[obol] Bird migration timing and global climate change

[DAVID IRONS]

Joel,

I think you just made my point about not wanting to start a debate about this topic on OBOL.  While I fully agree that current climate issues are a major cause for concern (we probably will find little dissenting opinion in this forum), the term "global warming" is overused, and in my opinion misleading.  If current trends continue, not every corner of the globe will be warmer, in fact some might be quite cooler.  Global climate change is accurate, global warming is not.  People who don't take the time to learn about CO2 issues, potential interruptions of thermohaline circulation etc., use "global warming" to explain things as simple as why it rained more in March of 2008 than it did in March of 2007 (just an example, I don't know which March saw the most precip), or why Western Tanagers showed up earlier this year than last.  Climate changes may have some bearing on such things, but as you point out with your handful of leaves story, they may not.  

Anectdotal human observations are inherently biased by the prior knowledge, experiences and the expectations of the observer.  Generally speaking, reports of birds on OBOL fall into this category.  Referring back to my discussion of Hammond's and Pac-slope call notes from yesterday.  I don't expect to hear these calls in mid-March and it is quite possible that I might not make the connection if I heard one of these calls on that date.  However, I fully expect that I might hear such call notes after about the 9th or 10th of April.  Additionally, I also don't waste my time going to Skinner Butte before about the first week of April because I know full well such a visit would produce a day list that I could compile on any day from December 1st through March 31st, and would likely yield no neotropical migrants.  If a Pac-slope or a Hammond's shows up on Skinner Butte in mid-March the odds are exceptionally high that I won't be there to notice it. 

What is important is that we keep making observations, reporting those observations and having discussions about what MIGHT be causing the variances in our observations, whatever those causes might be.  I was only attempting to point out that there are very plausible observer effort factors that might explain some of the earlier arrival detections we are seeing.  

