It’s winter and there is a wealth of vacant real estate just waiting to be explored. Not the brick-and-mortar sort, but the twig, grass and plant fiber variety.

Yes, I’m talking about bird nests, and the recent snow makes them easy to find. Look for that blob of white in the middle of a tree or shrub, and there just might be a nest underneath.

Our local bird population shows a wide range of size, habitat and behavior, and all of that is reflected in their nests. So take your camera, take a walk and record what you find to be examined in the luxury of a warm home. On a mild day, a notebook can be used to list location, size, shape and nesting materials. The challenge is in using the information to determine who the builder might have been.

Although no longer in use, the nests should be left where they are found.

In addition to the above-mentioned basic characteristics, certain features will help with identification. Is there mud, pine needles, feathers, mosses, lichens, hair or another specific material? Does it lay on the branches or is it constructed in the fork of several branches? Is it a cup, a hanging pouch or a platform?

A field guide to nests, such as Roger Tory Peterson’s “Eastern Birds’ Nests,” is very helpful and has photos of eggs as well as nests.

Following are descriptions of the nests of some of our common residents.

The American goldfinch builds a 3-inch diameter nest in which several upright, small branches grow together near the top of smaller saplings. The female builds the nest using spider silk to anchor it to the branch, then weaves the cup out of plant fibers and small roots. Since they nest in mid-summer, she uses available thistle or milkweed down to finish her nursery.

Cardinals will place their nest in dense growth 1 to 15 feet above the ground. The female builds a four-layer cup. The outside is made of twigs and sometimes trash, and given a nest shape by her beak and feet. Next is a leaf layer, third a layer of grapevine bark then an inside lining of grasses, stems, roots and pine needles.

Catbirds nests are similar to cardinals but will also incorporate mud.

Yellow warblers, summer visitors, build in the fork of a small tree. Nesting material includes grass, bark strips, deer hair, feathers and plant fibers. If a cowbird, a brood parasite, lays eggs in the nest, the warblers will build a new nest on top. I once saw one that was a foot tall.

Get outside and discover the surprises winter has to offer.

For many more nest descriptions, log onto allaboutbirds.org.

Steffen is an Ohio State University Mahoning County Extension Master Gardener volunteer.