Contributions by Ned Brinkley, Ted Floyd, and Jeff Wells.
Evening Grosbeak is a species as enigmatic as it is striking. When many thousands of them descended upon feeding stations in the East from the 1950s through the early 1980s, birding newsletters, magazines, and journals were filled with word of their complex movements and backyard antics. Despite the considerable expenses involved in hosting this species at a feeder—a large flock can consume more than $100 of sunflower seed per day—birders couldn’t get enough of these great finches. Because this bird still holds so much mystery, because of its charm, because of its fragile and threatened habitats, and because it is certainly a “data-deficient” species, as conservationists say, the ABA in 2012 elected to name Evening Grosbeak its Bird of the Year for 2012.
And of course that’s not the beginning of the story. In rich detail, ornithologist Arthur Norton recounted the “great migration” eastward of Evening Grosbeaks in winter 1915-1916 (Auk 35: 170-181). An even more remarkable eastward incursion was documented in winter 1889-1890; five articles appeared in April–June 1890 issues of The Auk. It seems the birders of yesteryear were every bit as compulsive about their records as we are!
We think of Evening Grosbeaks, and finches generally, as seed eaters, based on what we observe of their feeding habits in the nonbreeding season, when most of us have the pleasure of their company. But during the breeding season, Evening Grosbeaks, like many other passerines, require insect matter to raise their young. And as it turns out, spruce budworms, both the Eastern and the Western species, are their preferred food at this time of year. Many birders are aware the outbreaks of these insects are linked to surges in populations of the “spruce budworm specialists,” warblers such as Cape May, Blackpoll, and Bay-breasted, which feed these insects to young, sometimes raising several broods per season. Populations of these species also increased sharply in the 1960s and 1970s, when the grosbeaks were last abundant in the East. And many ornithologists are of the opinion that the last big “irruptions” of Evening Grosbeaks in the East were a result of the extensive outbreak of Eastern Spruce Budworm (Choristoneura fumiferana) during that period.
There are hints, collected by eBird and by ABA’s North American Birds reporting networks, that counts of the spruce budworm warblers—and even of Evening Grosbeak—are increasing in the past year or two, most notably in the past few weeks! Could this be a result of a resurgence of spruce budworm over the past several years? News coming from the Canadian boreal forest, where many Evening Grosbeaks nest, suggests that it may well be. Just in the past two years, the area of defoliation caused by spruce budworms has almost doubled in some areas, mostly in mixed forests with plenty of White Spruce or Balsam Fir, the trees preferred by Eastern Spruce Budworms. Ontario had outbreaks reported around Manitoulin, Espanola, north of New Liskeard, and around Sault Ste. Marie. Southwestern Quebec has had a growing and relatively severe outbreak for at least five years now. Foresters in neighboring New Brunswick, where they have not been troubled by the pest since the mid-1980s, are monitoring border areas for signs of spread. To the west, the Eastern Spruce Budworm infestation in northern Alberta and Saskatchewan has continued to grow slowly over the past five years, despite programs of aerial pesticide spraying. Farther west, British Columbia’s forests, as around Kamloops, have suffered from a plague of Western Spruce Budworm (C. occidentalis), which defoliates Douglas-fir. (Another species, the Western Black-headed Budworm, is also active in the past few years in British Columbia.) Could the recent small, scattered “flights” of Evening Grosbeaks, spanning from the Upper Midwest to northern New England to Appalachia, be the first signs of another wave of this species, such as we saw in the beginning in the late 1950s?
Click on the map to go to the interactive map at eBird.org
Evidence of a budworm-fueled resurgence of grosbeaks comes from the southern Rocky Mountains in the past several years, too. After many years of apparent paucity at such well-birded locales as Rocky Mountain National Park, Evening Grosbeaks are suddenly “everywhere,” “easy to find,” even “abundant”—if you believe the listserves and other sources of birder chatter. David Leatherman, a well-known Colorado birder and professional entomologist, notes that an ongoing budworm outbreak may be at play here. Particularly interesting and sobering is that the southern Rockies’ massive die-off of Lodgepole Pine—widely thought to be caused by human activity—may be driving the budworm outbreak, but much more study is needed to confirm this suspicion.
