Last Thursday I spent a whole day in Big Sur collecting poop samples from California condors. Why on earth am I doing this dirty work? Let me explain…
Numerous studies have found that lead poisoning from ingestion of spent lead ammunition is the primary cause of death in free-flying California condors. But what is happening to the condors that survive repeated lead exposures? I want to understand the potential adverse health effects of lead which may be accumulating in these individuals, as well as the potential impacts of these effects on survival and reproduction in the wild. Specifically I am interested in how chronic lead exposure can alter the response to stressors in the environment. Corticosterone, one of the hormones released during the condor stress response, is responsible for freeing up energetic resources for surviving a stressor and then storing energy stores for future recovery from that stressful event. In humans and other mammals, lead has been shown to impact the same brain region as chronic stress, and lead exposure can cause lasting alterations to the release patterns of corticosterone. In lead-exposed individuals the stress hormone can either be chronically elevated when no stressor is present, or the magnitude of change in hormone concentrations in response to a stressor is elevated, resulting in more corticosterone being released. This abnormal corticosterone release pattern can lead to changes in behavior, and inappropriate allocation of energy stores, both of which could impact the survival and/or reproductive output of these endangered birds.
So why condor poop? To assess the effects of lead on the condor stress response, I’ve been collecting blood, fecal, and feather samples from birds with different histories of lead exposure. Each sample type represents a different time scale of stress hormone released in response to a handling event: blood corticosterone is a direct and instantaneous measure of hormones in circulation, fecal corticosterone metabolites show a delay in elevation due to the time it takes for hormones to be eliminated via the gut, and feathers represent a longer-term integration of corticosterone release over 4-5 days. By looking at stress hormone responses in all three sample types, I will get a better overall picture of how the stress response might be altered in condors that have been exposed to lead more than others. As my experimental stressor, I use the capture and handling events already taking place for blood lead monitoring of the central California flock.
In order to collect fecal samples in a clean and timely manner with minimal stress to the condor, I developed a sampling kennel (pictured above) with a removable tray. This has allowed me to get sequential samples from individual birds and then map out and condor’s stress response to a handling event over time. I will collect enough samples to statistically compare stress response magnitudes in relation to individual lead exposure histories.
The free-flying condor population provides a unique opportunity to study this sub-lethal effect of lead since so much is known about each individual due to an intensive monitoring program, of which CondorWatch is an integral part!