North American birds are shrinking

ANN ARBOR, MICHIGAN — New research has found that tens of thousands of North American birds have become smaller in size since 1978.

Scientists examined 70, 716 dead birds — 52 bird species in total — that crashed into skyscrapers in Chicago.

The study, published in the journal Ecology Letters, found that 49 of these bird species had a reduction in the length of their lower leg bone by 2.4 percent.

Meanwhile, the average wing length of birds saw an increase of roughly 1.3 percent.

The authors of the study suggested that a change in the birds' size may be a response to rising temperatures caused by climate change.

They added that the birds may have evolved to have a wider wingspan to compensate for their smaller bodies and to help them migrate long distances.

Scientists said that animal species tend to be smaller in warmer regions and larger in colder regions. This is to help animals carry less heat in hot areas while those in colder areas need a larger body size to conserve warmth.

The researchers plan to use the data to look at the mechanics of how a birds' body changes in shape and size, according to CNN.

They also plan to examine whether the change is a result of developmental plasticity — an animal's ability to change its own development as a response to the changing environment.