In California, birders also witnessed an irruption of Evening Grosbeaks in fall 2010 “on a scale not seen since the late 1980s.” The flight began in September on the coast of northwestern California and the northern Central Valley and then spread quickly southward, reaching areas well south of San Francisco in October. West Coast irruptions of this sort, fairly frequent before 1990, were usually assumed to be of the grosbeak subspecies that nests in the high mountains of the state (brooksi). However, audio recordings of several 2010 grosbeaks from Santa Cruz County matched vocalizations given by birds that nest in the Pacific Northwest and throughout the northern Rockies, not those of California nesters. Could all of the birds seen in the California flight of 2010 have come from areas far to the north and northeast, where budworms had been very active? (And yes, like Red Crossbills, Evening Grosbeaks have distinctive Call Types. See: Sewall, K. B, T. R. Kelsey, and T. P. Hahn. 2004. Discrete variants of Evening Grosbeak flight calls. Condor 106: 161-165.) As is true of recent irruptions in the Northeast and the Rockies, the California flight involved much smaller numbers—in this case, about 600 birds were reported—than historical flights, but the geographic span of the flights has been similar.
In a provocative 1984 article entitled “How much is an Evening Grosbeak Worth?” (Journal of Forestry 82: 426-428), John Takekawa and Edward Garton argued that these “voracious” finches would prove a more effective, and cost-effective, way to control outbreaks of Western Spruce Budworm than to spray insecticides from the air, which cost about $1820 per square kilometer. Grosbeaks are free, unless they visit your feeding station. Unfortunately, few forestry officials have availed themselves of this wisdom, and campaigns that apply chemicals continue. And so it will be difficult, even impossible, to make sense of the ebb and flow of this great species’ populations in North America without suitable studies, ideally studies that examine the impact of budworms in very similar stands of treated and untreated forest.
Making the story of the population fluctuations of Evening Grosbeaks even more complex is the equally complex recent history of industrial land-use activities in its Canadian boreal forest breeding range. The scale of this industrial footprint—including forestry, oil and gas extraction, hydro-power, mining, and other activities—is immense, with approximately 180 million acres of the southern boreal forest already impacted. The forest in eastern Canada, the Maritime Provinces, and northern New England is now a changed landscape of much younger forests, often with fewer coniferous tree species than it had before the advent of industrial-scale logging activity. How these changes have affected or will affect populations of Evening Grosbeaks, other birds, and insects is uncertain, especially during the current period of rapid climate change. About 40% of Evening Grosbeak’s Canadian boreal breeding range overlaps with areas of intense industrial land-use activity—one of the highest proportions of any bird species. Only 9% of its Canadian boreal range lies within protected areas. Read more about this on the website of the Boreal Songbird Initiative.
Birders can contribute massively to our dim understanding of populations of Evening Grosbeaks by searching for them in appropriate habitats and seasons and submitting information to eBird. It’s helpful to include photographs in your checklists and whatever details on nesting and foraging you can provide. In that way, scientists trying to sort out the puzzle of this species’ changing distribution will have access to a large and informative database that includes clues on the phenology of migration and nesting.
In many ways, we know as little today about population instability in the Evening Grosbeak as we did a century ago. As Arthur Norton wrote in his article in The Auk:
It seems to require no draft upon the imagination, and no step into the realm of speculation, to realize that in this hasty review of this interesting history, we have seen the Evening Grosbeak, forced against the impassable barrier to its southern migration at the prairie region, slowly and steadily take its way eastward, to the Atlantic coast. Thus has our generation witnessed a species overflowing the bounds of its original habitat, and forming its route of migration along the line of congenial conditions as they exist today!
Time is replete with instances no less remarkable than this, but it is indeed rare that man is permitted to witness them in the making.
Norton’s words offer both caution and inspiration. On the one hand, the Evening Grosbeak story is complex. Unstable populations are an undeniable aspect of the species’ natural history, and our human understanding of the phenomenon has long been, and still is, rudimentary. We need to tread cautiously here. On the other hand, something remarkable is going on with Evening Grosbeaks right now. And today, as never before, we have the resources—both in terms of technology and widespread birder interest—to figure out, compellingly and definitively so, what is going on with Evening Grosbeaks. If you encounter this species in your birding, be sure to record accurately how many you saw, where you saw them, and maybe even try to work out which Call Type. And be sure to record your observations through eBird!
