- Urban avifauna is dominated by generalist species while the specialists are on a decline, finds the study.
- Certain bird species in cities are smaller in size compared to their counterparts in non-urban areas, are stressed and are more aggressive in nature.
- City planners need to rethink design, protect patches of native vegetation and water bodies to preserve the bird diversity in cities.
Eat everything, nest anywhere and be like Beyonce when singing for a companion. If a city bird were to give a country bird the top 10 survival techniques in a city, the first up on the list would be to not be a picky eater, followed by lowering nesting expectations and working on developing the vocal range. Omnivores have a higher chance of surviving in a city where the food sources are not so diverse but abundant, says a study by scientists to determine what traits influence bird survival in a city.
The scientists reviewed 226 papers that were published between 1979 and 2020 and aggregated information on five major groups of bird traits from around the world that have been widely studied: ecological traits, life history, physiology, behaviour and genetic traits. “There is a growing interest in bird watching among people which has sparked a citizen science movement to monitor birds around the country,” said Kulbhushansingh Suryawanshi, a scientist at Nature Conservation Foundation and Director, India Program of Snow Leopard Trust, who co-authored the study with researchers Swaroop Patankar, Ravi Jambhekar and Harini Nagendra.
Suryawanshi said that the State of India’s Birds Report published a year ago found that half of the 867 species that were assessed showed a decline over the past two decades. Since India is rapidly urbanising, there is a push from the central government to make our cities into ‘smart cities’. “We know very little about how these changes will affect bird diversity and abundance. This is an early effort to work in that direction,” he said.
One of the key findings of the study is that generalist species dominate the urban bird community while specialists show a decline in number. This could be due to a lack of specific food and shelter resources in urban areas, suggest the authors of the study. Certain cultural practices seem to influence the population of some species. For example, in India, the tradition of grain merchants to give a small portion of their goods to granivorous birds for good luck or meat being offered to scavenging birds as a religious practice in Delhi could favour the population of certain bird species like black kites (Milvus migrans) and house sparrows (Passer domesticus).
Birds need to adapt, have limited nesting choices
Be it humans, animals or birds, adaptability seems to be the key characteristic that makes city life enjoyable. The study found that those species of birds that make cities home are highly adaptable and get used to human activity and the perils of urbanisation. “The key differences (city bird vs country bird) are those which help them survive in cities. These include loss of fear of humans, neophilia, which is the willingness to explore novel food resources, higher aggression towards other species, change in song structure, higher clutch sizes etc.,” said Swaroop Patankar of Azim Premji University who co-authored the study. She, however, said it would be wrong to generalise these changes as different species differ, according to their inherent characteristics.
Not just their diets, nesting choices too play a part in determining how well birds adapt to urbanisation. Birds that use a variety of nesting strategies like nesting on artificial structures like buildings are more likely to do better in urban areas as compared to birds with specialised nesting preferences, stated the study. Birds that nest on-ground are the most affected by urbanisation while those that nest on high trees and in tree cavities have a better chance of survival in cities.
City birds sing louder and at more opportune times
Another striking survival trait of urban birds is the altered frequency and amplitude of their songs. In urban areas, low-frequency noise levels like that of traffic are high. This noise masks bird songs resulting in poor song transmission and hence, poor reproductive success. Urban birds are seen to modify song and call structure to overcome the hurdle. While some bird species sing at a higher frequency in areas with high anthropogenic noise levels, some other species like great tits and Eurasian blackbirds increase the amplitude of their songs, a phenomenon called “Lombard effect”, in order to be heard above the city noises. On the other hand, birds like European robins (Erithacus rubecula) choose to sing in the night to avoid song masking, says the study.
Physiologically too, urban birds seem to differ from their rural counterparts. Reduced body fat and larger brain size are some of the distinctive features of certain urban bird species, according to the review. And surprise, surprise! The city birds are as stressed as the humans if the increased level of plasma corticosterone hormone (CORT) secretion in some of the birds is any indication. An increase in the clutch size and brood size has also been noticed, perhaps to overcome the losses that occur during predation or the effects of urbanisation, such as mortality caused due to collision with cars or windows.
“The species which stand to lose the most from urbanisation are highly habitat-specific species like hornbills, which require mature forests with large trees for survival and lark and pipit species, which require grassland habitat,” said Patankar adding that some species of hornbills do differently. “Indian grey hornbills are seen to thrive in urban areas where there are large old trees present, as they make their nests in the trunk cavities of these trees,” she said.
So who really are the birds of a feather slaying the city life? Researchers said that black kites, rock pigeons, mynas, and house crows are found to be adapting well to city life. Certain species of flycatchers and warblers or garden birds like tailorbird, prinias and munias prefer to occupy urban green spaces. “Frugivores such as rose-ringed parakeets and barbets are doing well in cities that have fruiting trees and old trees which provide nesting and roosting habitats. So are the pelicans and painted storks and some species of ibises in managed urban wetlands. Peacocks are doing well in peri-urban landscapes. Barn owls are also successful in cities. They are also doing an important service by preying on rodents,” said Suryawanshi.
Plan cities better to support biodiversity, say researchers
Various ecosystem services that the birds provide apart, one can’t deny that it is magical to wake up to bird songs whether you are in a city or a village. If Indian cities were to harbour diverse species of birds, said the researchers, we need to maintain those remaining patches of native vegetation and small lakes and ponds and control urban predators of birds such as dogs, cats and rodents. “City planners need to understand the importance of designing suitable urban green spaces, which are not just aesthetically pleasing, but also support biodiversity,” said Patankar.
She said that manicured lawns, ornamental plants and trees will not do the trick but more fruiting and flowering trees and trees which provide good nesting sites as banyan (Ficus benghalensis) and peepal (Ficus religiosa) will. Another city design that is hurting the urban birds is the use of tinted glass windows on buildings—flying birds see their reflection in them and try to attack which leads to serious injury. “Protecting patches of native vegetation and water bodies is perhaps the most important thing that city planners can do,” said Suryawanshi adding, “Very often we see lakes and parks getting ‘developed’ where native vegetation is replaced with exotic plants and green lawns. This needs changing. Citizens need to use these spaces, but the vegetation that gets planted should be native and designed in a way to help maintain biodiversity.”
Patankar, S.; Jambhekar, R.; Suryawanshi, K.; Nagendra, H. Which Traits Influence Bird Survival in the City? A review. Land 2021, 10, 92. https://doi.org/10.3390/land 10020092
Banner image: Frugivores such as rose-ringed parakeets and barbets are doing well in cities that have fruiting trees and old trees which provide nesting and roosting habitats. Photo by Mittal Gala.