Purple
Martin
Housing
Standards
The following is a verbatim copy of the housing
standards sheet published by the PMCA. The link to
their original is here. http://www.purplemartin.org/main/housestandard.html
I copied it into this page only because I wanted to make
a few comments about natural gourds in relation to the subject of
housing standards.
Since the PMCA has already established a sheet
with some standards for houses, I'm using it as a base to increase
the comments to natural gourds as well and because I'm a gourd man,
as are a lot of other people in the country, I'd like to make some
additions that apply to gourds where applicable. Those
comments will be identified by "Gourd Comment:".
I'd like it known that I agree whole heartedly with the
drive to change martin housing standards so that life is made a
whole lot easier and safer, not only for us landlords, but for the
birds, as well. There are many sub-standard houses on the
market today and with all the research that's been done on martins
in the last couple of decades, it's time that we as landlords
utilize these findings and see to it that they are applied to martin
sites when and where ever possible and that sub-standard housing be
done away with and replaced with good, quality housing.
Standards for Purple Martin
Housing
PMCA/Edinboro Univ. of PA
Edinboro, PA
16444
814-734-4420
PMCA@edinboro.edu www.purplemartin.org
The breeding biology and management
requirements of the Purple Martin dictate the features of the
housing. Since a Purple Martin house must be placed in an open area,
in full sun most of the day, adequate ventilation, protection from
rain, and a white exterior (for coolness), are important features
for successful nesting. A martin house can be any size from 4 or 6
compartments on up.
Compartment size: Minimum size for each compartment is 6" x 6" x 6";
larger is better. A compartment that is 7" (wide) x 12" (front to
back) offers greater protection from predators and the elements. An
adult martin is approximately 7&1/2" long, and as the clutch
size averages from 4 to 6 young, there must be room for six to eight
birds in a single compartment, since parents sleep with their young
at night. With larger compartments, European Starlings can become a
serious problem, but a new design idea is being used to keep
starlings out of martin housing; see next item.
Gourd Comment: Natural gourds are also a
favorite with martins and like housing compartments, gourds should
also be nice and roomy. 9" in diameter should be a minimum for
gourds with 10" being even better. Martins are known to lay
larger clutches with the larger housing compartments and likewise
with the gourds. A lot of room is needed with a clutch of 7
young and a good 10" gourd has a full 78.5 square inches
available. These larger diameter gourds also allow the martins
to back out of the way of any predators' reach should they happen
by.
Entrance hole: The range of acceptable sizes for round entrance holes
is 1&3/4" to 2&1/4"; 2&1/8" is frequently used. Size of
2&1/2" is also usable, but not recommended. It is overlarge, and
admits predators (some species of small hawks and owls) more
readily, and also admits more rain, and cold air. Distance from
bottom of entrance hole to floor of compartment: 1" to 1&1/2".
Housing should also come with door plugs to close compartment holes
during the off season, and in early spring. This is essential for
keeping House Sparrows and European Starlings from taking over
martin housing. For houses that have the larger compartments, a
starling-resistant entrance hole is strongly recommended. These new
holes (SREH's) have been tested since the early 1990's and are
proving to be an asset in allowing martins a safe nesting place that
is not accessible to starlings. See sheet titled SREH for
details.
Gourd Comment: The use of Crescent SREH's in
gourds is also strongly urged, especially in the large natural
gourds. Starlings love them too and once they claim one for
themselves, will fight to the death for it. Whether it's an
established site or one just starting out, these holes have proven
to be effective in repelling the European Starling from getting a
foothold in a martin site. The following is a diagram of the
dimensional requirements for a Crescent SREH. As for location
on the gourd, the bottom line of the hole should be on the equator
of the gourd, keeping the 1 3/16 as accurate as possible.
Height and placement of
housing: A height of 12 to 20 feet is
recommended; no higher unless necessary, due to nearby trees or
other obstacles in the flyway. The higher housing is placed, the
more susceptible it is to wind and storm damage. Most commercial
pole systems are 12' to 15' high, after installation. Poles need to
be set in concrete, so 18 - 24" of the pole will be underground.
Some manufacturers offer a mounting socket, so if the owner wishes
to relocate the housing, he needs only to remove the pole from the
socket. Martins require a wide open area around their housing, and
martin housing should always be placed within 100 feet of people (a
house, or other active area), and at least 40 feet from trees,
farther if possible. In the southern half of their breeding range,
martins will sometimes nest within 15-25 feet of trees.
Vertical
accessibility: Any house or gourd system
should lower and raise vertically, which makes a telescoping pole,
lanyard system, or winch system an important feature. This is
necessary for two reasons: to allow for regular, sometimes daily,
removal of House Sparrow and European Starling nests; and, to allow
for safe and easy monitoring of nesting martins. House Sparrows and
European Starlings, two nonnative birds, are major factors in the
decline of Purple Martins. If they are allowed to nest in martin
housing, martins will not stay. House Sparrows and starlings will
chase off and fight with martins, break their eggs, and even kill
nestling and adult martins. Regular monitoring is also an important
part of successful martin management, allowing landlords to keep
track of how many young are in each nest, etc. If a nestling is
found on the ground, a system with vertical access allows it to be
quickly returned to the house, and to the correct nest compartment.
