Birds in the Amazon are adapting to climate change by getting smaller

Analysing 77 species of tropical birds in the Amazon reveals that they have all shrunk over the past 40-years and one third have developed longer wings.
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As they adapt to climate change, tropical birds deep in Brazil's Amazon rainforest are shrinking. They also develop longer wings.

Researchers analyzed data from 77 species of tropical birds over the past 40 year and discovered that they had all lost body mass. Some species experienced a loss of nearly 2 percent per decade. One third of the species examined also had longer wings.

The landmark 2019 study of birds that crashed into buildings in Chicago, Illinois found that they had lost weight and increased their wingspan over a period of 40 years. However, these birds were migratory. Researchers examined the records of 15,000 nonmigratory birds that lived in a tract of virgin rainforest just a few hours from Manaus, north-west Brazil to determine if the change was due to seasonal migration or changes in latitude.


Vitek Jirinec, a researcher at California's Integral Ecology Research Center, said that the findings were consistent with climate change.

Today's average temperature is 1.65degC higher in the dry season than it was in 1966. The weather patterns are more extreme with 13% more rain falling during the wet season, and 15% less during the dry season.

Continue reading: How to save biodiversity and the climate while simultaneously saving the planet

Extremely dry or wet seasons saw birds lose more mass. This could be due to short-term changes in their environment such as decreased rainfall that causes a decrease in the number and quality of insects the birds eat. The difference in wingspan and wing-to mass ratio was significant in one-third of the species. This suggests that the changes could have been more complex and long-lasting than just temporary.

Jirinec says that mass is an indicator of bird's body condition. You would expect them to lose weight if they don't eat enough. Why would they need more energy to fly?

Higher latitudes are more favorable for mammals and birds of the same species. The leading theory is that their smaller surface-area-to-volume ratio allows them to better conserve heat. Jirinec says that the reverse would allow smaller species to cool in hot climates and could explain why birds become smaller with increasing temperature.

The dramatic physical changes that have occurred in just four decades prove why stopping deforestation won't stop the continuing extinctions of animal species around the globe, according to Camila Gomez (ornithologist at Alexander von Humboldt Biological Resources Institute, Colombia), who studies evolutionary changes within birds.

Gomez says, "This study clearly demonstrates how human-induced climate alterations are having far-reaching consequences on biodiversity, even within pristine areas such as the heart Amazonia." These observed shifts are without doubt contributing to the observed decline in population of tropical birds and altering how these ecosystems function at its core.

Journal reference: Science Advances, DOI: 10.1126/sciadv.abk1743