Hello, tweets.

While catching up on old journals I just read an interesting article.

Koenig, Walter D. 2002. European Starlings and their effect on native
cavity-nesting birds. Conservation Biology 17: 1134-1140.

I'll just copy the abstract, which tells the story.

"European Starlings (Sturnus vulgaris) were introduced to New York City
in 1890 and have since become one of North America's most common
species. Starlings are aggressive competitors and commonly usurp
cavities of other hole-nesting species. These characters make it a
clear choice for a species whose invasion is likely to have
significantly affected native cavity-nesting birds. Using Christmas
Bird Counts and breeding Bird Surveys, I compared the mean densities of
27 native cavity-nesting species before and after invasion of sites by
starlings. Contrary to expectations, only 10 of the species exhibited
significant effects potentially attributable to starlings, and only
half of these were in part negative. However, in 2 of the 5 species
that showed negative effects, evidence for a decline in one analysis
was countered by an increase in the other, whereas in 2 others declines
were likely due to factors other than starling competition. Only
sapsuckers (Sphyrapicus spp.) [he combined Yellow-bellied, Red-naped,
and Red-breasted, as they weren't separated back in the old days]
exhibited declines potentially attributable to starlings that were not
countered by other data. Although declines may still occur if starlings
continue to increase, the results of this study fail to support the
hypothesis that starlings have had a severe impact on populations of
native birds. These results highlight the difficulties of predicting
the impacts of invasive species. Native hole-nesting birds have thus
far apparently held their own against the starling invasion, despite
the latter's abundance and aggressive usurpation of often limited
cavities."

This conclusion does not surprise me much, based on my own thoughts
over the years. I've always thought it was all too easy to blame
starlings for the decline of birds such as bluebirds and certain
woodpeckers, without paying sufficient attention to other ecological
factors in play.

Parenthetically, some years ago a lengthy paper on the negative effects
of nearly 800 bird introductions on other bird species all over the
world found relatively little (Ebenhard, T. 1988. Introduced birds and
mammals and their ecological effects. Swedish Wildl. Res. 13: 1-107.).
The invasion of exotic species can have severe consequences and should
justify extreme vigilance against it, but birds don't seem to be a
taxonomic group to worry about as much as many others. In fact,
increases in population sizes of *native* birds often seem to have more
consequences - e.g., predators such as Bald Eagles, corvids, and gulls
and brood parasites such as cowbirds. Even their effects are constantly
debated.

Dennis Paulson
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Dennis Paulson & Netta Smith
1724 NE 98 St.
Seattle, WA 98115
206-528-1382