Bird of the Month: Purple Martins
In the eastern portion of the United States, Purple Martins rarely nest in natural cavities; instead they nest almost exclusively in man-made housing. No other bird is as dependent on people as the Purple Martin is for their nesting requirement.
In the western portion of the United States, Purple Martins nest in natural cavities found in rocks and trees. They can occasionally be found nesting singularly in man-made structures such as gourds and single-unit nest boxes.
Purple Martins are the largest species of swallow found in North America.
Purple Martins molt into their adult plumage during their third summer, when they are at least two years old.
Purple Martins are almost completely dependent on flying insects for their food. They capture them while foraging on the wing at altitudes between 150 and 500 feet. Martins have been known to occasionally land and eat ants on the ground. They can also be lured to feed on mealworms placed on a tray feeder.
While Purple Martins do eat mosquitoes, in reality, they make up less than 2% of their daily diet. Mosquitoes are rarely out during the daylight hours when Martins are active and mosquitoes are usually found low to the ground and in thick vegetation where Martins rarely fly. Other flying insects, such as bees, wasps, beetles, mayflies, and flying ants make up the majority of their diet.
Purple Martins are highly vulnerable to extended periods of cold and rainy weather that can temporarily reduce the supply of their insect food.
Adverse weather kills more Purple Martins than all other factors combined. They do not forage for insects when the temperature is below 48°F, or when it is raining regardless of the temperature. Prolonged periods (three to four days) of temperatures below 55°F may lead to substantial die-offs.
During extended periods of cold weather, when Purple Martins have been unable to feed for at least two days, up to 10 birds will huddle together inside one nesting cavity in an attempt to conserve warmth.
Adult Purple Martins will usually return to the same colonial nest site year after year. It is the subadult birds (less than two years old) that will be attracted to a newly installed martin house. While they will often return to the same general area, less than 15% of the young martins ever return to their birth colony.
During spring migration, subadult (less than two years old) Purple Martins arrive back at least four to six weeks after the adult martins return. Your chances for establishing a new colony increases with the arrival of these subadult birds and extends for about another month.
Purple Martins will travel up to two miles away from their nesting site while in search of food.
Purple Martins spend the winter in South America, primarily in Brazil and Bolivia. Their migration route can cover between 5,000-7,000 miles and bring them over both land and large expanses of water. They usually migrate in small groups and martins are one of the earliest South American migrants to arrive back on the breeding grounds in the spring.
The common belief that the first returning Purple Martins are actually scout birds that guide other Martins to the colony is simply not true. The first ones back have no contact with later arriving martins until they too reach the colony.
Purple Martin parents bring food back to the young nestlings in the form of a tightly compress ball made of up to hundreds of small insects. As they continue to catch insects, the ball is compressed and held against the roof of the mouth by their tongue.
Research has shown that up to 30% of eggs laid by Purple Martins fail to hatch and of those that do, up to 30% of the hatchlings die before fledging out of the nest. Up to 65% of all fledglings fail to survive their first year.
The oldest known life span for a Purple Martin in the wild is almost 14 years old.
A single House Sparrow may destroy up to 15 Purple Martin eggs in the matter of a few minutes while the nest box is left unguarded.