Most people (including myself) are surprised the first time they learn that a huge percentage of birds migrate primarily at night. While the public is used to hearing about migrating hawks that are observed by day, or perhaps seeing geese in V formations up in the clouds in the late fall, I suspect that the majority of Americans have no idea that the vast majority of migrant songbirds are doing most of their travel at night.
Considering the diet of most of these migrants, it makes perfect sense. The majority of migrants that are headed to Central and South America are going there because the colder winters in North America mean their primary food source is not available: insects. Yet they can't just take off from Massachusetts and in one long flight make it to Mexico.
If they migrated during the day and merely slept at night, these birds would have a tough time catching enough insects while en-route to provide the energy necessary to keep them going for thousands of miles. However, by migrating at night, the birds can feed during the day, storing up energy for the next leg of their trip.
On a quiet night in the fall, you can sometimes hear small chip notes of migrating warblers or thrushes overhead. And they are among the millions of songbirds passing over the East coast while we sleep.
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