Return of the Ruby-crowned

We paddle our canoe across Tomales Bay in the drizzle, going in the morning to avoid the usual afternoon winds that kick up the waves. We spend a chilly day sitting by the fire; paddling along the shore; watching loons, tule elk, river otters, osprey, and even a bald eagle. The next morning I wake up to bright sunshine and grab my binoculars and camera. The trees along our small beach are alive with song birds. A tiny, bold bird with a white eye ring and wing bars hops through the hanging moss, coming quite close to me. It's a ruby-crowned kinglet, one of my favorite signs of fall.

Then back in Berkeley over the next few days, I see them everywhere: outside my office in a scrubby little live oak, and another in the juniper bushes by the parking lot.

Then a few days later on my regular bird walk in Tilden Park near Jewel Pond:

And even in my front yard:

You might notice that there are no ruby crowns in these photos. Only the males have red patches on their heads, and even they keep them hidden most of the time. They flash them to signal to a potential mate, or a potential threat.

These lively little birds are quite common in our area from fall through early spring, but then they all migrate to Canada or to high elevations in the Sierra Nevada and the Rockies to breed and nest. In summer, these kinglets are fairly specialized, spending most of their time high in conifers and eating only insects. During migration and in winter, they are more of generalists, living in all kinds of trees and bushes, and adding fruits, berries, sap, and nectar to their diet.

It is likely that the ancestors of migratory birds like these originally spent all their year in what is now their winter habitat. Later they evolved to migrate to their breeding grounds. There are huge disadvantages to migrating: most obviously, the massive energy expenditure to travel that far, but also the requirement to add evolve a new set of behaviors to suit the new, second environment. There must, therefor be an even greater advantage to this adaptation that outweighs the costs. It is likely that this advantage comes from reduced competition for food and nesting sites in areas that are too cold to support most bird species during the winter. Migration behaviors probably evolved gradually, with birds initially traveling shorter distances.

The details of ruby-crowned kinglets behavior during nesting season are not well known. It spends its summers high in tall trees, in relatively unpopulated areas. This bird that is so bold and common here in its winter home becomes mysterious each summer.

LINKS
Ruby-crowned kinglet information from the Cornell Lab of Ornithology
Ruby-crowned kinglet information from Audubon
Tilden Regional Park