In 2017 I was conducting bird surveys as a volunteer at the Manassas Battlefield National Park. I was helping to catalogue the presence of two species, The Northern Bob White Quail and the Henslow’s Sparrow. The Park Wildlife Management personnel and I were interested in seeking out the birds in selected areas of the Park
I would go out to the Bob White areas in the early morning hours so I could be there in time for sunrise. I usually went out earlier than necessary, and I walked well-known paths to be at the listening point while it was still dark. I would pack-out a folding chair and a thermos of coffee. When I got the listening point, I would sit and watch the stars in their motion across the night sky and see them fade as night turned into Dawn. At Dawn I opened my coffee thermos, and poured a cup, and toasted the new day.
The survey was conducted in the Spring and we would listen for the daybreak calls of the coveys of quail we hope to hear. There were twenty of these sites scattered around the Park. The Park personnel and I divided the sites up so we could cover all of them during scope of the annual survey.
The sky might be clear when I went out in the early morning before dawn, but on the ground it was dark. If I had not had several decades of experience in walking the Park, I might have gotten turned around. I wrote about my experience in an article titled Frosty Morning and published on this site on 15 November 2018.
The Park personnel and I would often talk about the birds of the Park and how we thought that they would be affected by climate change, especially as the average temperatures warmed in the more northern parts of the species’ range.
In order to develop a better understanding of the potential impact of climate change on bird species, I searched for related articles. A good one I found regarding bird species and changes in their range due to climate changes, was based on surveys of numerous species in Finland between 1974 and 2010.
The results are basically that yes, the ranges do change due to changes in climate. The ranges of the various bird species change with an expansion at the northern/top/cold edge. But the southern edge is not moving northward/poleward. Part of this is that a species would have to lose their niche, basically become extinct, in the southern regions in order to say that they are no longer using the southern/warm edge.
I had initially thought of a bird’s range as a box that would move north as the climate warmed. However, that does not appear to be the case. As it turns out the box stretches and gets bigger as the range extends to the North. The range expands northward with the increasing temperature and the birds take advantage of more range.
Climate change may affect a bird species physiologically in that its old range may become too hot or too wet for the bird species to thrive. They have to change or move. But these conditions, even if they do not directly affect the birds, may cause a portion of the bird’s range to become unusable at the level of the current population if a food source dies out due to the change in the overall climate, or if the food source moves out to a more acceptable range, or if the food source becomes unavailable at a time that it is need for the bird’s reproduction and life cycle. An example of this latter was published in Science New in 2006.
The first article I read about the impact of climate change on bird species was a 2006 article in Science News concerning the timing of the arrival of the European Pied Flycatcher in their nesting area. The article pointed out that the birds migrate based on the length of daylight in their wintering area in Africa. But the appearance of the caterpillars, the major food source at their nesting area for feeding their chicks, was based on temperature. With the northern temperatures warming earlier, by the time the birds arrived, the caterpillars had reached the next stage in their life cycle and are no longer available for the birds and their nesting brood. The numbers of the Flycatchers in some of their historic breeding areas had fallen by 90%. The study found “a correlation between declining Flycatcher numbers and the timing of the peak food for their chicks.”
I recently ran across a journal article concerning birds of China and the effect of climate change on their range. The article pointed out that the extension of a bird’s range may meet an obstacle that it cannot pass through. This might be a range of high mountains or an open ocean. The birds at that point have reached the limit of their range. The birds may well have to make a change in their diet or risk being unable to maintain the new range that they have colonized. For the birds to succeed in the new region they must find fruiting plants or insect or other food stuff available in an abundance on which the species colonizing the area can survive. This is especially hard if the new range is populated by a species that already relies on a limited supply of that food. The picture at the top of this article is a version of some of the charts from the article showing potential movement of species.
What about the Quail and Henslow’s Sparrow at Manassas? Will they have to move? So much of a bird’s ability to use a region is predicated on their ability to find suitable habitat. Destruction of habitat will force out a population. However, as the climate grows hotter and more humid over the next several decades these bird’s ranges may expand, but it is different for each species. The southern edge of the Quail’s range is well below us, extending into Mexico. I do not believe we will see a change in the population of Quail due to climate change. However, for Henslow’s Sparrow, here in the Mid-Atlantic region, we are between the breeding (northern) and the non-breeding (southern) range. We may lose our small, but for me dynamic, local population. There may be issues for the Henslow’s Sparrows in the southern reaches of their breeding range where we are located. as it becomes hotter and wetter. Only time will tell.
Article regarding study in Finland, The breeding ranges of Central European and Arctic bird species move poleward. may be found at: http://europepmc.org/article/PMC/3447813
Science News article (only available to subscribers to Science News) on European Pied Flycatcher may be found at: https://www.sciencenews.org/article/no-early-birds-migrators-cant-catch-advancing-caterpillars.
Article regarding range shift of Chinese birds under the potential of climate change: (PDF) Shifts in bird ranges and conservation priorities in China under climate change (researchgate.net)