Spring is a wonderful season for naturalists. The earth is awakening after a winter’s slumber. Our eyes and ears are tuned to the sound of the first spring peepers, the first Ruby-throated Hummingbird, the first blooming Trillium in the forest, the first leaves on red maples, and even the first black fly.
The documenting of these firsts in spring has a formal name, phenology. But being aware of phenological events is not just an academic exercise. Even in the 1700s, British farmers judiciously waited to plant their crops until particular species of migratory birds arrived. The farmers sowed their seeds according to an ornithological calendar.
For the past 23 years, I have been coordinating a volunteer-based phenology study to document the first arrival of over 100 species of Maine migratory breeding birds. Observers are asked to report their first sighting of as many of those species as they see along with their geographic location. We know have over 65,000 arrival dates. The project has taught us much about the timing and variability of the arrivals of the various migratory species that nest in our state.
To make this information available to any birder, I have developed a web application to allow a user to explore the data. I invite you to visit: https://hobbes.colby.edu/arrival/
A drop-down menu allows you to choose a species and slider bars permit you to select a year and display features. Clicking on the Data Summary tab will give the average, median and other summary dates for a species/year combination.
Tracking changes in phenological events is important in the face of global climate change. Although some people deny the role of human activities in leading to global temperature increases in the face of overwhelming evidence, the fact that the earth is warming is undeniable. The polar ice caps are melting, sea level is rising, and average temperatures are rising around the globe.
Many phenological events are driven by temperature. We have good evidence that the arrivals of migratory birds are earlier now than in past years. One such study compared arrivals of migratory birds in Worcester, Massachusetts and Ithaca, New York. Both of these areas have long-standing bird clubs with records of arrival dates extending back into the 19th century. Virtually all of their migratory species are now arriving earlier than they did 50 years and more ago.
Numerous such studies have corroborated the pattern of earlier arrivals. Several bird banding stations that have been operative for 60 years or more reveal the same patterns.
You can explore the Maine data for trends of earlier arrivals over the past 23 years. Just choose Year with the Radio Button at the bottom left and click on Scatterplot.
Although the graphs for most species show a downward trend, indicating earlier arrivals, most of those relationships are not statistically different. For perhaps multiple reasons, Maine migratory birds are not responding as strongly to climate change as birds nesting in states to the south of us.
Some of our migratory breeding birds winter within the continental U.S. (short-distance migrants) while others winter in tropical areas of the Caribbean, Central America and South America (long-distance migrants). Short-distance migrants seem to be more responsive to spring-time temperatures. When a northeastern spring is mild, the birds continue their migrations and arrive in Maine relatively early. In cold springs, the birds rightly delay their migrations until conditions improve, resulting in a late arrival.
The web app can be used to investigate these patterns. Choose a species and click on Temperature.Departure.from.Mean. Negative values of Temperature.Dependence indicate a colder than average spring; positive values indicate a mild spring.
Click on Scatterplot to see the relationship. Red-winged Blackbird shows a particularly strong effect.
Lastly, clicking on the NAO.Index radio button allows a user to see the effect of this hemispheric weather phenomenon (analogous to the El Niño effect in the Pacific).
[Originally published on April 16, 2017]
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at firstname.lastname@example.org