Late term fetus caudal luring behavior in a pitviper

With the advent of powerful imaging tools, the prenatal behavior of
vertebrates is far more complex than previously believed, especially
concerning humans, other mammals, and birds. Surprisingly, the fetal
behavior of squamate reptiles (lizards, snakes, and amphisbaenians), a
group of over 11,000 extant species, are largely understudied. Using
ultrasonography, 18 late-term pregnant copperhead snakes (Agkistrodon
contortrix) from a single population were inspected for fecundity (number
of fetuses). Unexpectedly, during the ultrasound procedure that involved
97 fetuses, we observed sinusoidal tail movements in 11 individuals from
eight different copperhead mothers. These movements were indistinguishable
from caudal luring, a mimetic ambush predatory strategy which is exhibited
by newborn copperheads and other snakes. Caudal luring is initiated
shortly after birth and is employed to attract susceptible vertebrate
prey. Using the same ultrasound equipment and methods, we tested for this
behavior in two species of rattlesnakes (genus Crotalus) not known to
caudal lure and none of the late-term fetuses showed any type of tail
movements. Prenatal movements in humans and other vertebrates are known to
be important for musculoskeletal and sensorimotor development. The fetal
behaviors we describe for copperheads, and possibly other snakes, may be
similarly important and influence early survival and subsequent fitness.