Previous research has established lead poisoning as the greatest threat facing California condors today. Yet, other than documented lead-mortalities, little is known about the impacts of lead poisoning on other important measures of condor population health, such as disease and impaired reproductive success. The concern is that lead is a well-known reproductive toxin and wild condors are reproducing below expected rates. Sub-lethal lead exposure is also known to impact the hormonal stress response, which in turn can reduce survival and reproduction. However, the extent to which lead exposure is altering condor stress response and reproductive success is unknown. I am measuring stress hormone concentrations in plasma, urate, and feather l samples using standard scientific methods to provide the first data on the effects of chronic lead exposure on condor stress response.
The vertebrate stress hormone response is activated by a perceived threat, either physical (e.g. starvation) or psychological (e.g. sight of a predator). The hormones released during this response, called glucocorticoids or stress hormones, alter metabolism so animals can better survive and recover from environmental (exogenous) or endogenous stressors. Previous studies on humans, rodents and one stork species show lead exposure inappropriately exacerbates the stress response. Importantly, elevated stress hormone levels have been implicated in reduced reproductive success in wild birds. Our findings may help explain why the reproduction rates of wild California condors, who regularly suffer lead poisoning have been substantially lower than expected since their reintroduction in 1992 and well below levels required to establish a self-sustaining population.
To measure a condor’s hormonal response to stress I collect blood, feces, and feathers during a capture and handling event. These handling events are already scheduled as part of the blood lead monitoring program so I am monitoring their response to a stressor that is relevant to the existing lead poisoning management protocol. I expect to observe hormonal stress responses of greater magnitude and duration in condors that have experienced more lead exposure than in condors that have been less exposed to lead (captive condors and wild condors with a history of less frequent lead poisoning).
Donald R. Smith (UC Santa Cruz)
Myra Finkelstein (UC Santa Cruz)
Christopher Tubbs (Institute for Conservation Research, San Diego Zoo Global)
Condor feathers, feces, and urates undergoing extraction for steroid hormones.