Tweets

I was at Marymoor yesterday morning in the thick fog. At one point, on the
slough, I could see a male Bufflehead. Squinting through my binoculars, I
could also barely make out a female right next to the male, but the male was
MUCH more visible.

It got me to wondering if anyone has considered differential predation as a
causal influence in sexual dimorphism. If predators (i.e. eagles, harriers,
falcons) took 5% of the males and 5% of the females, the population of
Buffleheads would be 5% less. But if the predators took mostly males because
they are more obvious, the breeding capacity of the Bufflehead population might
not be affected at all.

In discussions about gender differences in plumage, I have heard statements
that indicate that females are generally drab to avoid detection while on the
nest, etc. But under a differential predation hypothesis, the males would
become more obvious to differentially attract predation. That is, there would
be an evolutionary force making the males brighter, as well as a force making
the females drabber.

In thinking about this, my first question to myself was whether the birds could
evolve towards dimorphism when the brighter males would be more frequently
predated. It would seem that selection would work against this theory.
However, while it is a bit of a stretch, let me hypothesize that more of a
bright males' *daughters* might survive if their brothers were brighter.

Any thoughts?

== Michael Hobbs
== Kirkland WA
== hummer at isomedia.com