Rebecca Greenberg ’18
May 20th, 2016, 11:45 AM.
Jaw, ear, leg and breast faced me in full contraction; it was as though her whole body had eyes. Thus motionless for the past two minutes since I’d spotted her, she seemed a kind of organic satellite dish, extracting a signal exclusive to faculties of her species. Her eyes themselves were structures of their own ingenuity – bulbous turrets projecting far out from the sides of her head that could simultaneously see me and the rocks nearly behind her. I smiled through my binoculars as I recalled John’s outburst yesterday, “did you get to see their lashes yet?” This, from a man whose extent of self-expression up to this point had been the jolting purr of his Tacoma as it raced up the muddy two-tracks of the Range.
He was right, though. Well into week two of my fieldwork, this was my first time seeing a doe up close. And what a sight. Her neck, stretched to its full length, exposed two white boomerang-shaped patches well defined by her russet coat. Pinky-sized black horns crowned her brow like a diadem. And yes, the black orbs were surrounded by dark hairs rigid as windowsills. She again emitted the stifled snort that had first attracted me to her, and took a step toward me. I made to turn around, when I remembered the walkie-talkie in my hand.
“Rebecca to John.”
The doe took a few more steps and stopped.
“Found one. Thirty feet away. Spotted her when she snorted.”
“Ah, she must be hiding a fawn close by. Got her ID?”
The doe now walked steadily toward me.
“Not yet…she seems pretty tense. Is it normal she’s heading toward me?”
I took a few steps back.
“What do you mean, upset?”
“You know, bristled butt, stamping around.”
“Yeah. I mean, kind of?” I struggle to hold the walkie-talkie as I attempt to pick up my gear with my other hand. I see nothing of what he’d mentioned, only that she had just cut another ten feet between us.
“Yeah just stick around to get her ID, ok?”
Ha, easy for you, I want to say, all safe in your truck on the tour road. It’s a little different over here. I take a breath and hope my voice comes out neutral.
Aw, sorry girl, I say, realizing I’ve spoken less in sympathy for her maternal distress than in a growing fear for my own skin. I sit on my pack and pull my binos out again. Just gotta know who you are, then I’ll get away, I promise.
She tosses her head, ears flicking back and forth. Chill, I mutter, trying to focus the wavering lens. For an instant, her ear flicks backward. Ah! Yellow!
Or is it orange?
Her rump. The white patch has expanded into a rosette. This message I know well: it’s not just that I’m close to her fawn. We probably have company.
You’re definitely slower than a coyote, says my brain. I plop back down on my pack and put the binoculars to my face again, blood roaring in my temples.
I’ve always loved pronghorn because they look like they belong on the Serengeti but are just about as American as you can get. More ancient than deer and bovids[i] —the family of cattle, goats, and yes, the true African antelopes — pronghorn witnessed the extinction of the long-legged bear and the American cheetah and lion that roamed North America through the Pleistocene.[ii] However, they’re more or less still equipped for these mega-predators. Their 60 mph bursts of speed make them the fastest North American mammal;[iii] in the world, they are second only to the African cheetah. Unlike the cheetah, however, the pronghorn also excels at endurance and can maintain a steady 45 mph for miles.[iv] Though some young fawns in the Range do die to coyotes, pronghorn mothers more often give the offenders what John fondly calls their “aerobic workout” before they get too close.
This is, however, only the beginning of a pronghorn’s unique maternal care strategy. Unlike most young ungulates, a pronghorn fawn spends its early months lying curled up in the grass. Its dull-colored coat is effectively undetectable[v]. Every three to four hours, its mother visits for nursing. The fawn remains odorless because the mother thoroughly cleans up its rump and ingests its waste after it finishes suckling.[vi] Between milk meals, the mother lounges or grazes at the minimum distance required to avoid leading predators to her offspring. She does not face or move toward her fawn’s hiding spot more than is expected by chance. Finally, she randomizes her pre-nursing behaviors (grazing, reclining, standing) before going to her fawn so that none of them appear indicative of an incoming fawn visit.[vii]
According to John Byers, zoology professor and pronghorn specialist at the University of Idaho, pronghorn maternal behavior may even be improved by experience, in a process akin to learning. John has spent more than twenty years at the Bison Range in Charlo MT, an 18,000+ acre prairie refuge founded by Theodore Roosevelt in 1908 to protect the decimated American bison.[viii] In 1997, John demonstrated that fawn survival increases with the age of the mother.[ix] Several hypotheses could account for this change. First, mothers may increase metabolic investment in fawns as they age, as red deer mothers do.[x] Second, younger does may have a higher mortality than older ones. Neither hypothesis is supported by current data. Pronghorn reproductive expenditure has been shown to remain constant from a doe’s first birth to her last and doe mortality is consistently low in adulthood.[xi] The remaining yet heretofore untested hypothesis: fawns born to older mothers have higher survival rates because does refine their mothering strategies through experience they accumulated caring for previous offspring.
