Urban wildlife

Urban wildlife is wildlife that can live or thrive in urban environments. Some urban wildlife, such as house mice, are synanthropic, ecologically associated with humans. Some species or populations may become entirely dependent on humans. For instance, the range of many synanthropic species is expanded to latitudes at which they could not survive the winter outside of human settlements. Other species simply tolerate cohabiting with humans and using the remaining green spaces, in some cases gradually becoming more accustomed to the new habitat over time and eventually synanthropic. These species represent a minority of the creatures that would normally inhabit an area. For example, a 2014 compilation of studies found that only 8% of native bird and 25% of native plant species were present in urban areas compared with estimates of non-urban density of species.

Urban wildlife can be found at any latitude that supports human dwellings - the list of animals that will search human trash within settlements runs from tropical monkeys to polar bears in the Arctic.

Different types of urban areas support different kinds of wildlife. One general feature of bird species that adapt well to urban environments is they tend to be the species with bigger brains, perhaps allowing them to be more adaptable to the changeable urban environment.

Urban environments can exert novel selective pressures on organisms sometimes leading to new adaptations. For example, the weed Crepis sancta, found in France, has two types of seed, heavy and fluffy. The heavy ones land near the parent plant, whereas the fluffy seeds float further away on the wind. In urban environments, seeds that float far often land on infertile concrete. Within about 5-12 generations the weed has been found to evolve to produce significantly more heavy seeds than its rural relatives. Among vertebrates, a case is urban great tits, which have been found to sing at a higher pitch than their rural relatives so that their songs stand out above the city noise, although this is probably a learned rather than evolved response. Urban silvereyes, an Australian bird, make contact calls that are higher frequency and slower than those of rural silvereyes. As it appears that contact calls are instinctual and not learnt, this has been suggested as evidence that urban silvereyes have undergone recent evolution so as to better communicate in noisy urban environments.

Some urban species have a cosmopolitan (i.e. nonselective) distribution, in some cases almost global. They include house mice, cockroaches, silverfish, black rats, brown rats, house sparrows, rock doves and feral populations of domestic species.

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