I don’t know how many times I have traveled to the beach in winter, but the number is not small.
Regardless of the purpose of the trip, the binoculars and spotting scope will be in the car. I can always find a little time to check out the birds on the ocean. And there is always a reason (or excuse) to pull out the glassware.
Oystercatchers with over-sized red bills pry limpets off the rocks at low tide. A blizzard of winter gulls of a half dozen species or more present a fun challenge in identification. It’s even more sporting given there is a mix of all ages and plumages. And there is always a chance of seeing a rhinoceros auklet from the headlands. But given the number of times I have birded the coast, no real surprises remain, or so I thought.
I recently returned from Crescent City and enjoyed the modest number of birds. Only the rafts of surf scoters and scattered western grebes were obvious out on the bay. A few red-throated loons were riding the rollers farther out, while the scattered common loons remained in the harbor and closer to shore. As I watched, one of the common loons rose up and stretched. It limbered up its wings and revealed that it had no flight feathers!
Now, in my experience, this is all wrong. Most birds in forest, field and marsh replace their flight feathers in the summer just before fall migration. Summer is a time of plenty, and it takes a lot of energy to grow the large and strong flight feathers. I knew a few species such as cliff and barn swallows waited until they arrived on their “wintering” grounds before molting wing feathers. But this happens in South America during their spring, a time of plenty.
However, molting wing feathers in winter here in the Northwest made no sense to me. Then I saw a second loon do the same. This one, too, was grounded. I wasn’t dealing with an oddball. Something was going on here that was new to me.
As I thought about these temporarily flightless birds, it began to sort itself out. Birds usually molt flight feathers when they have a surplus of food. In the case of a bird as large as the common loon (they weigh about 15 pounds), they also need sufficient time to regrow the feathers.
Loons breed far to the north in the boreal forest and tundra. At high latitudes, food is abundant during the brief summer. The key word here is “brief.” Surplus food is not only used to grow feathers but also to raise young. Most of our local birds begin their molt as they wrap up the chore of feeding young. For the loon, the young take a relatively long time to mature, and given the brief summer, it’s likely that there isn’t enough time remaining for the adults to grow a full set of flight feathers. Why not wait until they return to the ocean? Fish off the coast don’t disappear in winter like insects in the Rogue Valley, and apparently the fishing is good.
There is always something new to learn.
Stewart Janes is a biology professor at Southern Oregon University. He can be reached at firstname.lastname@example.org.