Bruce

Your observations of CB Chickadee aggression toward Black Caps is
noteworthy. I know of at least one study that has looked at the niche
partitioning of between these two species. In general, Chestnut Backed
Chickadees forage further out on the branch tips and higher in the canopy,
and prefer conifers over deciduous. The situation becomes interesting on
the northern Olympic Peninsula, where Black Capped Chickadees, at least
formerly, were uncommon or absent in many areas. In these "insular"
situtations, CB Chickadees will expand their niche to include BC habitat.
On the Olympic Peninsula, Black Capped Chickadees now appear to be
invading many areas where formerly only CB's were found. This is in
association with logging and forest conversion to younger, deciduous
stands. Perhaps when individuals of the two species first come in contact,
there is some aggression, until the typical habitat use patterns are
established. Alternatively, you may simply have observed a nesting pair,
that was chasing out all chickadee intruders, regardless of species.
A recent article in Behavior Ecology found evidence for
antipredator benefits of flocking among titmice and other small birds.
Even though BC and CB Chickadees may suffer some foraging competition, the
benefits of antipredator behavior (vigilance, mobbing, etc.) may favor
coexistence, as the postings from other tweets have suggested occurs.
Say, I am planning to move back to the Oly Pen in the fall after I
defend my thesis; lets we will go out and have a word with these
chickadees....

Fred

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Behavioral Ecology Research Group
Dept. of Biological Sciences
Simon Fraser University
Burnaby BC V5A 1S6 Canada
phone: (604) 291-4374 Lab
291-5864 Office
fax: (604) 291-3496
email: fsharpe at sfu.ca

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