Dave Irons
Eugene, OR 
 
> From: joel.geier at peak.org
> To: obol at lists.oregonstate.edu
> Date: Sat, 19 Apr 2008 20:38:31 -0700
> Subject: [obol] Bird migration timing and global climate change
> 
> Hello folks,
> 
> Just two days ago, on Thursday afternoon, I was sitting in a lecture
> hall at Ecole des Mines in Nancy, France listening to the keynote
> address by one of the world's eminent global climate scientists, Jean
> Claude Duplessy. Little could I guess that this experience, and not the
> lifer STORKS that I saw from the train between Nancy and Strasbourg a
> few hours later, would be the most relevant thing for Oregon's birding
> list, when I returned home.
> 
> Dave Irons has raised some valid points regarding the problems with
> using "first arrivals" of bird species as indications of the effects of
> ongoing global climate change, or "global warming" as it is often
> referred to in the popular press. Lars Norgren has also made some good
> points about the difficulty of comprehending global climate change,
> within the span of a baby-boomer lifetime. I do have some disagreements
> with how Dave and Lars have characterized the climate situation, and its
> effect on birds, but let's start with some areas where I agree with both
> of them.
> 
> There are some significant problems with using statewide "first arrival"
> birding records as data for this purpose. Dave has accurately identified
> the main issues:
> 
> - Increased observer density over time;
> 
> - Increased monitoring in the southern part of the state;
> 
> - Increased knowledge of how to detect first arrivals by ear;
> 
> In fact, a few years back I boxed up the entire (25+ year?) run
> of /Oregon Birds/ to a Stanford researcher, so that she could have her
> students copy the state field notes, and then try to analyze the first-
> arrival data for a relationship to climate change. So far as I
> understand, she and her collaborators were unable to come up with a
> clear pattern that could be correlated to observed changes in climate.
> 
> The first issue that Dave raised (increase in observer density) is
> difficult to correct for, since we lack good numbers for how observer
> density has increased over time. As someone who deals with groundwater
> contamination and how it spreads as water moves underground, I find it
> helpful to think of bird migration as analogous to an "advective-
> dispersive" process:
> 
> Later on this spring when you're standing by a stream looking for a
> Northern Waterthrush, try tossing in a big handful of willow leaves and
> watch what happens. The main mass of leaves will move along at a speed
> equal to the average current. However, they will gradually spread out in
> the stream. A few will end up way far ahead of the main mass of leaves,
> and a few will lag farther and farther behind. 
> 
> This happens because different leaves encounter slightly different
> fluctuations or eddies in the stream current. For most leaves, the
> fluctuations more or less cancel each other out, so on average the
> leaves move at the same average speed as the stream. However, a few
> leaves with especially "good luck" will catch more bits of fast current,
> and move far out in front, while other leaves with "bad luck" will lag
> far behind. If the fluctuations in current that are encountered by a
> given leaf are purely random, the leaves end up being distributed
> according to the infamous "bell curve" (in statistical terms, the
> "normal" or Gaussian probability distribution), which spreads out more
> and more as the the leaves float downstream. Five miles downstream, the
> leaves might be spread out over a distance of nearly a mile.
> 
> To draw the analogy to bird migration, the "stream" is the basic
> instinctive urge to head northward in spring. The "eddies" or
> "variations in current" are the various things that individual birds can
> encounter along their migration trek. Maybe one bird decides to hunker
> down when it hits a neotropical rainstorm, or gets spooked by a predator
> so it veers to the left when its comrades veer right, with the result
> that it catches a different wind speed and either moves ahead or falls
> behind the migrant population as a whole. A bird that gets ahead of the
> main flock one day might encounter more favorable conditions the next
> day, and move even further ahead. 
> 
> Think of all the little events that can happen to individual birds as
> they move north, and how each of these events can spread out the flock,
> just like those leaves on the stream. By the time a given bunch of
> neotropical birds on average travel from Panama to Eugene, a few of them
> might be in Vancouver B.C. while a few still haven't made it past San
> Diego.
> 
> Going back to the leaves on the stream, now imagine that there's a
> "leafer" five miles downstream, who's very excited about seeing willow
> leaves floating by. So he watches for the first one that he sees
> floating by each day, and keeps track of the time. But he's kind of
> busy, so he can't check the stream every minute. Chances are, he'll miss
> the first few leaves, but he'll see his first leaf by the time 10 or 20
> have floated by. 
> 
> Suppose this "leafer" gets a few more friends excited about his hobby,
> and they check the stream at different times. The more "leafers" there
> are, the better the chance that one of them will spot one of the earlier
> leaves to float down the stream. So the apparent "first leaf arrival"
> time will become earlier, the more "leafers" there are.
> 
> Coming back to birds, this is essentially what happens when, from year
> to year, there are more and more birders checking places like Mt. Tabor
> and Skinner Butte. There is just a higher chance of an Oregon birder
> encountering one of the earlier arrivals.
> 
> Now suppose that one of our "leafers," who happens to be named Dennis,
> decides to set up camp about 100 yards upstream of the original leafer.
> On average, he's going to spot leaves a bit earlier than the rest.
> That's basically what happens when someone named Dennis decides to set
> up a bird banding station in SW Oregon.
> 
> Finally, suppose that our leafers improve their leaf-watching skills
> over time. Wait a second, I don't even want to go there with this
> "leafer" analogy! I guess I've reached the end of where it makes sense.
> But I guess it's easy to see how increased skill in detecting birds
> could have the same effect as more birders in the field, in detecting
> early arrivals.
> 
> Now let's come around to the climate change and its effect on birds,
> whether observable within our personal experiential windows or not.
> 
> First off, the scientifically accepted term is "anthropogenic climate
> change," meaning the portion of ongoing climate change that is
