of nest-site competitors is likely to prevent martins from nesting at unestablished sites, by claiming and aggressively defending the entire house. In contrast, a nest-site competitor in a cluster or string of gourds will only claim and defend one or two gourds (because they are so spread out), leaving all the others undefended and open for martin colonization. Gourds, then, are a good way for the beginner to attract a colony, or for the person unable (or unwilling) to discourage nest-site competitors.
Gourds increase the odds of attracting martins: For those who have not yet succeeded in attracting martins with a house, adding gourds can double their chances of success. For many people, just the addition of four gourds hung under their martin house is all it takes to turn failure into success. People who put up gourds frequently report success in attracting martins their very first season. When gourds are hung in combination with houses at unestablished sites, martins often ignore the houses until all the gourds are occupied. At established sites, however, house-nesting martins may take a season or two to start using newly-placed gourds, so be patient.
Gourds cost less: Gourds are the least expensive way to get into the martin hobby. You can order gourds from the PMCA online. Purchased, ready-to-hang, natural gourds are far less expensive than commercial or homemade martin housing, especially on a per active-compartment basis. Put up a conventionally-designed 12-unit martin house without porch dividers, and the highest occupancy you'll likely get is 6 to 8 pairs, due to male porch domination (i.e., aggressive males claiming several adjacent compartments by running up and down the porches, preventing full occupancy.) At a cost in the range of $80.00 to $135.00 for a typical aluminum, 12-unit martin house (without porch dividers), without a telescoping pole, that means you're paying between $10.00 and $22.00 per active compartment! A 12-pack of natural martin gourds shipped from the PMCA is $56.45, or $4.70 each, (Note prices subject to change) and since a properly-spaced cluster of gourds can get 100% occupancy, this means gourds offer a substantial price savings. And gourds are the only bird housing that is "free-for-the-growing."
Gourds weigh less: A good, thick, 10" to 12" gourd weighs only about one pound, making them extremely easy to raise and lower for weekly nest checks and year-end clean out, especially when mounted on telescoping poles, or along pulley-operated lines. Twelve gourds are significantly lighter than a homemade wooden 12-unit martin house - an important consideration when it comes to doing the recommended weekly nest checks.
Gourds are fun and challenging to grow: Growing gourds is great fun, and educational, too. You can learn about bizarre things like: plants that are sexually dioecious, the art of hand pollination, superior versus inferior ovaries, climbing vines, pruning techniques to increase yield, the option of building trellises, natural fertilizers, composting, peat pots, transplanting, harvesting, and curing. Best of all, you can experience the satisfaction of attracting martins to gourds you grew yourself. The whole procedure can be a wonderful experience for the entire family to share.
Gourds enable increased occupancy rates: In a properly-spaced gourd cluster, martins tend to claim and defend only one cavity per pair, whereas in a typical martin house, they may claim as many as 12 or more compartments by running around the common porch. This is known as "male porch domination" and it greatly reduces room occupancy rates in porched houses without porch dividers or private porches. In a cluster of gourds, adjacent entrance holes are spaced about two feet apart, instead of the crowded six-inch spacing common in most martin houses.
Gourds offer better protection from predators: When compared to a typical 6" x 6" nest compartment, gourds offer better protection for two reasons. First, because gourds can be hung so they swing in the wind, it is harder for owls, crows, jays, hawks, snakes, squirrels, cats, raccoons, and opossums to cling to the outside and reach in for a meal. Secondly, because gourds are so spacious inside and have a curved bottom, martins are able to build their nest almost twice as far from the entrance hole as in commercial martin houses, with the result that the eggs, adults and nestlings are safer from predators.
Gourds reduce premature fledging: Because gourds don't have porches, they tend to keep nestling martins inside, where they belong, until fledging age. Porches tend to encourage martin nestlings to wander out of their compartments long before they are physically capable of flight. Out on a porch, martin nestlings are vulnerable to the aggressive actions of other colony members that instinctively try to make them fly. Unfortunately, during these aggressive encounters, martin nestlings frequently get knocked to the ground where they are abandoned by their parents or eaten by a predator. Martins don't need porches - with their stiffened tails to use as a prop, they are adapted to perching vertically at abandoned woodpecker holes. Because of porches, we suspect more baby martins are 'knocked off' of houses, than 'fall out' of gourds.
