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 21%. 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 natural gourds
. Gourds not only are the oldest birdhouses, but they’re still also
the best.
Birdhouse Still the Best?Reprinted with permission from: Purple Martin Update 8(1): 25 Louise
ChambersPurple Martin Conservation Association,
Edinboro University of Pennsylvania, Edinboro, PA 16444
814-734-4420 www.purplemartin.org
