How many caterpillars does it take to make a chickadee?

I've been checking periodically on the bluebird nest box outside my kitchen window which a pair of Carolina Chickadees have claimed as their own this spring.

The pair chose the box early on and started building a nest and then they paused for a while, during a period in which it rained almost every day for about a week. But a week or ten days ago, they resumed construction on the nest, and yesterday, I decided it was time to check on their progress. Well, progress, indeed! Guess what I found?

  

The nest, it seems, is complete and the female had already deposited five tiny eggs there. The eggs are indeed tiny - no bigger than the tip of my smallest finger. It is hard to believe that it is possible for a fully formed chick to develop in one of them and hatch within a couple of weeks. Of course, the parents themselves are among our tiniest birds, weighing no more than a third of an ounce each. Surprisingly for such little birds, they do have fairly large clutches of five to eight eggs,  so this particular clutch may not yet be complete.

  

Finding the beginnings of this new chickadee family reminded me of a column that I read in The New York Times just about a month ago. It was by the entomologist Douglas Tallamy and was entitled "The Chickadee's Guide to Gardening." The point of his article was the importance of planting native plants in our gardens, plants that support local wildlife, including birds, by feeding the insects that they need to survive. For the chickadee chicks, this mostly means caterpillars.

Once the tiny chicks hatch, it takes them 16 to 18 days to develop sufficiently to fledge. During all that time, both parents are working as hard as they can from dawn until dusk every day to provide their growing and very hungry family with food. They bring food to the box, on average, once every three minutes all day long. Tallamy does the math and estimates that it takes from 350 to 570 caterpillars a day (depending on the size of the clutch) to keep the family fed. That's an incredible 6,000 to 9,000 caterpillars from chicks' hatching to fledging. And, with luck, at the end of that period, we have more one-third ounce chickadees to grace our world.

So, how can we help to produce all those caterpillars that chickadees and bluebirds and robins and woodpeckers and all the other nesting birds need to raise their families? We can plant trees that caterpillars can munch on without dying, and preferably without killing the tree. Oak trees, for example, are very good choices, says Tallamy. Lots of leaves there, food for caterpillars, and they are very hardy trees, impervious to a lot of insect damage. They are a much better choice than something like a Bradford pear, a non-native tree that is not so friendly to insects, and, moreover, is weak and short-lived. But the pear trees are beautiful when they bloom in the spring and lots of people plant them for that reason.

Fortunately, gardeners are becoming more educated and more aware of the interrelationships between plants and wildlife and the need to choose native plants for our gardens whenever possible. It's one of the ways that we can be better stewards of the land, better landlords for the birds that honor us with their presence in our yards.