Friends or Rivals? Prairie and Peregrine Falcons Share Pinnacles’ Cliffs

Two falcons stop visitors in their tracks at Pinnacles National Park in California: the prairie falcon and the peregrine falcon. Both raise their young on the same cliffs, and how they share — or fight over — that space still puzzles biologists. This June 2024 account comes from Gavin Healy of the San Francisco Bay Area Inventory & Monitoring Network's science communication team.

An adult female prairie falcon at her cliff-cavity nest. NPS / Gavin Emmons.

The 2024 season

Wildlife biologist Gavin Emmons has monitored the park's falcons since 2003, spending each spring with volunteers searching for nests. Falcon numbers have been fairly stable over the years.

Two prairie falcon nests had just fledged nine young, and eight more prairie falcon nestlings were still in nests. If all survived, nest success would be a little below average — yet likely better than 2023's. Winter rain patterns may affect how well prairie falcons nest.

Competing for cliffs

Both species need very particular nest sites: sheltered hollows in cliff faces, high enough to be safe from ground predators and to give a lookout over hunting grounds. Such spots are scarce, and competition for them may explain the confrontations biologists have seen. Since peregrines began nesting in the park again, Emmons has seen prairie falcons abandon cliffs where peregrines moved in, and prairie falcon numbers may be lower since the peregrines' return.

An adult peregrine falcon circling its territory. NPS / Gavin Emmons.

Or neighbors?

Yet the two sometimes nest close together:

• South Chalone Peak, 2020–2023: every year, the two species nested near each other, separated by a visual barrier. Both fledged young in 2021 and 2022; in 2023 the prairie falcon nest failed.
• Balconies, a rock formation on the park's west side, 2021 and 2022: both species defended nesting territories with little confrontation between them.

That mix of territorial rivalry and tolerance is what makes the relationship so intriguing.

Still an open question

The team doesn't yet know what it means. Peregrines have returned to nest at Pinnacles only within the last two decades, and spotting changes in trends and behavior takes years of monitoring. What is clear is that, between the two species, falcon numbers have held steady for a long time.

The park posts raptor advisories and more about its falcons on its website.

Sources

Based on "Friends, Enemies, Neither? Making Sense of Baffling Falcon Behavior at Pinnacles National Park," by Gavin Healy, San Francisco Bay Area Inventory & Monitoring Network, published by the National Park Service; rewritten in hubnx's own words.