Record breaking Pine Siskins!
November 29, 2020
Early this fall, sources (most notably the Finch Research Network, with their annual Winter Finch Forecast) predicted that the winter of 2020-21 was going to be a big flight year for many species of finches in the eastern half of the United States. These large invasions of boreal forest seed eaters into more southern latitudes are known as irruptions, and this year in particular has been one of the biggest recorded irruptions of Pine Siskins, a generalist seed eater and boreal forest breeder.
Irruptions generally track food abundance, and researchers are often able to predict the magnitude of a southerly flights by monitoring boreal forest and montane seed crops of mostly coniferous trees (like spruce and fir) but also in a few deciduous trees (like alders and birches).
Unlike the irruptions in the eastern United States, western irruptions tend to be less pronounced across the entire region at once (potentially as there is more suitable coniferous forest habitat for seed eaters), but can be very pronounced locally.
This year has been a particularly interesting year on the Farallones for irruptive finch species. Since August 26, we have recorded 159 Lesser Goldfinches, 23 Purple Finches, and 3 Cassin’s Finches (a rare migrant from high elevation conifer forests).
And most notably, this year we broke the island’s highest daily record for Pine Siskins on October 25. The weather that morning looked good for a migration fallout, with cloudy skies, 10 miles visibility, and very light winds. Island biologist Jim Tietz watched as a meager flock of a few siskins grew, and grew, and grew until there were at least 587 siskins zipping around the lighthouse in large murmurations, occasionally landing and covering their chosen perches. Jim was able to capture a video of the flock that former island intern Adam Searcy used to count the siskins.
The fall of 2020 at the Farallones has shown a substantial increase in Pine Siskins detected from the previous year with a 2106% increase (data from eBird). Even if our one big day is removed from the data, the increase is 475%, which is still a huge increase. It’s hard to compare our data to most mainland locations because observer coverage at those sites is too variable. However, the Palomarin Field Station (also Point Blue), just 20 miles to our northeast conducts daily area searches, and the number of siskins detected at the station this fall compared to last fall has increased 607% (data from eBird). This provides evidence that the numbers of siskins this fall are not just a phenomenon particular to the Farallones, and that this pattern is at least a bit more widespread.
Whether our largest daily recorded flight is related to anything happening with populations in the eastern United States, we cannot say for sure, but it is still very exciting!