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Global Study on Bird Colouration and Urbanisation
Successful urban birds sport different colours from unsuccessful ones
Context:
Juan Diego Ibáñez-Álamo (University of Granada) and Kaspar Delhey (Max Planck Institute) launched a study to explore how urbanisation affects bird colouration. Previous studies mostly focused on urban noise and its impact on bird communication, but little attention was given to how urbanisation affects appearance.
Study Details
- The study analysed colour data from nearly all bird species worldwide.
- Urban environments were found to be colour-diverse, challenging the urban colour homogenisation hypothesis (the idea that cities cause birds’ colours to become more uniform).
- The research was published on April 4, 2024, in Ecology Letters.
Unexpected Findings
- Colourful Birds Thrive in Cities: Contrary to prior expectations, the study found that bird species thriving in urban environments tend to be more colourful, especially in shades of blue, grey, and black.
- Brown Birds Struggle: Species with predominantly brown plumage, which are considered cryptic or camouflaged, tend to be less successful in urban areas.
Colouration and Ecological Factors
- Sexual Selection: Male birds typically have brighter colours to attract mates, while females are more cryptic to avoid predators while nesting.
- This difference is not significantly reduced in urban settings, contrary to prior beliefs.
- Colour Variations: Bird colour varies globally based on climate, habitat, diet, migration patterns, and mating systems.
- Some colours (e.g., red, yellow) come from carotenoids in food, while black/grey shades result from melanin.
Brown Plumage and Its Decline
- Brown as Cryptic Colour: Brown birds are usually found in forest understory, blending with the natural surroundings.
- However, in cities, brown becomes less effective because of the presence of concrete and asphalt.
- Urban environments, with their complex backgrounds, provide less camouflage for brown birds, which could explain why they are less common in cities.
Why Colourful Birds?
- Predation Risk: In urban settings, predation pressure may be lower, allowing birds to display more colourful plumage. This reduced risk may encourage more expressive colours.
- Food and Resources: Availability of food, light conditions, and nesting space all interact with plumage colour, influencing which birds thrive in urban environments.
Urbanisation as an Evolutionary Force
- Cities as Evolutionary Labs: Urbanisation is slowly pushing evolution in new directions, influencing not just bird songs but also plumage colours. This dynamic provides valuable insights into species’ adaptability.
- Biodiversity Implications: As biodiversity decreases globally, understanding urban wildlife and its adaptability is crucial. The study highlights the ecological and cultural significance of wildlife in cities.
Next Steps in Research
- Future Research: The study is only the beginning. Researchers aim to explore whether other organisms, such as insects and mammals, show similar patterns in urban environments.
- Arthropods, for example, are highly diverse and could follow similar trends.
Implications for Urban Wildlife
- Urban Avian Beauty: Contrary to the belief that cities are grey and lifeless, they host a unique form of avian beauty with diverse bird colouration.
- Cultural and Ecological Value: As cities continue to grow, understanding how urbanisation influences species’ traits can help create environments that are more hospitable to a broader range of species.
