For birds, drab is in fashion in our cities
Featured Image Caption: White-crowned sparrows in cities have darker, duller feathers than sparrows in the country (Image Source: “White-crowned Sparrow aka Un Piaf (In France)” by Big Grey Mare is licensed under CC BY-NC-ND 2.0).
Reference: Smith, S. H., Hessong-Brown, J., Lipshutz, S. E., Phillips, J. N., Rochefort, C., Derryberry, E. P., & Luther, D. A. (2021). Long-term changes of plumage between urban and rural populations of white-crowned sparrows (Zonotrichia leucophrys). Journal of Urban Ecology, 7, juaa038. https://doi.org/10.1093/jue/juaa038
What A Colorful World
Imagine living in a colorless world. Walking the red carpet would be lackluster. Dorothy would struggle to follow the yellow brick road to Oz. We would miss the joys of autumn colors or the bright yellow sun in an endless, deep blue sky. Luckily, our world is filled with colors that can change a mood or communicate something about us. We can choose the colors of our clothes to send a message about who we are or how we are feeling. Perhaps you decide to wear a yellow shirt because it makes you feel cheery and confident. Many animals use colors to communicate about their condition. However, animals cannot always pick and choose their coloration.
Bird feather color, for example, can communicate condition to a mate or a potential predator. Feather color can be passed down from parent to offspring but is also affected by many environmental factors, such as nutrition, hormones, and pollutants. While catching the eye of a mate with flashy colors, a bird may attract some unwanted attention from a predator in the process. Standing out or blending in is also highly dependent on the color of the background. We have drastically changed the backdrop as we continue to grow and expand our concrete jungles. Cities have traded bright greens for drab greys, nutrient-rich soils for paved streets, and fresh air for toxic pollutants. Added together, these factors significantly impact feather coloration and its relation to the background colors.
White-crowned sparrows are common in North American cities and the countryside, where the background colors differ substantially. These sparrows get their name from their white-capped heads that are contrasted by dark stripes. The so-called crown is often used as a signal of the bird’s condition and status. Much of the bird’s back is a rusty brown color that likely affects its ability to blend into the background. City pollutants and stress can cause an increase in dark pigmentation in the feathers. Lower food quality in cities is associated with duller feather color. Despite these harmful causes of darker, duller feathers, drab colors can be beneficial for city sparrows – allowing them to match the gray, uniform background in cities.
A team of researchers with lead author Shawn Smith wanted to test if white-crowned sparrows living in cities have darker, duller back and head feathers. They photographed white-crowned sparrows that were archived in California museums from 1895 to 1990. The city birds were from San Francisco, California, and the country birds were from Point Reyes (about 40 kilometers north of San Francisco) and Pescadero (about 40 kilometers south of San Francisco). The researchers analyzed the brown back and the black and white head of each bird from the photos. City birds had darker, duller backs with less complex colors than country birds, but the head feathers did not differ between city and country.
Keep it Colorful
The growth and expansion of cities present many challenges for animals that live there with us. For example, noise has become an increasing issue for birds that use songs to communicate. The findings from this study suggest that cities are also affecting the ways birds visually communicate with one another. The backs of white-crowned sparrows are darker and duller in the city, helping them blend in with the dark, dull pavement and buildings. The feather patterns were less complex in cities where vegetation was reduced and more uniform. The feathers with more dark pigment appeared to be more robust, degrading slower than light feathers. In cities with harmful pollutants, having tougher feathers is an advantage. On the other hand, the white and black feathers on the head are likely used for mate attraction, as the researchers found no difference between city and country birds.
When we rapidly change natural environments into concrete jungles, we present new and extreme challenges for native animals. While few animals – like the white-crowned sparrow – adjust to this new lifestyle, many are left vulnerable to extinction. Researchers have discovered some of the pressures that cities place on animal survival, but many are left to be uncovered. As hard as it may be to imagine a world without color, a world lacking diverse wildlife is far less fathomable.