2013 February – A Nest for Every Niche

(cont.)

Red tail hawk nest in a saguaro

Red tail hawk nest in a saguaro

Consider the challenges of providing a suitable location to raise a troupe of ever-famished baby birds in an arid desert where springtime temperatures normally reach triple digits. Desert plants don’t have the luxury of available water to help them soar tall and leafy, so native birds find other ways to shelter their young.

The cactus wren does her best for her kids. She places her nest in the arms of the forbidding cholla cactus, a fortress of barbed spines. The football-shaped nest is completely enclosed but for a hole in one end and provides shade and protection from predators. That’s not enough for the cactus wren, though. As soon as mom is sitting on eggs, dad starts building a decoy nest. These secondary nests confuse predators and provide shade for the adult birds later in the summer.

The other species that builds an enclosed nest is the verdin. These nests are like softballs, round twiggy spheres with tiny awnings over the doors. Placement of the door near the bottom of the nest, and placement of the nest on the outer end of branches of the tree, will ensure the parents easy frequent access to the begging nestlings.

Way bigger nests belong to raptors. A red-tailed hawk pair builds a sizable platform of sticks for the basic framework of their nest and finishes with a lining of soft grasses and bark. This edifice may be more than two feet across and at least as deep. The nest platforms often become a foundation that is used season after season by red-tails or other raptors who may add their own modifications. If no one’s at home when you spot a raptor nest, subtle details may reveal the identity of the current residents. Red-tailed hawks sometime add interesting features such as a snake skeleton or devil’s claw pods. Red-tails generally prefer easy access and a view, so they build their nests in the highest sturdy crook of a tall tree or sometimes on transmission tower platforms.

Harris’s hawks find more privacy in the sheltered middle of a smaller tree or in a secure crook of a saguaro, generally about 10-30 feet off the ground. These chocolate-colored raptors live in a social order, and breeding groups of up to seven hawks work together to build the nest and raise young.

Ravens are rambunctious and messy, and sticks and bits of building material may be found on the ground beneath their nest. They will also excrete more whitewash on the sides of the nest.

Bald eagle nests can become enormous, as large as 65 square feet as annual renovations add to the bulk. Arizona’s bald eagles live near waterways and search for a nest site in the tallest tree, where they build in a crook near the top. When trees aren’t available, bald eagles sometimes nest on cliffs.  Eagles cozy up their nests by creating a lining of plant material such as soft grasses and fibers of cacti.

It’s the hummingbird, of course, that constructs the thimble-sized nest. The Anna’s hummingbird nests in December and January. She constructs her nest from downy materials such as thistle and feathers bound together with rodent hair and spider webs. Only an inch and a half across, its thick walls insulate both eggs and mom from the cold. The Sonoran desert’s amazing diversity is exemplified by the astounding range of size, building materials, timing and location of bird nests.

Sources:
Bird Nests and Eggs by Pinau Merlin
Raptors of Arizona edited by Richard Glinski

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