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Monday, May 17, 2010

Why are Baby Birds Bigger than Parent Birds?

I know the statistics show Americans have become larger over the years. So as I watch the Starlings feeding huge babies, I’m wondering if birds are getting bigger too?

What a good question? As most dinosaurs would tell us (if they weren’t extinct), there is evidence that being big can be bad for surviving. Being small has long been thought to help things survive extinction by having larger populations, greater genetic variation, shorter time to maturity, and fewer resources to suvive.
In a study done by paleontologists on a collection of bird ancestor bones approximately 65.5 million years old, it was found that there was a general increase in size for the birds in three of the four families. The big point of interest is the Ornithuromorpha, the last of these four families, got smaller over time and is the only family of birds who have members that managed to survive the Cretaceous–Tertiary extinction event.

So as Americans get bigger and stronger, I believe birds find their best chance at survival is if they stay small.

I couldn’t find any recent study on the size of birds, but based on observations of birds from the 1800’s to the present there is no obvious change in birds’ size unless helped along by farming practices.

Keep the questions coming and I’ll answer them as best I can. You can also chime in if I get something wrong.


Anonymous said...

Baby birds look bigger because of their down! Small fluffly feathers puff them out. When they mature and lose their down, they slim down to look like their parents.

Wild Birds Unlimited Mid-Michigan said...

New research has found that some birds are getting bigger. The reason for the growth is believed to be climate change, but therein lies a mystery: The birds should be getting smaller as the climate warms, not bigger.

In the study, published in the journal Global Change Biology, Goodman and LeBuhn suggested two reasons for this exception.

One is that the birds are storing more fat to counter the greater number of extreme weather events that most climate scientists link to climate change. Bigger birds can survive storms better than can smaller ones so natural selection is choosing those with bigger bodies and wingspans.

The other theory is that the birds are eating a different diet. As the climate warms, plants change as does the population of insects birds might eat. That could contribute to larger birds.