Humans are becoming ever more urban in their habits, yet it is only recently that scientists have attempted to quantify the impact of urbanization on levels of biodiversity around the world. One striking recent global analysis of bird and plant diversity showed just how dramatically the built environment hits birds. For every species spotted in a given urban environment, there are typically more than 10 in an equivalent area of non-urban habitat.
This might sound like a dismal statistic, but it is also an opportunity — a valuable benchmark against which improvements can be planned.
“There are many reasons why urban biodiversity matters,” said Mark Goddard, a biologist at the University of Leeds and one of the authors of the recent paper.
For a start, many of the world’s major cities are located in prime locations that are naturally rich in species and still support a significant number. Singapore is the standout example, a city in which it is possible to spot 347 native birds, of which 12 are on the International Union for Conversation of Nature Red List of Threatened Species.
In India, thanks to the reverence that Hinduism places on cows, elephants and monkeys, there is room for all these animals in even the busiest of cities. Indeed, when conditions in the countryside get really hostile, the urban environment may be the best place for animals to be.
This was probably the case for Hanuman langur monkeys during a severe drought in Rajasthan in 2000 that caused around half of the non-urban population to die off. In Jodhpur, where the animals had access to plenty of food and water, there was almost no change in the population size.
Among primates, it is baboons that do best in a human-altered world. One of the best-studied urban populations is in Cape Town, South Africa, where the Chacma baboon has been living cheek-by-jowl with humans since at least the 15th century. In spite of the increasing pressures on the wild spaces around the city, the local baboon population is estimated to have risen from 365 in 1998 to 475 in 2011.
Part of the baboons’ success is their strong social network, their unfussy diet and behavioral adaptability. In urban settings like Cape Town, baboons appear to have honed their raiding skills, zipping into densely populated areas to steal high-value human foodstuffs.
Similarly, the Barbary macaques of Gibraltar, emboldened by their friendly contact with tourists, have been carrying out forays further into human territory, raiding dustbins and running amok. Black bears in Nevada also make grub out of garbage, with urban bears far less active yet far heavier than their wild counterparts.
Even carnivores, it seems, can survive the big city, though they are probably benefiting from the abundance of rats and other rodents (which make up almost half their diet) rather than human food. In Chicago, researchers conducting the largest urban study of coyotes in the world have found these animals are more active at night, which brings them into less frequent contact with humans and traffic.
Other species have come up with different solutions to city life. There is good evidence, for instance, that urban great tits deliver their songs faster and at a higher pitch so they can be heard above the hectic soundscape. In Belo Horizonte in Brazil, black-tufted marmosets have altered their sleeping habits, carefully selecting trees that domestic cats cannot easily climb.