Page 26 - 2006 DT 12 Issues

Night Shift cool dusk hours to begin their forag- and South American nocturnal bats
ing or hunting, retiring once again as that live on the nectar from rainforest
s shadows lengthen and the the sun rises. flowers are specially adapted to see
light slowly fades over the Others must compromise. They in ultraviolet (UV) light because the
Adesert mountains, animals and forage or hunt only in the twilight hours flowers they visit are characterized by
humans alike prepare for the coming of dawn and dusk when they are less a strong reflection of the UV-spectrum
night. For some, it is time to hide and visible to predators but are still able to at night.
rest. For others, their day is really see in the half-dark (some rodents and Nocturnal animals have very large
just beginning. These are the night reptiles; mule deer; rabbits, etc.). This eyes with larger pupils, lenses, corneas
hunters. behavior is called “crepuscular.” and retinal surfaces that increase their
In the desert, animals must adapt Depending on the season, loca- sensitivity to light. The photoreceptor
to the stress of high temperature and tion and type of environment, some layer of the retina in nocturnal ver-
moisture loss experienced during the animals may exhibit any or all of these tebrates is packed with rods, which
mid-day heat. The tails of antelope behaviors as the situation changes. The are especially sensitive to low light
squirrels are white gopher snake, for levels, but the trade-off is fewer cones,
on the underside. example, which which provide color vision and enable
When these highly is mainly diurnal, sharper images.
active squirrels will change its Driving down a desert road at
stop to rest, they behavior to noc- night, you might notice bright eyes
use their tails as turnal at the peak mirroring your headlights. When light
little umbrellas of summer heat. strikes the retina, some of it passes
to shade their The coyote is the through it striking a special reflective
backs and heads. ultimate oppor- membrane called the tapetum lucidum.
They can also be tunist and may be The tapetum collects and re-emits
seen lying flat on seen at any time of light back to the retina, allowing it to
the ground with day or night. re-absorb the image, improving the
their legs spread A l t h o u g h eye’s efficiency. Some of the light,
out, “shivering” temperature is however, still escapes absorption and
to dissipate heat. the prime factor is transmitted out the pupil causing the
They are diurnal, motivating these eye to glow. Various pupil specializa-
remaining active behaviors, it is tions allow the animals to limit the
throughout much not the only one. incoming light during the day to avoid
of the day, as do a minority of Availability of food and/or special over-stimulating their night-sensitive
other animals (most birds, including hunting adaptations also play a part. eyes. The tapetum, though different in
raptors; chipmunks; many lizards Because many animals share the same structure and composition in different
and amphibians;). prey, adapting sleep patterns to differ- animals, is present in the eyes of many
Most desert animals, however, ent work shifts is an effective strategy aquatic animals and insects, as well
are mainly nocturnal (kangaroo that creates a good balance and avoids as mammals.
rats; packrats, blacktail jackrabbits; competition for survival. Most birds are diurnal, but the
desert cottontails; bobcats; coyotes; Bats are the reigning specialists barn owl is exclusively a night hunter,
mountain lions; kit foxes; grey foxes; of the night. Nocturnal bats of the flying low over the ground on silent
geckos; some snakes; many insects American desert are highly adapted wings, snagging small mammals, and
and arachnids, etc.). Hidden away in to hunt from dusk to dawn through occasionally, small birds. The great
their burrows, under rocks, deep in their ability to echolocate. Crepuscular horned owl hunts mainly at night
the sand, in cool caves, dens or other bats have keen eyesight for low light, from its perch or from the ground and
shelters during the day, they await the but for not day hunting. Some Central will eat anything from grasshoppers

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