{"id":22818,"date":"2026-03-07T18:03:40","date_gmt":"2026-03-07T18:03:40","guid":{"rendered":"https:\/\/readtrends.com\/en\/peregrine-falcons-bay-area-decline\/"},"modified":"2026-03-07T18:03:40","modified_gmt":"2026-03-07T18:03:40","slug":"peregrine-falcons-bay-area-decline","status":"publish","type":"post","link":"https:\/\/readtrends.com\/en\/peregrine-falcons-bay-area-decline\/","title":{"rendered":"Bird flu rips through another beloved Bay Area species &#8211; SFGATE"},"content":{"rendered":"<article>\n<h2>Lead<\/h2>\n<p>Since mid-February scientists have been confronting an H5N1 outbreak that has killed at least 30 elephant seals in a colony of more than 1,300 at A\u00f1o Nuevo State Park, 55 miles south of San Francisco. That marine-mammal event coincides with a newly posted Feb. 14 preprint showing a dramatic, multi\u2011year decline in Bay Area peregrine falcons. Researchers tracking nests for 26 years report nest occupancy plunged after the global 2020 H5N1 surge and by 2025 only roughly a third of monitored territories were active.<\/p>\n<h2>Key Takeaways<\/h2>\n<ul>\n<li>Since mid-February 2026, an avian\u2011flu outbreak at A\u00f1o Nuevo has been linked to at least 30 elephant seal deaths in a colony of over 1,300 animals.<\/li>\n<li>A Feb. 14, 2026 preprint from a team spanning Santa Cruz, Oakland, San Francisco and Idaho analyzed 26 years of peregrine nesting records across the Bay Area.<\/li>\n<li>Nest\u2011territory occupancy fell from near\u2011complete use before 2022 to about 65% in 2023 and roughly 36% by 2025, a drop the study summarizes as a 64% decline since 2022.<\/li>\n<li>Peregrines\u2019 diet \u2014 largely other birds \u2014 plus individual birds eating up to 500 prey items a year likely raises exposure risk to H5N1.<\/li>\n<li>Where adults survive to breed, pairs can raise an average of four chicks (and as many as five in some seasons), offering a route to recovery if enough adults persist.<\/li>\n<li>Monitoring depended on a long-standing volunteer network; documented nesting sites include UC Berkeley\u2019s Campanile, Devils Slide, Alcatraz, and a downtown PG&#038;E building.<\/li>\n<li>Scientists warn the decline is proceeding faster than historical losses from DDT in the mid\u201120th century and that further declines are possible until population immunity increases.<\/li>\n<\/ul>\n<h2>Background<\/h2>\n<p>Highly pathogenic avian influenza (HPAI) H5N1 expanded globally after 2020, infecting hundreds of bird species and spilling into mammals in some regions. The virus transmits via contact with infected saliva, feces or through consumption of infected prey; clinical signs in birds can range from subtle reproductive problems to sudden death. Historically, peregrine falcons recovered from severe mid\u2011century declines caused by DDT after intensive conservation and nest protection programs; their recovery has been a celebrated conservation success in the Bay Area.<\/p>\n<p>The new preprint places recent peregrine losses in that longer historical arc by using nest\u2011territory occupancy as a survival proxy. Because peregrines are territorial and often return to the same cliffs or structures each year, an absent pair likely signals mortality or long\u2011term displacement. That methodological choice allowed the team to leverage consistent, decade\u2011spanning observations collected by scientists and a network of dedicated volunteers across the region.<\/p>\n<h2>Main Event<\/h2>\n<p>The A\u00f1o Nuevo incident \u2014 the first confirmed detection of the virus in California marine mammals \u2014 prompted intensive testing after dozens of seals showed sickness and at least 30 were reported dead. State and university labs continue diagnostic work to trace the outbreak\u2019s origin and map its spread. Those marine infections arrived as researchers were completing an analysis of peregrine nesting records across 47 historically monitored territories.<\/p>\n<p>The peregrine study, posted as a preprint on Feb. 14, 2026, compiled 26 years of annual checks at sites from the Marin coast to San Francisco and the East Bay. The authors recorded near\u2011complete occupancy from 2000 through 2022, then documented a sharp fall: 65% occupancy in 2023 and about 36% in 2025. The loss of so\u2011called floaters \u2014 unpaired birds that normally fill vacated territories \u2014 suggests mortality may exceed what simple absence counts show.