Landlords who do not monitor their site will not know if predators
such as rat snakes, raccoons, or owls have raided the site at night.
Such raids usually result in permanent abandonment of the colony
site. If a landlord is alerted to the situation through monitoring,
he/she will be able to take steps to protect the colony site, by
adding a predator guard to the pole, and owl guards to the house.
Orientation marks, for raising the house to the correct orientation
after nest checks, and a locking mechanism, to keep the house from
spinning or twisting in the wind, are important. If landlords do not
reorient compartments to face the same compass directions after each
nest check, the martins will become disoriented, and abandon their
nests. A locking mechanism on the lower portion of the pole will
prevent accidents or vandalism. A tilt-down housing system, on a
hinged pole, is not recommended, as it cannot be accessed once the
martins begin nesting. Tilt-down systems do not permit landlords to
remove sparrow and starling nests, or monitor martin nests, and thus
are not functional, and should be avoided.
Gourd Comment: There are a
number of different rack designs available for use to hold gourds
and it is agreed that the vertical accessibility is a must.
Any 'good' designs today are vertical access in nature and this
applies to any gourd setups. The persistence of Sparrows and
Starlings will require daily access and vertical raising and
lowering of the gourd rack is a must and as stated, non-functional
designs should be avoided.
Porches: Porches are not a requirement, but if porches are
included, they should be equipped with dividers, or separated so
nestlings cannot walk to other compartments. Porch width should be
at least 4". Railings on porches are optional. If railings are used,
the gap between railing and porch floor should be 5/8", or less.
Railings that have gaps any wider than this can trap nestlings and
adult birds.
Gourd Comment: Gourds do not require
porches, outside or inside. Outside porches only make it
easier for starlings and sparrows to usurp a cavity. As for
inside, simply supply enough material to bring the nest level up to
the bottom of the entrance hole.
Perches: Martins will use additional perches placed above or
below the house. Perches at each entrance hole are not desirable,
and will only encourage House Sparrows and starlings.
Gourd Comment: Likewise, perches at the
entrance holes of gourds are not required and, as stated, will only
attract pest birds.
Wooden houses: Only untreated wood (no pressure-treated wood, no
chemically-treated wood, etc.) should be used for bird houses;
pressure-treated wood is recommended for mounting posts, if wooden
posts are used. The exterior should be painted white, or come with
instructions to paint the house white. Interior of compartments
should be unpainted. Stock of 3/4" thickness is best, as it offers
better insulation against heat and cold. Due to weight, wooden
houses are best mounted with a winch for raising and lowering.
Smaller wooden houses, 6 or 8 compartments, 25 lbs. or less, may be
mounted on a telescoping pole. Cypress or cedar are best choices for
longevity; pine or redwood would also work. Exterior plywood will
not last as long as solid stock.
Gourd Comment: Natural
gourds will last much longer if treated with Copper Sulfate. A
20 minute dunking in this mixture (1 lb Copper Sulfate to 5 gal
water), will make a natural gourd last up to 20 years or even
longer if properly cared for. And remember, the thicker the
wall, the better for insulation.
Plastic houses: The exterior color should be white or a very light
color. It is very important that the walls and roof are opaque,
admitting no sunlight. Translucent plastic will overheat quickly in
the sun, killing nestling martins. Ultraviolet inhibitors will
extend the life of the housing, which will be out in the elements
and sun. A layer of insulation added to the attic, or above the
upper tier of compartments, is desirable.
Gourd Comment: With
the introduction of the new plastic gourds to the market, these
rules also apply to them. Many plastic gourds that are mass
produced today are not properly designed nor fit for the safe
rearing of martins. Many are much too small, have too large an
entrance hole and are not accessible to remove pest bird
nests. If plastic gourds do not have the large diameter size,
SREH's and easy accessibility into them, then they should not be
used.
Metal housing: A white exterior is preferable; roof can be white also,
but this is not a strict requirement. A layer of insulation added to
the attic, or above the upper tier of compartments, is very
desirable. Heat waves, and cold spring weather, can contribute to
mortality of nesting martins. Overheated nestlings will jump out of
their housing, and die on the ground. Spring weather can include
late snow storms, when no food is available for martins. An
insulated house gives them a better chance of surviving without food
for two or three days, until weather warms up, and flying insects
are available again.
Gourd Comment: Likewise,
natural gourds should be painted white. Unpainted gourds will
get just as hot as an unpainted house and the young will perish from
over heating.
Floor texture: Flooring in both metal and plastic houses is too
slippery to allow nestlings to keep their footing (similar to a dog
on linoleum), and a sub-floor of textured material should be
provided. Nestlings on slippery flooring sometimes develop
abnormally, with permanently splayed legs, and this fatal
abnormality is easily prevented by providing a textured floor.
