Field Notes Connections
~ by Jim Eagleman
Fall brings a big change to the plant world. It is time to promote more of their own kind. They do this by producing flowers that mature and produce seeds. Seeds can be in the form of pods, nuts, or“ stick-tights,” and the packaging is crafted to ensure seeds get distributed. Wind, water, and burs caught on animal fur, aid in the distribution.
Some fruits stand out against changing color leaves called foliar flags, signaling migrating birds to stop and feed. Studying the need for birds to replenish energy expended during long flights helps us learn what routes they take and where plants grow. It’ s been theorized by biologists that plants can extend their range by being attractive to moving birds who distribute seeds along the way. The study of migration isn’ t just to learn more about bird behavior, it can help us understand the important role of plants, how they survive, and how they move.
Studies have also revealed that the amount of sugar or fat in fruit supplied to birds varies at different times of the year.
In summer, when birds are on the nest, they are sedentary and use short distance flights to feed. While incubating, a task requiring lots of energy, they feed on multi-seeded fruits that have a greater chance to germinate locally. These plants grow in ideal habitats where birds have chosen to rear their young. Short flights are powered by the sugars in the fruits we also enjoy, such as raspberries, blackberries, and blueberries.
In contrast, when long-distance fuel is required, it’ s the single-seeded fruits, high in lipids and maturing later in the year, that are available enroute: dogwood, spicebush, multi-flora rose hips, sassafras drupes, and pokeberries, to name a few. These plants have been shown to extend their range, from historic reports.
Do bird requirements for fuel cause plants to produce food at a time it’ s needed? Possibly. This is called a“ selective pressure,” where food choice can cause a plant to change. Over time, it results in plants responding to the wildlife community that exploit them.
Our pokeberry plant grew well over summer and in late fall as I write this. It leans against the screened-in porch. A recent, cold rain collapsed branches, and the plant is now a mass of thick stems, some with clusters of purple berries still attached. This example of a fatty fruit that ripens in late summer-early fall matures just in time for the robins,
58 Our Brown County • Nov./ Dec. 2025