Spring nesting season is in full swing now, and bird nests of all shapes, sizes and materials abound in our woods, fields and backyards.

The smallest nest, of course, is that of Georgia's tiniest bird, the ruby-throated hummingbird. Made partly of lichens, the nest is so small that a quarter barely fits into it. On the other hand, a bald eagle's nest, made of large sticks and limbs, may be more than 6 feet across and weigh more than a ton. (Georgia's eagles just wrapped up their nesting season.)

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Orchard orioles have nest-building down to a science.

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But in my estimation, one of the most interesting, best-engineered nests of any bird in the state is that of the orchard oriole, a migratory species common this time of year. I came across an orchard oriole nest — a bag-like structure tightly woven from green grass — the other day in a sweet gum tree along a trail in the Charlie Elliott Wildlife Center in Jasper County near Mansfield. Training my binoculars on the nest — hanging in the fork of a limb some 10 feet off the ground — I stood for several minutes admiring the builder's innate engineering skills.

Although the orchard oriole often is overshadowed by its snazzier, more famous cousin — the brilliant orange-and-black male Baltimore oriole — it is in nest-building that the orchard oriole appears to excel. The Baltimore oriole's nest is larger and itself a marvel of engineering, but several bird experts contend that the orchard oriole's nest, built by the female, surpasses the Baltimore's in beauty and ingenuity.

(A few Baltimore orioles nest in the higher elevations of Georgia's mountains, but most of those seen in the state are migrants passing through.)

Working steadily for about six days, the female orchard oriole builds a hanging pouch nest, usually suspended from the end of a limb 10 to 25 feet off the ground near a pond, river or other water body.

An admirer of the orchard oriole's nest-building skills was America's most famous ornithologist, John James Audubon, who wrote: "They [orchard orioles] resort to the meadows, or search along the fences for the finest, longest, and toughest grasses they can find, and having previously fixed on a spot either on an apple tree, or amidst the drooping branches of the weeping willow, they begin by attaching the grass firmly and neatly to the twigs more immediately around the chosen place. The filaments are twisted, passed over and under, and interwoven in such a manner as almost to defy the eye of man to follow their windings. All this is done by the bill of the bird."

More orioles

Orchard orioles, North America's smallest oriole, are relatively common in spring and summer in Georgia, except in the higher mountain elevations. Their breeding season, at its peak now, will continue through June. By late August, most of the birds will be gone — one of Georgia's earliest neo-tropical species to depart for winter grounds in Central and South America.

The female orchard oriole usually lays three to five eggs that hatch in about 12 days. Both adults brood and feed the young while they are in the nest. The young fledge 11 to 14 days after hatching. After the young leave the nest, the parents split the brood and each adult takes care of half of their offspring. The young stay with the adults until fall migration.

While the Baltimore oriole may be more famous, the male orchard oriole, with its bright chestnut-and-black plumage, also is striking — one of Georgia's most attractive songbirds. The female, with her bright olive and yellow underparts, is eye-catching in her own right.

Unlike many other songbirds, which sing to attract females and to defend territory, the male orchard oriole sings mostly to lure a mate. It's much less territorial than other songbirds, and that may be why it often nests near kingbirds.

Kingbirds are exceptionally defensive, and will attack any bird — even red-tailed hawks — that approaches their nest.

The orchard oriole has a hearty appetite for caterpillars, beetles and other insects, but it also has a distinct sweet tooth, favoring fruits, berries and nectars. Many folks attract orioles to platform feeders by putting out orange slices and grape halves. Orchard orioles also occasionally sip nectar from hummingbird feeders.

The bird gets its name, in fact, because one of its favorite haunts was fruit orchards. Now, because of heavy pesticide use and intensive pruning of orchards, the bird rarely shows up in those places.

Another serious problem for the oriole is the brown-headed cowbird, which lays its eggs in oriole nests and tricks oriole parents into raising the cowbird babies. In some areas, cowbird "parasitism" affects 50 percent of oriole nests.

In the sky

The moon will be last quarter on Tuesday. By the end of the week, look for it to rise about midnight and set around midday, says Fernbank Science Center astronomer David Dundee. Mercury is low in the west just after dark. Mars also is in the western sky just after dark. Jupiter rises out of the east about midnight. Saturn is high in the southwest at dusk.