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Begging: the question

My wife and I have a bird feeder outside our kitchen window. Yesterday I saw an adult male cardinal feeding some of the seed to an immature cardinal not much smaller than he was. I guess it's hard to say "no", but should he have?

This week's paper, "The adaptive value of parental responsiveness to nestling begging" by Uri Gordzinski and Arnon Lotem, published online in Proceedings of the Royal Society, may have answered this question.

Their experiments used pairs of sparrow siblings raised by humans. They simulated either a "responsive parent" (giving more food to whichever of the two birds "begged" more), or a "nonresponsive parent" (picking which bird got more food at random).

The weight gain of the baby birds (averaged over the two siblings) was 2.8 g with the simulated responsive parent, but only 2.2 g with nonresponsive (random) feeding. The difference appeared to be due to wasted food: with random feeding, twice as much food that was supplied was not eaten, presumably because it was given to a bird who was not begging because not hungry. The authors suggest that responding to begging also reduces the chance that a nestling will miss being fed often enough to affect its growth, which could happen with random feeding.

So kin selection would favor responsive rather than nonresponsive behavior. Genes for responding to begging are common because baby birds are more likely to survive if their parents respond to begging -- and the babies have a 50:50 chance of inheriting the same genes.

The same issue has an article looking at the effects of grandparents on the reproductive success of their children. In contrast to grandmothers, grandfathers that live longer don't end up with more grandchildren, at least in Finland. This seems like something that might vary among societies. But what if your grandfather is a cardinal?

Comments

As I recall, cardinals are strange birds: the female buggers off after the young fledge, and the male cares for them. Might this be a simpler solution to your observation?

Of course, the next question is: "why the males?"

I didn't know that, and that's a good question. But I mainly wondered why an adult was feeding a bird able to fly to the feeder and feed itself.

lots of birds do this. i've seen magpies and robins myself. birds grow very fast and even though they have reached (near) adult size they may not have the independence to forage for themselves. besides, it's easier for the little guy to get fed than to go find its own food. (humans do this too.)

I am glad you enjoyed our paper!

We studied younger nestlings than your cardinal fledgling, but the principle is much the same: because of their different genetic makeup (parents share the same proportion of genes with all chicks while each chick shares only 50% on average with it's full siblings) the chick is selected to beg for more resources than the parent is selected to give. This is termed "parent-offspring conflict" (Robert Trivers, 1972), and is probably the basis for the begging behavior one can observe. We have found that parents will do better when they determine food allocation according to begging intensity, than when they allocate the same amount at random. But this doesn't mean that they allocate the amount of resources corresponding to the chick's optimum. So, The adaptive decision for your male cardinal may very well be to ignore the chick - if eating the food itself will result in higher fitness gain than giving it to the chick.

Thanks again,
Uri


Uri Grodzinski

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