Q We have two cardinals coming to our feeder and they seem healthy except that their heads are completely bald. It looks rather grotesque, and I'm wondering if they might have some sort of disease.
A This is the time of year for reports of bald cardinals and blue jays. Your birds aren't diseased; they're probably molting.
For some unknown reason, a few birds lose all their head feathers at once, instead of molting in staggered fashion, like other birds. The head feathers invariably grow back, but it is a bit disconcerting to see these beautiful birds looking so unhandsome.
Twin beaks Q I was fortunate enough to find a hummingbird nest and have been keeping an eye on it as the baby birds grow up. Will the dominant youngster push out the other one so only one survives?
A You're lucky to be able to observe a hummingbird nest -- from a distance, I'm sure. I don't think you need to worry about siblingcide in hummingbirds. Most female hummingbirds lay two eggs and unless disaster strikes, both twins grow up and fledge from the nest.
Disappearing act Q My dog got fairly close to a robin's nest along our fence line, and the robins were very agitated, although the fence kept the dog away. Later we noticed that the nest was empty and wondered if the parents moved the baby birds.
A Birds don't move their nestlings -- when the young birds leave the nest it's under their own power. It's possible that the youngsters were just old enough to fly away from the perceived danger posed by your dog.
The other possibility is a sadder one: Your dog may have provided a scent trail for another predator, possibly a cat or other mammal, to use to find the nest and eat the young.
Taking turns? Q Our bird house has been very successful this season. First chickadees raised a family, then wrens moved in. The wrens are just about ready to leave and sparrows are perching on the box. Are the sparrows waiting to occupy the house when the wrens leave?
A It's lucky that the wrens waited for the chickadees to fledge, because wrens are usually much more impatient, and will puncture eggs or kill the youngsters in order to take over a nest box.
Now that sparrows have discovered the box, the wrens may be in danger themselves, because sparrows are notorious for killing nestlings and even adult birds in order to claim a nesting cavity.
The best defense is an entrance hole that is too small to admit sparrows. If it's larger than 11/4 inches in diameter, you might want to buy a metal piece at a wild bird store to narrow the hole so sparrows can't get in.
Val Cunningham, a St. Paul nature writer, bird surveyor and field trip leader, can be reached at valwrites@comcast.net.
