DEAR JOAN: Something has been a mystery since winter, and I can’t find the answer.

I love all living things — except a few indoor insects — and crows are high on the list. An adorable pair of crows bill and coo outside my window with the smaller one soliciting grooming from the larger. Another calls loudly, peering in the window to demand dry cat food.

The mystery was a flock of crows mobbing a single crow. The aerodynamics were stunning with loops, figure eights, swooping up, hurtling down, intense speed, amazingly missing each other at top speed and packed closely together.

At first it seemed this was a coupling with the group interested, but, as one after another dived at one bird, I was exhausted and can imagine how the solitary crow felt. But she or he kept going for 15 minutes without being injured. Then the whole murder flew away from my sight. What was going on?

I’ve seen similar behavior in cats. One feral cat is an absolute pariah from the others. For seven years, he has been disliked and attacked repeatedly by every cat he comes in contact with. Is he violating some cat code I’ve missed? Or is his (justified) fear releasing pheromones that promote attack? He seems sweet to me, but not to his peers.

Ria Tanz Kubota, El Sobrante

DEAR RIA: Crows are very interesting and intelligent birds. They also are, for lack of a better term, rather opinionated.

Their flocks are like families. Some crows in the family are related — parents and offspring — and others are just bonded to the group. Like human families, they have occasional fights and spats among themselves, but the fights usually don’t last long.

Crows can have a strong dislike for a single bird that is outside the family. It might be that the crows think the bird is encroaching on their territory, or it might be a sick or injured bird that the crows believe may attract predators that will threaten the flock as a whole.

The flock will chase, harass and even kill the bird that has somehow crossed them, unless and until the offending crow leaves the area. That seems to be what you witnessed.

Cats can have the same group mentality, seeking to protect their makeshift family and territory. The picked-upon cat is not part of the core clowder — a group of cats — even though he has been around for a long time. The cats just aren’t willing to let him or her in. The cat’s sin might be being too domesticated for a group of true feral cats.

Isolation is for the birds

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Is it one or two snakes shedding skin in my backyard? If you’re running out of things to keep the kids occupied during this shelter in place, the Golden Gate Audubon Society has published a series of bird-related educational activities including “Listening Bingo,” “Bird Detective,” “Hummingbird Math” and ways to help the birds in your neighborhood.

The printable sheets, available in English and Spanish and free to download, are geared to elementary-school age children. The web page also includes links to bird activities from National Audubon, Cornell Lab of Ornithology and Golden Gate’s Osprey cam.

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