Animals Wildlife Why Do Purple Martins Have Such Big Houses? By Mary Jo DiLonardo Senior Writer University of Cincinnati Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science, and anything that helps make the world a better place. our editorial process Mary Jo DiLonardo Updated May 17, 2019 Purple martin houses typically have many rooms and are often painted white. LagunaticPhoto/Shutterstock Share Twitter Pinterest Email Animals Wildlife Pets Animal Rights Endangered Species Some birds are happy to make their nests anywhere. A sturdy tree branch, gutter or any birdhouse works just fine. But flashy purple martins like snazzy accommodations. You often see their multi-room homes perched high in the sky, as the colorful residents flit in and out. Here's the scoop on why these interesting birds have such fascinating homes. Homes depend on where you live Purple martins in the western United States primarily nest in cavities, reports Audubon. They'll find old woodpecker holes or spots in trees. Sometimes they'll even nest on the ground between large boulders. In the Southwest, they'll find holes in giant cactuses. <<< mobile-native-ad >>> Although some purple martins in the eastern U.S. nest in holes in buildings or cliffs, tree habitat is limited and competition is fierce from other birds. That's why most rely on nest boxes that people put up for them in their yards. They're now the only bird species entirely dependent on humans for supplying them with a place to nest, according to Texas Parks and Wildlife. They like crowded living Purple martins can nest in colonies of two to 200 pairs. passion4nature/Shutterstock Purple martins are known as colonial nesters, which means they like to nest in groups. The Purple Martin Conservation Association says a purple martin house should have at least four compartments, but six to 12 compartments is ideal to start a martin colony. The compartments in the houses should be at least 6 inches by 6 inches, but purple martins prefer larger cavities, says the Texas Parks and Wildlife Department. An ideal size is 7 inches wide by 6 inches high and about 12 inches deep. Circular entrance holes to each compartment are usually around 2 1/8 inches in diameter, but a range between 1 3/4 and 3/8 inches is acceptable. Purple martins can nest in colonies of two to 200 pairs, according to Birdwatching.com, so that's why they need condominium-type housing for all their friends and family members. Why height is key Purple martin houses are high on poles so that birds can easily soar in and out of them. Warren Price Photography/Shutterstock Martin houses must be mounted on a post or pole at least 10 feet high. Don't attach them to a tree because predators, like cats or raccoons, could access the nest. Martins prefer to glide right into their homes so their nests should be in an open area where they can sail straight into the opening without having to stop. Birdwatching.com says they don't want to dodge telephone wires or maneuver around trees or buildings. Ideally, no trees taller than the height of the martin house should be within about 60 feet of the birdhouse. The house should be on some sort of pulley or winch system so you can raise and lower it easily. That way you can clean the house, check on the nestlings and evict any unwelcome visitors like house sparrows and European starlings, points out the Texas Parks and Wildlife Department. Both of these bird species are very aggressive toward martins. When fighting for nesting sites, they can attack or kill birds, reports the New York Purple Martin Project. Other purple martin enemies include owls, snakes, raccoons, hawks, squirrels and feral cats. Experts suggest attaching predator baffles around the pole to prevent snakes and raccoons from reaching the nest. Cages or guards around the house can prevent hawks and owls from attacking the nest. Color matters Most purple martin houses are white. That's because white reflects heat, keeping the house (and the nestlings) cooler. The birds also seem to be attracted to white houses. It might be because the entrance holes are dark, making them easier to spot against the white house. Other purple martins also show up more easily against a white background, making the home easier to find by other martins looking for the home. The gourd option A collection of gourds offers purple martins lots of rooming choices. Sergey Demo SVDPhoto/Shutterstock Native Americans hung up hollowed-out gourds for purple martins centuries ago, reports Cornell. Many people use natural or plastic gourds to attract purple martins today. Ideally, gourds should be 8 to 13 inches in diameter with an unpainted interior. They should have access doors with the same size entrances as conventional martin houses. They also should be painted white and ideally have baffles and guards to protect from predators. Although gourds can be harder to clean than traditional birdhouses, they have many advantages. They are lighter weight, so they are easier to raise and lower. They also swing and sway, which martins like and predators don't. Predators also have trouble accessing gourds. Because cavities are spaced farther apart and there are no common porches, there is often a higher occupancy rate than in traditional purple martin houses, according to Texas Parks and Wildlife Department. And because there's no continuous porch, older nestlings can't enter their neighbor's rooms to steal food from younger birds.