Common moorhen Gallinula chloropus
It's not much of a coincidence that many of the worlds most widespread bird species also happen to thrive in cities. If an animal can adapt to many different habitats, chances are fairly good that it can adapt to urban habitats. Barn swallows, black-crowned night herons, cattle egrets, and barn owls are all found on multiple continents and in and around hundreds of the world's cities. To this list we can add the common moorhen, or gallinule. Though most comfortable in a marsh or swamp, the moorhen is happy to forage along drainage ditches and canals, and other places where urban water is maintained or mitigated. They feed on a wide variety of small aquatic animals as well as some plant foods. The one I saw at a rest stop near Heathrow was cleaning up crumbs below cafe tables.
They swim without the benefit of webs or even the flattened toe lobes that their close relatives, the coots, have. Their toes are elongated to facilitate walking across floating vegetation. For whatever reason, their range excludes the northern coasts of North America, but they can be found almost everywhere else in North and South America, throughout Europe, and in habitats in Africa, Arabia and Asia. Only very dry places, very cold places, and tropical rainforests have no common moorhens.