Nature Notes

Written by Tolly Beck
Tolly Beck is the horticulturist at Lasdon Park and Arboretum in Westchester County. She was formerly a horticulture educator for New York Botanical Gardens in the Bronx and Cornell Cooperative Extension of Rockland, NY.

Fall Bird Migration

 Early fall is the time of year that many of our local birds are leaving for their southern migration.  They have spent the last few weeks putting on weight in preparation for their journey.  Weight gain for birds is often triggered by the shortening of day length.  As the sun begins to set earlier each day, birds know it is time to increase the energy-rich polyunsaturated fats in their diets.  Birds that have been eating seeds all summer will switch to an insect rich diet. The fat that is accumulated by this switch is needed for in-flight energy.  Birds start their journey by burning fat instead of protein and carbohydrates, avoiding the phenomenon known to endurance runners as “hitting the wall”.

 The majority of land birds migrate at night.  These are primarily birds that have a forest habitat and are not agile fliers.  Night migration offers them cooler temperatures, less air turbulence, and protection from large birds of prey.  During the day night migrators can drop down to feed and rest.  This presents a wonderful opportunity to see birds that are not usually found in our local area. 

 The Cornell Lab of Ornithology estimates that each autumn an average of 4.7 billion birds leave the U.S. over the southern border heading to the tropics. The fall migration is always much larger than the spring migration because birds are now leaving their breeding grounds and their young are making their first migration.  We can help migrating birds that pass through our area by putting out suet, sunflower seeds and water in which to bathe and drink.  Welcome them for the brief time they visit and wish them a safe journey.