Q: Why have my hummingbirds disappeared?

Q: Why don't the orioles come to my grape jelly anymore?

Q: What's happened to my cardinals?

A: One answer pretty much fits most of the questions about birds seeming to disappear in high summer: Birds are very busy at this time, as they rush to feed their nestlings a diet almost entirely made up of insects and spiders, and are eating insects themselves. This high-protein diet ensures that young birds grow at an explosive rate and are able to leave their nests quickly, before predators find them. Another factor is that berries and other fruits are abundant at this time of year and parents can feed these to older nestlings. Once nesting season is wrapped up, adult birds and their youngsters should begin appearing at feeders again.

Wren time

Q: In mid-July wrens were just starting to build with their typical small twigs inside my nest house. Wasn't this late in the season?

A: Wrens are among the bird species that raise two broods during the summer, so the birds in your backyard sound right on schedule for starting a second nest. Other birds that nest twice in the breeding season include Northern cardinals, ruby-throated hummingbirds, American robins, Eastern bluebirds and, unfortunately, house sparrows.

Foster parenting

Q: For several days I've been seeing what I believe to be a juvenile cowbird following and pestering some type of sparrow. I know that cowbirds will lay their eggs in other birds' nests, is this what's happening in this case?

A: I'll bet you're right and my guess is that the young cowbird is demanding food from the chipping sparrow that raised it. These tiny sparrows are often forced to be foster parents to cowbirds.

Birdbath sludge

Q: Some sludge is building up on the sides of my birdbath and spraying with the hose doesn't get rid of it. I don't want to stop offering water, so what can I do?

A: There are products on the market that claim to eliminate the problem of algae buildup in birdbaths, but a much simpler solution is to buy a brush with sturdy plastic bristles. Scrub down the birdbath every couple of days, give it a good hose spray and it will be as good as new.

Summer stoppage?

Q: I enjoy feeding birds but I'm hearing that we don't really need to feed birds in summer because their natural habitats offer plenty of food. Do you agree that summertime is a good time to shut down the bird feeders?

A: You raise an interesting point, and it's true that in July and August berries, other fruits, seeds and insects are widely available to birds. But summer bird feeding allows us the chance to observe birds that are here only during the warm months — the hummingbirds, orioles, bluebirds and grosbeaks, for example. Most experts agree that birds don't rely on our feeders for their daily calorie budget, except on the coldest winter days. What feeders do is bring birds in where we can see them, and this makes it worth feeding them even in summer, for many of us.

Bird count

Q: How many kinds of birds do we have in Minnesota?

A: There are a number of ways to answer this, but one way is to look at the number of species that nest in the state each year, and the answer is 235 species. The Minnesota Ornithologists' Union counts 313 bird species that have been seen in the state in at least nine of the past 10 years.

Disappearing mallards

Q: This is the second year that a mallard hen has built her nest in our backyard, next to the garage wall. We checked one time when she was away and there were eggs in there. But one day the mallard was gone and the nest was empty, with no sign of eggshells or any disturbance. Had the eggs hatched after dark and she led them away?

A: Sorry to say, this sounds as if a fox or raccoon got to the nest, frightened the hen away and ate all the eggs. If the eggs had hatched you'd find eggshell remnants in the nest. Even if they had hatched, the mother duck wouldn't move her brood in the dark, it would just be too dangerous to be out at a time when many predators are active.

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.