December 18, 2020
IS YOUR FEEDER FULL?
By Michael O’Brien
This has been a weird year in a lot of ways, but some of it has been good. For example, here in Cape May, we’ve been enjoying the largest finch flight in the twenty-five years that I’ve lived here. Representatives of eight different finch species have graced us with their presence in recent weeks, with Pine Siskins and Red Crossbills in record numbers, and Evening Grosbeaks making their best showing since the early 1980s. Watching the feeders has been a lot of fun!
In fact, birders across much of the Northeast have been experiencing what experts are calling a “superflight” of finches over the past few months. During this “irruption,” which may be the largest in a half century, every species of boreal finch is moving south, including Evening and Pine grosbeaks, Purple Finch, Common and Hoary redpolls, Red and White-winged crossbills, and Pine Siskin. In addition to these species, other boreal breeders, including Red-breasted Nuthatch and Bohemian Waxwing, are also on the move. These irruptions of boreal breeders are linked to natural cycles in seed and fruit production by various boreal tree species, the staple diet of these birds. In years when seed and fruit production are high (known as “mast years”), these species stay north during the winter. When production is lower, birds need to move elsewhere to find food. Each species has its particular preferred foods, so in most years, some species move more than others. This year, crop failure was particularly widespread, forcing all of these species to move south in large numbers.
Another reason that the scale of this year’s invasion is so large has to do with high breeding success over the summer. High summer cone crops benefited crossbills and Pine Siskins, and at the same time, an outbreak of spruce budworms provided an abundant food source utilized by Purple Finch, Evening Grosbeak, and Pine Siskin, as well as Red-breasted Nuthatch.
Not all of these species visit feeders, but many of them do. Smaller finches like redpolls and Pine Siskins prefer smaller seeds, particularly thistle. Sunflower seeds are preferred by most of the other finches, but note that Evening Grosbeaks seem to have a strong preference for tray feeders over tubes. Pine Grosbeaks prefer fruiting trees but will also visit feeders with sunflower seeds. Both crossbill species specialize on various conifers and only rarely visit feeders.
As a side note, if you happen to encounter Red Crossbills, try to get a recording of their flight calls. Red Crossbill taxonomy is complicated, with at least nine different “types” across North America. Each of these types specializes on particular types of conifers, and differ in core range. However, when food supplies are short, they wander and can show up well away from their typical ranges. In appearance, they differ only subtly in bill size, overall body size, and color intensity. The only reliable way to distinguish them is by analysis of their flight calls. Even if you don’t have a fancy recording device, you can still get diagnostic audio with any smartphone by using built-in voice memo or video apps, or any kind of recording app that you download. And if you do get recordings, please share them by adding them to your eBird checklist. By doing so, you will help researchers understand the movements of these fascinating birds.
Happy finching, and keep those feeders full!
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