<\/p>\n<p>Field teams and volunteers intentionally kept precise nest coordinates sparse in public reporting to avoid disturbance, but they confirmed that losses include high\u2011profile territories such as the Campanile at UC Berkeley, Devils Slide, Alcatraz Island, and an urban PG&#038;E roost. Observers note some recent arrivals in formerly vacant sites, but researchers emphasize it is too early to call a rebound.<\/p>\n<h2>Analysis &#038; Implications<\/h2>\n<p>The study\u2019s central argument rests on exposure pathways: peregrines feed almost exclusively on other birds, many species of which now serve as reservoirs for H5N1. Consuming infected prey or scavenging near contaminated sites elevates the chance a peregrine individual receives what the authors describe as \u201ca bad lottery ticket.\u201d Over a year a single peregrine may take hundreds of birds, multiplying exposure opportunities relative to many other raptors.<\/p>\n<p>Demographically, the falcons\u2019 decline is troubling because adult survival underpins replacement. If adults survive winter and reach breeding season, reproductive output is strong \u2014 commonly averaging four chicks per successful pair \u2014 which could permit recovery if enough adults remain. But the marked reduction in floaters and the rate of territory abandonment imply losses that reproduction alone may not quickly offset.<\/p>\n<p>Comparisons with the mid\u201120th century DDT crisis are instructive: the current pace of decline is about twice as fast, the authors say, though the mechanisms differ. DDT suppressed reproduction via eggshell thinning; H5N1 appears to be causing direct mortality in adults and juveniles. The rapid trajectory raises management questions about intervention options, from focused monitoring and rescue of sick birds to broader surveillance of prey populations and coastal mammals.<\/p>\n<h2>Comparison &#038; Data<\/h2>\n<figure>\n<table>\n<thead>\n<tr>\n<th>Period<\/th>\n<th>Occupancy (approx.)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>2000\u20132022<\/td>\n<td>~near 100% of monitored sites<\/td>\n<\/tr>\n<tr>\n<td>2023<\/td>\n<td>65%<\/td>\n<\/tr>\n<tr>\n<td>2025<\/td>\n<td>36% (~one\u2011third)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n<p>The table summarizes nest\u2011territory occupancy used as a proxy for breeding adults. The authors quantify a 64% drop in occupied territories since 2022. That rapid collapse contrasts with the prolonged decline and gradual recovery pattern seen under chemical threats decades ago and highlights the acute, transmission\u2011driven nature of current losses.<\/p>\n<h2>Reactions &#038; Quotes<\/h2>\n<p>Researchers emphasize both the scale of the data set and cautious hope where nests remain occupied.<\/p>\n<blockquote>\n<p>\u201cThe depth of the data is something we\u2019re really proud of. And while the situation seems grim, as long as there are nests, there is hope.\u201d<\/p>\n<p><cite>Zeka Glucs, Predatory Bird Research Group, UC Santa Cruz (lead author)<\/cite><\/p><\/blockquote>\n<p>Co\u2011authors and independent scientists warn the virus could continue to press populations until more birds develop immunity.<\/p>\n<blockquote>\n<p>\u201cTheir chance of getting a bad lottery ticket, so to speak, is just much higher than it is for other birds.\u201d<\/p>\n<p><cite>Bruce Lyon, emeritus professor, UC Santa Cruz (co\u2011author)<\/cite><\/p><\/blockquote>\n<p>Outside reviewers note regional patterns may mirror those elsewhere and urge continued monitoring.<\/p>\n<blockquote>\n<p>\u201cWe are going to have to wait until the population develops enough immunity to this before we turn a corner.\u201d<\/p>\n<p><cite>Bryan Watts, conservation biologist, William &#038; Mary (independent expert)<\/cite><\/p><\/blockquote>\n<h2>\n<aside>Explainer \/ Glossary<\/aside>\n<\/h2>\n<aside>\n<details>\n<summary>H5N1, nesting behavior and &#8216;floaters&#8217;<\/summary>\n<p>H5N1 is a highly pathogenic avian influenza strain that spreads via contact with contaminated bodily fluids, surfaces, or infected prey. Peregrine falcons are territorial raptors that often reuse the same nest location annually, making long\u2011term site checks a useful proxy for adult survival. &#8216;Floaters&#8217; are otherwise healthy, unpaired birds that normally fill vacancies quickly; a lack of floaters following territory abandonment suggests elevated adult mortality. Reproductive potential is high for surviving pairs, often producing three to five chicks in successful seasons. Citizen and professional monitoring networks are crucial for detecting rapid population changes.