Darryl Jones at Culturico:
Cities are, indeed, the opposite of natural ecosystems. Net sinks of energy and materials, they are hot, noisy, poisonous and dangerous. They are constantly changing, often for frivolous or even wasteful reasons. Very few non-human species can cope with such chaos and stay away. Some species, however, see opportunities where others find only disturbance and stress. Cities offer countless productive chances for those willing and able to adapt. Those that take up this challenge share several crucial characteristics, including: already being abundant in the neighbouring landscape (10), having a generalised diet (with granivores being at a great advantage given the ubiquity of feeders)(11), demonstrating innovative foraging capacity and often belonging to groups with proportionally larger brains (12). Clearly, the latter two features go hand in hand.
One additional characteristic, however, can be regarded as a prerequisite for making the first steps into a human-dominated environment: the ability to tolerate the presence of humans.