How many billion birds are there in the world?

Q: I've always wondered how many birds there are in the world, as in total number. Does anyone know?

A: I'd always wondered about this, too, until I read an excellent book called "Bird Migration, A General Survey," by Peter Berthold. For many reasons, including variability from season to season, ornithologists only cite a wide range. Berthold uses a figure of 200 billion to 400 billion birds currently living on this planet. However, with many birds facing severe population declines (some species are down by 50 percent or more) due to their living places being taken over by agriculture and development and factors like climate change, that spread may be revised downward one of these days.

Q: A Cooper's hawk has been terrorizing the birds in our backyard all summer. Will he give them a break by migrating this fall?

A: Sorry to say, that hawk may stay in the area all winter, now that he's learned that your feeders attract birds he can hunt. Even though most Cooper's hawks migrate to Central America to feed on songbirds in the winter, a few remain here.

It's tough to know whether to leave feeders up to help sustain your backyard birds, knowing that some may be snatched by the hawk, or bring feeders in to prevent birds from visiting, thereby ending the hawk's easy hunting. I'd vote for leaving the feeders outside, knowing that some birds may become prey, but others will manage to flee to hiding places when the hawk comes around.

Q: The only birds that I've ever seen in our birdbath are robins and catbirds. Why don't I see smaller birds bathing? They perch on the rim to drink but they don't hop in and I'm wondering whether they're afraid of drowning.

A: All birds bathe in one way or another, even ducks and geese, which spend most of their lives on the water. I see small birds like chickadees, goldfinches and even tiny chipping sparrows taking baths in my birdbath every day in the summertime. You may have hit on the answer when you mentioned birds' fear of drowning. Many birdbaths simply are too deep for small birds, or the sides are glazed and slippery, so they avoid bathing in them. A quick fix for such deep basins is to place a brick or stone in the center for smaller birds to stand on.

Q: A cardinal built her nest outside my kitchen window, giving me a perfect view of the events in the nest. What surprised me was how little time the young birds spent in there — one day they were waiting for a meal from their parents, the next thing I knew they had flown away.

A: Young songbirds leave their nests as soon as possible for two reasons, and a key one is to evade predators. Cats, raccoons, squirrels and many others watch for adult birds coming and going on feeding forays, or listen for youngsters begging noisily for food. The helpless nestlings make for an easy meal for such predators.

The other reason is to escape nest parasites. Young birds produce a great deal of poop, which their parents carry away early on. As the young get older they back up to the edge to poop over the rim, but not all of this waste makes it outside the nest. This begins to attract insect parasites, some of which feed on the blood of young birds. So the sooner the nestlings become fledglings the better for them.

Q: We had a birdhouse for bluebirds in our yard this year, and I'm not sure what kind of bird used it. But it's pretty messy inside and I wonder if I should clean it up.

A: Once the birds have left a nest box, it's a good idea to sweep out all the nesting material and chip off any poop pasted to floor or walls. At this time of year you can go ahead and give the box a cleaning by spraying the inside with the garden hose and leaving the door open until the box is dry.

Some time ago a reader asked why flocks of Canada geese were flying northward in the summertime. My answer should have noted that these were young birds that weren't raising families. These "molt migrants" were heading north to secluded lakes while they molted new flight feathers. During this several-week period they're unable to fly, making them vulnerable to predators. Larger, secluded lakes provide better protection. Thanks to author and bird enthusiast Don Grussing for providing this information.

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.