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 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. 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 created a web app that allows viewers to explore the data (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 levels are 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 ago and more.
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 at my web app. 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 spend the 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 springtime 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 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 Nino effect in the Pacific).
Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at
whwilson@colby.edu
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