At first, the loud whistles sounded like someone trying to get my attention, but it was early, and there no one else at home.

The whistles persisted from high atop a silver maple on the edge of the yard. Baltimore orioles were back, and two dueling males were setting up territories.

So I wasn't surprised when a few e-mails arrived from readers reporting orioles feeding at hummingbird nectar feeders. I get these notes every spring, and invariably the writer asks if orioles drinking nectar is unusual. It isn't.

Vividly-colored orange, black and white, Baltimore orioles eat fruit and nectar, as well as a variety of insects and spiders. So do orchard orioles, which are a bit smaller and less conspicuous than their more gaudy cousins. Male orchard orioles have rich chestnut rumps and underparts; the rest of the birds are black. Females of both species are a much duller olive-yellow.

Both Baltimore and orchard orioles often visit hummingbird feeders. However, orioles are considerably larger than hummingbirds. The acrobatic balancing act that's required to use most hummingbird feeders makes getting a free meal a frustrating experience.

To make it easier for orioles to get a backyard snack, consider buying a specially designed oriole feeder. Perches and ports on oriole feeder are larger to give orioles better access to the nectar.

And don't be surprised to see a parade of other visitors using nectar feeders. More than 50 species of birds are known to sip nectar. Among the nectar drinkers to look for: woodpeckers, titmice, chickadees, nuthatches, thrushes, warblers, tanagers and house finches.

If you're not convinced that orioles deserve a special feeder, consider their normal diet. Among their favorite insect foods are hairy caterpillars, such as eastern tent caterpillars and fall webworms. More importantly, orioles eat gypsy moth caterpillars. Any natural enemy of these pests, which destroy thousands of acres of deciduous forests annually, deserves encouragement.

Most birds avoid hairy caterpillars because they are difficult to swallow. Orioles and a few other birds such as tanagers and cuckoos don't let a few nasty hairs discourage them. They hold hairy caterpillars in their bill and whack them against a branch until most of the hairs fall off. Then it's down the hatch.

Orioles can also be attracted with a variety of other foods. A dish of live meal worms is irresistible to most insectivorous birds. Orioles love oranges, so nail orange halves to platform feeders or dead branches. And try a spoon full of grape jelly in a heavy dish such as an old ash tray to attract orioles, catbirds and Carolina wrens. The cheapest generic jelly at a dollar store will suffice.

A final favor for orioles is to provide nesting material for their expertly woven, pouch-like nests. Fill a suet basket with strands of string, baler twine, yarn, used dental floss, or long human or animal hair. Cut the strands 6 to 10 inches long, just enough to weave but not so long that they might entangle or strangle the birds. Before long, you'll have a variety of nesting birds in your debt.

Female orioles take 4 to 8 days to weave the nest, which they suspend from the fine outer branches of tall elms, sycamores and poplars. This delicate location makes it difficult for larger predators to reach the nest. Though the female builds a new nest each year, she often builds it in the same tree or even the same part of the tree as she did the year before.

When the nest is complete, it cradles a clutch of four or five eggs. The female incubates the eggs for about two weeks and then both parents share the duties of raising the brood. The young leave the nest when they're about two weeks old. Unlike many local birds, orioles raise only a single brood each year.

Updates from my backyard: Ruby-throated hummingbirds finally showed up at my feeders on May 2, and at 9:30 p.m. May 4, I heard at least two whip-poor-wills singing in the woods. Talk about a lullaby ...