IS FULL OF EXCEPTIONS
or false? All birds lay eggs. Mammals give live birth to their young.
Only male deer have antlers. All owls are nocturnal. Hummingbirds and
warblers are always diurnal. These statements are true. Mostly. But
there are exceptions, and some of them are utterly fascinating.
about the ecological and behavioral traits of different animals is one
of the most enjoyable pursuits in the field of biology. We have literally
millions of living species on earth, and the human tendency is to categorize
groups into more manageable units. For example, salamanders, oak trees,
and starfish have little in common with each other, other than being
living things. But within any one group similarities and consistencies
exist. And each group has attributes peculiar to it that can be used
in most instances to differentiate it from other groups, even more closely
related ones, such as frogs from salamanders, pine trees from oaks,
and sea urchins from starfish. But our rules for distinguishing among
biological groups often dissolve in the face of scrutiny. Exceptions
commonly held belief that no mammals lay eggs is one of those exceptions.
Which brings us to the aquatic duckbill platypus of Australia. Platypuses
easily qualify as one of the strangest mammals in the world. The female
lays one to three eggs that she curls around in a burrow for about 10
days before they hatch. The mother has mammary glands that produce milk
for the babies for more than three months. The males are one of the
few venomous mammals in the world. The venom glands are located on the
hind feet, which have a sharp, protruding, grooved spur. Platypuses
also use special organs on the flat, duck-like bill to detect electrical
impulses created by prey such as worms, insect larvae, and crayfish
in dark, murky waters.
egg-laying mammals, found in Australia and New Guinea, are spiny anteaters,
also called echidnas. With their rounded little bodies, which are covered
with spines, these terrestrial creatures look pretty much like hedgehogs.
Depending on which scientist you talk to, two to five species exist.
Echidnas typically lay one egg, which is incubated in a body pouch.
Not to be outdone by their duck-billed, web-footed relatives in being
strange, echidnas have no teeth.
group most commonly encountered by us on an everyday basis is composed
of the placental mammals, which are most of those outside of Australia.
Most people are also familiar with marsupials, such as kangaroos and
possums, which raise their young in pouches. Platypuses and echidnas
qualify as an exception among mammals. They fall into an evolutionary
tangent distinct from either placental mammals or marsupials and are
placed in a third, less commonly known category of mammals known as
the other animals mentioned above, the general worldwide rule for deer
is that only males have antlers. These are shed and regrown each year.
However, one type of deer, reindeer (caribou), is distinctive in that
females as well as males have antlers, a single exception to a rule
that holds for more than 90 other species.
for how we categorize the time of day or night that birds fly. While
owls are indeed characteristically nocturnal hunters, barred owls in
the Southeast and the northern pygmy owl in the West can be active and
capture prey in the daytime. But the northern hawk owl, found in the
upper regions of North America from Alaska across Canada, is the undisputed
daytime owl. As residents in the land of the midnight sun, during the
summer they must either be active during the day or starve. As for birds
that we normally think of as active in the daytime, among hummingbirds,
warblers, and many other migratory species, nighttime flights are common.
about the assertion that all birds lay eggs? Is there an exception to
that rule? Yes, but its not like the exceptions discussed above.
Male birds do not lay eggs.
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