Gourds offer superior compartment drainage: In martin houses, what drainage there is, drains down into the nest compartments below, increasing the wetness of lower compartment nests. Since martins build their nests up against the curved back wall of gourds, they usually stay drier than nests in conventional martin houses. In addition, a properly-drilled gourd has five or more 1/4" drainage holes.
Gourds eliminate porch-invading behavior in pre-fledged nestlings: In houses with common porches connecting adjacent compartments, nestlings frequently crawl between rooms trying to kleptoparasitize (i.e., steal) incoming food from their smaller neighbors. This porch wandering behavior has repeatedly been shown to occasionally cause the death of the host young, and occasionally even the porch wanderers. Obviously, this is not a problem in gourds.
Gourds are durable: Good martin gourds are nearly as hard as plywood. When gourds are painted, preserved, and treated correctly (i.e., cleaned out between seasons, brought inside for the winter, treated with a wood preservative, hung so they don't strike against each other, and repainted periodically), they can last up to 30 years.
Gourds are conspicuous to cavity-hunting martins: A large cluster of gourds would seem to be more conspicuous to a cavity-hunting, migrating martin than is a single martin house with an equal number of compartments. If so, a landlord's efforts would more likely be rewarded.
Gourds are easy to clean nests out of: Martin nests are quite easy to clean out of gourds. Just stick the long handle of a wooden spoon into the gourd to break up the mud cementing the nest together. The contents will then come out easily by turning the hole downward and shaking and pulling the contents out through the hole. Rinse with a garden hose. The entire process takes only a few minutes per gourd. Some commercial martin houses require disassembly for nest removal and cleaning.
Gourds have aesthetic, natural appeal: Because gourds are a dried fruit, martin gourds are the most natural type of martin housing you can offer. Because they are tear-drop shaped and swing in the wind, they are quite aesthetic and make a beautiful addition to any yard.
Not all of the attributes of gourds are positive. Just like houses, if gourds are not used and maintained properly, they can actually be detrimental to martins. Natural gourds require more annual maintenance than aluminum houses or plastic gourds. They will need to be treated with copper sulfate and repainted periodically. Careful inspection for cracks is a must. Nests take slightly longer to remove than from an easy-opening martin house. Nestlings are more difficult to remove for inspection and banding. There are gourds on the market that are not recommended (e.g., the popular, 7-inch diameter, chocolate-colored, one-piece plastic gourd), because they are too small for safe martin rearing). Of course, natural gourds that are not thick-shelled and at least 8 inches in diameter are also not recommended. Gourds require much more space to store than a single martin house, except for some of the plastic gourds that come apart for cleaning and storage. Some landlords with a limited amount of yard space for martin housing, may feel that gourd clusters take up too much space, compared to the smaller area a house occupies.
Because gourds have so many positive attributes, so few negative ones, and have several advantages over conventional housing, we encourage all martin enthusiasts to give them a try - we bet you and your martins won't be disappointed.
| 1. When gourds are not treated with any type of preservative. The repeated wetting and drying of raw, unpainted gourds will cause them to crack. Always paint the outside of gourds with some form of water-repelling, oil-based paint. The PMCA also recommends soaking gourds in a copper sulfate solution as a "wood" preservative. This prevents rotting.
2. When gourds are not painted white. Gourds should be painted white to reflect the heat of the sun. This helps keep the nesting chamber cooler for the nestlings. A glossy white, oil-based paint will work best.
3. When small gourds are used. Martin gourds should be at least 8" in diameter, preferably 10"-12." Martins will use gourds smaller than 8", but lay smaller clutches of eggs in them and also have higher mortality rates due to fallout from severe overcrowding of nestlings.
4. When thin gourds are used. Gourds should be at least 1/4" thick, but gourds 3/8" to 1/2" thick are the best. The thinner the gourd, the poorer its insulating qualities and the more likely it is to crack.
5. When weather-caused cracks aren't repaired. Should a crack develop, patch it immediately with a quick-drying caulking or spackle.
6. When old nests aren't cleaned out between seasons. Molds and mildews can grow under old nests and cause the bottom of gourds to rot out. Also, fleas that attack nestling martins can over-winter in old nests. So always clean the old nests out of gourds and take your gourds inside by late August.
7. When left out to weather all winter long. Leaving a gourd out 12 months of the year will drastically shorten its life. Store them inside.
8. When hung so they can strike each other in the wind. Gourds that are placed so close together that they swing and hit, not only can crack, but they also are frequently abandoned by the birds. Space them out.