<\/p>\n<\/details>\n<\/aside>\n<h2>Unconfirmed<\/h2>\n<ul>\n<li>Direct epidemiological links between the A\u00f1o Nuevo marine\u2011mammal outbreak and peregrine declines have not been established; cross\u2011species transmission pathways remain under study.<\/li>\n<li>The total number of peregrine mortalities across the Bay Area is not yet confirmed; occupancy loss is a proxy, not a count of dead birds.<\/li>\n<li>Whether the H5N1 strain involved in seals and local birds is identical in all cases awaits full genomic confirmation from labs still processing samples.<\/li>\n<\/ul>\n<h2>Bottom Line<\/h2>\n<p>The preprint and the A\u00f1o Nuevo seal outbreak together signal a broader, multi\u2011taxon ripple of H5N1 across coastal California. For peregrines, high adult exposure risk combined with the absence of replacement floaters produces a rapid contraction in breeding territories that could take years to reverse.<\/p>\n<p>Immediate priorities are continued diagnostic testing of affected marine mammals and birds, expanded surveillance of prey species that can serve as reservoirs, and coordinated volunteer monitoring to measure occupancy and detect early signs of recovery. If enough adults survive to breed, strong reproductive output offers a realistic pathway back, but scientists caution that population\u2011level immunity and time will both be necessary.<\/p>\n<h2>Sources<\/h2>\n<ul>\n<li><a href=\"https:\/\/www.sfgate.com\/bayarea\/article\/bird-flu-peregrine-falcons-21959370.php\" target=\"_blank\" rel=\"noopener\">SFGATE \u2014 regional news report summarizing the preprint and field observations (news)<\/a><\/li>\n<li><a href=\"https:\/\/www.cdc.gov\/flu\/avianflu\/\" target=\"_blank\" rel=\"noopener\">U.S. Centers for Disease Control and Prevention \u2014 avian influenza overview and guidance (official public health agency)<\/a><\/li>\n<li><a href=\"https:\/\/biology.ucsc.edu\/\" target=\"_blank\" rel=\"noopener\">UC Santa Cruz Biology (Predatory Bird Research Group \/ academic research context)<\/a><\/li>\n<\/ul>\n<\/article>\n","protected":false},"excerpt":{"rendered":"<p>Lead Since mid-February scientists have been confronting an H5N1 outbreak that has killed at least 30 elephant seals in a colony of more than 1,300 at A\u00f1o Nuevo State Park, 55 miles south of San Francisco. That marine-mammal event coincides with a newly posted Feb. 14 preprint showing a dramatic, multi\u2011year decline in Bay Area &#8230; <a title=\"Bird flu rips through another beloved Bay Area species &#8211; SFGATE\" class=\"read-more\" href=\"https:\/\/readtrends.com\/en\/peregrine-falcons-bay-area-decline\/\" aria-label=\"Read more about Bird flu rips through another beloved Bay Area species &#8211; SFGATE\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":22813,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"rank_math_title":"Bird flu rips through Bay Area peregrines - SFGATE","rank_math_description":"A Feb. 14 preprint and a mid\u2011Feb outbreak in A\u00f1o Nuevo link H5N1 to steep peregrine declines in the Bay Area\u2014nest occupancy down ~64% since 2022; experts race to track spread.","rank_math_focus_keyword":"peregrine falcon,avian flu,H5N1,Bay Area,nest occupancy","footnotes":""},"categories":[2],"tags":[],"class_list":["post-22818","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-top-stories"],"_links":{"self":[{"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/posts\/22818","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/comments?post=22818"}],"version-history":[{"count":0,"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/posts\/22818\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/media\/22813"}],"wp:attachment":[{"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/media?parent=22818"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/categories?post=22818"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/readtrends.com\/en\/wp-json\/wp\/v2\/tags?post=22818"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}