Wednesday, December 3, 2008

Happening Right Now: Crossbill Invasion

From Birding Central, Kenn writes: In the northeastern quadrant of the U.S. and adjacent southern Canada, this is shaping up to be a huge winter for northern invaders. I’ve written already about Pine Siskins invading southward, and that push is continuing, with flocks reported all over the east. Northern Shrikes have appeared in unusual numbers, and so have Snowy Owls, with many around southeastern Canada and the Midwest. Flocks of Evening Grosbeaks have put in brief appearances in several places. Now, just within the last few days, flocks of White-winged Crossbills have set the hotlines buzzing all over Ohio.

Of all the "winter finches," White-winged Crossbills are the most nomadic. They specialize on cones of spruces, hemlocks, and tamaracks, using their trademark crossed bill tips to pry open the cones and get to the seeds. The map here shows their overall range in North America -- but they are never present throughout this range at once. They concentrate where there are bumper crops of cones, nesting and raising their young where the food is abundant at practically any time of year. When the cone crop fizzles and the food supply declines, flocks of crossbills fly fast and far in search of the next good feeding area. The purple area on the map shows the limits of their year-round range; within those limits, the same birds might nest in Quebec one year, Alaska the next, Ontario a few months later, sweeping back and forth across the continent to find the cones.

The dashed blue line on the map shows the (very approximate) southern limit of their winter wandering. They certainly don’t come south to this line every year, or even once every five years. The classic setup for an invasion is to have a huge crop of spruce cones in eastern Canada, so that the crossbills nest and raise lots of young, followed by a crash in the cone crop in fall. When that happens, White-winged Crossbills may suddenly appear all over Ohio and surrounding areas -- as they have in the last few days.

A birder who knows the callnotes might detect these birds anywhere, the flocks passing overhead in rapid flight. To get a sit-down look at White-winged Crossbills, birders are seeking out places where northern evergreens have been planted. Parks and cemeteries with lots of hemlocks have been productive here. The crossbills appeared in the Cleveland area last Saturday, in Toledo on Monday, in Columbus today. There are probably hundreds more flying around that no birder has seen yet.

3 comments:

  1. Wow..I just found out you two do a blog...how exciting for me. I thank you for the informative posts.

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  2. Thanks, Dawn! We've been talking about doing this for quite some time and finally decided to bite the blog bullet and do it.

    We're pleased that you enjoy it.

    Kim & Kenn

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  3. I'm also excited to see you guys are blogging, and was especially psyched about your White-winged Crossbill post. Coincidentally I just wrote about my experience since we're witnessing the invasion here in the Finger Lakes and Southern Tier of NY.

    Looking forward to more of your posts!
    -Mike

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