Mrs. Gould’s sunbird (Aethopyga gouldiae), which is found in Southeast Asia. Image by Jason Thompson via Wikimedia Commons (CC BY 2.0).
Alexander von Humboldt (1769-1859) was a German naturalist and geographer. He explored North and South America in the 1800s. He observed, measured, and described many plants, animals, and geographic features.
On his travels, von Humboldt noticed that animals appeared much more colorful in the tropics – regions near the equator – than in temperate and polar regions. Other naturalists observed the same thing. Proving that tropical organisms are more colorful has been challenging. But new technology is helping scientists confirm this observation.
Scientists examine coloration in tropical and temperate birds
A group of scientists from England and Hungary wanted to find proof that tropical birds really are more colorful than their temperate cousins. To do this, they used special imaging technology to examine the colorfulness of birds.
For this project, the scientists chose to study a group of birds called the passerines. Passerine birds are also known as perching birds because their feet are adapted for perching on branches. Passerines make up 60% of all known bird species. Sparrows, finches, and warblers are some types of passerines that you may know.
The scientists photographed males and females of more than 4,500 bird species from around the world. They used special techniques to measure feather color on each bird. Their total dataset included more than 36 million measurements!
A black-chinned mountain tanager (Anisognathus notabilis), a bird endemic to the high-altitude forests of Colombia and Ecuador. Image by Andy Morffew via Wikimedia Commons (CC BY 2.0).
What did the scientists find out?
After analyzing their data, the scientists found that tropical birds are indeed more colorful on average than temperate birds. Passerine birds from the forests of the Amazon, West Africa, and Southeast Asia are on average 30% more colorful.
This research confirms what Humboldt and others suspected 200 years ago. Birds really do come in a much broader range of colors in the tropics.
Banner image of a painted bunting (Passerina ciris), a bird native to the forests of Central America. Image by Andrew C via Wikimedia Commons (CC BY 2.0).
Why are tropical birds so colorful?
There are several possible reasons that tropical birds are more colorful than their cousins in temperate latitudes. One reason may be from pigments in the fruits that tropical birds eat. Rainforests like the Amazon have an abundance of fruits like mango and acerola cherry that are rich in carotenoids. Carotenoids are a group of yellow, orange and red organic pigments.
Birds cannot produce carotenoids that give them their bright colors – they must eat them. The diversity and abundance of tropical fruits found in the tropics may result in more colorful birds there than in colder climates.
Birds may not be the only animals that are more colorful in the tropics than in other parts of Earth. This color pattern may also exist in fish, insects, and flowers. Scientists are still working to understand the interesting color patterns of animals around the world.
Citation:
Cooney, C.R., He, Y., Varley, Z.K. et al. Latitudinal gradients in avian colourfulness. Nat Ecol Evol 6, 622–629 (2022). https://doi.org/10.1038/s41559-022-01714-1
