Certainly, a city is defined as a dense accumulation of human-made constructions-- buildings, roads, blue and green infrastructure. But are dense accumulations of constructions unique to humans? Not really.

We can think about this is in several different ways. Many animals build nests or burrows, which may be very complex structures. And many animals build their nests and burrows in dense colonies, which are sometimes very extensive. Many arctic birds—penguins and albatross, for example—live in large colonies but make no or very basic nests. These are perhaps less like cities and more like giant campsites. Other birds, like weaver birds in Africa, fill up trees with their nests. Each tree is like a village. Many rodents also build their individual burrows in colonies. For example, prairie dogs, and my favourite rodent, the Chilean degu, make “cities” of burrows that expand outwards into less-dense “suburbs” which are occupied in years with high population. Degu and prairie dog colonies also provide shelter and food for many other species, including reptiles, other mammals, and insects. When I studied degu colonies I liked to talk about the “gardens” formed on the degu’s grazing lawns. By eating the herbs that grew within the colony, the degus favoured the persistence of a diverse set of flowers, and “pruned” them into what are called rosette habits, which is when the plant grows flat against the ground in a rosette shape, rather than standing up.

The plants and animals that degus and prairie dogs live with in their cities are not exactly the same ones that we favour in our cities. There is some overlap, because both humans and other city-builders often create lots of disturbed areas, which favours pioneer plants. However, humans do not facilitate the existence of grazing-tolerant plants, or snakes living in our basements. But why not? Maybe by studying coexistence with biodiversity in other species’ cities, we could learn a few design tricks for increasing the biodiversity in our cities.

We can’t skip over insect colonies, such as termite mounds, ant nests, wasp and bee nests. Whether made of geometrical patterns in paper or wax, or by the collective action of moving tiny grains of sand or wood pulp, they are certainly amazing architectural feats. As cities, they seem sterile and functional, like the long empty, white corridors of spaceships in most space adventure films. However, there are some other species sharing these spaces, such as the fungus farmed by leaf-cutter ants, or the caterpillars of Lycaenid butterflies.

Finally, in some cases animals form cities out of their own bodies. I am thinking of coral reefs, of course. The algae- cnidarian symbiosis that makes corals forms huge colonies, which provide habitat for many fish and other aquatic species. Trees, for that matter, also each provide spaces inside their trunks, under their bark, and in their branches and leaves, for the nests of many large and small species, from squirrels, owls or oran-utans, to beetle larvae and ants.

In short, a city is a very dense “colony” of the kind constructed by humans. Although most cities look more or less similar today, made with concrete, bricks, asphalt, steel, and glass, we should also remember that vernacular architectures of the world are more varied and might accommodate different kinds of biodiversity in “human colonies” of different sizes, densities, structures, textures, porosities, etc.
If you want more information, there are numerous books on “animal architecture.” This is a classic: Animal Architecture, by Karl von Frisch. Animal Architecture Karl von Frisch

--Meredith Root-Bernstein