Migration in Motion
Crisp mornings, crunchy leaves, and the call to migrate. Autumn ushers in transition and transformation within the natural world. It also means our feathery friends are on the move.
Migration is the seasonal movement of birds between wintering and breeding grounds, essentially following the region of optimal resources. When food sources and temperatures decline in the north, many species will go south to spend winter where there are greater resources (food and nesting territory are top priorities). As spring warms and blooms, they will return north in time for a bounty of food and nesting locations, providing the optimal resources to reproduce. And so the cycle continues.
A microscopic view of a bird’s feather at 10x magnification. (Photo by Faith Forry)
While many species migrate, some are able to stay put year-round despite the cold with adequate food supplies. Short-distance migrants will make a short journey, perhaps to different levels of elevation. Medium-distance migrants might travel the spanse of a few states. Long-distance migrants move between the U.S. and Canada to Central and South America.
Not to state the obvious, but birds don’t exactly have Google Maps or a handy GPS to map their journey. No, birds utilize much more complex (and reliable) navigation systems, which differ across species. To start, birds will exhibit zugunruhe, or migratory restlessness, in the direction in which they will fly. Solar compass navigation involves birds using the sun to find their direction. As the sun moves across the sky, birds compensate for this solar movement by shifting their direction by about 15 degrees every hour. Stellar compass navigation involves using star orientation to lead their path; this method is utilized by birds which migrate at night (such as waterfowl). While orienting themselves by the North Star would seem plausible, as it maintains a rather fixed position in the sky, birds do not seem to use the North Star for navigation. Instead, birds orient themselves according to constellations close to the North Star, as using more than one star is essential if one or more stars are hidden by clouds during the night. Although, stars rotate around the North Star throughout the year. Some species have mechanisms for time compensation while others do not. While migrating during the day or night, birds will use landmarks such as mountain ranges, coast lines, waterways, and even cities to orient themselves. Other mechanisms of navigation include innate homing instincts, olfactory cues, and sensing the earth’s magnetic fields. It goes without saying, but the complexity of their traveling instincts is remarkable; yet, there is still so much about their navigation which is not fully understood and has yet to be discovered.
Fall in Pennsylvania means prime viewing of raptor migration. According to the Pennsylvania Department of Conservation and Natural Resources, hawks can commonly be spotted in Pennsylvania’s ridges during October. Kestrels, merlins, and peregrine falcons are often sighted throughout October, and goshawks and golden eagles are seen in November. Around the same time in November, waterfowl will be arriving at Pennsylvania's lakes and ponds from their northern breeding grounds. To learn more about fall migration in Pennsylvania and for a list of state parks and prime locations for viewing this miraculous migratory phenomena, visit https://www.dcnr.pa.gov/GoodNatured/Pages/Article.aspx?post=17. You can stay up to date by viewing a live map of bird migration forecasts at https://birdcast.info/ (The Cornell Lab of Ornithology, Colorado State University, and UMassAmherst).
Written by Faith Forry — September 23, 2020
Drawing of migrating birds from Canva.
