By Ryan F. Mandelbaum:
This past summer, intense wildfires burned millions of acres of land across the American west, killing more than 30 people, shrouding cities in an apocalyptic red haze, and spewing plumes of smoke that clouded out the Sun as far away as the East Coast. Some of those fires, notably the Badger Fire, ripped through Idaho’s Sawtooth National Forest—the heart of the west’s newest bird species, the already-threatened Cassia Crossbill.
Hundreds of firefighters in the field worked to bring the Badger Fire and several smaller fires under control, but not before the blazes ripped through around 90,000 acres in the Sawtooth National Forest’s South Hills. This isolated section of lodgepole pine forest hosts the Cassia Crossbill, a species consisting of only 6,000 individuals. As officials and forest-fighting hotshot crews are amid putting the fires to an end, ecologists are worried about what the species’ fate might be.
Scientists led by the University of Wyoming’s Craig Benkman first declared the Cassia Crossbill its own species in a 2009 paper. Initially, the bird was the ninth of at least ten North American populations of the Red Crossbill species, divided based on their “call type,” where birds predominantly mate and flock only with birds that make the exact same “kip kip” call when they fly and not with those whose flight calls slightly vary. Each of the call types are typically found in certain locations—Type 1 in the Appalachian Mountains and Type 2 in the Mountain West, for example—but will “irrupt” far and wide when cone crops fail. However, the Cassia Crossbill stays put in Idaho’s South Hills and Albion Mountains.
Benkman’s team began to uncover the story of the Cassia Crossbill in 1996 while looking for isolated pockets of conifer forests that might host non-migratory pockets of crossbills—and importantly, pockets without red squirrels which outcompete crossbills for the seeds in the cones. The search brought them to the South Hills, where they observed crossbills that seemed to be locked in an evolutionary arms race with the local lodgepole pines, evolving increasingly large beaks as the pines evolved cones with thicker scales. The team began to measure the bird and study its DNA, proving through genetic testing that Cassias bred with other call types only .7% of the time, lower than the 5% hybridization threshold typically required to elevate a population to the species level. The American Ornithological Society’s North American Classification Committee added the bird to its list of North American bird species in 2017.
Fires are a major factor in the Cassia Crossbill’s ecology. These birds specialize on lodgepole cones older than 2-5 years. The cones of the South Hills’ lodgepole pines are serotinous, meaning they open up under high heat, allowing them to reproduce. This means that long periods without fires cause large cone crops to age and accumulate, giving the birds access to huge stores of food. When the fires happen, the trees reproduce—but the amount of food decreases until the trees mature once again. Too many fires, or one large fire, and there might not be enough food for the birds.
The relationship between the Cassia Crossbills and the Lodgepole Pines in southern Idaho hangs in a natural balance—one which humans are disrupting. Anthropogenic climate change has created warmer conditions and more drought, leading to more frequent and stronger fires. Forest management practices have also been blamed for more intense fires. Stronger and more frequent fires can either impact the birds directly, should they get caught in the wildfires’ path, or indirectly, by causing the cones to dump their seeds before the birds can eat them or not allowing enough time for cones to mature and accumulate for the birds to eat them.
As fire frequency and intensity increases in the American West, researchers are already worried about the fate of the Cassia Crossbill. In fact, the fires might even cause the crossbills to venture out of Cassia County for the first time on record. “This species already hangs in the balance” says crossbill researcher and founder of the Finch Research Network Matt Young, “and given that population levels will most assuredly drop to very low numbers after these fires, it’ll be important that the South Hills, and the smaller Albion Mountains to the northeast where the Cassia Crossbill also exists, are managed in a way that will protect the remaining population of this unique and threatened species.”
The recent wave of fires, most notably the Badger Fire sparked on September 12, 2020 near Badger Gulch, are especially worrisome, given the sheer area that they burned. And if these fires haven’t harmed the birds, then climate change eventually will—extended periods of warm temperatures already cause cone seed release events that lead to crossbill declines, according to recent work by Benkman, while eventually, warmer weather and changing conditions are predicted to extirpate the lodgepole pine from the South Hills.
Credit for Badger Fire photo on previous page Forest Service/InciWeb
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