Surge in unusual suspects

The eastern United States and to a much lesser extent Minnesota are experiencing a banner year for irruptive boreal birds, including a "superflight" of finches. This is according to a report from the Cornell Lab of Ornithology and the American Birding Association.

An irruption is a migration of large numbers of birds to areas where they aren't typically found.

Why do these birds move south out of their boreal homeland?

They feed on conifer seeds and spruce budworms. This past year conditions for seeds and worms aligned. Consequently, there was ample food for nestlings, and a very successful hatch.

By late fall they had more or less eaten the pantry clean and moved south to find food.

Being seen are representatives from eight finch species: pine siskin, common redpoll, hoary redpoll, purple finch, pine grosbeak, evening grosbeak, red crossbill, and white-winged crossbill, plus red-breasted nuthatch. Reports were gathered from several sites including Hawk Ridge in Duluth.

"Entire populations of trees will synchronously produce millions of seeds in some years but produce none in others," the report's authors wrote. It is theorized that this is in order to blunt the impact of predation: in this case by squirrels.

Spruces produced ample cones for white-winged crossbills, pine siskins and one of the 10 red crossbill types in northeastern North America, leading to high breeding success in the area, according to the report.

Ontario and Quebec are experiencing one of their most intense spruce budworm outbreaks in 40 years. This has led to population booms in evening grosbeak, purple finch, and to a lesser extent, pine siskin and other finches, the authors said.

Evening grosbeaks are undergoing their largest irruption in more than 20 years, according to the authors.

From reports on a state birding e-mail list and the eBird collection of data from birders, not many of these birds have reached Minnesota in noteworthy numbers. But it's early. Maybe some snow would help.

Cornell Lab of Ornithology's eBird is an internet bird sighting collection point. Checking that in mid-December I found one report of evening grosbeak, one of white-winged crossbill, and one for Bohemian waxwing. For the entire state.

Our feeders in west Hennepin County attracted six purple finches and one red-breasted nuthatch. Winter is young, however.

Jim Williams