Today I was fortunate to photograph these stunning evening grosbeaks in southern Indiana. It was an unusual opportunity, because these birds are not typically seen south of the Great Lakes. Evening grosbeaks and other “winter finches” do not truly migrate. Instead they wander the boreal forests of Canada, “boreal” meaning northern, the opposite of “austral,” meaning southern. Think “aurora borealis” - the northern lights, and Australia - the “southern land.” Winter finches are nomads who move about depending on availability of food. This year, they are present in large numbers, well into Kentucky and even Tennessee. We were expecting them. So why are they here? And how did we know they would come?
Evening Grosbeak (Coccothraustes vespertinus) | Monroe County, Indiana
500mm | 1/1,600th second | f/7.1 | ISO800
They are here because they eat the seeds of conifers like spruce and white pine (i.e., pine cones), and this year the seed crop in the boreal forest was poor. Why was the seed crop poor? Seed production was down because of an unusually large outbreak of spruce budworm. Outbreaks of spruce budworm have an unfortunate compound effect - they provide an abundant food source in the spring when evening grosbeaks are breeding, but they have a negative effect on the availability of the very seeds that the increased population of birds needs to survive the winter. In short, spruce budworm means more winter finches competing for a smaller food supply, which means they have to look elsewhere, and “elsewhere” means south. Scientists monitor the seed crop of the boreal forest. Upon observing the significantly decreased output, they correctly predicted that winter finches would irrupt to the south. Today I saw my first evening grosbeaks, but earlier this year I also found my first purple finches, pine siskins, and red-breasted nuthatches. The nuthatch is not really a finch, but it is impacted in the same way. We have also had crossbills, both red and white-winged, in Kentucky, all for the same reason.
Female Evening Grosbeak in Flight | Monroe County, Indiana
500mm | 1/2,500th second | f/9.0 | ISO1250
“When we try to pick out anything by itself, we find it hitched to everything else in the Universe.”
Why the outbreak of spruce budworm? Well, partly because spruce budworm populations are cyclical and it’s just how the strange math of population growth and decline works. But also because of another unfortunate “double whammy.” Spruce budworms reproduce more rapidly in warmer conditions, and warmer, dryer summers stress the trees of the boreal forest. Increasing global temperatures means more budworms in weaker trees. And more budworms in weaker trees means more evening grosbeaks are fledged with less food to eat the following winter. In reality, it is far more complex than this, but the complexity of hundreds or thousands or millions of cause and effect chains like this overlapping only proves the point more fully - we are all interconnected, often in ways that are hard for us to understand.
Greg
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Bonus Bird Trivia:
Why is it called an “evening” grosbeak? The evening grosbeak, whose species name is vespertina, got its name for the same reason as the vesper sparrow - it was long thought that they sang only at dusk, just as monks sing vespers - the evening prayers, vesper being the Latin word for “evening.”
One female evening grosbeak in a flock of nearly one hundred in Monroe County, Indiana
500mm | 1/1,250th second | f/8.0 | ISO720