Natural & Seasonal Cycles

When Jefferson in March 1784 encouraged his friend Madison to “keep a diary” of weather observations, his specification of the “heads or columns” under which Madison should record data included these: “10. shooting or falling of the leaves of trees, of flours, and other remarkeable plants. 11. appearance or disappearance of birds, their emigrations &c. 12. Miscellanea.” Despite some unusual word usage and spelling, we can see that Jefferson wanted Madison to keep track of when trees leafed out and blossoms appeared in the spring, trees lost their leaves in the fall, the arrival and departure of migratory birds, and other occurrences of interest. (“In the miscellaneous column,” Jefferson wrote, “I have generally inserted Aurora boreales, and other unclassed rare things.”)

Jefferson did not consistently track seasonal phenomena in his own meteorological records, but more than 200 of his daily entries contain notations relating to plants or animal life. His zoological observations were primarily of wild creatures, such as the appearance of migratory birds or start of the frogs’ chorus in the spring. (An exception was his notations about when his mockingbirds, which were companion animals in his household, began to sing.) His notes on plant life, on the other hand, were predominantly of cultivated species, including not just garden vegetables such as peas, strawberries, asparagus, and cucumbers, but also trees such as cherries, apricots, and almonds. For both animals and plants, he was especially interested in a few key species that he considered to be seasonal markers. He named several of them in a letter he wrote to his 11-year-old daughter Maria on 13 June 1790 while he was on a trip to New York City: “We had not peas nor strawberries here till the 8th. day of this month. On the same day I heard the first Whip-poor-will whistle. Swallows and martins appeared here on the 21st. of April. When did they appear with you? And when had you peas, strawberries, and whip-poor-wills in Virginia? Take notice hereafter whether the whip-poor-wills always come with the strawberries and peas.” Swallows, interestingly, do not feature in his meteorological records, but purple martins, whip-poor-wills, peas, and strawberries appear multiple times. He was watchful of those favorite seasonal markers even during his residence in France in the 1780s, when he noticed, although less in his weather records than in other documents, his encounters with peas, strawberries, and nightingales (the songs of which substituted for the calls of whip-poor-wills in America).

By keeping track of these occurrences, Jefferson was collecting information related to what today is called phenology, the study of natural seasonal cycles and their relationship to climate. This area of science didn’t exist in Jefferson’s period – according to the Oxford English Dictionary, the word phenology, which is a blending of the root of “phenomemon” and the ending “-ology” – only appeared in the 1880s. Yet people in earlier periods were aware of connections of plants and animals with the seasons. Jefferson and others took the step of plotting details of seasonal change against the calendar, with an intention of tracking the information over multiple years. (Although Jefferson did not mention almanacs in connection with this activity, they provided a model for organizing cyclical occurrences with reference to the calendar.) The most striking example of someone tracking phenological data before the science was even defined is provided by the writer Henry David Thoreau (1817-1862). Over a period of years in the middle decades of the 19th century, Thoreau systematically recorded seasonal information about a large number of living species around his home in Concord, Massachusetts, as well as such weather-related phenomena as the freezing and thawing of Walden Pond. (For the utilization of Thoreau’s data by scientists in addressing questions of ecological and climatic change, see Richard B. Primack, Walden Warming: Climate Change Comes to Thoreau’s Woods [Chicago, 2014].)

Thoreau’s notes help ecologists examine variations through time, many of which can be attributed to the substantial climate changes brought about by human activity beginning in the Industrial Revolution. Although Jefferson’s notations about plants and animals are far fewer in number than Thoreau’s, they do indicate when, in his time and in the places where he was, some seasonal transitions occurred. Jefferson’s observations also tell us something about the species themselves in that period, such as geographical ranges or numbers.

Use the selection boxes on the left side of the Search page to find entries with notations to animals and plants, by category and by individual types within each category.

To learn more about intersections of animals, plants, and seasonal cycles in Jefferson’s observation records, click on the images below.

Plants, Animals, & Seasons


Discover seasonal and climate information regarding some of the animals and plants in Jefferson’s records.

Interactive Visualizations

Explore some of the interactive visualizations created from Jefferson's observations.