With the recent arrival of a large flock of evening grosbeaks at our feeders, my mind has drifted to one of the main reasons these birds, which are native to the Pacific Northwest, are here in the East: the spruce budworm.

[And this, of course, sends my memory plunging down the rapids of my stream of consciousness to my days at forestry school, where a good friend from New Jersey, who was a huge Bruce Springsteen fan (it was the ‘80s, after all), referred to this forest pest as the Bruce Spudworm. The spoonerism has stuck with me ever since. I therefore dedicate this post to Cynthia.]

Evening grosbeaks (Coccothraustes vespertinus), often called grospigs around here because of their propensity for emptying birdfeeders at lightning speed, are striking birds. They are big and chunky, the males stunning in yellow, black and white. We see them mostly in the winter, when flocks descend upon birdfeeders and inhale all the seed in a matter of minutes. Once in a blue moon a few might hang around in the summer, but winter seems to be their season.

Even so, one cannot count on seeing evening grosbeaks every winter, for they are rather nomadic, showing up in great numbers one year, and then disappearing, sometimes for years at a time. This sporadic pattern has been documented for well over a century, and there seems to be a tie-in with the spruce budworm.

The spruce budworm (a type of moth, actually) comes in a couple different flavors: the western worm (Choristoneura occidentalis) and the eastern worm (Choristoneura fumiferana). The western spruce budworm is, as you may have guessed, native to the western part of North America. It didn’t turn up in the United States (from Canada) until 1914, when it was first reported in Oregon. Since then, it has spread across much of the Pacific Northwest towards the Rockies, its larvae devouring the foliage, staminate flowers and developing cones of conifers throughout the region.

Here in the Adirondacks, we are blessed with the eastern spruce budworm. Also a native insect, the first major outbreak recorded in the U.S. was in Maine in 1807. The next major outbreak was in 1878, and since 1909 there have been several waves of devastation. In the east, balsam fir is the insect’s tree of choice, so you can imagine the impact this would have on the Adirondack forest. Spruces are also consumed (hence the name), and even hemlocks on occasion, but nothing is hit quite like the firs.

Like many forest insect pests, the spruce budworm’s havoc is wreaked in a cyclic pattern: it’s always out there, eating away at the trees, but the infestation only becomes problematic when the population suddenly swells and takes over the forest. With the spruce budworm, the cycle is about every 40 to 60 years.

Enter the evening grosbeak. Way back when, evening grosbeaks were only seen on occasion in the Pacific Northwest (there were much fewer people in the woods back then). Slowly, they started moving eastward, and by 1854 they had come as far east as Toronto. In the winter of 1889-90, huge flocks were seen in New England. Then they disappeared again for another twenty years. In the winter of 1960-1, evening grosbeaks appeared as far south as Georgia, with huge flocks taking over feeders and forests across the eastern U.S. I bet a lot of birders were thrilled to add them to their lifelists!

It is believed that these irruptions (a sudden sharp increase in the relative numbers of a population) were in large part due to the birds’ fondness for spruce budworm larvae. Although primarily seed eaters, specializing in extracting seeds from the cones of spruce and fir trees, grosbeaks supplement their diets with tasty insect snacks, and spruce budworm seems to be a favorite. Scientists believe that these birds followed the western spruce budworm eastward, and then started snacking on the eastern spruce budworm. When pest populations irrupted, the birds followed close behind.

The sudden increase in spruce budworm larvae can result in a catastrophic loss of spruce and fir trees, adversely affecting the timber industry and forest ecosystems. In order to deal with this, chemicals were employed to combat the insect pests. Unfortunately, birds that eat the larvae (including Tennessee, bay-breasted and Cape May warblers) were also negatively impacted. In fact, studies have shown that evening grosbeaks will not return to areas that have been sprayed for spruce budworm, even if the larvae population increases.

In an effort to try to cut down on the use of toxic chemicals, research has been done to determine if biological controls can be used instead. Science has discovered both a virus and a fungus that infect spruce budworms, but unfortunately neither is particularly deadly – at least not at a level that would benefit the forest. The bacteria B.t. (Bacillus thuringiensis) has been proven effective for small infestations (fewer than 50 larvae on an 18” branch), but major infestations (more than 8000 eggs per 100 square feet of foliage) are barely touched.

Maybe we should try breeding warblers and grosbeaks and have them in stock to release when infestations occur.

Since the last major outbreak of the eastern spruce budworm was in the ‘60s and ‘70s, we should be about due for one. Some birders are speculating that this might explain the great numbers of grosbeaks at the feeders, and the reports of more warblers downstate. Whatever the reason, it’s nice to see the grosbeaks, even if their presence means more trips to the feed store for seeds.