COMMENTARY BY DR. DAVE SAMUEL
We know that our weather has been changing all over the globe. Witness the fires in Australia. About 16 million acres burned in New South Wales and Victoria. When you consider West Virginia is 15 1/2 million acres, you realize just how big those fires were, and are (they are still burning in some areas). Then there is melting permafrost changing the landscape of the Arctic North at a rapid, increasing rate. Then there is Venice, flooded Venice, and that city may never be the same. The question is, why are these things happening today?
The answer is simple, climate change. Years of extended summer drought left the Australian landscape dry and the forest floor littered with combustible material. Lightning fires were inevitable. Warm weather is melting the Arctic permafrost, which stores huge amounts of greenhouse gasses. That can’t be good. In Venice, climate change caused the highest tides in 50 years. No way to prevent that city from high water.
These are just a small sampling of the effects of climate change on our planet. So it should not come as a surprise to learn that climate change is also impacting birds. Every spring, hundreds of bird species leave their wintering grounds and fly north. Over the next three months, we’ll witness that migration through West Virginia.
Once here, food for adults and newborn nestlings is critical. Birds must time their arrival when insects, flowers and other foods are at their peak so that nestlings will have the greatest chance for survival. However, spring temperatures are changing. Plants are flowering earlier than ever before. Insect hatch times are changing. How will that affect breeding birds?
There have been several studies examining the timing of spring green-up and bird arrival. Are birds shifting their arrival time to compensate for a changing climate and the resulting shifts in avian food resources? It turns out that many species have made rather rapid shifts in the time they normally arrive, while others are making slow shifts, and a few are not changing their arrival times at all.
Here is the problem bird’s face: Photoperiod (day length) is the primary cue to get birds started on their long trek north. Photoperiod doesn’t change, but conditions at the wintering grounds, along the migration route, and on their breeding grounds do change. Somehow, birds have to adjust their departure time, or adjust their migration speed as they come north. They’ve always had to adapt to climatic shifts throughout evolutionary history, but in recent years, those climatic differences are much greater. Thus, if birds arrive and nest early, chicks hatch before peak food is abundant. If they arrive late, there might be fewer nest sites and declining food resources. Timing is everything.
One 12-year study (2000-12) showed arrival of migratory birds occurred earlier in most of the country, especially in eastern North America (that’s us). They examined data for 48 migratory bird species and found that green-up dates advanced significantly in the breeding ranges of 27 bird species. Those changes were 1 1/2 days per year. Interestingly, most birds also changed their arrival dates, but only by a mean of 0.7 days/year. So, in general, birds are changing their arrival dates in response to climate change. What researchers learned is the difference in arrival time in birds is not due to temperature, but rather to green-up time and the subsequent changes in insects and other foods.
The overall problem is the birds aren’t changing the time they arrive on their breeding grounds at the same pace as changes in green-up time. Even more concerning is the fact that over the 12 years of study, the interval between arrival and green-up has steadily increased. We don’t know what the long term meaning this has for some birds. Twelve years of data isn’t much when looking at something this complicated, so time will tell just how much climate change is affecting nestling survival.
The debate over the causes of climate change will go on. Are these cyclic changes that occur every thousand years or so, or are they man-caused changes brought about by overloading the human carrying capacity of the planet? Is the timing of spring bird migration the “canary in the mine” signal that we are getting closer to a global problem of huge proportions? Lots of questions, with answers way above my pay grade. But what the birds are telling us is that we each need to do our part to reduce all forms of pollution to maintain our quality of life.
Dr. Samuel is a retired wildlife professor from West Virginia University. His outdoor columns have appeared, and continue to appear, in Bowhunter magazine and the Whitetail Journal. If you have questions or comments on wildlife and conservation issues, email him at drdave4@comcast.net.
