Hi Joel,
Thanks for these explanations and clarifications. Very helpful. I
absolutely take your point about the problem drawing a conclusion regarding
climate-change effects on migration. And I admire those fictitious names in
your reply to Alan! I thought I could beat the rain this morning and just
go enjoy observing some Rufous, but alas, the window between light and rain
was too narrow. Still, the Violet-Green and Tree Swallows weren't
bothered, and it was a lovely sight watching around 50 of them zip and dip
above the north end of Delta Ponds.
Good birding to all,
Rebecca
On Fri, Mar 22, 2019 at 6:49 AM <clearwater@xxxxxxxx> wrote:
Hi Rebecca,
Thanks for your comment. I noted those parts but they don't fully address
the issue that I described. This isn't exactly in my wheelhouse either, but
I deal with some similar issues in sampling of groundwater contaminant
plumes.
The elimination of checklists was used to screen out locations with too
few ebird checklists (i.e. low temporal density of observations) but this
does not address the problem of locations where observer density has
increased.
The logistical regression seems to be aimed at determining the median
first arrival date for the remaining set of observers in an area (the
author calls this "mean first arrival date" but the procedure that he
describes should yield an approximation of the median rather than the
mean).
If all observers were independent, then this median value *could* be seen
as comparable, in some average sense, to the first arrival date recorded by
a single observer sitting in a lonely cabin by the woods, in the same place
a century ago.
But observers in the modern network are not independent (as illustrated by
the fact that we're all discussing Rufous Hummingbirds by e-mail right
now). A single report of an outlier on the leading edge of the arrival
curve, communicated through eBird and other digital means, triggers an
intensified focus on that species and its expected habitat.
In the case of Rufous Hummingbirds, I'd guess that everyone reading this
spent a little more time watching their feeders after they saw the first
reports -- I sure did! The northward range expansion of Anna's Hummingbirds
and development of a birdfeeding industry are also confounding factors.
More observers are likely to have feeders out and filled already in
February. That increases the chance of one observer picking up an early
migrant, then alerting the local network of observers.
The "median first detection date" for a dense network of observers is
going to be conditioned on the first detection in the network, most
plausibly leading to a forward shift in the apparent first arrival date.
Correcting for this bias is difficult but should have at least been
discussed in this type of paper.
The argument concerning "the expertise of historical observers" is
speculative at best, and possibly based on a faulty premise. Modern
observers are equipped with much better optics, identification guides,
audio recordings, etc. as well as historical knowledge regarding when to
expect certain migrants. Along with use of attractants such as hummingbird
feeders, playback devices are now in widespread use. This author attempts
to discount these factors by citing biographical information about a single
historical participant who reported the first Rufous Hummingbird in one
locale for more than 20 years. Such a record, if you think about it, could
only be possible in a very sparse local network of observers.
I suspect that your final remark here, "... it does seem an interesting
way to bring two citizen-scientist data sets into conversation" is a among
the main reasons why this paper was accepted for publication. It's good to
see someone trying to work with the historic phenology data, considering
the diligence that it represents. But I'm skeptical of its use for
supporting this kind of conclusion about climate-related impacts.
Joel
On Thu, 2019-03-21 at 20:55 -0700, Rebecca Hartman wrote:
Hi Joel,
If I understand the article, he tried to address this issue with theelimination 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.
Rebeccajournal as prestigious as the Wilson Journal.
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
which is a key factor affecting the studied variable, "mean first arrival
There is no correction for, nor discussion of observer density,
date."
easily-recognized species such as Rufous Hummingbirds as a random process,
If you consider detection of first arrivals for
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.
project that Jessica Zelt led.
I'm a big fan and supporter of the North American Bird Phenology
study cited in this paper, by providing her with boxes full of old journal
I also helped Stanford researcher Dena MacMynowski on the 2007
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.
response to global climate change. But this type of analysis is not strong
The timing of spring migration *may* be creeping forward in
evidence, even if it supports what most of us believe.
--
Joel Geier
Camp Adair area north of Corvallis
--
Dr. Rebecca Hartman
Associate Professor of History
History Department
Eastern Oregon University
http://eou.edu/history
541-962-3599
