Song birds are shrinking

Bergmann’s rule posits that populations and species of larger sizes are found in colder regions while in warmer regions species are smaller.

A study published yesterday in the Journal Ecology Letters reports that over the pervious four decades there has been, on average, a 2.4 percent decrease in the size of the length of the tarsus bone, a standard marker for bird size,  in a sample population of over 70,000 birds from 52 species. The changes in tarsus length were correlated with the increase temperature. The lead authors of the study suggested two explanations for the decrease in body size.

“The first is developmental plasticity, in which individuals that mature in warmer temperatures tend to develop into smaller adults,” Weeks explained. “The second is natural selection, in which smaller birds tend to do better — in survival, reproduction, or both — in warmer temperatures, leading to a shift in the average size of individuals in a population.”

In addition, the study found consistent increases in the wing length of 1.3 percent in 40 of the species. The reason for in increase in wing length is unclear  but the authors hypothesized that increasing wing length may represent a compensatory adaptation to maintain migration as reductions in body size have increased the metabolic cost of flight. Like many of the consequences of climate change, the changes measured in bird size, are not perceptible to the naked eye.

There is a good summary of the study here by the Audubon society.

Click any image for slide show.


24 thoughts on “Song birds are shrinking

  1. Interesting stats; evolution and adaptation are ongoing all around us. Of note, human life expectancy has dropped. Might not be such a bad thing after all.
    Love your bird portraits, a panel of good friends. 🙂


    1. Hi Eliza, i did hear human life expectancy is going down and being driven by things like suicide, depression and alcohol. Seems that while birds may be adapting to their environment to a small degree humans, at least in our industrial-developed western cultures, are not.


          1. I read mostly science fiction, and while some of it tends to to apocalyptic the book I’m currently reading has a more optimistic tone. Birds are still singing on earth.


          2. It would be nice to have a few science fiction movies depicting the earth and humanity if climate change marches on at full speed. Both positive and negative. We need the humanities to combine with real science.

            Liked by 1 person

    1. Thanks, and thanks for the link. I think the only way humanity will come to realize the effects we are having on the planet is by combining the sciences with the humanities in a way that humans can directly relate to such as the art-based approach you linked to. Thanks for the link and we will check out the site.


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