Is the Oldest Birdhouse Still the Best?
Reprinted from: Purple Martin Update 8(1): 25
Purple Martin Conservation Association
Natural gourds were the first "bird houses." Today, gourds still make great homes for martins. In fact, research shows that gourds make the very best martin housing available since they avoid many of the weaknesses of commercial houses.
In Update 3(2), "Gourd Homes for Purple Martins, Pros and Cons," James R. Hill, III, noted: gourds provide larger, deeper nest cavities than housing with 6" x 6" rooms; are attractive to martins; have better occupancy rates; are predator-resistant; reduce premature fledging; and overcome a weakness of most housing designs (i.e., shared porches.)
Gourds have good success in initial martin attraction. In his paper: "Purple Martins Take to Gourds," published in Update 1(3), Dr. Jerome Jackson examined the ratio of martins and sparrows per apartment in gourds versus houses. In a questionnaire distributed to martin landlords in 32 states and 5 provinces, he found that Purple Martins preferred gourds while sparrows did not. This attraction is not limited to the southern United States; martins nest in gourds in every part of their breeding range. The only exceptions are the southwest and the mountain states, where martins nest strictly in natural cavities.
Another gourd asset is their larger, deeper nest compartments. A 10" or 12" gourd is better housing than a 6" x 6" house compartment. Martin landlord and bander Dean Mosman, of Elkhart, Iowa, published "The Martin Research of Darwin Mosman" in Update 2(4). In his 14-year study on compartment-size preference, martins were offered both 6" x 12" and 6" x 6" compartments. The martins showed a strong preference for the larger compartments, 79% to 24%. Large compartments mean less crowding, less predation, drier nests, and fewer premature fledgings.
Many studies have confirmed the value of larger nest compartments. In his article: "How to Enlarge the Compartments in Aluminum Houses," in Update 5(1), Don Wilkins of Park Rapids, MN, concluded: "It is apparent that we have converted a 12-room house into a 6-room house, which may not appear to be progress. The dividends will appear when you compare nesting success and occupancy rate, before and after the conversion. The enlarged, 6-room house will fledge more young." Dr. Charles R. Brown commented on the value of larger nest compartments in his Update 4(4) paper: "Inadequacies in the Design of Purple Martin Houses," noting that 6" x 6" compartments are promoted by housing manufacturers, but no data is presented to support their position. Brown suggests entrance holes be placed at least 2" above the floor, rather than the 1" found in manufactured housing. Deeper cavities offer protection against sparrow/starlings raids, and reduce egg losses.
Gourd nests have higher occupancy rates than conventional housing designs. In his Update 3(2) article: "Wooden Gourds," Don Wilkins reported that clusters of single wooden boxes that emulated a gourd cluster had higher occupancy rates (100%) than conventional houses (67%). Natural gourds also offer better insulation against heat and cold than aluminum. Tests conducted by Dr. Jerome Jackson, using sophisticated temperature probes, found that martin nests in natural gourds and wooden houses stayed cooler in hot weather, and warmer in cool weather, than nests in aluminum housing. Weather is a major cause of mortality in martins, so housing with good insulation is essential.
Finally, a 14-year research study at PMCA headquarters shows that martins have the highest reproductive success in gourds, closely followed by wooden houses, with aluminum houses finishing in last place. Martins lay larger clutches in gourds and wooden houses, and hatch and fledge significantly more young per nesting attempt than martins nesting in aluminum 6" x 6" housing.
In summary, gourds are attractive to martins, and help minimize nest-site competition. A cluster of gourds gives each pair of martins more privacy, so they spend less time defending their territory. The lack of a porch is an advantage in several ways; first, lacking porches, gourds will have fewer fallouts. Second, common porches promote male porch domination, which leads to lower occupancy rates, and permits porch wandering by nestlings, which can cause mortality of the wandering nestlings, and of any nestlings whose compartments they invade. Gourds are safer from predators, because they lack a porch for predators to perch on, and because of the swinging motion. Gourds offer larger nest cavities, which lead to larger clutches and more young fledged. Gourds offer better protection from the weather because of their insulation, and because nests are built farther from the entrance hole and blowing rain.
Of course, we're not talking about the same gourds that Native Americans put up so long ago. Today landlords paint gourds white and add improvements like access doors and canopies, or they use plastic gourds equipped with these features. Thousands of years ago, martins switched from natural cavities to gourds, because, among other reasons, they had higher reproductive success in gourds. With the innovations and improvements now in use, martins continue to have their highest reproductive success in gourds. Gourds not only are the oldest birdhouses, but they're still also the best.
Copyright 1997 by Purple Martin Conservation Association. All Rights Reserved.
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