Most authorities agree that, like climate change, the range
expansion of Anna's Hummingbird is part of the impact of global
environmental caused by the human footprint. Introduction of
non-native plant species, urban micro-climates and the general
warming of the west coast have all contributed to the expansion
of Anna's Hummingbird, White-tailed Kite, Red-shouldered Hawk,
Western Scrub Jay, Black Phoebes, etc.

The impact on Rufous Hummingbirds is probably minimal, however.
They really only interact at artificial habitats created in backyards.
Rufous Hummingbirds are more aggressive (at least in my yard) and
run the Anna's out. Anna's Hummingbirds and Rufous Hummingbirds
have very diffierent breeding site preferences.

I'd be more worried about all the rat, pigeon and crow habitat
we're creating.....

Subject: Is the range of Annas hummingbirds artifically being extended by humans?
From: "Rob Sandelin" <floriferous AT msn.com>
Date: Tue, 21 Feb 2006 15:17:17 -0800

So when I read about the levels of human intervention in keeping Anna's
hummingbirds here I wonder if this is such a good idea. What are the
ecological impacts of the actions of artificially supporting high levels of
these birds? Do they compete with, perhaps drive out the native Rufus
hummingbirds? Assuming early flowering resources are limited, what impact
does this unnatural residency of Annas have on migrating Rufous? Do they
pass disease or parasites to other birds? Are we propping up a species that
perhaps does not belong here to the detriment of others? It seems like its
one thing to provide nutrients to native birds throughout the winter, maybe
its another thing to artifically support the winter range of a species.


Rob Sandelin
Naturalist, Writer
The Environmental Science School
http://www.nonprofitpages.com/nica/SVE.htm


--
Mike Patterson
Astoria, OR
celata at pacifier.com

SNOWY OWLS on the Lower Columbia - links to current information
on the 2005 irruption event:
http://home.pacifier.com/~neawanna/SNOW/SNOW20051120.html