I'm mildly but not entirely surprised that this paper got published in a
journal as prestigious as the Wilson Journal.
There is no correction for, nor discussion of observer density, which is a key
factor affecting the studied variable, "mean first arrival date."
If you consider detection of first arrivals for easily-recognized species such
as Rufous Hummingbirds as a random process, then with more observers you'd
expect that "mean first arrival dates" should creep toward earlier in the year,
even if the actual migration phenomenon is unchanged.
I'm a big fan and supporter of the North American Bird Phenology project that
Jessica Zelt led.
I also helped Stanford researcher Dena MacMynowski on the 2007 study cited in
this paper, by providing her with boxes full of old journal records from Oregon
Birds etc. She and her colleagues reached a much more credible conclusion, that
"first arrival dates" are not a robust estimator of the timing of bird
migration.
The timing of spring migration *may* be creeping forward in response to global
climate change. But this type of analysis is not strong evidence, even if it
supports what most of us believe.
--
Joel Geier
Camp Adair area north of Corvallis
