In the name of climate #12: animals are getting smaller due to the climate crisis

According to researchers, in recent decades many species of birds, fish, mammals, amphibians and plants have grown smaller due to higher temperatures caused by human activities, putting their survival at risk.

One study conducted on over 70,000 specimens of migratory birds that collided with skyscrapers in Chicago between 1978 and 2016, after recovering and preserving them, concluded that at least 50 species of common birds in North America had shrunk on average by 2.6 percentage points, and that even their bone structure had reduced: “a general reaction to climate change”, confirms the study.

There’s more: according to research from 2017, in the last six decades the “menhaden” fish, which mainly lives in the Gulf of Mexico and off the Atlantic coast of the United States and Canada, has shrunk in size by 15 percent on average. The same has happened to a species of salmon living in the Tana river in the north of Finland: in 40 years males have lost around half of their body mass, while females reduced by 10 percent.

As well as fish and birds, the trend has also been seen in mammals: researchers who analysed wild mice in Doñana National Park in southern Spain discovered that the local rodents weighed up to one third lighter than forty years ago. This phenomenon would appear to follow Bergmann’s rule, according to which warm-blooded mammals and birds are larger at lower temperatures and smaller at higher temperatures: indeed larger animals lose heat more slowly in temperate climates, while smaller ones do so more quickly in hot and dry climates.

These recent observations have been seen before: a study on fossils found that specimens of several species also grew smaller during the geologic period that began around 56 million years ago, the Eocene, when temperatures increased between 5 and 8 degrees in 10,000 years. The problem is that due to human activities the planet is warming ten times faster than ice age averages, and animal species may not have enough time to adapt without running the risk of extinction.