Urban ecology

I was walking near the edge of town when I flushed a pigeon-sized bird. I would have ignored it except the brown streaking suggested raptor. I watched as the juvenile sharp-shinned hawk rose over the branches of the lone white pine in the Agway parking lot, which was adorned with cones.

Often humans forget that the non-human denizens of the city are also growing, reproducing, and striving all around them. This is a small city, but it’s definitely an urban island among forested hills. The boundaries between urban and rural are a lot more porous in reality than in our heads. Also on my walk I saw bright rose hips where months ago there were roses; and larches, which are the one of the few deciduous conifers, with yellow needles ready to fall. Today I watched a squirrel bring a leaf to a drey (squirrel nest) built in a tangle of ivy growing up a building. I’ve seen deer prints mingling with student tracks at the university on the hill.

But the doors aren’t wide open. By their nature, islands exclude certain immigrants while favoring others, and urban islands are no exception. Rats and mice could never have survived a transoceanic journey before there were boats. Far-ranging sea birds, or migrating birds flown off course, could eventually discover distant islands on their own. The hazards of the city are mostly within – cars, road salt, lawnmowers, pesticides, heat absorbed by the roads and buildings, construction, etc. The face-paced lifestyle may be incompatible with the slow maturation of trillium, but it’s well suited to the fast maturing and rapidly reproducing dandelions.

The trillium which grows in our forest is native to North America, while dandelions are native to Europe. The city is a melting pot for more than just humans. North American gray squirrels mingle with European starlings and pigeons. Those same squirrels can be found in England, where they negatively affect native red squirrels. Of all the species making up the great diversity of life on Earth, only a fraction really excel in the urban environment with its stress and disturbance yet abundant waste and lack of competition. These hardy species are often transplanted far from their original home, either purposely or accidentally. The city is the McDonalds of ecosystems, with many of the same species found regardless of whether you are in Honolulu or New York.

But any community is at its core a group of individuals responding individually to the unique set of variables that makes up their niches. So while sharp-shinned hawks are still restricted to North America, some have discovered a winter food source in the feeder birds and house sparrows of the cities. The birds still need forests for breeding, and therefore aren’t permanent residents, but they are one of many species which make up our urban ecosystem.