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The peregrine falcon is the fastest bird in the world, reaching speeds up to 186 mph during a dive. Following near distinction from DDT in the 1970s, the peregrine population has resurged—but in recent years, its numbers began to drop nationwide. While the exact cause is unknown, several scientists speculate the highly pathogenic avian influenza (HPAI), H5N1 is to blame.
At Pinnacles National Park, the falcon seems to be doing well. Gavin Emmons, biologist and raptor specialist, told BenitoLink that in general the park has seen an increase in the peregrine population.
“The first territorial pair of peregrine falcons returned to Pinnacles in 2004, and has been nesting annually since 2005,” Emmons said. “As of 2025, our peregrine falcon population had increased to four nesting pairs. Numbers of young that have fledged successfully over the years have fluctuated but are generally increasing.”
Emmons added that he did not know if there was a decrease in the county overall and there is no funding or staffing to conduct a county-wide census, or survey efforts to determine trends for peregrine falcons generally.
Emmons said peregrine and prairie falcons compete for the same nest sites—cliff-cavity nests—but feed on different prey sources, with peregrines primarily predating on birds and prairie falcons feeding on rodents such as ground squirrels. Prairie falcon numbers—both territorial pairs and total fledglings at the park—have fluctuated, but may be decreasing somewhat in recent years. It’s possible that this is in part due to increased peregrine falcon presence, with peregrines at least sometimes out-competing prairie falcons for nest sites and territories.
Emmons cautioned that there is not enough information to tell out how much the H5N1 virus, commonly known as bird flu, might be affecting falcons.
At Pinnacles, peregrines are monitored through the breeding season, from January to July. Scientists monitor the timing of breeding cycles, foraging ecology, reproductive behavior, reproductive success and the impact of rock climbing in the park.
Because peregrines primarily feed on birds, and because the loss of peregrines in coastal areas is greater than losses inland, scientists speculate that bird flu is the cause of the falcon’s decline—waterfowl are known carriers of the H5N1 virus.
These falcons have been sighted throughout the county, though no actual numbers are recorded, and apart from Pinnacles no official monitoring is in place.
Tim Gallagher, former editor-in-chief for Cornell Laboratory of Ornithology’s Living Bird, wrote in an article for Audubon that “the evidence is circumstantial but compelling” to conclude that bird flu is the culprit. “According to the USDA, avian influenza has been confirmed in more than 50 dead Peregrines nationwide since 2023—but this is certainly much lower than the actual figure. After a falcon feeds on a sick bird, the raptor usually just flies off to a cliff or other distant perch and ends up dying there within a couple of days. It doesn’t leave behind an easily accessible corpse to test.”
In an article for biographic, David Bird, who formerly led the Avian Science and Conservation Centre at Quebec’s McGill University, said peregrine falcons could be picking up the virus “after preying on shorebirds, seabirds, and waterfowl—transitory populations that may have been infected on poultry farms.”
According to envioliteracy.org other threats to peregrines are:
- Pesticide Use: The widespread use of DDT in the mid-20th century had a devastating effect on peregrine falcon populations. DDT caused eggshell thinning, leading to failed nesting attempts and a massive decline in numbers. Though DDT is largely banned in many places, other pesticide use remains a concern, potentially impacting their prey and thus indirectly affecting falcon populations.
- Habitat Loss and Fragmentation: As natural habitats are destroyed or altered through urban development, agriculture, and deforestation, peregrine falcons lose suitable nesting and hunting territories. The fragmentation of habitat also isolates populations, reducing genetic diversity and making them more vulnerable to disease and other threats.
- Predation: While adult peregrines have few natural predators, young peregrines are vulnerable to predation from large birds of prey such as great horned owls, gyrfalcons, and golden eagles. This predation pressure can be particularly impactful in areas where peregrines are trying to reestablish themselves away from urban environments.
- Direct Human Disturbance: Human activity in and around nesting sites can cause significant disturbances, leading to nest abandonment, reduced breeding success, and stress on the birds. This includes activities like rock climbing near nest locations during the breeding season, as well as general disturbance from human noise and proximity.
- Shooting and Trapping: Historically, falcons have been targeted by humans for perceived competition with game hunting or out of misguided fear. Though less prevalent now, these actions still pose a localized threat in some areas. Poaching of eggs and young falcons also contributes to the problem.
- Collisions with Man-Made Structures: Peregrine falcons, though agile, are still susceptible to collisions with buildings, towers, and wind turbines. These structures can be particularly hazardous during hunting dives or migrations, leading to injury or death.
- Fungal Infections: These falcons are susceptible to fungal infections they may acquire from their prey. This can lead to illness and even death, particularly among young falcons.
- Territorial Disputes: While they often form long term bonds fights between peregrine falcons over territories can result in serious injuries, further threatening individual survival and population health.
Other falcon species in California and in San Benito County are THE American kestrel and merlin. Though not common, the crested caracara has also been sighted in the region. There are no notable reported drops in the populations of these species.
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