One of the most spectacular things to see a swan do, is for it to stand up in the water and spread its wings. They don’t seem to do this very often, but I wondered what triggered the activity. I think I have figured it out.
Here is the object of the exercise. While normally in the water, the wings are tight by the swan’s side, now they are spread as if flying. But a swan does this only for a short time, maybe once (or a couple of times) a day. Why?
Early one morning, I then went and spent a long time quietly watching a group of about 18 swans. It gave strong credence to my suspicion.
The day began with feeding in the shallows. This went on for some time.
Next began a session of preening. This is where the swans repair their feathers. Among other things, the swan uses its bill to interlock feather barbules that have become separated. I speculated that although feathers might now be repaired, many could still be misaligned, one feather to the next. This is where the spread wing comes in.
This swan is part way through its wing spread. It will take a few more flaps to straighten all the feathers.
Not all spread-wing sightings were made by a solo swan (or in presence of a partner). A number were made in a small crowd. Juveniles also spread wings.
In the end, one of the greatest tests that the spread-wing was just a part of preening is the numbers. There were about 18 swans in this group and about the same number subsequently stood and flapped their wings.
But, it is a grand conclusion to feeding and preening.