California condors are chronically poisoned by lead
In 1982 there were only 22 California condors left in the world – so it is not surprising they are considered one of the rarest birds on earth! To save condors from extinction captive breeding programs were established. The captive breeding program has been very successful, and today there are over 400 condors, approximately half of which are in zoos and half in the wild. However, this success is only due to the daily efforts of large numbers of zoo staff, biologists and volunteers, who maintain the breeding program, as well as monitor every wild condor almost every day.
The main threat to free-flying California condors was believed to be lead poisoning but the full extent of this threat was not known when we started our research program about six years ago. So, we performed a comprehensive study to investigate the impact and source of lead exposure to condors. We found that since the release program began condors have been chronically exposed to harmful levels of lead. Alarmingly, almost half of all condors in the wild in California have had lead poisoning severe enough to require medical treatment and in a recent study, the majority of adult condor deaths were attributed to lead poisoning (10 out of 15 adult mortalities for which cause of death was determined, see Rideout et al. 2012 for details on the causes of mortality in California condors).
California condor 286 being treated for lead poisoning at the California condor breeding facility, Los Angeles Zoo. Unfortunately 286 did not survive his lead poisoning episode, which is tragically not uncommon given that lead poisoning has been shown to be the number one reason that free-flying juvenile and adult condors die. Photo courtesy of Mike Clark
We used lead isotopic analysis, which can provide a signature of the sources of lead exposure, and showed that lead-based ammunition is the principal source of lead poisoning in condors. Condors are scavengers and when they feed on a carcass that has been shot with lead ammunition they can ingest some of the lead, and even a few small fragments – equivalent to a couple of grains of sand – contain enough lead to poison a condor. Our research also showed that the condor’s current apparent recovery is solely due to intensive ongoing management and, if this management is stopped, the condors will once again be at risk for extinction within a few decades. Ultimately we determined that the condor’s only hope of achieving true recovery is dependent upon the elimination or substantial reduction of lead poisoning. For more information on this study see Finkelstein et al. 2012.