Why do peregrines nest on buildings and bridges instead of cliffs?

“Raptors imprint on their natal nest sites.  Consequently, they choose a similar situation several years later when they reach maturity.”(¹)

This explains why they’ve chosen to nest at the Tarentum Bridge, pictured above.  The adult female, nicknamed Hope, was born on the Benjamin Harrison Bridge in Hopewell, Virginia.  That bridge is such a dangerous place to fledge that Hope was hacked in the Shenandoah Mountains, but she remembered where she was born and picked a bridge when she chose a place to nest.

There are exceptions to the natal imprint rule.  Though Dorothy’s daughter Maddy was born on the Cathedral of Learning, a 40-story Late-Gothic Revival building, she chose the I-480 Bridge in Valley View, Ohio.  I can’t think of anything less like the Cathedral of Learning than this.  (The nest is at a broken patch of concrete on the bridge support.)

The exceptions have saved at least one species from extinction.

Mauritius kestrels used to nest in tree cavities but monkeys were introduced to the island and ate the eggs and young. By the 1960’s the kestrels were down to two pairs — almost extinct — when one of the pairs decided to nest on a cliff ledge where the monkeys couldn’t reach them. That nest was successful, their youngsters nested on cliffs, and the species rebounded.

The exceptions benefit the rule.

(photo of Hope at the Tarentum Bridge (blue structure) by Sean Dicer.  Photo of Maddy’s nest site at the I-480 Bridge at Valley View (busy highway) by Chad+Chris Saladin.
Today’s Tenth Page is inspired by and includes a quote(¹) from page 444 of Ornithology by Frank B. Gill.)