But what would excellent pronghorn motherhood entail? It’s already hard to beat your average pronghorn mother, whose meticulousness was fine-tuned through ages of selection by the extinct predators with whom her species coevolved.[xii] John believes older mothers may actively look for predators before a visit and then move their fawn to a location out of sight of the original location after nursing.[xiii] The aim of John’s fieldwork last summer was to test this hypothesis by recording maternal behavior of the breeding females on the Range.
This is where I came in. Last November, I came across a popular science article on pronghorn mate selection based on his research and emailed him in case he’d be conducting more fieldwork. He told me he was, and agreed to take me on for the maternal behavior project. With a stipend from the University of Idaho, I spent 3 weeks at the Range as one of his two assistants, sharing a bunkhouse at the edge of the refuge with a few other student interns. Eight hours a day, seven days a week, John staked us out on grassy ridges to watch does. Peering at pronghorn through a scope from his truck, he’d give us our targets – does whose swollen teats suggested they were attending one or more hiding fawns. We recorded the mothers’ pre-nursing behavior, the time of nursing and licking bouts, the distance between both of the fawn’s hiding spots, and whether or not the first hideout was out of sight of the first. Results from the analysis of these behaviors at the University of Idaho will determine whether there is a significant association between age and a given pattern of maternal behavior.
Whether or not the results are conclusive, research at the Range revealed a thing or two about my own interests. I have decided to pursue a similar focus on reproductive behavior with deer mice at the Hoekstra Lab. Not to mention that the fieldwork was a privilege in itself. Tourism at the Range is limited to drives on the main tour road to minimize disturbance and deaths from bison charges. There are not many who can boast of walking up the tall grassy hills with a scope at her back beneath the curious gaze of a young coyote. Or of turning around one morning from a two-hour observation to meet the eyes of a bison bull ten feet behind, a pyramid of woolly locks and soaring shoulder. Heart pounding, I was rooted to the spot. But the gaze broken and the beast gone, all I could think was a wistful already?
[ii] Lott, D. F. (2002). American bison: a natural history. Univ of California Press.
[iii] Byers, J. A. (2003). Built for Speed: a Year in the Life of Pronghorn. Harvard
[iv] Byers, J. A. (2003). Built for Speed: a Year in the Life of Pronghorn. Harvard
[v] Lott, D. F. (2002). American bison: a natural history. Univ of California Press.
[vi] Byers, J. A. (2003). Built for speed: a year in the life of pronghorn. Harvard
[vii] Byers, J. A., & Byers, K. Z. (1983). Do pronghorn mothers reveal the locations of their
hidden fawns?. Behavioral Ecology and Sociobiology, 13(2), 147-156.
[viii] National Bison Range (2013). US Fish & Wildlife Service. Retrieved from https://www.fws.gov/refuge/National_Bison_Range/about.html
[ix] Byers, J. A. (1997). American pronghorn: social adaptations and the ghosts of
predators past. University of Chicago Press.
[x] Clutton-Brock, T. H., Guinness, F. E., & Albon, S. D. (1982). Red deer: behavior and
ecology of two sexes. University of Chicago press.
[xi] Byers, J. A. (1997). American pronghorn: social adaptations and the ghosts of
predators past. University of Chicago Press.
[xii] Byers, J. A. (2003). Built for speed: a year in the life of pronghorn. Harvard
[xiii] Byers, J.A. (2015). Uncovering experience-based changes in pronghorn maternal behavior. Grant proposal, National Geographic.