Year after year they'll return to bring you the joy of watching their mating, nesting, and feeding habits close up.
Purple Martins are the largest of the North American swallows and one of the few birds that allow you an opportunity to have a hands on approach to bird watching.
These birds measure about 8 inches in overall length. The tail is slightly forked. Adult males in their second year or older are entirely black with a glossy steel blue sheen. These second year adult males are the easiest to identify.
Adult females in their second year are dark on top with some of the blue sheen. The underparts are lighter. Subadult females(those who've made a single migration trip) look like adult females without the steel blue sheen on the back.
Subadult males are a little easier to identify. Looking similar to females, but they have solid black feathers on their chest in blotchy, random patterns.
Older adult males generally return first from their wintering grounds in Brazil to claim nesting cavities at the same site as the previous year, provided that nesting site is still available. On occasion, adult females will get to the nesting site first. Males will try to attract a female to a selected nesting cavity of his choosing.
The female will pick which she desires and the male, regardless of which cavity he may have preferred, will follow the female to her selected site.
About four weeks after the adults arrive, the subadult Martins (those returning from their first migration) will begin returning to mate for their first nesting season. The young males may fight with each other and the older males in order to mate with any available females.
As a rule, those males that are in full adult plumage, second year or older, tend to be preferred by the females for breeding.
East of the Rockies, the Purple Martin is almost totally dependent on man-made housing. It's important for the individual hosting these swallows to provide the best housing and management techniques they can provide.
These birds prefer nesting in larger cavities than was previously thought. Most manufactured housing was a 6 inch by 6 inch cavity. Smart manufactures are making housing cavities with more depth, approaching 11 inches deep and 7 inches wide. Natural and Plastic gourds are used and provide the martins deep and wide nesting cavities. Gourds can also provide protection from flying predators like owls from reaching in to attack the nestlings.
The nesting behavior can be watched with relative ease. Females will begin gathering nesting materials and bringing them back to the nest cavity. Flying to the top of a tree she will tear a leaf off with her beak and bring it back to the nest site.
If you watch a single pair you may notice each time the female enters the nest the male will sing a few notes his song. This may be to let her know he is nearby while she is inside the nest. The nest is made from natural material available in the area: pine needles, grass, sticks, straw and leaves. Nest building takes anywhere from 1 - 2 weeks.
The female will lay from 3 - 7 eggs with the average about 4 per clutch. Generally speaking, younger females lay fewer eggs than more mature females. Incubation is done by both birds with the female carrying out the bulk of incubation. An interesting note for birdwatchers not familiar with Martins is that incubation is not continuous. The eggs are covered with leaves and both male and female may go feeding with the eggs unattended.
This can be a dangerous time as House sparrows, House Wrens, or Starlings can enter and destroy the eggs during this time.
Incubation last for about 15 - 17 days. The young will stay in the nest anywhere from 28 - 32 days before leaving. Once the young fledge the nest the parents will continue to feed them and teach them to catch their own food.
Once the young learn to fly and catch their own food they will go their own way and will no longer be dependent on their parents for their survival.
Often the young are brought back to the nest at evening during the first week or two after fledging. If hawks or owls have been a problem the young may not return after fledging. Also, if conditions of the nest site have been poor due to mite infestation or wet nest, the young may never return at night.
The aforementioned issues are good reasons for doing nest checks and using good management practices when hosting Purple Martins.
Purple Martins are aerial insectivores. They only catch insects while flying to eat. Their diet consist of Dragonflies, damselflies, cicadas, grasshoppers, katydids, moths, butterflies, wasps, beetles, stink bugs, mayflies, bees, midges, and horse flies.
The myth about Martins feeding on mosquitoes is just that, a myth. While they may eat a couple, mosquitoes are not a primary food.
These birds have many predators and it is incumbent on Martin landlords to do all they can to protect the birds they are hosting. Predators include: Hawks, snakes, raccoons, European Starlings, House Sparrows, Owls, and cats.
Using predator guards and netting on poles will keep snakes and 4 legged predators from climbing the pole and killing the martins.
Trapping and eliminating European Starlings and House Sparrows is a must for the Martins to survive. These two introduced species do more harm to our native cavity nesters than any of the native species. Our native birds have not developed defenses against these two species of bird. Keeping cats indoors at least during fledging time can be helpful.
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