Fallout of Owls

Even though the week is only half over, we have already had two instances of weather-related fallouts of owls at MSRW’s owl-banding station at Historic Mill Creek Park near Cheboygan.

Astute observers are familiar with migrant fallouts, when birds pause migration and come to the ground in large numbers. There are two main causes. One is geographical – migrants cross a large water body, such as the ocean, and come to the ground at the first land they encounter, exhausted and needing to refuel after many hours in the air. These occur at predictable places and times, such as peak spring songbird migration along the Gulf Coast of the U.S.

The second cause is weather-related – migrants encounter severe weather, such as rain, snow, or fog, and opt to come to the ground rather than fly through the foul weather. This can occur anywhere and can result in some spectacular numbers of birds, usually songbirds, in unusual places. For example, a few years ago in my home state of South Dakota, several days of dense fog during peak sparrow migration grounded tens of thousands of white-throated and white-crowned sparrows in little prairie towns in an eight county area. Most veteran birders have fallout stories of their own. Even raptor watchers, such as those at MSRW’s hawk watch, observe weather system impacts on the degree and direction of raptor migration.

What distinguishes these examples is that observers are able to SEE the effects of weather on bird migration. But we can not see owl migration and thus we don’t really understand how weather affects them. Owl migration banding stations can shed light on this mystery. Sunday night started out with reasonable weather until just after midnight when we suddenly caught two owls. Within 20 minutes, it started to rain and kept raining until daylight. This is a typical situation when we experience owl fallouts at banding stations. Owls will come down 15 to 45 minutes before the rain hits, and we know we need to get them banded and released, and close the nets quickly. Last (Tuesday) night was slightly different. Again, the weather was quite nice to begin with but we weren’t catching many owls. But at 2 AM, six owls showed up in our nets. Just as we were extracting the last of the owls from the net, a dense fog rolled in and the Mackinac Bridge foghorn started up. Apparently the owls didn’t want to fly through the fog and came down to roost. So our owl-banding station not only helps understand migration routes and speeds through the area, but also what affects owl migration.

Season Totals (March 15 through April 6):

Northern Saw-whet Owl: 81 (75 new, 6 recaptures)

Barred Owl: 1

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