To get to the supermarket, I walk from the apartment where we’re cat-sitting through Danehy Park in North Cambridge. Danehy Park is built on top of a landfill. It has soccer fields, baseball diamonds, a couple of playgrounds, and a few picnic tables under the trees that grow along the main bike path. There are generally quite a few people, and some dogs, in the park — not the kind of place where you’d expect much in the way of wildlife.

Yet without even looking very hard, I saw three bird nests on my walk across the park: two American Robins nesting in trees right over the bike path, and a Northern Mockingbird nesting in some shrubs right next to one of the playgrounds. I also heard a Flicker, some Common Grackles, several Song Sparrows, and several Red-winged Blackbirds — presumably, these were all males singing to define their nesting territory. It’s remarkable that so many birds could live in such a heavily developed landscape, in a limited ecosystem with apparently very little biodiversity. This made me wonder about the fecundity that I might have seen in pre-Columbian times.