Biology Reference
In-Depth Information
ally paused only briefly, rarely rattling, and resumed activity. Once I crawled under a
juniper, frustrated by a confusing signal from superfemale 21; after several minutes of
scrutinizing litter for a glimpse of scales, I sat up to think about things—and spotted her
inches from my face. Coiled on a yard-high branch, she didn't so much as flinch while I
edged out of strike range, thankful we'd never traumatized her during capture.
As hunters, blacktails proved to be pretty standard vipers. They waited next to logs,
woodrat nest entrances, and rabbit trails for hours or even days on end, head drawn
back and ready to strike, occasionally successful but usually not—we estimated that
each snake ate as few as three to five meals a year. Woodrats were staple prey, but fe-
male 12 seemingly specialized on squirrels by coiling against tree trunks, with her head
pointed up. After swallowing prey, the rattlers often crawled up to several dozen yards
to a crevice or other shelter, where, safe from predators, they protruded a meal-laden
body loop into sunlight to aid digestion. Late one fall, however, female 8 ate what I
suspected was a desert cottontail, so big she could scarcely pull up under the nearest
shrub, and although I feared she couldn't process her meal because of the chilly nights,
after nine days of basking the lump disappeared and she made it into hibernation. We
failed to learn much about the biology of young rattlers, though we found one about a
month old that had swallowed a brush mouse slightly exceeding its own weight.
Like most vipers, blacktails don't gain enough energy each season to bear young an-
nually, so well-fed, receptive females are always in short supply. By late March both
sexes emerge from hibernation high on the slopes and move across the ravines to hunt,
except females who mated the previous summer—these will seek out nearby gestation
sites and await birth. As summer rains begin, males crawl hundred of yards daily at
about a body length a minute, seeking mates. One went between my feet, presumably
because I'd straddled a female's unseen chemical trail, and another investigated Dave's
pant legs as he sat taking notes; neither snake acted defensive, let alone aggressive.
Courtship can last for days. It consists of the male tapping his chin and tongue-flicking
along the female's back, then wrapping his tail around hers—at which point she opens
her vent or, more often, slaps his tail back with an audible clacking of rattles. After paus-
ing for a minute or two, he resumes courting. If another male approaches, the rival suit-
ors topple each other with their foreparts, a sort of limbless arm wrestling that results
in one of them, usually the smaller, leaving. Copulation can last for at least twenty-two
hours—and, as we observed, a large male may, even in the midst of mating, fight of an
intruder that tries to displace him.
Our most exciting finding has backstory, a long-prevalent view exemplified by this
quote from Laurence Klauber's 1956 opus,
Rattlesnakes:
“There is no final evidence
that young rattlers stay with their mothers for more than a day or so at most; if they are
found together there is no proof the young are more than a few days old or that their
high school massasauga project, I'd found a female and eleven young and noted their
cloudy, pre-shed eyes, not realizing this meant she'd been attending them—despite hav-
ing read a 1942 paper by my Missouri mentor Paul Anderson, who had “considerable
evidence that . . . [mother copperheads and timber rattlers] remain with the young for
female cottonmouths were found with thirteen newborn young nearby . . . [an] incident
so striking I regard it as guarding behavior. . . . Aggregation prior to and following birth
