#19,320
Twice last month (see here, and here) we looked at the enormous impact of HPAI H5 on raptors and other scavenger birds around the globe. Previously - over 2023-2024 - we followed attempts to protect endangered California Condors against the avian flu threat.
For those like me - born in the 1950s - this has an oddly familiar ring to it, as we witnessed a similar steep decline in raptors and songbirds due to the overuse of DDT and other chlorinated hydrocarbons, famously exposed by Rachel Carson in her 1962 book Silent Spring.
While demonized by many, that book eventually led to the banning of DDT in 1972, followed by the slow recovery of condors, eagles, and falcons. But it was a close thing, as by 1980 the California Condor was all but extinct.
These are just what has been reported in the U.S., and represent only a tiny fraction of the actual losses. While we lack good numbers, the impact of H5Nx on avian and mammalian wildlife around the globe has been staggering (see Nature Reviews: The Threat of Avian Influenza H5N1 Looms Over Global Biodiversity).
First a link to, and the abstract from, the study; followed by an excerpt from a press release. Follow the links to read both in their entirety. I'll have a bit more after the break.
Authors: Glucs, Zeka E., Hunt, W. Grainger, Kilpatrick, A. Marm, Ambrosini, Jan, Armstrong, Daniel J., et al.
Source: Journal of Raptor Research, 60(3) : 1-11 Published By: Raptor Research Foundation
URL: https://doi.org/10.3356/jrr26022Abstract
After rebounding from near extirpation during the organochlorine era, breeding Peregrine Falcons (Falco peregrinus, hereafter peregrines) in California are again facing adversity, this time consistent with an outbreak of a highly pathogenic avian influenza (HPAI; Alphainfluenzavirus influenzae).
Following the first detection of the H5N1 variant clade 2.3.4.4b of HPAI in California wild birds in July 2022, we assembled data from long-term monitoring (2000–2025) of peregrine breeding territory occupancy in the broad vicinity of San Francisco Bay to examine possible impacts on falcon populations. Prior to the outbreak, 47 focal breeding territories had shown nearly complete occupancy by pairs (98.5% of 390 territory-years), with very few vacancies, single birds in attendance, or subadult pair members.
Within 8 mo of the outbreak, occupancy had dropped to 65.1%, and 2 yr later (2025), only 36.2% of territories remained occupied. Territories were increasingly occupied by single birds after the outbreak, but it is unclear whether these were survivors or floaters attempting to fill vacant territories where both pair members had perished. The high vacancy rates also signaled an impact upon floaters (nonbreeding adults) that normally buffer breeding territory occupancy in healthy peregrine populations. From October 2022 through November 2025, 17 peregrine fatalities were diagnosed with H5N1 within our study area.
Evidence that H5N1 caused these territory vacancies includes (1) the temporal coincidence of occupancy loss with the outbreak and (2) the lethality of the virus to peregrines and its confirmed presence in their prey in our study area. Our study reaffirms the value of long-term territory occupancy monitoring in this sentinel species.
Three years ago, in Avian Flu's New Normal: When the Extraordinary Becomes Ordinary, I wrote about the numbing effect that comes with the constant barrage of disturbing HPAI H5 reports from around the world.
Raptor Research Foundation
Highly Pathogenic Avian Influenza (HPAI) featured prominently in the news during 2020 as it took the lives of millions of birds across the globe. While the worst seems to be behind us, population-level effects are just now emerging. A new study published in the Journal of Raptor Research, titled “Rapid Decline of Nesting Peregrine Falcons in the San Francisco Bay Region of California Synchronous with an Outbreak of H5N1 Highly Pathogenic Avian Influenza,” reports an alarming decrease in the number of occupied territories for a population of Peregrine Falcons (Falco peregrinus) that has maintained a longstanding presence in coastal California. As top predators, peregrines show warning signs when the health of their food web is jeopardized. They indicated the threat of DDT to wildlife in the 1960’s, and they are once again sounding the alarm to those who know where to look.
Highly Pathogenic Avian Influenza (HPAI) is an infectious disease that typically remains at low levels in wild bird populations. However, in 2020, the variant H5N1 emerged and ran amuck in what is now considered one of the most severe disease outbreaks to affect large animal populations ever recorded. Infections were documented in 400 bird species and at least 50 mammal species that year. Waterbirds are particularly susceptible to becoming carriers of HPAI, so predators and scavengers that feed on them are at a higher risk of exposure. Peregrines are master bird hunters and therefore primed to encounter this bird-born illness. However, it can be challenging to verify cause-of-death for raptors because of their low densities and the challenge of finding their carcasses, so raptor biologists must employ other tools to investigate population-level responses.
Lead author on the study Zeka Glucs, Director or the Predatory Bird Research Group at the University of California Santa Cruz, worked with a team of researchers to compare the presence of Peregrine Falcons on known territories in the Bay Area before and after the H5N1 outbreak, which was first detected in the state in 2022. They accessed a long-term dataset from 2000-2025 to examine trends in peregrine presence, underscoring the importance of maintaining research that spans decades.
The team found that prior to the H5N1 outbreak, 47 peregrine territories in the Bay Area were consistently occupied with stable breeding pairs. Following the outbreak, peregrine presence on these same territories dropped by 65% in three years, and the decline continues.
Events that were nearly unthinkable five years ago (e.g. Repeated trans-Atlantic introduction of avian flu from Europe, the spread of HPAI H5 across the length of South America, numerous spillovers of H5 into mammalian species, the arrival of HPAI H5 to Antarctica, and most recently to Australia ) have now become `the new normal'.
Even if HPAI H5 never sparks a pandemic in humans, it is already a panzootic affecting the entire globe. One that already manifests itself in higher food costs, increased food insecurity, and growing public health and surveillance costs.
How the loss of millions of wild birds and mammals will ultimately affect humanity is a matter of debate, but it is hard to envision a good outcome.
Meanwhile, H5N1 marches on.
