Q I've had four green herons hanging out in my pine trees and making the strangest sounds. Are they common in our area?

A Yes, green herons are commonly found around the edges of lakes and ponds throughout the metro area during the warm seasons. It sounds as if green herons nested in one of your trees and their offspring are getting ready to fly away. They do make an odd, raspy sound, called their "skeow" call. They're smart birds, known to use bait to catch fish, as you can see in this video: www.youtube.com/watch?v=Porp5v5lLKk.

Bark-lined nests

Q This spring I noticed crows stripping and carrying off long strips of bark from my linden tree. It was fascinating to watch and I'm wondering if they were using the bark strips for a nest or is this one of their little quirks?

A They probably were lining their nest, since crows are known to put bark strips to this use (along with other materials, such as animal fur and plant fiber). And it's not only crows: Late this summer I watched as an American goldfinch pulled thin strips from the inner layer of an ash tree, after the outer layer had been stripped away, possibly by crows.

Mallards change colors

Q When do male mallards start looking like themselves again?

A As you've noticed, mallards lose their colorful feathers after breeding season and wear a drab coat, resembling females for some weeks. Because they replace their wing feathers at this time, they're unable to fly. By late August or early September the males once again exhibit those characteristic bright green heads and are able to fly.

Finches flock to salt

Q I have a salt lick for deer outside my cabin and have noticed goldfinches coming in to peck the salt, but no other types of birds. Is this unusual?

A Finches seem especially attracted to salt, whether on the roadside in winter, or at salt licks like yours, possibly due to a dietary deficiency. But salt is also a known toxin to finches and other birds: One researcher has found that a major cause of finch deaths along roadsides seemed to be their ingestion of salt along with the grit they picked up to help them grind up seeds. Another researcher set up mist nets around a salt lick and ended up attracting more than 600 finches. The conclusion seems to be that finches are attracted to salt, whether it's good for them or not.

Catbirds fade into background

Q This spring a pair of catbirds nested in my back yard and raised two babies, sharing the grape jelly and oranges with the orioles. Then they disappeared at the beginning of August, and I wondered if they migrate that early.

A I love having catbirds around and am glad when a pair of catbirds raise their family out back, feeding their nestlings on the insects, berries and fruits they find there. Catbirds become very quiet and stealthy as the young leave the nest, a good survival tactic, and might have been invisibly hiding in your shrubs and vines. This species normally remains in the area until late August, but it's possible that your birds headed to a staging area prior to migration.

High-altitude temps

Q I can't find any information about something I've wondered about for a long time: When temperatures are below freezing or when flying at high altitudes, do birds protect their eyes by flying with them closed?

A That's an interesting question and I'd say that birds must have their eyes open when they fly, since visual cues are very important while in flight, and they always need to keep an eye out for predators. For birds that fly in flocks, they need vision to maintain a proper distance from each other. Birds have been recorded flying at 10,000 feet and even higher, where temperatures are very low. However, eyes are tough organs, able to withstand temperature extremes.

Suet-eating robin

Q A few weeks ago I noticed a robin eating the suet. This seems unusual to me, or is it normal?

A It's a bit unusual for a robin to be dining on suet at this time of year, but not unheard of. Robins relish a high-protein diet of worms and insects in warm seasons, and suet is another source of protein. I think you're seeing a very smart robin who's taught himself a new trick by watching other birds at your feeder.

Jelly-eating finches

Q I don't see orioles at my feeders this late in the season, but the house finches love eating the grape jelly. Is this good for finches, or should we stop feeding them when the orioles leave?

A Don't worry about finches eating the jelly you put out for orioles. Just about any bird that enjoys fruit (orioles, house finches, catbirds, cedar waxwings and others) will enjoy jelly, too. It won't hurt them, and provides an easy treat.

Nest box cleanup

Q After the wren family flies away, should I clean out their house, or leave it for them as it is?

A It's always a good idea to clean out a nest box after its occupants -- whether wrens, bluebirds, tree swallows, chickadees, etc. -- complete one nesting cycle. Young birds poop in the nest material, insects begin to invade, and all in all, a used nest is a mess. Toss the old nest away, whisk out the box, and it's ready for its next bird family.

Robin longevity

Q How long do robins live?

A If a robin manages to make it through its first year of life, then on average it can live about six years, although there is a record of a banded robin that lived almost 14 years. However, only about 25 percent of young robins survive all the hazards in their world to celebrate their first birthday.

St. Paul resident Val Cunningham, who leads bird hikes for the St. Paul Audubon Society and writes about nature for local, regional and national newspapers and magazines, can be reached at valwrites@comcast.net