The documented history of nesting peregrine falcons in California dates to the late 1800s when outdoor enthusiasts enjoyed the hobby of egg-collecting.  Hundreds of ‘sets’ or clutches of peregrine eggs wound up becoming integrated into the ornithological specimen collections at various academic institutions, most notably the British Museum, the Western Foundation of Vertebrate Zoology, UC Berkeley’s collections, and a few others. 

These early collections provided an incredible repository for comparing pre-DDT (pre-1940s) eggshell thicknesses with post-DDT eggshell thickness.  These data were pivotal in understanding the post World War II decline of peregrines worldwide, and formulating management programs aimed at recovery.  Scientific use of the historical data on peregrines was discovered and pioneered Dr. Derik Ratcliffe, Chief Scientist for Britain’s Nature Conservancy Council. This work was expanded to include North America by collaborating with Dr. Joseph Hickey (Univ. of Wisconsin, Madison) and his graduate student at the time, Dr. Daniel Anderson (Professor Emeritus, UC Davis). 

     Numerous scientific papers were published documenting the decline of peregrines over four decades.  But one was seminal to the topic - in 1967 Dr. Ratcliffe’s published Decrease in Eggshell Weight in Certain Birds of Prey, in which he developed the Ratcliffe Index, considered the most reliable measure of relative eggshell thickness.   The earliest collected samples were the result of dedicated hobbyists, yet excellent field naturalists, who were out collecting and trading bird eggs among themselves.  The scientific results derived from these eggs, decades later, became the indisputable evidence needed to prove to the world that the environmental effects of chlorinated hydrocarbon pesticides, namely DDT, were the cause of a devastating global decline and near extinction of peregrines (and other predatory bird species).    

     The shocking finding of ‘endangered status’ for peregrines around the world lead to decades of research over much of the world, extensive population monitoring, and ushered in innovative captive breeding and large-scale release programs by the Peregrine Fund over a wide geographic area aimed at restoring an endangered species that seemingly was sliding toward extinction. 

     The Peregrine Fund’s scientists developed and field tested innovative management techniques, and then applied them on a large scale to stop the trend toward extinction.  Captive breeding and the release of large numbers of captive-bred young stemmed the decline and lead to the recovery of peregrines throughout their range .  The United States banned the use of DDT domestically. These efforts collectively turned out to be one of wildlife conservation’s most celebrated success stories. 

     Through research, captive breeding, and releases into the wild, peregrines recovered from their precarious ‘endangered species’ status to one of no longer needing the legal protections that such an ominous designation required.  It took decades of focused efforts, and the dedication of many peregrine experts and their associates to return peregrines populations to sustainable and stable numbers.  Remarkably, peregrine falcons were entirely removed from the infamous Federal (and State) list of ‘endangered species’ on 25 August 1999.

     Now, some two decades after ushering in a substantial reestablishment of a robust and self-sustaining population throughout their worldwide range, the 2020s have revealed a new threat to peregrines.

      It seems indisputable that Avian Flu is having a devasting effect on peregrines in many areas around the world.  Much remains unanswered about the possible long-term effects of this new development, so stay tuned.

The CPP is participating in what has become a global assessment of this latest threat to peregrines.  We are asking for your help in the research effort, at least for California’s contribution to a global effort.  Please read more about how you can help with this important research effort.