In 2019, a group of American scientists analyzed more than 70 thousand birds of 52 species. In general, since 1978, their mass and size have decreased, and the tarsus (the bone in the lower part of the limb) has decreased by 2.4%. The wingspan has increased by 1.3%. The researchers suggest that the cause of the changes is global warming, and their consequences can be extremely harmful to the planet.
Scientists already know that global warming affects animals in different ways: from changes in the distribution of some species tochanges in the color of others. However, now it is the turn of one more value – size. In biogeographythere is a Bergman rule: among similar species of warm-blooded animals, the larger ones are those that live in colder climates. This is logical: it is easier for large animals to keep warm, and for small animals it is easier to cool down when it is hot. The reason is the ratio of the size of the animal’s body to its surface area. Likewise, one large piece of ice in a glass will take longer to melt than several small cubes. Accordingly, when the climate gets hotter, animals gradually shrink in the process of adaptation.
Not only birds
Let’s go back to the animals. It’s not just the birds that are shrinking. The same patterns were revealed in the analysis of populationsdeer ,rodents ,insects andfish . A 2017 study, for example, found that over the past 65 years, the average body size of Menhaden – a small fish from the Atlantic Ocean – has decreased by 15%. Moreover, fish do not have warm blood, so Bergman’s rule does not apply to them. Whereinthe reason for their shrinkage is still global warming. Because of it, frogs develop abnormally quickly and eventually grow smaller.
A similar thing has already happened in the history of the planet. About 56 million years ago, at the turn of the Paleocene and Eocene,there was a sharp warming. In just 10 thousand years, the average temperature increased by 5-8 ° C. During this period, many species, including mammals,decreased – the researchers noticed this by measuring the teeth of the fossil. However, it is worth remembering that the problem with climate change caused by human actions is not in warming itself – such processes are characteristic of the history of the Earth. The danger lies at an unprecedented pace. By 2040, the planetwill be 1.5 ° C warmer compared to the middle of the 19th century. After that, the sharp rise in temperature will only continue. We heat the earth tenfoldfaster than standard processes.
The real danger
Animals simply do not have time to adapt. For many species, body shrinkage translates into fewer offspring. For some ectothermic organisms (receiving heat from the environment), including amphibians, their small size complicates their ability to survive in drought – the body surface shrinks, respectively, water is absorbed in smaller quantities. However, the most harmful consequence is the disruption of food chains. For example, if a predator shrinks more slowly than its prey, it must eat more to get full. ByAccording to biologist Jennifer Sheridan, “if all animals were reduced at the same time and the same, there would be no problem.” The main danger is inconsistency. To prevent this, it is necessary to take decisive measures to combat global warming.