> attributable to human activities as opposed to other ("natural") causes
> such as variations in earth's orbit and inclination relative to the sun,
> solar sunspot cycles, volcanism etc. 
> 
> There is very little doubt that this amounts to "global warming." The
> Intergovernmental Panel on Climate Change (IPCC) states in their 2007
> report (http://www.ipcc.ch/ipccreports/ar4-syr.htm):
> 
> " There is very high confidence that the global average net effect of
> human activities since 1750 has been one of warming, with a radiative
> forcing of +1.6 [+0.6 to +2.4] watts per square meter."
> 
> It is a serious misconception to say that the main issue is an increase
> in atmospheric carbon, although atmospheric carbon (principally in the
> form of carbon dioxide or CO2) is indeed a major driving force of
> anthropogenic climate change. In this respect, the IPCC has strengthened
> their conclusions since their previous report in the 1990s. Atmospheric
> carbon concentrations are a direct problem for a few things such as
> coral reefs (since increased CO2 in the atmosphere affects the chemical
> equilibrium relationship between the calcium carbonates which make up
> coral reefs versus dissolved calcium in sea water). However, the
> indirect effects of increased CO2 (along with other anthropogenic
> greenhouse gases including methane and nitrous oxide) on global
> temperatures are the main concern for our natural ecosystems in Oregon.
> 
> It is also a serious misconception, and frankly silly, to worry about
> the political implications of using the term "global warming." Global
> warming is well-documented and beyond controversy. What has been
> slightly controversial, at least up until recently (and only by a
> handful of naysayers), is the anthropogenic component of global warming.
> With the latest IPCC report (see link above) , the anthropogenic
> component is beyond real political controversy. The current U.S.
> President and the three leading candidates for his job have all now
> acknowledged this, though some of them took longer than others. 
> 
> Anyway, it is silly to censor one's self based on political perceptions.
> There might still be a few holdouts in Congress but there are no
> holdouts among serious scientists working in the field of climate
> research (I'm sorry, but our so-called "Oregon state climatologist"
> doesn't count in that category, even if some lesser-known scientists at
> OSU, with real Ph.D.s, are legitimately part of that group). 
> 
> Lars stated that Oregon has had higher mean temperatures over some 7000
> of the past 12,000 years of the postglacial epoch. I'm not sure where he
> gets those exact numbers, but they are believable if one looks at the
> oxygen isotope record from deep-sea sediments, which are considered to
> be one of the more reliable proxy measurements for global temperatures.
> 
> However, quoting those numbers in such a way can be very deceptive,
> since this obscures the fact that our Earth has been in the later
> portion of an interglacial period during this time. Based on what is
> well-known about variations in the earth's orbital parameters (referred
> to as the Milankovitch cycles), since about 10,000 years ago when the
> earth came out of the Younger Dryas glacial episode (see Daansgaard et
> al., "Evidence for general instability of past climate from a 250-kyr
> ice-core record," /Nature/ 364:218-220), our Earth has been in a
> relatively stable or gradual cooling phase, up to the onset of the
> Industrial Revolution. What's happened due to recent human activities is
> that we've switched from gradual cooling to precipitous heating of the
> planet.
> 
> You might think it's good, that we're staving off the inevitable next
> glaciation by pumping carbon into the atmosphere. But we've overshot the
> natural mark, and (according to the models) will very soon be causing
> more rapid climate change than natural ecosystems have ever had to deal
> with -- meaning that the rate of migration of climate belts will exceed
> the natural rate at which long-lived species such as trees can shift
> their ranges.
> 
> The real issue of concern is not simply climate change, or even
> anthropogenic climate change. It's PRECIPITOUS climate change, like our
> planet has never seen before, except in a few instances that are
> recorded in the fossil record as catastrophic "mass extinctions."
> 
> What does this mean for Oregon birds?
> 
> I think it's a mistake -- and frankly unrealistically OPTIMISTIC -- to
> expect that birds will be a leading indicator for climate change. I
> guess that most of us were brought up with the idea that birds are a
> leading indicator of environmental problems, which was true for problems
> like pesticides. However, climate change is different, since the species
> that are most quickly affected are the less mobile species, like plants
> and frogs and salamanders.
> 
> What is clear is that major aspects of Oregon's climate have already
> started to change, as exemplified by spring snow melt. Anecdotally, a
> Wheeler County rancher that I regularly stop by to talk to tells me that
> his irrigation water coming off the Ochoco Mountains is running one and
> a half to two weeks earlier in spring now, than it did thirty years ago.
> An article in this month's issue of /Physics Today/ (Levi, 2008, Physics
> Today 61:4(16-18) or see www.physicstoday.org) confirms his impressions
> with quantitative hydrologic data: The fraction of precipitation
> remaining as spring snow and the minimum winter temperatures in western
> mountain ranges, as well as the center of timing for the Columbia River
> basin flows, have all shown significant shifts relative to annual
> variation, over the past 50 years.
> 
> Oregon's birds will need to adapt to such changes, or else miss out on
> their prime windows of habitat suitability. Over time, we can expect
> that natural selection will favor subpopulations that show up a bit
> earlier, on average, since they will encounter more suitable
> conditions. 
> 
> However, it's an open question whether birds can adapt as quickly as the
> climate is changing. Going back to the leaf analogy, early arrivals
> likely have more to do with random variations in the "currents" that
> affect individual migrant birds along the way, rather than any genetic
> propensity to leave Panama at an earlier date. 
> 
> Thus natural selection may not be all that quick or effective in
> producing bird populations with a genetic propensity to migrate earlier
> in the season. Mother Nature hasn't often had to deal with changes like
> the one that our species is presently imposing on the system. When she's
> had to, she hasn't done so well.
> 
> Good birding while it lasts,
> Joel
> 
> --
> Joel Geier
> Camp Adair area north of Corvallis
> 
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