Phenology Calendar

Every year, the Aldo Leopold Foundation continues on the Leopold family legacy of keeping phenology records with the publication of the annual Phenology Calendar. Each month of the calendar features beautiful images of animals, plants, and insects with corresponding sidebars written by Dr. Stanley Temple, professor emeritus of the University of Wisconsin – Madison and recent inductee to the Wisconsin Conservation Hall of Fame. Various dates throughout the month indicate when certain phenological events may begin to occur, such as the start of sandhill crane migration or the first bloom of bottle gentian. Unlike other calendars, the Phenology Calendar not only helps you to keep track of events happening in your life, but also aids you in noticing what is happening in the natural world around you.

2024 Phenology Calendar Cover


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“…phenology is a very personal sort of science. Once he learns the sequence of events, the phenologist…may even fall in love with the plants and animals which so regularly fulfill his predictions.” – Aldo Leopold

Phenology and Leopold

Phenology is the study of annual events in nature that are influenced by seasonal changes such as climate and weather. Have you ever noticed when Baltimore orioles first arrived in the spring? Perhaps the first time you saw the rose bushes bloom in your yard? If so, you were observing a phenological event! Phenology is as easy as noticing the changes in nature that are occurring in the wild or even in your own backyard.

Left: Aldo Leopold journaling at Shack, Right: Leopold’s phenological records, 1899

Aldo Leopold began keeping phenology records at a young age at his childhood home in Burlington, Iowa. He greatly enjoyed figuring out the connection between phenological events such as the return of a migratory bird and the budding of a tree in spring. Leopold continued to record phenological observations throughout his whole life, and passed on his love of all things nature to his children. After purchasing the Shack in 1935, the entire Leopold family took part in weekend Shack phenology observations. His eldest daughter, Nina, continued adding to the family’s phenology records until her death in 2011. Today, the staff at the Aldo Leopold Foundation maintains the Leopold family tradition of yearly record keeping.

Left: Nina with the “essentials” at the Shack, Right: Nina taking phenology notes later in life, Below: Nina’s phenology notes, 1978

The data collected by the Leopold family along with other natural resource professionals around the state have allowed scientists and community members to track seasonal and climatic changes in Wisconsin for close to 90 years. Many natural events are now happening days to weeks earlier in the year due to a warming climate. Like the Leopold family, your family can also take part in phenology observations and help future scientists who study climate change. Phenology is an exciting educational activity that gets the whole family outside and engaged in nature.

“Keeping records enhances the pleasure of the search and the chance of finding order and meaning in these events.” -Aldo Leopold, “A Phenological Record for Sauk and Dane Counties, Wisconsin” for Ecological Monographs (1947)

Everyone Can Be a Phenologist

Whether you are a phenology enthusiast, casual observer, or just someone who enjoys nature, the Phenology Calendar is for you! With new photographs, informational sidebars, and phenology data added each year, there is always something to learn regardless of your phenology experience.

The Phenology Calendar may originate in Wisconsin, but the data in the calendar can apply to anyone living in the United States. Using Hopkins’ Law, which states that phenological events vary at the rate of 1 day for each 15 minutes of latitude, 1.25 days for each degree of longitude, and 1 day for each 100 feet of altitude, you can figure out when phenological events will occur in your area. Click here to access a table with Hopkins’ Law applied to popular Midwestern cities.

Phenology Calendar

Do you enjoy observing and exploring nature? Have you ever wondered how plants and animals synchronize their growth and survival with seasonal changes in the environment? If you answered “yes” to either of these questions, then the Phenology Calendar is for you!

The 2024 Phenology Calendar is now available for purchase! Secure your copy today, and get your holiday shopping done early—the calendar is a great gift option for the nature lover in your life! Click here to learn more about the 2024 Phenology Calendar.

Phenology Calendar 2023

Purchase your copy of the 2024 Phenology Calendar today!

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“Phenology… is a “horizontal” science” which transects all ordinary biological professions.  Whoever sees the land as a whole is likely to have an interest in it.” -Aldo Leopold, “A Phenological Record for Sauk and Dane Counties, Wisconsin” for Ecological Monographs (1947)

In The News

Interested in learning more about phenology? Click the links below to read more about the history between Leopold and phenology.

A Life-Long Passion for Phenology
Phenology: Tracking Nature Through the Seasons
A Phenological Record for Sauk and Dane Counties, Wisconsin, 1935-1945 (1947)

Phenological changes reflect climate change in Wisconsin (1999)
Record-Breaking Early Flowering in the Eastern United States (2013)

Featured photography courtesy of John Cordes, Dave Freriks, Eric Preston, Jim Stewart, Erik Thomsen, and Ted Thousand.