We document causes of death in free-ranging California Condors (Gymnogyps californianus) from the inception of the reintroduction program in 1992 through December 2009 to identify current and historic mortality factors that might interfere with establishment of self-sustaining populations in the wild. A total of 135 deaths occurred from October 1992 (the first post-release death) through December 2009, from a maximum population-at-risk of 352 birds, for a cumulative crude mortality rate of 38%. A definitive cause of death was determined for 76 of the 98 submitted cases, 70% (53/76) of which were attributed to anthropogenic causes. Trash ingestion was the most important mortality factor in nestlings (proportional mortality rate [PMR] 73%; 8/11), while lead toxicosis was the most important factor in juveniles (PMR 26%; 13/50) and adults (PMR 67%; 10/15). These results demonstrate that the leading causes of death at all California Condor release sites are anthropogenic. The mortality factors thought to be important in the decline of the historic California Condor population, particularly lead poisoning, remain the most important documented mortality factors today. Without effective mitigation, these factors can be expected to have the same effects on the sustainability of the wild populations as they have in the past.

Over the past 30 years, the California condor (Gymnogyps californianus) population has rebounded from 22 individuals to over 200 birds living in the wild. Historical impacts to the population have been largely anthropogenic. In this study, we explore mortality and cause of death data from condors that died during the years 2010-2014 and compare these to mortality data described by Rideout et al. in 2012, covering the years 1992-2009. In addition, morphologic and genetic analysis of the contents of the upper gastrointestinal (GI) tract was performed on the 2010-2014 condor mortalities to determine animal origins of the last meal eaten. The maximum population at risk within this time frame was 329 birds. During this time, 88 condors died and underwent post-mortem examination, and 41 birds were lost to tracking efforts and presumed dead (crude mortality rate of 39%; 129/329). A cause of death was determined for 66 of the 88 necropsied birds. Lead toxicosis remained a significant negative factor in condor population recovery, being related to the deaths of 37 adult and juvenile condors (proportional mortality rate 56%). Compared to condors succumbing to other causes of death, cattle were less often part of the last meal of lead-intoxicated condors. Based on these data, continued efforts to mitigate the impact of lead on California condors should be pursued.