Q: Do birds re-use their old nests? After watching how hard they work to build a nest, it seems it would make sense for them to use it again.

A: Good question, and in almost all cases, once young birds head out into the world, that's it, their nest is never used again. If you've had a chance to look into a used songbird nest, you'll see why: After young birds fledge, their nests are in pretty bad shape, fouled by nestlings' dried poop and invaded by insects. The walls are usually mashed down under the pressure of youngsters' feet. For these reasons nests are built to last only one season. There are exceptions, the most notable being bald eagle nests, as well as those of great blue herons, osprey and other large hawks, many of which re-use their nest for many years. Some birds that nest very late in the summer, like the cedar waxwing, have been observed pulling apart abandoned songbird nests to scavenge building materials.

Life spans

Q: It occurred to me to wonder about the life spans of two of my favorite back-yard birds, the blue jays and the cardinals.

A: Like all birds, blue jays and cardinals suffer very high mortality during their first year of life — there's a steep learning curve in confronting the many dangers in their world. But if they make it past their first birthday, then blue jays are fairly long-lived, with seven years being their average life span. (The oldest known wild blue jay lived for 17 ½ years.) Cardinals don't live as long, averaging three to four years, but birds as old as 15 have been captured in bird banders' nets. Cardinals are such conspicuous birds and very visible to predators, which may help explain their shorter lives.

Sap sipper?

Q: It always makes me chuckle when I hear or see the phrase "yellow-bellied sapsucker," because it sounds like something from an old cartoon. Does this bird really suck sap?

A: Even though it has plenty of comic potential, the name of the yellow-bellied sapsucker is very apt. This woodpecker drills holes in trees and licks up the flowing sap. But it's not really a sapsucker, more of a sap sipper, using its tongue to absorb sap much like a paintbrush picks up paint.

Homemade 'Halo'

Q: Sparrows have completely taken over my feeders and I don't know what to do, short of taking them all down. Several people have told me that those "halo" devices don't work for them. Can you help?

A: I've heard good things about this pest-deterring product, but several readers have written that it doesn't work on their sparrows. I was thinking of buying one to test it, but my husband wanted to try making a homemade version first. He used old golf balls tied to filament line (the kind used in weed whackers), first drilling a hole through each ball, and then threading the line through the ball and knotting it. Next he drilled four holes in the feeder's domed roof and strung the lines through each hole and knotted each end. The balls hold the line down on four sides of each feeder, and this homemade halo is doing a great job of deterring the local sparrows. The theory behind this is that sparrows aren't very adept fliers and prefer to avoid obstructions. For the price of four old golf balls and a package of line you may have the secret to a sparrow-free feeder.

Serving up songbirds

Q: A blue jay chased a sparrow into our picture window, and then picked up the unconscious or dead bird in its beak and flew off. What fate do you think befell the sparrow?

A: Blue jays are members of a very brainy bird family, and this one seems to have taught itself the trick of driving small birds into windows, then snatching them up as they lie stunned on the ground. I'd bet that the sparrow ended up in the blue jay's nest, since at this time of year jays are on the lookout for protein to feed to their nestlings, and a small songbird would provide a number of nourishing meals.

Cardinal rescue

Q: A young cardinal fell out of its nest in one of our shrubs and was just standing on the ground, with its parents calling nearby. The crows in the trees overhead seemed to be very interested, so I picked the young bird up and returned it to its nest. Did I do the right thing?

A: You did exactly the right thing. Midsummer is a time when many young birds tumble out of their nests, either as they test their wings or as growing siblings edge them out. If there are no predators around, these almost-ready-to-fledge youngsters can survive just fine as their parents continue to feed their chicks in the nest and on the ground. But if, as in this case, danger lurks nearby, then it's good to lend a hand, either tucking the youngster back in the nest or hiding it among thick shrubbery. If you have questions about whether a young bird can survive on the ground, call the Wildlife Rehabilitation Center, 651-486-9453.

Rare bird?

Q: I was very excited to see an unusual bird at our hummingbird feeder. After looking it up in a bird book, it has to be a Wilson's warbler. Is this unusual at this time of year?

A: Very unusual, so much so that your back yard would be inundated with birders wanting to see a Wilson's warbler — if that's what it was — in your county in the summer. These small birds nest far to the north of here, so its presence in July would be a rarity. It's great that you sent a photo to nail down the bird's identification, and I'm sorry to say it was a more common bird, a goldfinch, but I can see why you were confused. Both a Wilson's and a goldfinch are yellow birds with black caps, but one way to tell them apart is the strong black and white pattern on the wings, like those on the bird at your feeder, clearly identifying it as a goldfinch.

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