Purple Martin Physical Traits And Nesting Behavior

[Steve Kroenke]

Purple Martin Physical Traits And Nesting Behavior

Purple martins are swallows and members of the family, Hirundinidae. Other swallows include the barn, tree, violet-green, cliff, cave, rough-wing and bank. These birds share some common physical traits such as a sleek body profile, long and narrow pointed wings without slots, short legs and strong feet, and a flattened and soft bill with a wide gape. These traits reflect an aerial life style of hunting flying insects and limited exposure to movement on the ground or within vegetation.

Some of the physical characteristics listed above not only relate to high speed flight in the open sky, but also to the martin?s cavity nesting behavior. There are nesting related reasons for stiff tail feathers, short legs with strong feet and sharp nails, and a slender profile.

Stiff Tail Feathers

Martins have stiff tail feathers which complement the sleek body profile and may aid in aerial flight maneuvers such as sharp banking actions. But there is another functional adaptation of stiff tail feathers: serve as a brace when martins hang vertically on nest cavities without porches. For possibly thousands of years martins nested (and still do out west) in woodpecker cavities in dead trees or limbs. So, the stiff tail feathers may have gradually evolved partially in response to martins clinging to holes in dead trees. This behavior is still very much evident when martins cling to the entrances in gourds without porches. Martins will hang on the entrance holes to their nesting cavities, look in, and then lift themselves up to enter. The tail feathers are stiff to provide some support as martins cling to the entrance holes to gourds or natural cavities.

Woodpeckers, also, have stiff tail feathers to serve a similar function, particularly as they climb tree trunks and brace themselves in front of their nesting cavities.

Short Legs With Strong Feet And Sharp Nails

Birds which spend most of their time off the ground and flying in the open don?t need long legs for walking or hopping. Martins are good examples of these birds. Martins are awkward on the ground and they don?t hop; they tend to waddle.

Martins have short legs with relatively strong feet and sharp nails and those attributes may relate to nesting behavior. Martins nested for eons (and still do out west) in vertically deep woodpecker cavities which are relatively narrow inside and rustic. Short legs are ideal for moving up and down in those types of cavities and clinging to the coarse interior substrate. And the strong feet with sharp nails are perfect adaptations for climbing those rustic walls of natural cavities and even hanging on them from the inside. Natural gourds are good surrogates for woodpecker cavities, particularly from the rustic angle. Martins can easily climb up the surface of a vertically deep natural gourd and exit the entrance. Additionally, I have observed martin fledglings land at the base of a tree and then climb up the bark, using their sharp nails and short legs.

Chimney swifts, also, have short legs with strong feet and sharp nails to cling vertically to the insides of brick chimneys and hollow trees.

Slender Profile

A svelte torso is ideal for cutting through the air when a martin is pursuing a dragonfly or escaping from aerial predators at high speeds. Such a slender profile is also adaptive for entering woodpecker holes and then climbing down those narrow cavities to reach the nesting chamber. Since the inside dimensions of a woodpecker?s nesting chamber are relatively small considering the size of woodpeckers, a martin?s sleek body shape would fit nicely into such a cavity.

When a woodpecker rests inside its cavity, it will often cling to the wall vertically, thereby minimizing the need for roomy interior dimensions. Woodpeckers don?t lie down in their cavities like a human would in a bed. Young woodpeckers may press their chests/bellies against the side of the cavity and rest in that position rather than lay prostrate at the bottom. In this way a large brood of flickers, for example, can be raised in a relatively small diameter nesting chamber. Woodpecker cavities sacrifice horizontal girth for greater vertical depth.

The same nesting behavior may apply to martins, too, and martins can lean against the back of a gourd or house compartment so that they their bellies/chests are parallel with the cavity sides. I will sometimes see my gourds slightly tilted upward at nighttime when the martins have moved to the back to be as far away from the entrance as possible. The martins may be sleeping against the back of the gourd rather than stretching out in the nest. I have also shined a flashlight into the openings of aluminum houses at night and I could see the martin shapes pressed up with their chests/bellies against the compartment back wall.

Purple martins have stiff tail feathers, short legs with strong feet and sharp nails, and a slender physique. These physical characteristics are functional for both a life in the open skies and nesting in cavities. Martins may have evolved these attributes, in part, as a result of nesting for thousands of years in natural cavities such as those prepared by woodpeckers.

Steve Kroenke

[Donnie Hurdt MN]

I learned somthing again from your writings. I diddent know that martins slept the way you described they do. I just took it for granted that martins slept in a more horizontial position or in the nest bowl. Thanks for the info.