20 Falcon Fledglings Take Flight at Pinnacles in 2024, Despite Challenges

By Science Communication Specialist Jessica Weinberg McClosky, San Francisco Bay Area Inventory & Monitoring Network

Peregrine falcon female adult calling defensively from territorial perch. Early in the season, the monitoring team found a very normal 12 pairs of falcons claiming territories—eight prairie falcon and four peregrine falcon pairs.

NPS / Gavin Emmons

July 2024 - The falcon monitoring team at Pinnacles National Park began their field season in January. They started off noting which pairs of prairie and peregrine falcons were staking out which cliff faces as nesting territories. Now, after recording all of the season’s small dramas, they’ve watched the newest generation of falcons take to the skies. It’s on the small side, but a bit bigger than last year’s. The park lifted raptor advisories accordingly around the cliff nests that the fledglings left behind. However, some areas may remain closed to protect wildlife. If you are considering climbing or hiking off-trail at Pinnacles, always check our list of sensitive areas when planning your trip.

Early in the season, the monitoring team found a very normal 12 pairs of falcons claiming territories—eight prairie falcon and four peregrine falcon pairs. When two of the prairie falcon pairs opted not to nest, it became clear this season would not shatter any records. Ten pairs went on to hatch nestlings, but the team’s nestling tally took several hits as two prairie falcon and two peregrine falcon nests failed. By the end of the season, the team found that six falcon pairs raised a total of 20 fledglings. That’s up from the 17 fledglings counted last year, although only prairie falcons experienced the bump in success.

The monitoring team counted 17 prairie falcon fledglings and three peregrine fledglings, for a total of 20 fledglings this year. That's lower that the 1984–2023 average of 27.9 fledglings, but higher than last year and just within the normal range of variability.

Four prairie falcon pairs raised 17 fledglings this year, up from three pairs raising 10 fledglings last year. Meanwhile the two successful peregrine pairs only raised three fledglings this year, down from three pairs fledging seven last year.

The falcon nest failures this year were somewhat unusual. Most often, nests fail during egg incubation, while this year’s all occurred after nestlings had hatched. Wildlife biologist and falcon monitoring team lead, Gavin Emmons, suspects the failures may have been due to predation (such as by great horned owls), due to the timing and intensity of this year’s rains, or both.

Prairie falcon nestlings at 25-27 days old in their cliff cavity nest. Six falcon nests succeeded this year, out of ten that hatched eggs. The nest failures may have been due to predation (such as by great horned owls), due to the timing and intensity of this year’s rain, or both.

NPS / Gavin Emmons

But what does rain have to do with it, and how could rain and predation share blame for a falcon nest failure? Emmons’ theory starts with heavy early winter rainfall leading to high vegetation growth that hides ground-based prey from nesting falcons’ sharp eyes. That could explain falcons deciding not to nest, or to abandon nests. And if falcons are struggling, his theory continues, other aerial predators like owls could have similar trouble hunting when non-native grasses grow dense during the nesting season. These other birds of prey might compensate by turning their foraging attention from the ground to the cliff cavities full of falcon nestlings.

That doesn't mean Emmons is always concerned for the falcons when it rains. Too many dry years in a row, and he figures falcon prey populations could plummet to a point where good visibility wouldn’t matter. But also, more analyses are still needed to confirm how strong the link between falcon breeding success and early winter rains might be. National Park Service data scientists are crunching the numbers this year as they also look at Pinnacles falcons’ vulnerability to escalating climate change.

Stay tuned for more Pinnacles falcon updates next spring, as the monitoring team embarks on its 40th season of falcon monitoring!

For more information

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

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