Hi Joel,
If I understand the article, he tried to address this issue with the
elimination of numerous checklists based on a four-parameter best- fitting
logistic curve model. Then he argues near the end of the article that,
"Given the expertise of historical observers and their specified task of
identifying first arrivals (Zelt et al. 2012), one could argue that
historical first arrival dates would more closely approximate true first
arrival dates than extracting mean first arrival dates from eBird
checklists. If this is the case, then the comparative method described in
this paper would have the tendency to underestimate climate related
advancements in birds." (p. 541) Granted, this stuff is way outside my
wheelhouse, and I have no idea how other studies construct statistical
models, but it does seem an interesting way to bring two citizen-scientist
data sets into conversation.
Rebecca
On Thu, Mar 21, 2019 at 7:13 PM <clearwater@xxxxxxxx> wrote:
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
