It's time to watch for a really weird bird at backyard feeders. It's a cardinal, but its head and neck are naked. It looks like a negative image of a miniature vulture -- red body and naked black head.

Cardinals are normally robust and commanding in their brilliant crimson plumage. But every summer a few "bald" cardinals appear (and sometimes other bald birds, too). I've always attributed the condition to a bad case of ectoparasites -- mites and or bird lice that actually eat feathers.

But others blame the condition on an unusual molt pattern. Normally song birds molt, or replace their body feathers, just a few at a time, so it's hard for even a keen observer to notice. For all the head feathers to fall out at once would certainly be unusual and hardly beneficial. The skin could get sunburned by day, torn up by thorns and tree branches, or badly chilled at night or during rain storms. One of the purposes of feathers, after all, is to protect the body from the elements.

Even ornithologists familiar with the problem cannot agree on an explanation. Like me, David Bird of McGill University in Quebec and author of "The Bird Almanac" (1999, Firefly Books), always assumed this was a parasite problem. But a colleague, Rodger Titman, argues strongly for the unusual molt explanation.

"Rodger has convinced me that an irregular molt is the better answer," Bird says.

Sylvia Halkin, an ornithologist at Central Connecticut University, has suggested in print that unusual feather loss may be due to a traumatic injury.

Chris Thompson, an ornithologist who has studied molt extensively, also blames abnormal feather replacement for shaggy looking birds. But completely naked heads, "are not normal," he says. "When birds molt, new feathers push out the old ones, so a head should never appear completely naked. Parasites might be the answer."

If you see a bald cardinal (or other bald bird), blame molt if the bird looks like it's having a bad hair day. But if the head is completely naked, it could be parasites or perhaps trauma from an injury. In any case, the feathers will grow back in four to six weeks.

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