DEAR JOAN: This question may fall into the same category as “how many angels can fit on the head of pin,” but I thought I would ask anyway.

We were petting our 7-pound female tabby, Millie, and I suddenly decided that I would unscientifically figure out how many individual pieces of fur she has. So I tried to figure her approximate surface area and figure how much fur per square centimeter or square inch.

Our unscientific research came up with between 15 million and 20 million pieces of all types of fur. I have no idea if this is even in the ballpark but thought you might have or know of a resource for the approximate answer, within 50 pieces of fur, more or less (only kidding).

Thanks for any info, and in answer to the unasked question, yes, I do have other things to think about.

Dean Glover

Bay Area

DEAR DEAN: Oh good, a math question. Those never get me into any trouble.

In the absence of a volunteer to do the counting, I did some research and the most often quoted estimate that I found is 60,000 hairs per square inch on the cat’s back, and 120,000 hairs on the underside.

Of course, the breed of cat offers some variables.

I’ve provided the numbers, it’s up to you to do the actual math. All I know is that’s a lot of hairballs.

DEAR JOAN: Three or four years ago, two birds made a nest behind one of the speakers on my deck. Because I could easily see their activity from my family room chair, they were fun to watch.

They have come back every year since. They must have a good GPS system.

Looking at my Peterson Field Guide of Western Birds, I believe that they are California towhees, mainly because of the rust-colored throat on the male.

On Super Bowl Sunday they returned. The robins also have showed up, as well as other birds. I look forward to a new family of towhees.

Bob H.

San Jose

DEAR BOB: California towhees are fun birds to watch. Their call is described as sharp, metallic sounding “clinks,” delivered from atop bushes and shrubs, some of which are meant to warn other towhees that a particular territory has been claimed.

Towhees will aggressively defend their territory from other towhees, interlopers and their own reflections, but they are more friendly toward humans.

They don’t seem particularly fearful of us, and you’ll often find the birds hopping around picnic tables or patios where humans are congregated. If you leave a door open to your house, you may even find one bopping along the floor in search of food.

Many birds return to the same nesting grounds each year, and it appears that your pair, or their offspring, are fond of that spot behind the speaker.

The nest is a cup shape, constructed of grass and weeds, twigs and strips of bark, lined with soft grasses and hair. The female generally lays three to four pale blue eggs with dark speckles.

The birds are ground feeders, eating mostly seeds and insects.

The conspicuous presence of paired birds is a sure sign that spring is coming. Robins are the traditional harbingers of spring, but I’d love to know what birds people look forward to welcoming back into their yards.

Contact Joan Morris at jmorris@bayareanewsgroup.com. Follow her at Twitter.com/AskJoanMorris. Read more of her Animal Life columns at www.mercurynews.com/animal-life.