Wooden floors do not cause this problem. Some commercial housing
offers textured metal sub-floors, or slide-out wooden nest trays.
Both prevent the problem, and make end-of-season nest cleaning
easier. It's also important that sub-floor material drain well, and
not retain moisture. Materials such as outdoor carpeting are not
suitable.
Gourd Comment: One good
thing about natural gourds, they need no extra work done on their
floors. Their natural interiors are easy for the matins to
walk on without any difficulty. However, they do need 4 or 5,
1/4" diameter drainage holes drilled around the bottom to allow any
water that may get into them to escape.
Compartment
access: Hinges or other mechanisms to open
compartments easily, without destroying the nest, or causing eggs or
young to fall out, are very important. Access to individual
compartments during the nesting season allows for easy removal of
House Sparrow and European Starling nests. Compartment access also
facilitates regular monitoring, and cleaning at season's end. Some
designs now feature removable nest trays that allow for easier
monitoring and cleaning.
Gourd Comment: Natural
gourds can be fitted with a 4" plastic jug top (available from the
PMCA) that allows easy access into the gourds for whatever
reason. Whether it be adding nesting material, cleaning out
pest bird nests or simply doing a nest check, these access ports are
a new and necessary device that the landlord will
cherish.
Predation: A pole predator guard should be part of the system, or
information on how to add a pole predator guard should be included.
Any type and size of pole, wood or metal, is easily climbed by
several predators of Purple Martins, including raccoons, rat snakes,
and squirrels. Wood posts or poles can also be climbed by domestic
cats and bobcats. Aerial predators, such as hawks, crows, and owls,
will also raid martin housing. Conventional 6" x 6" x 6"
compartments offer no protection; owls can easily reach to the back
of the compartment. Crows and hawks will often take nestlings that
are waiting at entrance holes. The solutions are either an external
barrier guard, like a bird cage, fastened against porches, or,
deeper compartments, with offset entrances, and internal
baffles.
Common features to incorporate
in all types of housing: Since martin
houses are placed in the open, fully exposed to wind, rain, and
summer sun, good ventilation, drainage, and insulation are important
to the well-being of the martins. Materials and construction methods
should be chosen for their ability to withstand windstorms and
hailstorms. The roof overhang can be extended to help protect upper
compartments from rain. Ventilation holes should be under the roof
overhang, so rain won't enter through ventilation holes. Drain holes
in the floor of each compartment will allow blowing rains to drain
quickly. Several holes in the floor of each compartment are
required. Raised sub-floors, or larger compartments, also offer
protection from rain. When larger compartments are available,
martins choose them over smaller compartments, and place their nests
as far from the entrance as possible. This protects them from
predators and rain. Martin nestlings do not become feathered until
they are 10 days old; they are susceptible to hypothermia, and will
quickly become chilled in a rain-soaked nest. Extreme heat can also
be deadly to nestlings, and adjustable ventilation louvers added to
the exterior of housing are used by some manufacturers. These allow
extra air to cool the house during hot weather, and can be closed
during cool weather.
A martin house should be easy to
maintain, and durable. Since most people leave the poles up year
round (some also leave houses up, plugged shut), any treatments to
reduce weathering and rusting on the pole will prolong the life of
the system.
Some manufacturers of martin housing
also offer accessory items, such as bait-traps for House Sparrows
and starlings, and a trap-door, sized to catch House Sparrows, that
fits onto the martin house. Extra perches and owl guards that fasten
to the exterior of the house are also popular items.
Gourd Comment: Traps can
also be used in natural gourds as well if the proper access door is
added. Again, just about all the features that a house
utilizes can be installed in a natural gourd. Just as much can
be done with a rack of gourds as can be done with a
house.
Literature
required: If manufacturers include the
following information with the housing, it will greatly benefit
potential landlords: the breeding range of Purple Martins in North
America; how to place housing appropriately; how to determine if a
yard is appropriate habitat for martins; when to open up housing in
spring; and, the importance of keeping other species out. (Nonnative
species through nest removal, trapping, shooting, or use of
starling-proof entrance hole. Native species, such as bluebirds,
Tree Swallows, wrens, flycatchers, are all federally protected; they
may not be trapped, etc. The key to management of native species is
timing and monitoring; erect suitable boxes for native species, and
keep the martin housing closed until competing birds are nesting in
single boxes erected for their use.
Information
sources:
The Complete Birdhouse Book, by
Donald and Lillian Stokes;
Stokes Purple Martin Book, Donald and
Lillian Stokes and Justin Brown; 1997. Little, Brown and
Co.
Enjoying Purple Martins More, by Richard A. Wolinski; 1994
by Bird Watcher's Digest Press.
Homes for Birds; 1991.
Department of the Interior, U. S. Fish and Wildlife Service.
How
to Attract Purple Martins, by James R. Hill, III; 1988. Purple
Martin Update.
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Chuck Abare
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Woodside Gardens
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