California Condors are not only the largest avian scavenger in North America, they are a species of cultural significance for the Yurok Tribe of Northern California. Yurok ancestral territory is in the heart of the historical range of California Condors and the tribe has been working with Klamath Bird Observatory research associate, Dr. Jared Wolfe, to assess the feasibility of condor reintroduction. The researchers used Turkey Vultures and Common Ravens as surrogate species to determine the amount of lead and mercury avian scavengers are exposed to in Humboldt and Del Norte counties of Northern California. Their results were published by the American Ornithological Society’s Condor: Ornithological Applications journal as “Feasibility of California Condor recovery in northern California, USA: Contaminants in Surrogate Turkey Vultures and Common Ravens”.
“Lead poisoning is the number one threat to condor recovery thus far and an understanding of exposure in local avian scavengers is crucial prior to establishment of new release sites” says Chris West, Senior Wildlife Biologist with the Yurok Tribe. “Condors ingest lead from scavenging animals or offal from animals that were shot with lead bullets. In addition to lead, mercury exposure from feeding on washed-up marine mammals may represent an additional, at this time unassessed, threat that reintroduced condors must contend with.”
Here are three important highlights from the study:
• Although lead levels detected in ravens were lower than levels detected from a similar study conducted in Wyoming, there was still a significant increase in lead exposure during the hunting season in Humboldt and Del Norte counties.
• Lead detected in vultures and ravens increased with distance from coastline suggesting a connection to the greater availability of inland public lands accessible to hunters in Humboldt and Del Norte counties where the study occurred.
• Mercury detected in vultures and ravens decreased with distance from the coastline indicating that scavenging birds are likely exposed to mercury from marine resources rather than at inland locations in Humboldt and Del Norte counties.
“These results highlight some of the conservation challenges associated with condor reintroduction” says Dr. Wolfe. “Recognizing these challenges, the Yurok Tribe has done an excellent job working with the hunting community to switch from lead ammunition to condor friendly non-lead ammunition.”
The researchers believe that continued outreach to hunting communities will limit the amount of lead on the landscape for all avian scavengers and, crucially, for future populations of condors. Hunter outreach and a California-wide ban on the use of lead ammunition for hunting scheduled to go into effect in 2019 may present new opportunities for California Condor recovery in Yurok ancestral territory and beyond.
CLICK HERE to view the paper Feasibility of California Condor recovery in northern California, USA: Contaminants in Surrogate Turkey Vultures and Common Ravens by Christopher J. West, Jared D. Wolfe, Andrew Wiegardt, and Tiana Williams-Claussen.