ON BIRD WINGS AND CLIMATE CHANGE—NEW EVIDENCE OF WARMING

A recent study of thousands of song birds found that they are shrinking in size over the last forty years.  Is this the result of climatic warming? 

It’s very difficult proving certain questions in a satisfyingly conclusive method.  Does tobacco smoking cause lung cancer?   Well we can correlate lung disease with smoking very nicely,but correlation is not causation.  Eventually, we developed enough correlative  evidence to feel confident that indeed there is a causative relationship there...and we have thankfully done so with tobacco use.  

We have similar “proof” problems in  regard to global warming or “rechauffement climatique” (climate reheating) this phenomenon involving a massive and complex atmosphere is much more difficult to make conclusive statements about.  Is it heating?  What are the causes of its “rechauffement”?  Meteorologists and climatologists have carefully recorded temperature data from many sites over the earth’s surface, but not all of them show a clear trend toward warmer temperatures.  Weather and climate phenomena are variable, the atmosphere is complex, many factors can mask the trend lines in our graphs . These data often reveal both spikes of high— and low temperatures. Some sites record periods of excessive high temperature, while others record low readings.  Massive snow storms and unexpected outbreaks of polar air masses which do not fit the hypothesis also may be difficult to understand or explain ‘as warming”.  Though we now have an enormous bank of data which supports the contention that our atmosphere is warming,  these many perturbations in the atmosphere give “the climate deniers” ammunition to claim that what we are experiencing may just be a figment of someone’s over-active imagination.   

But as in the “tobacco wars” of the past, more and more observations and data points eventually help flesh out the case for a glacially slow, but none-the-less certain warming trend in the atmosphere—toward warmer and warmer air.  Warmer air that is almost certainly the result of increasing levels of greenhouse gases such as human-generated carbon dioxide from burning fossil fuels. 

The most recent scientific data which points to a warmer atmosphere comes from the realm of ornithology (the scientific study of birds).   The inescapable fact is that birds are critters most intimately adapted to the earth’s complex atmosphere. They live their every  moment of life dependent upon the physical properties of the air.  Many species of song birds (and other classes) fly hundreds or even thousands of miles though this complex fluid as they make their seasonal migrations.  To survive these challenging journeys they must be highly adapted to the physical properties of the air in which they fly to survive.  Even small changes in air temperature can alter the efficiency of flight over these long distances to which the birds must be well adapted to survive. .  Birds are relatively short lived animals, which reproduce annually  and thus are capable of rapid   evolution  over relatively short periods of time.  Furthermore, they are a class of organisms which have been studied in great detail over many scores of years and in which even small changes in anatomy can be detected and documented. 

The Wall Street Journal (by Robert Lee Holts, December 4, 2019)  reported on a study by The Field Museum of Natural History in Chicago, (published in Ecology Letters, Dec 4, 2019). The investigation headed by Dr Brian Weeks of the University of Michigan and his colleagues measured and analyzed more than 70,000 specimens of 52 different bird species which died in collisions with high rise buildings in Chicago over a forty year period from 1978 to 2012.  Weeks and his colleagues measured the weights and sizes of the birds and the lengths of their wings.  As a result Weeks and his colleagues were able to document changes in songbird size and wing length over at least forty generations. They found that over the period studied all of the species decreased in size while in many of them their wings grew slightly but measurably and significantly longer.  

So what does this mean? It’s a well-established observation  that animals —across almost all classes and genera are larger in northern climates  than those which live in warm climates (See Bergman’s Rule) .   The reason for this is what we may call a— physical imperative—which  has to do with the physical relationship between volume or body mass and surface area.  (Imagine the surface area as related to internal volume  of a large sphere like a beach ball. Compare that to that of a small sphere like a golf ball.  The golf ball has more surface area per unit volume than the beach ball. )    For this reason It may be an advantage to be larger in a cold climate, since a larger body has less surface area per unit body mass, and this smaller surface area aids larger animals in conserving heat energy.  The converse holds for animals in warmer climes.  It is either unnecessary for them to be larger (and an advantage to be smaller) or simply the evolutionary  advantageous lies in the more effective cooling of a body of smaller mass since a smaller body has more surface area per unit volume.  

In the species of birds that are resident or non-migratory, for example the common  Blue Jay which ranges across many states from north to south in North America, we find those in the south are typically much smaller than those in the north.  Another classic example is the size of the Red Fox which also ranges widely over different climate zones. This species is smaller in the south and much larger in the north of its range.  I can attest to the fact that the Florida Black Bear is very much smaller than those of the same species that I have seen in Vermont.

Weeks and his colleagues found in the 52 species of song birds studied, over the 40 years.that all exhibited changes such that  “as the bird’s bodies got smaller, their  wings gradually got longer”.  The changes in weight and wing length were very small, but significant over all the ages, species and sex of birds studied.   The study authors suggest, the bird’s lower body mass may relate to less ability for fat storage, an essential factor on their long migrations. Longer  wings may be an adaptation for this purpose. ( Alternately longer wings (as this author suggests) may be an adaptation to flying long migration flights  in less dense (warmer) air.  Lower density air may reduce wing “lift” and warmer air may require longer wings to maintain lift.) 

Those birds too large, or with wings too short, simply do not make the challenging migration and die.  They do not reproduce.  Those that do survive pass on their genetic pattern to their young.  
The Weeks team, studying over 40 generations of birds,  found that the changes in existential adaptations (to warmer air) resulted in song birds which were smaller and with longer wings. 

The fact  that all the different species of song birds are all changing in the same way consistently over the period of time studied,  the only reasonable conclusion  seems to be that Week’s songbirds are adapting to warmer air temperatures.  Holts WSJ piece (op cit) notes that the author Brian Weeks stated: “We can say with fair amount of confidence that the changes are associated with increasing temperatures. ”

This study is not reliant on the collection of temperature data from points on the globe that have variations in elevation, humidity, wind and other factors including human error that may affect these data.  Weeks study is based upon the the measurable morphological changes in animals which for their very survival are highly dependent upon being perfectly adapted to long periods  of flight in an atmosphere of some given physical characteristics. The changes reported can not be explained in any other way than that the medium in which these critters fly has changed over the last 40 years. It’s average temperature has risen and the animals have adapted to those changes with morphological response to warmer temperatures.   

It’s noteworthy that the WSJ piece also noted that similar studies of birds decreasing in size in Australia and South Africa have been recently reported. 

No question—the atmosphere is warming. 

WSJ author Robert Lee Holts also added a few interesting facts about the frightful mortality of these birds which have been so useful in documenting climate change. 

Holts reports  that domestic cats kill 3 billion birds annually.  Yes that is billion birds!!!

That is a figure based on data from US Fish and Wildlife Service and the Smithsonian Migratory Bird Center. This is a national disgrace!  These are song birds which are protected by international treaties.  The author adds that  Cornell Lab of Ornithology at Cornell University figures reveal that high rise building i n the USA kill another 600 million migrating birds annually.  Another example of human stupidity. .