Tuesday, April 10, 2007

A problem for the penguins, and where did the sparrows go?

A couple of nights ago, I was watching last year’s extremely popular documentary, March of the penguins. It was bitter-sweet, watching the emperor penguins struggle to make it inland, struggle and take care of their one single egg, struggle and bring up their one single chick, and hard to watch the many chicks that died due to the cold, or lack of food, or predators.

For a moment, I sat up wondering….if a pair of penguins mate just once a year, and have just one chick, and a huge bunch of chicks die, how come the penguin population is still slowly increasing?

And then I smacked my forehead, since the answer was obvious.

So, reader smarter than an eighth grader, here’s the question from middle-school hell. If emperor penguins mate once a year, have one chick each, and there is (exactly) an 80% mortality rate (meaning the chicks die) before the chicks reach adulthood, what must happen in order to ensure that the penguin population remains stable or increases? The answer will be a precise number.


Yesterday, I saw this big, fat sparrow. It was almost big enough to be a pigeon. But that just reminded me of my childhood, and the dozens of sparrows I would see everywhere, in and around my hometown of Bangalore, as well as in Chennai or Hyderabad or other cities I would spend my holidays in. There were sparrows everywhere, and they were perhaps the most common birds in the cities after the ubiquitous crows and ravens. We even had a pair of sparrows try to breed in a rain pipe on our terrace once.

But the last few times I’ve visited India, I can hardly see a sparrow. Perhaps there are none left in the cities.

Where have they all gone? Are our modern houses, which have no nooks or corners for the birds to nest, little disasters for the birds? And why don’t (the few) gardens in Indian cities (both public parks as well as residential yards) have any birdhouses or broken pipes or something the sparrows can nest in?

The cities were a nicer, livelier, more welcoming place with the sparrows around.


Anonymous said...

Well, penguins mate just once a year, but my guess is that it's once a year, /every year, rwww.adight?

Sunil said...

yes ofcourse, they come back every year.....and that is only part of the answer. This is a math question, remember :-)

So.....if 80% of the chicks die every year, and of course not all adults come back the next year (being eaten by seals and whatnot), what else needs to happen, for the population to actually increase??

Anonymous said...

are you hinting at gender balance by any chance? There has to be an exactly equal number of male and female penguins

Unknown said...

Increase due to kids >= adult death rate => steady or increasing population

Assuming equal proportions of males and females, there would be 50 kids born for every 100 adults of which 10(20%) would live. Therefore less than 10 adults must die on an average, each year.

Sunil said...

anonymous....gender imbalances (with a slight preference of females over males) play a small role in this, but not the major role.

yhac...you're absolutely right. If 80% of the chicks die, it pretty much has to mean that the adults have to have a very good survival rate. That's really interesting, since you would think there are plenty of seals etc preying on penguins, and the death rate would be higher. So, clearly, the penguin population has to be so large that a 10% kill rate is sufficient penguins being eaten by a lot of seals. And limited deaths due to other natural factors and age. So, it looks pretty good for you if you are an adult penguin!