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There is a lot of activity going on in the avian world these days. Birds have one thing on their minds: raising their young! That is why migratory birds return to our area year after year; it affords them a good place to raise young with an ample food supply and room to avoid excessive competition from other birds.

If you sit and watch for a while, you can see this activity. You will see the seemingly aggressive bird-to-bird chases of either an interested male toward a female or a male-to-male territorial dispute.

You will also see birds carrying nesting material, stick by stick, blade of grass by blade of grass. They are painstakingly fashioning this material into nests unique to their species that will serve as a platform to lay eggs and raise and protect their young.  

Just as birds can be identified by their markings, so they can be identified by their nests.

For example, the familiar robin uses soft mud from worm castings to reinforce a cup-shaped nest built from grasses, twigs, rootlets and moss. If the mud washes away or crumbles, the bird will rebuild the nest.  The nest is large, 6 to 8 inches across and 3 to 6 inches high, and is usually located in the lower half of a tree or in gutters, eves and light fixtures.

The female lays three to five greenish-blue eggs in each clutch. She may lay eggs two to three times during the breeding season, resulting in up to 15 young birds.

In contrast, the cerulean warbler, a long-distance migrant and declining species that uses our large forests to raise young, builds a small nest in the mid to upper canopy of a tree, often concealed from the top by leaves and twigs on the nest branch itself. The warbler weighs less than half of an ounce — compared to the 3-ounce weight of the robin — and its nest is proportionately smaller.

The interesting thing about cerulean nests built of bark fibers, grass stems and hair is that the materials are bound together with spider web. Spider web is about one-tenth the diameter of a human hair, but it has incredible strength; it is 10 times stronger than a strand of steel of the same weight.  

Unlike robins, cerulean warblers will usually only have a single clutch of one to five eggs during a season. This is probably due to the fact that they don’t have time for a second clutch before they have to migrate back to Central America. If the  first nest fails, to save time the female recycles the spider web from the failed nest to start a new one.

If you would like to see birds in action, join other birders for Audubon’s annual Bird-a-thon, on Saturday, May 15. It’s a way to enjoy nature and help raise funds for conservation and education.  For more information, call the Audubon Center at 860-364-0520 or go online to sharon.audubon.org.

Scott Heth is the director of Audubon Sharon and can be reached at sheth@audubon.org, (subject line: Nature Notes).