Mixed Success for Breeding Falcons as 2020 Season Ends at Pinnacles National Park

Prairie falcon male adult making an aerial food delivery (of western meadowlark prey) to a recent fledgling, at South Chalone Peak. This year, four prairie falcon pairs fledged a total of 14 young at Pinnacles National Park.

NPS / Gavin Emmons

July 2020 - Prairie and peregrine falcons have finished nesting for the 2020 breeding season at Pinnacles National Park. As a result, the park has lifted its raptor advisories for the remainder of the year. Only a partial closure is still in effect at Machete Ridge. Raptor biologist Gavin Emmons and a team of volunteers kept track as a combined total of 22 young falcons fledged from cliff cavity nest sites across the park. For prairie falcons, it was a below-average year, while for peregrines, it was their best year yet. The monitoring team also tracked 34 nests from nine other raptor species.

Of the nine prairie falcon pairs occupying territories, seven nested, and four successfully fledged 14 young. That’s a bit below average across the board, but especially in terms of fledgling numbers. Over the past 35 years of monitoring, prairie falcons have raised an average of nearly 26 fledglings per season. Nestling predation, perhaps by ravens or great horned owls, is a likely culprit for two of the three prairie falcon nest failures this year, although Gavin can’t totally rule out other factors like rodenticide exposure.

Meanwhile, peregrine falcon pairs occupied four territories, and set their first record of the year when all four pairs nested. One nest failed, but the other three pairs fledged all eight of their known nestlings, setting another monitoring program record. Peregrines have been making a comeback in Pinnacles ever since 2004, when a pair returned to the park for the first time following their extirpation in the 1950s due to DDT.

In other raptor news, this year’s noteworthy nesting pair of white-tailed kites successfully fledged three young despite low availability of their preferred prey (California voles) in the park. Later, the monitoring team discovered those fledglings flying with two additional kite fledglings. Perhaps not one, but two white-tailed kite nests succeeded in the park this year! Also exciting is that five Cooper's hawk pairs nested in the park, four of which fledged young. These forest hawks are important to document because they are sensitive to disturbance. They’re also tracked as a species of concern by the California Department of Fish and Wildlife.

For more information

• Pinnacles National Park Raptor Advisories
• Pinnacles National Park Raptors webpage
• San Francisco Bay Area Network Prairie and Peregrine Falcon Monitoring webpage
• Pacific Coast Science & Learning Center Prairie & Peregrine Falcons webpage
• Contact Raptor Biologist Gavin Emmons

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