Birds capable of flight travel wherever and whenever they please. Compared to the land space humans have populated, there is still extensive air space within and above urban areas for birds to roam, making them one of the most noticeable aspect of nature in cities aside from insects and flora. Some flight birds also roost in elevated places much like how Singaporeans live in high-rise buildings. Might urban areas be a suitable habitat for both humans and birds?
Adapting to urban life
The broad environmental tolerance of urban bird species may allow them to adapt to human environments more easily then rural bird species (Bonier et al., 2007). Sol et al.(2005) finds that birds with larger relative brain size are able to respond better to new environmental conditions with their enhanced cognitive skills. Check out the crows in the video.
Some urban birds have been observed incorporating cigarette butts into their nests. Suárez-Rodríguez et al. (2013) finds that this reduces the number of nest-dwelling ectoparasites. However, potentially toxic chemicals in cigarette butts could harm the birds too.
Møller (2008) found that the relative flight distance of urban bird populations was lower than their rural counterparts and was positively related to the number of generations of the urban population since urbanization, “suggesting that as time has passed, urban and rural populations have diverged in terms of flight distance.”. This means species found in urban environments are not inherently adaptive but individuals of a species that can adapt to urban life are selected for. In other words, the mynas and pigeons in Singapore can tolerate close distances with humans might not be because it they are an adaptive species but because they are the descendants of individuals who can.
Change in the songs of urban birds are also observed. Patricelli & Blickley (2006) discussed the changes in the frequency, amplitude, temporal and timing aspects of urban bird songs. Birds can adjust the frequency of their songs in response to the low frequency urban noise and/or increase the amplitude or loudness of their songs but this could be limited by the size of the bird and the energetic costs of singing louder. Temporal structure refers to the timing of modulations, notes and syllables in a vocalisation which can affect ability of other birds to detect the call while timing refers to the time of the day the birds sing.
Bonier (2012) reviewed findings regarding endocrine ecology of urban birds and concluded that “The current urban endocrine ecology literature does not reveal any consistent patterns, but has demonstrated that populations of birds in urban habitat often exhibit differences in endocrine traits, particularly hormone concentrations, when compared to conspecifics in nonurban habitat.”. This shows even more changes that the urban environment can inflict on birds.
Bird in black
The common myna is considered a feral species in Australia and was declared among “100 of the World’s Worst Invasive Species” by the International Union for Conservation of Nature (IUCN) in 2000. Introduced to Canberra in 1968, they have become one of the most common feral birds in Canberra with increasing concern over their impacts on local biodiversity such as competing with native species for nesting hollows (Tidemann, 2001). In Singapore, mynas are also considered as pests mostly due to it being a nuisance to humans but locals are quite tolerant of them. After all, we do not have to clean up after them and most are not aware of the threats to local biodiversity by exotic species.
There are 2 species of mynas found in Singapore. The Javan myna prefers green patches among residential areas while the common myna prefers the rural landscape (Lim et al., 2003).
Mynas can be kept as pets and they are able to imitate sounds too. Most of us take little notice of these very abundant birds in Singapore but they are being admired and demanded in other countries.
The common hill myna (Gracula religiosa) does a way better job.
Not all benefit
In a study by Lim & Sodhi (2004) in Singapore, generally the number of native species decreases with increasing levels of urbanisation while the number of exotic species increases. Insectivorous species, shrub nester and primary excavator abundance decreased with increasing urbanisation due to the lack of food and nesting sites. Meanwhile, granivourous, frugivorous, tree nesters and secondary cavity nesters increase in abundance due to availability of food from anthropogenic sources and nest sites in tall shade trees and human structures.
Chong et al. (2012) reveals increasing abundance of bird species in Singapore over the past 10 years but many of them are exotic. This study investigated the change in bird abundance over the past decade and compared their results to another survey done in 2000-2001. The Javan myna in the study area was found to have (status: exotic) increased from 1955 to 3238. You see them everywhere in Singapore.
Some birds are able to adapt well to our urban environment and provide a tiny slice of nature for us to see. However, they are also considered pests by humans when they make too much noise, dirty places with their droppings and threaten local biodiversity. I have noticed huge numbers of mynas crowding around one or two trees making so much noise and the pavement below the tree will be covered in their droppings. Meanwhile, urban areas do not provide suitable nesting sites or proper food for many other bird species especially native species who are adapted to forests and mangroves in Singapore. With increasing urbanisation, many bird species will still be threatened as they cannot adapt to live alongside us in our cities.
Perhaps more emphasis should be placed on creating specific habitats for different bird species rather than simply greening urban areas. Birds are able to move around freely and choose places most suitable for them but in Singapore, we are only made up of islands. The mainland has mostly been urbanised and since birds do not recognise country boundaries, if they do not find a suitable habitat here, they have no other places to go except to leave the country entirely. Furthermore, urban environments can act as a force of selection that causes phenotypic and genetic divergence within bird species resulting in a sort of urban subspecies different from that of the rural population. This means we would not exactly be preserving the species in their natural or original form.
Bonier, F. (2012). Hormones in the city: Endocrine ecology of urban birds.Hormones and behavior, 61(5), 763-772.
Bonier, F., Martin, P. R., & Wingfield, J. C. (2007). Urban birds have broader environmental tolerance. Biology letters, 3(6), 670-673.
Chong, K.Y., Teo, S., Kurukulasuriya, B., Chung, Y.F., Rajathurai, S., Lim, H.C., Tan, H.T.W. (2012). Decadal changes in urban bird abundance in Singapore. Raffles Bulletin of Zoology. Suppl. 25: 181-188.
Lim, H. C., & Sodhi, N. S. (2004). Responses of avian guilds to urbanisation in a tropical city. Landscape and Urban Planning, 66(4), 199-215.
Lim, H. C., Sodhi, N. S., Brook, B. W., & Soh, M. C. (2003). Undesirable aliens: factors determining the distribution of three invasive bird species in Singapore. Journal of Tropical Ecology, 19(06), 685-695.
Møller, A. P. (2008). Flight distance of urban birds, predation, and selection for urban life. Behavioral Ecology and Sociobiology, 63(1), 63-75.
Patricelli, G. L., & Blickley, J. L. (2006). Avian communication in urban noise: causes and consequences of vocal adjustment. The Auk, 123(3), 639-649.
Slabbekoorn, H., & Ripmeester, E. A. (2008). Birdsong and anthropogenic noise: implications and applications for conservation. Molecular Ecology, 17(1), 72-83.
Sol, D., Duncan, R. P., Blackburn, T. M., Cassey, P., & Lefebvre, L. (2005). Big brains, enhanced cognition, and response of birds to novel environments.Proceedings of the National Academy of Sciences of the United States of America, 102(15), 5460-5465.
Suárez-Rodríguez, M., López-Rull, I., & Garcia, C. M. (2013). Incorporation of cigarette butts into nests reduces nest ectoparasite load in urban birds: new ingredients for an old recipe?. Biology letters, 9(1), 20120931.
Tidemann, C. R. (2001). Mitigation of the impact of mynas on biodiversity and public amenity. School of Resources, Environment & Society, the Australian National University.