Imagine the rhythmic croaking of cranes as they announce their arrival in spring, or the sudden pulse of color across the landscape as plants begin to flower. These events, marking changes in the life cycles of organisms, are the phenomena of interest to phenology, literally the "science of appearance." People have used phenological observations for centuries to maximize crop production, prepare for seasonal allergies, and anticipate optimal birdwatching conditions.

Aldo Leopold, Wisconsin’s conservation hero and author of A Sand County Almanac, kept phenological records partly in order to track relationships among species, and partly as a hobby. The Leopolds made phenology a family affair, with all the kids joining in the fun of being the first one to observe a certain bird on the wing or a new bloom! In fact, one might read A Sand County Almanac as an elaborate "phenology journal," recounting the family’s experiences and observations during their times at "The Shack," their now-famous weekend getaway and site of their pioneering work in ecological restoration.

What the Leopolds could not have anticipated is just how useful their records would prove to be for documenting climate change. Aldo’s records span 1935 to 1945; in 1976, Aldo’s daughter Nina Leopold Bradley and her husband Charlie resumed marking the dates of blooms and birdsongs at the Leopold Reserve. These two sets of data, collected in the same location over the span of nearly 70 years, offer a unique opportunity to assess the effects of climate change on the life cycles of plants and animals in Wisconsin.

Changes in the timing of phenological events may reflect warmer average temperatures; the life cycles of many organisms are cued by temperature as a signal of good conditions for growth and reproduction or abundant food. Many of these organisms, such as early spring-blooming plants and birds that migrate short distances, have now commenced their spring activities 2–3 weeks earlier than they did in Aldo’s time. On the other hand, some late-summer prairie plants actually bloom later as summer stretches longer in than in the past. But the Leopolds’ records show that other organisms, such as long-distance migrant birds whose cycles are guided by daylength rather than temperature, have kept the same phenological "schedule."

One noteworthy plant whose date of first bloom has advanced by nearly three weeks is the Compass Plant, star of the "Prairie Birthday" essay in the “July” section of A Sand County Almanac. During the 1930s and ‘40s, Compass Plant began to bloom, on average, on July 15; today, it would no longer find its place within the “July” chapter, as its average date of first bloom over the last ten years is June 26.

Nina suggests that by paying attention to the comings and goings of birds and keeping track of what’s in flower, we come closer to realizing the Leopolds’ vision of a Land Ethic, or the extension of the human conscience to include and build relationships with our “biotic community.” Plus, it’s a lot of fun! As Nina says, “all my friends have become phenologists.”

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