A little over a month ago cliff swallows began building nests at Nature Boardwalk. These avian architects slowly constructed a small ledge under the Lester E. Fisher Bridge by using their beaks to bring back small amounts of mud from the edge of the pond.
Mud walls are built on the sides of this ledge, completely enclosing the nest except for a small entrance on one side. Upon completion, the inside of the nest is lined with feathers, and the female swallow will lay between three to six eggs. Incubation generally lasts two weeks, and both parents will take turns sitting on the eggs.
Last week we heard faint chirps coming from a few of the cliff swallow nests on the east side of the bridge. Now young cliff swallows (below) can be seen with their heads out of the entrance, not so patiently waiting for their parents to bring back food.
It takes around 20–25 days for cliff swallows to fledge, so if you want to see them, come out to Nature Boardwalk in the next week or so. We estimate that fledging will occur by August 20 at the latest.
Mason Fidino is coordinator of wildlife management for Lincoln Park Zoo's Urban Wildlife Institute.