[obol] Bird migration timing and global climate change

[Joel Geier]

Darrel & All,

We should make be clear that the database for understanding global
climate change is not especially short-term. 

Isotope partitioning in deep-sea sediments gives us a record of sea
water temperatures and global ice volumes, going back at least 2.5
million years. See Imbrie et al., 1984 in Berger et al.
(eds), /Milankovitch and Climate/, Reidel Publishing Company, p.
269-305. Ice cores from Greenland give a higher-resolution record for
the most recent 120,000 years (as described in the Dansgaard reference).

Bringing this back to birds and what things we can observe in the field,
Dave has pointed out the hazards of using "first arrival" data to judge
changes in bird migration. This is simply a particular case of a general
concept in statistics: the extreme values of a dataset are not its most
robust indicators.

A more robust indicator would be peak arrival or passage dates: those
times when a Phil Pickering sees hundreds of thousands of loons flying
north past Boiler Bay, or a Wilson Cady finds 50 Western Tanagers in his
cascara trees, or a Craig Miller reports thousands of Snow Geese or
avocets at Summer Lake, or a Darrel Faxon (with still better ears than
he lets on) hears beaucoup Swainson's Thrushes flying over Thornton
Creek before dawn. Unfortunately, keeping of such records by
recreational birders usually comes down to a few individuals who, as
Darrel notes, might go through changes in ability over the years.

The most rigorous, relevant data come from banding stations, hawk
watches, or other types of systematic surveys that sample the entire
progress of migration, in a given, fixed location each year. In our
region, most such surveys have only recently been established, but
biologists in other parts of the world (for example Britain and Sweden,
have accrued a much longer record of systematic observations, going back
at least to the time of Linnaeus.

Our region also suffers from a relatively brief folk record of bird
observations. The aboriginal inhabitants did not keep written records,
and much of their oral tradition was lost through the disease, wars,
forced relocations, and deliberate suppression of native cultures that
accompanied the Euro-American expansion into this area.  

However, it's different in other parts of the world such as Japan,
China, and Europe. Consider those storks that I saw on Thursday evening:
The record of when they show up to nest on rooftops in the Low Countries
(Netherlands etc.) must run back close to 1000 years. They are
conspicuous birds and figure prominently in European folk culture. The
same goes for (Eurasian) Blackbirds in England and cranes in Japan.

I presume that these longer-term records from other parts of the world
form the basis for the references to birds, in the following quotation
from the 2007 IPCC report:

> There is very high confidence, based on more evidence from a wider
> range of species, that recent warming is strongly affecting
> terrestrial biological systems, including such changes as earlier
> timing of spring events, such as leaf-unfolding, bird migration and
> egg-laying; and poleward and upward shifts in ranges in plant and
> animal species. Based on satellite observations since the early 1980s,
> there is high confidence that there has been a trend in many regions
> towards earlier ‘greening’ of vegetation in the spring linked to
> longer thermal growing seasons due to recent warming."

If we want to try to expand Oregon's contribution to this body of
knowledge, we should consider which migrant birds figure most
prominently in our current "folk culture." We probably shouldn't focus
on birds that are practically invisible, like Hammond's Flycatchers.

>From my stints as a field-notes editor, I would have to say that Turkey
Vultures and Rufous Hummingbirds are the birds that really get noticed
here in western Oregon. TVs are problematic because there is a mix of
short- and long-range migrants. Rufous Hummingbirds, as true neotropical
migrants, might be a better species to focus on, especially since such a
wide variety of people are fascinated by them. 

How long has the practice of keeping hummingbird feeders been popular? I
know they've been around all of my conscious lifetime (at least back to
1965). It might be profitable to seek out records of people who have
kept hummingbird feeders over the decades.

Happy birding,
Joel

--

Joel Geier
Camp Adair area north of Corvallis