Does size matter? Ornithologists seem to think so


Courtesy of Getty Images

Amazon birds such as the Ringed Antpipit found in Oxapampa, Pasco, Peru is one of 77 species being studied for declining body mass.

Giselle Pineda, Staff Writer

From the common ostrich at a little over nine feet tall to the Bee Hummingbird standing at two inches, birds come in a variety of shapes and sizes. However, recent research shows that birds, particularly those from the Amazon, are shrinking in physical size possibly due to climate change.

The National Audubon Society, an organization founded in 1896 with the mission to protect birds, along with various other ornithologists reported that endotherms, animals that are able to generate internal warmth like birds, are shrinking.

These animals are evolving because of significant changes in their climate. The reason scientists have linked climate change to the evolution of birds is because whenever the ecosystem’s temperature went up the Amazon birds would evolve into smaller sizes.

“Many species have lost about 1 to 2 percent of their average body weight per decade,” stated Jonathan Lambert in his article “As the tropics warm, some birds are shrinking,” which explained some of the research. 

Scientists have been tracking Amazon birds for the last four decades and several scientific observational studies point to an increase in surface temperature as the culprit for decreased body mass. These birds are not only shrinking in body but also expanding their wingspan, according to Science News for Students.

Researchers such as Vitek Jirinec, whose latest paper “Morphological consequences of climate change for resident birds in intact Amazonian rainforest” presents the research on the phenomenon.

“Longer wings may be helping [birds] fly more efficiently” and use less energy, noted Jirinec. This in turn could help the bird as temperatures rise. “But that’s just a hypothesis.”

Amazon birds aren’t the only species shrinking, however. A study from David Willard, a professor and the collections manager for the famed Field Museum in Chicago, showed that migratory birds were actually shrinking in size. He started this study by collecting deceased birds that would crash into his workplace’s windows. He began doing this work in 1978, which is why he was able to notice the significant changes in sizes. Because of this research, many scientists assume that it is not only specific species that are shrinking, but possibly all endothermic species. 

Over the course of the years, Willard was able to see changes in their sizes. The birds that he observed included a few from the Amazon, and this is how they found out they were shrinking in size. This case was able to lead scientists to the conclusion that global warming and climate change were the causes for birds shrinking in size and number.

Although climate change is seen as the key reason why these birds are shrinking by some, others believe that there are other causes besides global warming. Some believe that this is simply a universal phenomenon that is occurring naturally. It is also believed that these natural adaptations are occurring for reasons of survival from natural causes or predators. 

“The way it was explained to me and makes more sense is that evolutions are often caused by random changes that usually occur from adaptations the animals go through in order to avoid predation from larger carnivorous organisms,” said senior Kailey Keisler. “So rather than the weather causing anole lizards, for example, to grow longer limbs it makes more sense that a random genetic mutation occurred in order for that lizard to have longer limbs to better climb and grass branches to avoid predators that aren’t able to climb. I literally had a project on this and it made more sense this way than saying heat caused it.”

Central’s own Environmental Science teacher, Mr. Bartenslager, agrees with Keisler in that there may be other factors besides climate change. 

“Science doesn’t ‘prove’ things, and it’s hard to determine cause and effect without conducting laboratory experiments,” stated Mr. Bartenslager, a science teacher at Palm Beach Central. “You would need to have populations of birds raised in two different temperature settings over time to determine if an increased temperature does indeed cause body size to decrease.” 

Some have also speculated that this shrinkage could impact predator/prey relations or even cause a mass extinction of related species. In predator/prey situations, the majority of birds in the Amazon eat insects, and their predators don’t only consume them but other animals as well. Experts have concluded that there would not be a major change to the ecosystem, except for an increase or decrease in insect consumption based on the bird’s metabolism. 

This information gives rise to the question of what will eventually happen to birds that are shrinking. Although scientists have no real answer at the moment, it is assumed that the birds will either continue to shrink until they cease to exist or the evolution will stop once the birds have completely adapted to their new climate.