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Archive for Sunday, February 8, 1998

S A LOT TO LIKE ABOUT THE SMART PIGEON.

February 8, 1998

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Some recent dialogue from a local grain elevator is worth listening in on.

Onlooker: Why are there so many pigeons everywhere? The cities seem full of them, and they even infest TV commercials.

Pigeon-fancier: Feral pigeons are good at what they do. They are intelligent, urbane, sexy and photogenic. Additionally, people deliberately feed them.

No, seriously, I think we have too many pigeons.

I'm serious -- pigeons have a high reproductive rate, and they find food readily, whether or not we feed them. It surprises me that they aren't more numerous.

High reproductive rate? I thought pigeons laid only 2 eggs at a time.

Yes, they lay two eggs per clutch. But, they have many clutches each year, plus a long egg-season. In eastern Kansas they average six and a half clutches, or 13 eggs, per year. That's as many as turkeys or some of the ducks.

Why do they lay just two eggs at a time? Wouldn't it be simpler to lay 13 and be done with it?

Simpler and ineffective. A pair of pigeons can rear only two squabs at a time.

But turkeys can take care of a brood of 13. What's the matter with pigeons?

Turkeys don't feed their chicks -- they just lead them around in safe cover and the chicks find seeds partly by instinct and partly by watching their mother. But, pigeons feed their young with pigeon milk.

I've heard of that, but always thought only mammals made milk. That's why they're called "mammals."

Yes, you're right about mammals. Pigeon milk is real, but it probably should be called "pigeon cheese." Adult pigeons make it in their crops, it is full of fat and protein, and it is the main food of the squabs for their first four days or so. Without it, the squabs die.

So, one adult makes enough pigeon milk to feed one squab? And that's why they lay just two eggs in a clutch?

Correct. But after a week or so, food for the squabs includes more and more seeds, the adult diet.

Pigeon milk isn't real milk, however; is that a fact?

That is a fact. But there are other facts you should know, and they might not make you any happier. First, the making of crop milk is stimulated by secretion of a hormone called "prolactin," the very same hormone stimulating production of milk in mammals. Second, the first identification and isolation of the hormone was made by a team of researchers working on pigeons, and much of what we know about the biochemistry of prolactin was learned from studies of laboratory pigeons.

I see what you mean. I am accustomed to thinking of pigeons as pests, or "flying rats," as they are sometimes called. Are these birds the ones used in lab work?

No, lab pigeons are specially reared for biomedical research. Distinct strains have been developed that have reduced genetic variation, which is desirable when a piece of research is replicated.

But the street pigeons are dirty and disease-ridden, right?

Not usually. Dirty and disease-ridden birds have high mortality. The average pigeon is a clean and tidy bird, and spends a large amount of daily time preening its feathers, cleaning them and aligning the feather structure so that it will be efficient in flight. Pigeons bathe in water. They use their preen glands and a powder from their down feathers to lubricate and weatherproof their feathers. Feather parasites are located and removed. Also, females look very carefully at a male's plumage at the time of pair formation, and tend to choose males with first-class feathers. They judge inborn quality by the surface appearance of the other bird.

Well, where did I get the idea that pigeons are dirty and spread diseases? Is all that just nonsense?

Nearly so, but the story is long and complicated. Are you sure you want to hear more?

Maybe.

Firstly, every species of bird that has been studied by epidemiologists is known to be subject to diseases, and some of these may be transmitted to humans; you know about birds being reservoirs of influenza viruses?

Yes. Big news last month.

Well, many other pathogens live in, on, or around birds; wild ones as well as domestics. Periodically, the U.S. Public Health Service takes field samples of wild birds and tests them for bacteria, viruses, fungi and parasites. Birds in and around cities are are especially targeted for collecting, and pigeons are easy to catch, and tend to be over-represented in PHS samples. Because the probability of finding pathogens increases in accord with sample size, pigeons have a substantial list of them. This may account for the idea that pigeons are more disease-ridden than other birds.

But, if pigeons are especially common in cities, shouldn't we pay more attention to them than to other birds?

Pigeons may only appear to be abundant in cities. Pigeons are relatively large and they are more easily identified than many other kinds of birds. Pigeons loaf and forage in social groups and move between successive feeding sites in flocks, and flocks are more readily seen and identified than are single individuals. House sparrows, starlings, house finches, robins, goldfinches, house wrens, cardinals, chimney swifts, grackles and a few other species are more common than pigeons in most Kansas towns. If the public welfare is seriously impacted by birds, we should know as much about these others as we know about pigeons.

These are unsettling considerations. I am at least ill at ease, if not otherwise.

A little knowledge is a dangerous thing?

I'm asking the questions here. Aren't you an advocate of pigeons? Can you speak about them without speaking for them?

Certainly, I am an advocate. Pigeons are remarkable creatures. They can find their way home when at a distance using the position of the sun or by the force lines of the earth's geomagnetism. Locally they use odors, such as scents of flowers in bloom. They learn readily and have keen memories. And ...

Wait a minute -- are you talking about homing pigeons or street pigeons?

Both -- homers are merely specially bred strains of pigeon. Feral pigeons are capable of most of the feats of homers, but they take longer to return home and a larger percentage of them never make it back. Homers are larger, faster and less social than ferals, but otherwise are much the same as those you see around town.

Next you'll be telling about how smart pigeons are.

As I said, they are good learners. If you haven't heard about Jack and Jill, you might not believe what some pigeons can do.

Jack and Jill?

Jack and Jill were White Carneaux pigeons, bred for the hotel restaurant trade but living in behavior labs at Harvard University. They were trained to get their food by pecking keys on a keyboard. When the birds were hungry, Jack would press a key labeled "what color," which would light up a window labeled "what color" in Jill's chamber. Jill would then look behind a screen and see what color was there (red, green, or yellow, to which she had been conditioned), and then peck a key with the name of that color on it. Jack, who could see what Jill was doing, would see the name she pecked and then press the key reading "thank you," which would release food for Jill; then he would press a key of the color that Jill had selected, which released food for him. So the birds were using colors and the symbols for those colors in the process of feeding themselves. And, symbols are the tools of reasoning.

You mean pigeons can think?

That's the way it looks.

But, the birds were conditioned to use the colors and the words in an artificial setup; I hardly think that's a fair test of basic mental ability.

Why not? The process involved sending the birds to school to get an education. And the results are what you would expect from Harvard students.

-- Richard F. Johnston is professor emeritus at the Kansas University Natural History Museum and a member of the Kansas Ornithological Society.

Richard Johnston/Special to the Journal-World

Pigeons swarm around a girl as they forage in a public square.

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