The magic of Harvest Moon birdwatching

The moon provides the perfect backdrop for watching birds migrate at night. Observers with spotting scopes and small telescopes can watch the show anytime the moon is at or near full. Photo illustration: Bob King

Where is the interface between the cosmos and planet Earth? Everywhere. Watching birds fly across the shiny coin of the Harvest Moon last night was but one example.  Every September anyone with a telescope magnifying 30x and up who happens to look at the full moon can’t help but notice the occasional silhouettes of migrating birds fluttering across the moon’s face.

Many birds migrate at night both to conserve energy and avoid predators. Identifying the many warblers, blackbirds, sparrows, vireos, orioles and other species that fly across the moon while we sleep may be next to impossible, but seeing them is easy.  Just for fun, I counted the birds in the five-minute interval between 10:57 and 11:02 p.m. last night while looking at the moon at 76x through my 10-inch telescope. The total came to 16, which multiplied by 12 yielded an hourly count of 192 birds.

The reflection of the Harvest Moon creates a fiery squiggle in Amity Creek last night near Duluth. Photo: Bob King

As you might suspect, most of those birds crossed the moon from north to south (about two-thirds) with the other third traveling either east to west or northeast to southwest. Only one little silhouette flapped back up north in the ‘wrong’ direction. Who knows. Maybe it veered off course to pursue a nighttime snack.

According to the Chipper Woods Bird Observatory, located in Indianapolis, most nighttime migrators begin their flight right after sunset and and continue until about 2 a.m. Peak time is between 11 p.m. and and 1 a.m. Bird typically migrate at altitudes ranging from 1,500 to 5,000 feet, but on some nights, altitudes may range from 6,000 and 9,000 feet. I could tell the high ones from the low ones by their size and sharpness. Nearby birds flew by out of focus, while distant ones were very sharply defined and took longer to cross the moon.

Watching birds pass across the moon is a very pleasant activity and reminiscent of meteor shower watching. At first you see nothing, then blip! a bird (meteor) flies by. You wait another minute and then suddenly two more appear in tandem.  Both activities give you that delicious sense of anticipation of what the next moment might hold.

The best time to watch the nighttime avian exodus is around full moon, when the big, round disk offers an ideal spotlight on the birds’ behavior. It’s a fine sight to see one of Earth’s creatures streak across an alien landscape, and another instance of how a distant celestial body “touches” Earth in unexpected ways.  If you’d like to learn more about birdwatching by moonlight, check out the Chipper Woods webpage.

10 thoughts on “The magic of Harvest Moon birdwatching

  1. Hi Bob,
    Yours looks to be a fascinating blog. Consider yourself bookmarked ;)
    I hauled out my dusty old Meade 2080LX3 in hopes of seeing the Pinwheel supernova, and found you while googling around for a decent location map image. Thanks a million for providing such a good one! Between the full moon, distant city light and what not… have yet to resolve the supernova, but did haul out the lounger last night to stare at the moon. So far no migrating birds in East Texas. Thanks for taking the time to put up such an informative site.

    • Hey MBZ,
      Nice to meet you and thanks very much! East Texas must mean a full moon very high in the sky last night. Good luck with the supernova. It’s still hanging in at magnitude 9.9/10.0. By the end of this week, it will be much easier to see without competition from the moon.

      • Thanks for the encouragement to stay up late. Nice to meet you too! I have Ursa Major mostly blocked with just the handle (phew) poking up past the treetops. If the moon would just knock off all the glowing business long enough for me to catch a glimpse… sure would be exciting. Took all my persuasive powers to get my husband to help set up the tripod and scope. Sure wish I still had the youthful durability to handle that heavy scope alone (…and stay up all night ;)

        • MBZ — That’s right. The Dipper would be quite a bit lower for you than here in Duluth. I think that’s cool you’re so psyched to see it. Let us know when you finally meet the SN face to face.

  2. Hello Astrobob,
    Could I get permission to use your picture of birds migrating past the moon at night? I’d like to show it to people coming to a nature program about animals that fly at night. We are doing the program twice this summer. I think it is so interesting that you can spot migrating birds this way, wow!!
    Sincerely,
    Avery Gunther

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