9. When hung so they twist in the wind. Gourds should be hung so they swing in the wind, not twist in wind. The compass orientation of the gourd's entrance hole should not change while blowing in the wind.
10. When entrance holes are cut too high or too low. Entrance holes cut too high allow more rain water to come in. Holes cut too low can allow small nestlings to inadvertently tumble out. Always test how a gourd hangs before cutting the entrance hole, then center the cut on an exact vertical face.
11. When hung on lines stretched between trees. Martins will rarely use gourds hung on lines stretched between two trees. They instinctively know squirrels and other predators can easily reach their nests. Hang them between poles instead, or on specially-designed gourd racks.
12. When drainage holes are not used, are too small, too few, or are allowed to get clogged with debris or paint. Inadequate drainage allows gourds to fill with rain, which can soak the nest or drown its occupants.
13. When hung in ways that make weekly nests checks difficult or impossible. Gourds should be hung on telescoping or winch-operated poles, or on lines that can be lowered by pulleys, so that weekly nest checks can be done. Non-manageable gourd systems should be replaced with ones that can be easily lowered. Don't be afraid to check the nests once a week.
|A gourd rack built by PMCA member, Joseph L. Cassiere, II, of Monroe, Louisiana. It is a greatly-improved version of the plan the PMCA first published in Update 1(1). He writes: "This year I wanted to expand my colony site, which consisted of two 24-compartment, metal houses. My goal was to provide housing that was the most beneficial to the Purple Martins, yet have the capability of discouraging and policing the advances of European Starlings and English House Sparrows. After receiving the plan for the PMCA's gourd rack that could be raised and lowered without disturbing the nesting martins, my decision was made. The scouts arrived here on February 7th this year. The gourd rack was not erected until April 15th, which is late in the martin season for Louisiana. Amazingly, the subadults immediately started inhabiting the gourds! What is so remarkable is that these subadults were most likely not raised in gourds, and I am assuming that they had never seen gourds since no one in my vicinity uses them. When I did a nest check several weeks later, 13 of the 16 gourds had clutches of eggs in them! I'm now a firm believer in gourds!" Mr. Cassiere was so impressed with the success of this gourd rack that he volunteered to create highly-detailed, full-scale blueprints for the PMCA to resell (Mr. Cassiere is an architect in an architectural firm that has a computer-aided drafting system and a large-scale plotter.) Twice, he flew up to Pennsylvania to fine-tune the design with PMCA officials. His assistant, Ronnie Bryan, also spent innumerable hours behind a computer perfecting the drawings. Full-scale blueprints of this highly-successful, pulley-operated gourd-hanging system are available from the PMCA here.|
| 1. Gourds only last one or two seasons. A gourd can last over 30 years if properly prepared, preserved, and maintained.
2. Gourds get too hot inside. Research has shown that martin nests built in thick, white-painted gourds stay just as cool as nests in wooden housing, and cooler than nests in aluminum housing.
3. Baby martins fall out of gourds. Far fewer baby martins fall out of gourds than fall out of houses. This is because the porches found on most houses encourage nestlings to wander out onto them long before they are physically capable of flight. Unfortunately, once on the porch, nestlings are often knocked to the ground by non-parental martins, where they perish. Because gourds lack porches, baby martins stay inside them, where they belong, until they can fly.
4. Gourds are difficult to clean at the end of the season. Removing a martin nest from a gourd is a very simple task, taking only a few minutes per gourd.
5. Martins will only use gourds in the southern United States. Martins will nest in gourds throughout their entire breeding range.
6. Gourds are difficult to monitor. When gourds are mounted on telescoping or pulley-operated poles, they are quite easy to monitor. Simply shine a flashlight in each hole to observe and record its contents.
7. Gourds are brittle and will break easily. Even though gourds are a dried fruit, martin gourds are nearly as hard as plywood.
8. Nests get wet in gourds. Nests in gourds stay drier than nests in commercial aluminum housing, even housing equipped with subfloors. This is because gourd nests are about three times bigger and thicker than nests in 6" x 6" house compartments, plus gourd nests are built up the curving back wall, up to 10" from the entrance hole. Finally, gourd drainage is superior to house drainage, because gourds have curved bottoms and numerous drainage holes.
Copyright 1991 by Purple Martin Conservation Association. All Rights Reserved.
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