Irruption Alert: Astonishing Pine Siskin Nocturnal Migration

By Ryan F. Mandelbaum:

On Sunday, October 11, Astronomer and Field Ornithologist Timothy Spahr captured sounds almost never heard in recorded history: the raspy call notes of Pine Siskins migrating at night. This month, these teeny finches have shattered expectations across the entire country.

Pine Siskins are out in full force in both the west and the east, descending on trees, bushes and feeders in noisy flocks and delighting birders who may not have seen this finch on their home turf in years. This autumn’s mega flight has not only broken records, but taught us more about the bird’s irruptive behaviors more generally.

Passerine birds like warblers and sparrows typically migrate at night, but ornithologists consider Pine Siskins to be exclusively diurnal, or daytime migrants. However, from October 10 to October 16, 2008, scientists Michael Watson, Jeffrey Wells, and Ryan Bavis recorded 190 Pine Siskins migrating at three sites near Gardiner, Maine for the first time in published history. This year, Spahr’s recording station in Middlesex County, Massachusetts once again picked up the flight calls of Pine Siskins migrating from 11pm until dawn, totaling several hundred birds. 

“It was really fantastic to hear Pine Siskins with the Swainson’s and Hermit Thrushes giving nocturnal flight calls amid a backdrop of duetting Great Horned Owls.” Spahr said.  

What’s going on? The 2008-2009 season was marked by an enormous movement of Pine Siskins as well, probably in response to depleted conifer seed crops in their native montane and boreal habitats. Watson, Wells, and Bavis hypothesized in their 2011 paper that Siskins might only express this trait in response to a severe food shortage, forcing them to take on a nocturnal migration pattern more typical of other songbirds. It’s likely that Pine Siskins are undergoing the same stresses this season, causing them to shift their behavior once again.

Even those without recording equipment can tell you that this year has been a historic one for Pine Siskins. On the morning October 11, birders at Higbee Beach in Cape May, New Jersey recorded a flight of over 5,000 birds. Around the country, Siskins are now frequent fixtures at well-known migratory pit stops; clouds of Siskins seem to outnumber goldfinches in my native New York City’s parks.

As impressive as the numbers are the locations where these birds are moving. A comparison of eBird maps between August and October shows that Pine Siskins are irrupting even in the western half of the United States, where irruptive bird behavior is less studied. Pine Siskins have already reached the Gulf Coast in the East earlier than previous eBird records, reaching New Orleans on October 12. A flock of 20 even showed up in Bermuda, where this bird is only rarely spotted.

We’ll continue tracking this year’s epic Pine Siskin flight. In the meantime, remember to log all of your sightings to eBird, and keep your feeders stocked with thistle/nyjer seed.

Photo Credit Ryan F. Mandelbaum

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