Eaters of the Purple Sage

Last Friday, I woke up before my alarm.  This in itself wasn’t unusual—even for me—but the fact that I’d jumped the gun on an alarm I’d set for 4:00 A.M. was.  I was due to meet my mentor, Destin Harrell, at the Cody BLM office, and ride shotgun with him to count grouse.

Both species of sage grouse—the “greater” found across much of the west, and the “Gunnison’s” limited to Colorado and a sliver of Utah—gather at sites called leks in the spring, where dozens or hundreds of males display and occasionally clash in the hope of attracting mates.  They depend on the sagebrush year-round, not only for their habitat but for a good majority of their diet.  Although the adaptations they’ve evolved to obtain nutrients from the sage are fascinating*, they also make the grouse poorly suited to non-leafy foods, and probably easily outcompeted in other habitats by species like pheasant or turkey.

*I won’t go into detail, because someone might be reading this while eating.

The greater sage grouse is estimated to number in the hundreds of thousands**, but its range has been reduced and fragmented by roads, cities, agriculture, and energy infrastructure (renewable or otherwise).  The long-term spread of invasives like cheatgrass, combined with intense fires that destroy sagebrush over large areas, has contributed further to their vulnerability.  Finally, their reliance on leks for mating creates “linchpins” that can magnify the effects of habitat loss.  If a lek is converted to human uses—or even encroached on too closely by roads, power lines, gas wells, or wind turbines—it’s almost guaranteed to be lost, and any sage habitat surviving nearby may lose its remaining grouse as a result.  (Unfortunately, if humans visit a lek too often, or make too much of a scene while there, the same thing can happen, which can make public outreach on sage grouse a tricky prospect.  It’s an unforgiving example of how, as Aldo Leopold noted, “conservation of wildness is self-defeating, for to cherish we must see and fondle, and when enough have seen and fondled, there is no wilderness left to cherish.”)

**By contrast, there are probably fewer than 5,000 Gunnison sage grouse.

The lek was empty when we arrived; so close to sunrise, there should have been birds everywhere, and we were initially nervous that Something Had Happened.  A little while after we stopped the truck, though, a few males started to return.  Once they got close enough to each other, the strutting and tail-fanning started up again.  More came back, in ones and twos, and soon everything seemed normal—at least, as best as I could judge, never having seen the species before.  Since we hadn’t spotted any birds fleeing as we approached the lek, it probably hadn’t been the truck that disturbed them.  Since there weren’t any other fresh vehicle tracks nearby, either, the most likely explanation was that some other animal—a predator like an eagle or coyote, or possibly a pronghorn or wild horse—had passed through and scattered them as we were still picking our way along the track from the highway.

The last male arrived at about 8:00, making for a count of fifteen—and one female.  If the ratio were that skewed for the population at large, this would be a matter of some concern, but according to Destin, males will display for as many days as they can, while females typically visit for only a few days in a season, and try to choose a mate quickly.  This lets them nest and raise the chicks in relative safety, away from other broods that could attract predators or create competition for food.  The hen at this lek gave a few of the males a once-over, but was apparently deferring her decision for another day, and spent a lot of her time eating.  Some of the less motivated males did the same.  As long as we stayed in the truck, they’d probably ignore us, but if we opened the door or raised our voices they’d scatter.  One way or another, they’ve evolved to be wary of humans—a trait that has probably saved more than a few of them from the stewpot, but one that can prevent them from breeding if a lek is disturbed.

(Somewhere in Wyoming:  the lek, at about 7:00 A.M.  For a closer look at similar sites, visit the Cornell Ornithology Lab’s media collection at http://macaulaylibrary.org/search?taxon=Centrocercus urophasianus&taxon_id=11996311&taxon_rank_id=67&tab=video or the Fish and Wildlife Service’s video archive at https://www.fws.gov/greatersagegrouse/video.php)

There was no wind that I could tell—although by the time we rolled the windows up and crept away, a thin film of dust had settled on my notebook.  Except when one of us noted another bird’s arrival, or rechecked the count, there was hardly a sound except for ravens in the distance, and the music of the grouse.  Every few moments, one male or another would flex his neck and wings, shaking his air sacs with a “toonk-toomp” and a hoot of entering or escaping air.  Sometimes, we could make out the sound of his wings whisking against his body feathers.  When two birds caught each other’s attention and faced off, they cackled quietly, but the two or three scuffles that resulted from these confrontations were silent, apart from the beating of wings.

From both a scientific and a management perspective, it’s not a good idea to humanize wildlife too much.  Watching the grouse, though, it was difficult not to.  When one of the late arrivals briefly took flight to cross a rut full of muddy water, I thought of a man in an immaculate suit, trying to navigate puddles in the street.

(It was the farther-away of these two birds.  Again, the resolution needs work, but it does highlight how effective the non-display feathers are as camouflage.)

More significantly, when I noticed that the males weren’t trying to crowd or “herd” the hen, in the hopes of mating with her, it was tempting to characterize them as more “courteous” than some of the species I’ve observed in the past.  After thinking for a moment, though, it was clear that if any of the males approached the hen more aggressively, all of them would risk losing their chance if they didn’t do the same.  Even if only one male, or a few of them, acted too aggressively, the female would probably abandon the lek; she might then risk predation or exhaustion from crossing unfamiliar or inhospitable ground to find a mate elsewhere, and both she and the males would risk not mating at all this season.  At this point, there’s no way of proving that this was how the males’ restraint evolved, but it makes for a decent starting hypothesis.

Even this early in the spring—or perhaps this late in the winter, considering that it snowed again over the weekend—there were a lot of other species active.  On the way to the lek, we glimpsed a trio of mountain plovers in our headlights (regulars in the Bighorn Basin, but possibly endangered and definitely poorly understood), and heard a sage thrasher calling in the dark when we got out of the truck to assess a creekbed crossing.  After leaving, while searching for other possible leks nearby, we came across a sage sparrow, several horned larks, and dozens of pronghorn.  Like the grouse, sage thrashers and sparrows depend on sagebrush ecosystems, but they’re far more tolerant of humans, and more resilient to habitat disturbance.

After all of that, the golden eagle that crossed in front of us on the drive back to the office almost seemed anticlimactic.

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