by Bryce W. Robinson
While searching for Golden Eagles in the west desert of Utah this past week, I came upon a large wetland preserve, Fish Springs National Wildlife Refuge. As I travelled through the preserve, heading east, I noticed many large swans scattered about the ponds. I haven’t had much experience with these large birds, so I took it as an opportunity to learn more of the two species that are natural to North America.
I took photos of a number of individuals, recognizing that it may prove fruitful in studying the birds. I knew the relative difference between the Tundra Swan- Cygnus columbiana, and the Trumpeter Swan- Cygnus buccinator, but to be honest I couldn’t at the time distinguish a Tundra Swan lacking yellow lores from a Trumpeter Swan. I chose to rectify that by studying the differences.
I use David Sibley’s guidebooks for my general birding purposes. He is in my mind the best birder in the country, and maintains a diligent study coupled with his invaluable ability to accurately illustrate birds. He is, no doubt, something to aspire to. In my guidebook, I found a quick tip discussion of differentiating the two swans. It is well done, but after doing further research on the internet, I discovered a more in depth discussion of the subject on his blog. You can view it for yourself here.
I will not attempt to reiterate his discussion here, not only to avoid redundancy, but to ensure I do not portray any information inaccurately. What I would like to discuss is something I noticed with the Tundra Swans I was watching the other day. Each bird has variation in the presence of yellow on their lores. I have yet to really explore the literature to find out if someone has studied this, but I find it fascinating and wonder what is responsible for the variation. I took a few photos of individuals. You can see the difference between each bird here.
These birds each show a degree of difference in the yellowing of their lores. As I stated before, I do not know what is responsible for the difference. Possibilities include that the yellowing could be a function of age, sex, or status, much like the black breast patch in the male House Finch, functioning as a symbol of dominance. The yellow lores could also be individually distinct, aiding in individual recognition.
I find the difference fascinating. And here is yet another avenue for a path to knowledge and further study in the world of birds.