On Friday I did a long day hike around Cutthroat pass in the North
Cascades. While eating lunch in a cluster of trees there were waves of
birds, various warblers, Townsends solitaires, white crowned sparrows and
others. They would drift in and sort of build up in numbers until finally a
few would head out to the next clump of trees, followed shortly by the
others in a loose group. Over the course of two hours I watched this
bunching then moving behavior and got curious so I climbed up the hill to
get a broader view. The birds were following a very consistent pattern of
movement. They would fly into a group of trees, stay there for a few
minutes as the "wave" gathered in number, then move to the next clump of
trees. Each "wave" of birds used the same groups of trees, flying
consistently from one tree group to the next. The tree groups they choose
to use all had krummholtz growth mixed with some taller trees. I did not see
a single bird which varied from this pattern, although I only watched for
two hours. I hiked further down the trail and the same use pattern was
repeated about a mile away. I made sense since the krummholtz growth
provides dense cover and there was an actively hunting prairie falcon
working the area. At one point the falcon perched above the largest gap
between two group of trees and then stooped as birds moved between the gap,
chasing a larger bird (robin?) into the dense growth before pulling up. I
saw the falcon three move times working the gaps between the tree islands.

Rob Sandelin
Naturalist, Writer, Teacher
Snohomish County
Whose legs are still a bit sore from the mileage