Amazon birds shrink but grow longer wings in sign of global heating

A study found that Amazonian birds are shrinking but having longer wings. Scientists believe global warming is the reason.
Recent papers have reported that birds are becoming smaller. However, because the subjects were migratory birds, there were many factors that could have explained these results. These include hunting, pesticide use, habitat loss, and even hunting.

This new study was done on non-migratory birds living in virgin rainforest. The results were identical: birds are becoming smaller and the warm climate is the only variable.

The research was conducted at the Amazon Biodiversity Center near Manaus in the Brazilian Amazon. Scientists have used the remote area since the 1970s as a test site to study the impacts of development and deforestation on the ecosystem.

Scientists have captured and examined birds in the region for generations using a consistent method: they use mist nets to catch them, weigh them, and measure their wings.

Manmade climate change has caused birds to appear to shape-shift in remote areas of the Earth. Vitek Jirinec

Scientists have found that almost every non-migratory bird species has decreased in size over the past 40 year, according to data gathered from 77 species. A third of them have longer wings.

Researchers believe that global warming is responsible for the morphological shift. The region has experienced a temperature increase of 1.65C during the dry season, and 1.0C during the wet season since 1970. The wet season is becoming wetter, while the dry season is getting drier.

Vitek Jirinec (lead author), Philip Stouffer, his advisor, and others published a paper last year reporting declining populations in nine non-migratory bird species at the control sites. They concluded that climate was the sole factor responsible for the observed changes.

The majority of birds found in the paper, which was published in Science Advances is located within a few kilometers. However, the researchers discovered that some species had decreased by almost 10% in 40 years of measurements.

Jirinec of the Integral Ecology Research Center (California) said that changes in temperature or precipitation, or both, must be a part of the findings.

How can climate change affect the avian body? Bergmann's rule, a 150-year-old principle that explains why avian bodies are changing is one explanation. This rule states that closely related organisms tend to be smaller when they are closer to the equator. It is believed that larger bodies retain heat better.

Vitek Jirinec and an Amazonian motmot. Photograph by Vitek Jirinec

Jirinec's paper suggests that the Amazon could be experiencing the same phenomenon: smaller bodies are being caused by increased temperatures.

Scientists believe the increased wing length is more mysterious, but that birds may need to fly farther. The scientists were not sure if the changes were due to evolutionary pressures, which could have led to individuals with more successful breeding or if the birds were simply changing their shape to adapt to the new environment.

Jirinec wonders if the same pattern could be occurring elsewhere. He said, "Who knows where this could be occurring?"

Mario Cohn-Haft is an ornithologist with the National Institute of Amazonian Research Institute (Manaus). He says the research concerns him. It also gives him reasons to be amazed at the genius of nature. "It's amazing to imagine birds adapting to changing environments," he said.

Cohn-Haft stated that despite these concerns, there was still room for optimism. He suggested that now-sedentary species could migrate to better habitats if their wings were longer. He suggested that they might not be the passive, sitting ducks we had imagined.