Or, how likely is a condor to survive from one year to the next, given the different things a condor does or does not do. Understanding the things associated (or possibly affecting) a condor’s survival is key to managing them to optimize their chances of survival year after year.
Condors start breeding around 5 years of age (give or take – everyone is an individual!) so in order to replace itself, each generation a condor pair has to survive at least until they successful raise two chicks (or really a bit more than two to account for mortality). Then, condors are believed to be able to live up to 70 years! (or more – who knows??) The current flock is made up of young individuals, with the oldest just barely approaching middle age (e.g., Orange 21, the southern flock patriarch, is ~36, while the senior birds in the central flock are only ~20). Eventually carcass gatherings should include long-lived individuals that win the survival lottery — bird equivalents of your great-grandma at the family reunion, passing on stories of where the best dead things are found, how to avoid those pesky ravens and so on.
Vickie Bakker (the lead author) and I as well as other members of our science team just published a paper on condor survival “Effects of lead exposure, flock behavior, and management actions on the survival of California condors (Gymnogyps californianus)” in the journal EcoHealth that is available via online first at http://link.springer.com/article/10.1007/s10393-015-1096-2
For those interested, here is the abstract that summarizes the paper:
“Translocation is an increasingly important tool for managing endangered species, but factors influencing the survival of translocated individuals are not well understood. Here we examine intrinsic and extrinsic drivers of survival for critically endangered California condors (Gymnogyps californianus) whose wild population recovery is reliant upon releases of captively bred stock. We used known fate models and information-theoretic methods to compare the ability of hypothesized covariates, most of which serve as proxies for lead exposure risk, to predict survival rates of condors in California. Our best supported model included the following predictors of survival: age of the recovery program, precipitation, proportion of days observed feeding on proffered carcasses, maximum blood lead concentration over the preceding 18 months, and time since release. We found that as flocks have increased in size and age, condors are increasingly likely to range more widely and less likely to be observed feeding on proffered food, and these “wilder” behaviors were associated with lower survival. After accounting for these behaviors, we found a positive survival trend, which we attribute to ongoing improvements in management. Our findings illustrate that the survival of translocated animals, such as highly social California condors, is influenced by behaviors that change through time.”
The main thing we found is that although managers are making progress in decreasing mortality risks for condors, the behaviors affecting survival most – such as feeding at the feeding stations where CW photos are taken – are also changing through time, and these changing behaviors tend to increase mortality risk for condors. So, like most things in life, “it is complicated”. As the flock has grown in size the birds are doing different things and this underscores the importance of CW to help us understand how a bird’s behavior at the free-food buffet (aka proffered feeding sites) is changing over time and affecting their survival and lead poisoning risk. So, thank you to all you do on CW!
And of course, we can’t have a blog post without a photo of a condor – this is one of my favorites – taken by Gavin Emmons
FYI – this paper will be part of a Supplementary Issue in EcoHealth on Health and Disease in Translocated Wild Animals that is a result of a symposium that I attended in the spring of 2015. For more information on symposium see http://www.zsl.org/science/whats-on/health-and-disease-in-translocated-wild-animals.