Along a wooded trail in Constitution Lakes Park in southeast Atlanta last weekend, our eight-member birding team was trying to identify and count all the little birds that we could see flitting among the leafless tree branches — part of the annual Intown Atlanta Christmas Bird Count.

Making our efforts a little tricky, however, was that the birds high up in the trees appeared mostly as dark silhouettes in the morning light of the cold, overcast day.

Skilled birders, however, use many different clues to identify species, even those obscured by shadows. One of my fellow team members, for instance, was Nathan Farnau, whose bird lore knowledge is encyclopedic. “Blue-headed vireo,” he said, pointing to a bird on a high branch. I would have missed it, so I asked Farnau for clues in identifying it.

A first clue that it might be a blue-headed vireo, he said, was that it was chunkier and had a shorter tail than those of the more common Carolina chickadees, tufted titmice and other small birds frequenting the treetops. It also did not have a crown like a titmouse.

Then, when the bird emerged for a few seconds from the shadows, Farnau could see through his binoculars a flush of yellow on its sides and a spotless white belly, distinct features of the blue-headed vireo. Next, its distinctive white eye rings, or “spectacles,” framing its eyes came briefly into view. Finally, Farnau got a fleeting glimpse of the bird’s blue-gray head.

Together, the clues added up to a blue-headed vireo, he said.

Farnau, 40, said his store of knowledge comes from a keen interest in birds since childhood. “You might call it an obsession,” he said. His birding skills also come from countless “field trips,” years of poring through bird books, tips from other experts, the Internet and other sources.

Altogether, 13 teams — all members of the Atlanta Audubon Society — tallied a record 86 species during the daylong bird count. Other teams’ highlights included a Lincoln sparrow, marsh wren, rufous hummingbird, orange-crowned warbler and an American kestrel.

In the sky: From David Dundee, Tellus Science Museum astronomer: The moon, new Saturday, will be a thin crescent low in the west at dusk Monday. All of the currently visible planets rise in the east: Venus, about an hour before sunrise; Mars, about five hours before sunrise; Jupiter, before midnight; and Saturn, two hours before sunrise.