Condor Watch photos suggest tantalizing patterns in the evolution of social networks of California condors
For several years, devoted Condor Watchers have carefully documented feeding positions and chatted about scale antics and juvenile floofs.
Thanks to a new addition to our team, Lisa Natale, a graduate student in the Interdisciplinary Quantitative Biology Program, and the Ecology and Evolutionary Biology Department at CU Boulder with a background in pure mathematics, we’ve now had our first detailed look at the data and we’re excited to share the results!
From your annotations of feeding station images, we’ve created snapshots of what the condors’ social network looked like for seasons between 2006 and 2013. (To get a sense of how we get from pictures of hungry condors to images like those below, check out our earlier post.)
While these network snapshots may look like crude connect-the-dots artwork, there is a lot we can glean from them. Clusters of dots represent groups of birds commonly seen feeding together; the tighter the cluster, the more interconnected the group of birds. Likewise, a lack of connection between two birds indicates that they were not seen feeding together in the given time period.
To some degree, disconnected groups of birds are explainable by geography—birds that frequent feeding stations in Central CA are unlikely to be seen with those feeding in Southern CA—but disconnects may also arise from behavior like social avoidance.
These network snapshots begin to shed light on the social structure of the condor population, and in particular how it changes through time. This was the foundation we needed to begin exploring whether and how a bird’s social status affects its risk of lead poisoning, something we are very interested in as lead poisoning is the number one threat preventing condor recovery.
Initially, we hypothesized that dominant birds suffer greater exposure to lead, as they feed earlier among the group. Because condors are equipped with beaks designed for tearing into existing wounds in a carcass, rather than making fresh wounds, we believed that feeding earlier would mean feeding closer to the initial wound site. In abandoned game, this may be a lead bullet entry point. Hence, dominant birds feeding early may be at higher risk of ingesting a piece of spent lead ammunition.
Our condor social network snapshots and the positions of birds through time during a feeding bout allow us to explore this idea by inferring feeding hierarchies among the birds. From these hierarchies, we can assign individual birds a social rank in the population and examine whether this rank influences their risk of poisoning going forward.
Using the Condor Watch data accumulated to date, a condor’s rank is not a reliable predictor of whether it will suffer poisoning in the near future. Interestingly, prediction accuracy increases when we look at networks generated on shorter timescales. Unfortunately, these short-timescale networks must be built with smaller pools of photo data. We are hopeful that the links between social rank and lead poisoning risk may become clearer as we accumulate additional data to allow definition on short timescales.
One factor that may obscure the links between dominance and lead-poisoning risk and increase the predictive accuracy of short timescale networks is the striking lack of stability in condor social networks, especially early in the release program.
The evolution of the social structure apparent in our preliminary analyses is exciting and presents many interesting angles to pursue! We are especially curious to learn what contributed to social instability among the condors early in the release program and what factors led to increasing social stability through time. Better understanding of what is disruptive to condor flock structure may help us preserve the integrity of the social network of this highly managed population as it grows over time. A stable social network may prove to be a critical piece of successful recovery for these gregarious birds.
We couldn’t do any of this without you! So please, keep on clicking to tell us which birds appear where. Thank you for your efforts and care; with every picture you annotate you are enabling this and further research. We are deeply grateful for this opportunity to be working with you to aid and understand these awe-inspiring birds.