Evening Grosbeak irruption

 

An elegant pair of Evening Grosbeaks (male, top) perch in the top of an Eastern Hemlock (Tsuga canadensis) in Ashland County, Ohio. I made this image last Saturday, and there were about 50 others in the area. Bonuses included a pair of Common Redpolls, and two flyovers of small groups of White-winged Crossbills.

In regards to winter finches, the big news this winter is the Evening Grosbeak. These robust, vociferous birds of the north woods used to stage regular southward irruptions into Ohio and points south, but these incursions have become nearly non-existent in recent decades in much of the east and Midwest. Thus, a newer crop of birders is reveling in easy opportunities to cast eyes on these extraordinary birds. Evening Grosbeaks quickly recognize feeders, and are about as likely to turn up in someone's yard as anywhere. If a ravenous flock does materialize, prepare to budget more for sunflower seeds. Flocks foraging in the wild are often smitten with Box-elder (Acer negundo) seeds. This maple holds its fruit well into winter, and is common throughout Ohio.

Map courtesy of Birds of the World online/Cornell Lab of Ornithology. If you want a superb source of avian information, this comprehensive compendium of bird monographs is a must. GO HERE for subscription information.

The Evening Grosbeak's stronghold is in western Canada and western U.S. mountains. About a century ago, this species began moving eastward, eventually colonizing boreal forest regions all the way to the east coast. The expansion is sometimes tied to an increase in use of Box-elder as a planted ornamental tree. I have my doubts - not that these grosbeaks like Box-elder fruit, but that a sudden proliferation of plantings caused the species to stage a large-scale eastward expansion.

Box-elder is very much of a successional species, flourishing in cut-over and disturbed habitats, in addition to its typical floodplain habitat. The grosbeak's expansion correlates with the widespread logging of the early 20th century. The great swaths of cut-over landscapes would have probably made for great opportunities for Box-elder, in many areas. As reforestation and maturation of eastern forests has increased markedly since, habitat changes probably have made this food-rich tree far less frequent than during the grosbeaks' expansion. Widespread deforestation may have stimulated temporary production of other fruit-bearing woody plants favored by grosbeaks, too, such as hawthorns and plums.

The grosbeak's eastern expansion may be a case of boom and bust. Declines in eastern populations over the last few decades are clear, and may be tied to large-scale shifts in habitat, especially forest composition and age. But the reasons for ebbing grosbeak populations are imperfectly understood.

This map is courtesy of Ethan Kistler, who has been tracking the extent of Evening Grosbeaks in Ohio this fall and winter. Such maps are a great way to share current information, which Ethan has been doing, and stimulate reports in unmapped counties.

As of now, grosbeaks have been reported in 59 of Ohio's 88 counties. Let me know in a comment if you have a record for one of the unmapped (white) counties. I'd bet a peck of finches that Evening Grosbeaks have been in every county thus far. Birds at feeders can't be missed, but wild-foraging birds certainly can, especially if one is not familiar with their calls.

GO HERE to listen to Evening Grosbeak calls. It's a pretty easy one to learn, and knowing the vocalizations will up your odds of finding this species. Pay special attention to the "calls" as you're unlikely to hear the "songs" down here in winter.

If you haven't already, I hope that you get the opportunity to see Evening Grosbeaks this winter. It might be many winters to come before we get another invasion.