Leafy Cities

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I received a question the other day from a fellow who lives in Ontario, Canada. He said that while walking around his town’s leafy downtown he noticed lots of birds but when he walks the nearby woods he doesn’t notice nearly as many. He wonders what’s going on.

The key to his question is “leafy downtown.” Some birds are quite at home in a well vegetated city or suburb. Robins, some sparrows, chickadees, nuthatches, woodpeckers, blackbirds, starlings, etc. In fact, the population of these city-adaptable birds is on average 30% higher in the city than in the adjacent woods.

In the London suburb of Lewisham, the ten most common birds are the House Sparrow, Wood Pigeon, Blue Tit, Rock Dove, Eurasian Starling, European Blackbird, Goldfinch and Robin, the Great Tit, and the Common Magpie. In the Chicago suburb of Willowbrook, they are the Blue Jay, Black-capped Chickadee, White-breasted Nuthatch, American Robin, Mourning Dove, House Finch, Ruby-throated Hummingbird, House Wren, Northern Cardinal, and Common Grackle. And many less common species are found in both areas.

Cities can be busy and noisy places. To make a living in such an environment birds have to deal with traffic, noise, toxic substances, artificial lights, domestic pets, unusual food sources, and the less than happy apartment dweller who abhors bird droppings on the windowsill. But across the world, over 2000 bird species make cities their home for some of their life. The density of a city-dwelling bird species includes the geographic location of the city, its age, climate, and topography; the most influential factor is the amount of the city covered by urban structures. The more buildings there are in an area, the fewer birds there are; conversely, the more vegetation in a city, the more species of birds. See The Impact of Urbanization on Birds.

Manhattan’s Wall Street or downtown Detroit are not bird friendly places, but why would a city of any sort be attractive if it just added flora? Well, the urban structures provide more places to nest – ledges, edges, gutters, nooks and crannies on and between buildings. And there is more food. People and their activities discard food scraps which attract insects. An abundance of food and places to nest allows the birds to have smaller territories and so more territories can fit in a given space. And with so many physical niches, there are more places to hide from predators, especially cats.

There are more cats in the cities and suburbs. But studies have shown that birds more easily escape from cats in the city simply because there are more hiding places nearby. Birds even learn to let the cats approach them more closely in the city because they know shelter is nearby.

And lights. One would think that lights would deter birds. On the contrary, lights provide more time for finding food. A study in a couple of cities in Austria found that European Blackbirds averaged more broods in the city than in the nearby forests because they had more time to forage.

But vegetation is necessary, not only to provide even more food and shelter, but to make the birds more comfortable. They evolved with vegetation and still depend on it. So, urbanization isn’t all bad, but the message for us bird lovers is that we need a leafy downtown.

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