Why is it that there are so few, if any, Black Swifts nesting at those
wonderful waterfalls along the Columbia east of Portland?

I figured it must be their low elevation. These birds want to be close
to the clouds when they leave the nest. Two things this summer
convinced me there is more to it than elevation.

1. I saw an evening swift come into the middle of a small, foothills,
low elevation waterfall. (500 feet)

2. I took a good long close look at some of these waterfalls and pretty
as they were, there really didn't appear to be any place to build a
nest.

Here is my reasoning. The waterfalls along the Columbia pretty much
share the same geologic history. Massive lava flows cool and the
Columbia cuts a gorge through the basalt. No twisting, folding,
cracking. These waterfall faces are made of columnar basalt. When it
cracks, the cracks run up and down. The birds try to build a nest and
the nest keeps falling down the crack and water keeps falling on their
little heads.

It frustrating for them so they look for waterfalls that have
fracturing that provides a flat surface for their nest and a nice roof
over their heads. I believe that if the rock of the falls is
unstressed columnar basalt it usually will have no suitable nesting
sites and so no nests.

We checked out Langfield Falls which is worse than basalt, some big
cobble conglomerate that looks like it came from the back of a cement
truck. No swifts here.
http://www.waterfallsnorthwest.com/waterfall.php?num=439&p=0

If my reasoning is correct it might offer an explanation not just for
the Columbia Gorge but for much of the Washington and Oregon nesting
distribution.

Oops this got too long.

Sorry

Larry Schwitters
Issaquah