Social and Individual Dynamics
of a Predator-Prey Episode
The following scenario is a composite of observations made
by members of our labs on what happens between Califor-
nia ground squirrels (Spermophilus beecheyi) and northern
Pacific rattlesnakes (Crotalus oreganus). We present it to il-
lustrate many of the themes of this chapter.
A northern Pacific rattlesnake has left its hibernation
site in central California and has begun hunting for pups
in a colony of ground squirrels. By crawling through the
colony and interacting with a series of adult squirrels, the
snake discovers the burrow system of a female (call her
9G), who stands her ground and even confronts the serpent
(fig. 26.1a), behavior more typical of females with young
than without. After interacting with 9G, the snake termi-
nates the encounter and settles itself into an ambush coil in
the mouth of one of the peripheral entrances to her burrow
system (fig. 26.1b).
It is the season when rattlesnakes are active, and many
squirrels already appear nervous, but they become more so
as this rattlesnake passes through the colony. 9G and many
other squirrels pause frequently to produce the snake-
typical signal of tail flagging if they encounter a snake-
like object (fig. 26.1c) or near burrow entrances or tall grass
where snake risk is high. This flagging is contagious, in-
ducing tail flagging and other signs of snake concern in
squirrels that have not directly contacted the snake.
Over the next several hours, three adult squirrels from
adjacent home ranges that do not have pups at risk come
across the snake as it lies in ambush. On separate occasions
lasting a few minutes, each of these adults exhibits several
cycles of cautious close approach, extension of their heads
in elongate investigative postures, tail fluffing as their stress-
response system is activated, backing away from the snake,
tail flagging, and reapproach. The third squirrel is attracted
by the antisnake activity of the second, who relinquishes its
position when the third initiates investigation of the snake.
The second remains nearby monitoring for awhile, but then
drifts away. The snake responds only with tongue-flicking.
None of these squirrels spends as much time with the
snake as 9G already has, and certainly not as much time as
9G is about to. The third adult’s antisnake behavior catches
9G’s attention, and 9G’s approach supplants the third squir-
rel (fig. 26.1d). After a few cautious bouts of investigation,
9G begins to throw substrate (loose soil and leaf litter) at
the snake with her forepaws, and the snake strikes defen-
sively, a maneuver that our squirrel easily evades. Two of
9G’s pups pop their heads out of a burrow entrance about
8 meters away, and 9G breaks away to join them.
The snake begins to crawl toward 9G and her pups, and
both 9G and a pup move to meet the snake. The pup reaches
the snake before 9G does, and actually begins to confront
the snake using most of the same motor patterns as its
mother (fig. 26.1e). The snake strikes the pup, and the pup
reels to a third burrow entrance where 9G joins it. Trailing
the pup to the same entrance, the snake clears the substrate-
throwing mother (fig. 26.1f) out of the way with a defen-
sive bite, locates the dead pup and begins to swallow it.
Even though 9G was hit and injured by the snakebite, she
is still able to walk. At this time, almost 4 hours after her
first contact with the snake, the mother begins to move her