Mating and Having Babies
Most North American
mammals do not pair up for life. Males and females find each other
during mating season and go their separate ways soon after, leaving the
females to raise the young.
Who Gets to Mate?
Male mammals of many species battle to decide who gets to mate. They may
use calls, have staring contests, bite, kick, or butt heads. Usually the
winner is decided before there are any serious injuries.
Male
Dall’s Sheep in head-butting contest. © Hugh Rose/Visuals Unlimited
Why Fight It Out?
Because the strongest healthiest male is the best choice for fathering
youngsters that will grow up to be strong and healthy, too.
Litters and Lifespans
Mammals that have only one or two babies at a time usually live
for many years. A bat can live for 30 years, a long time for a
wild animal. Most bats give birth to just one baby each spring.
Animals that do not live very long, like mice and other prey
species, breed several times a year and have large litters.
The Meadow Vole has lots of babies—it has to, since it may live
for only a year. In their speedy cycle of life and death, female
voles start having babies when they are just 8 to 12 weeks old!
They have up to 12 litters a year, of 2 to 10 young each time.
The Grizzly Bear can live 15 to 35 years. A female may give
birth once every three years, usually to two cubs at a time.
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Meadow Vole
babies in nest. © Scott Camazine - Photo Researchers, Inc.
Grizzly Bear
cub. © Michael Giannechini - Photo Researchers, Inc.
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Humpback Whales.
© Dave B. Fleetham - Visuals Unlimited
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Singing for a Mate?
Male Humpback Whales gather in their breeding grounds and
“sing,” producing a series of chirps, cries, and other sounds.
Individuals sing for 10 or 15 minutes at a time, but the entire
group may go on much longer. Naturalists aren’t completely sure
why Humpbacks do this but suspect it is how males tell females
they are good partners for mating.
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Den
Babies
Many mammals have their babies in dens or burrows. The den is a
safe place, hidden from people and predators. It might be inside
a fallen tree or beneath a dense tangle of rocks and brush.
Weasels build a soft nest using fur from animals they have
killed. The den may be the abandoned burrow of a chipmunk or
pocket gopher or a hollow spot under a tree stump. Weasels have
four to eight babies in a litter, all born blind and without
hair.
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Short-tailed Weasel babies in nest. © Roger A. Powell - Visuals
Unlimited
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Lodge
Babies
Baby beavers, called kits, are born inside the family lodge, a
large mound of tree limbs and mud with a hidden chamber inside.
Kits are born with their eyes open and a full coat of hair.
Within a week they are excellent swimmers.
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American Beaver with kit in lodge. © Robert Lankinen - The
Wildlife Collection
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Bottle-nosed Dolphin
mother and baby. © Daniel J. Cox - naturalexposures.com
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Ocean
Babies
Baby dolphins are born in deep water and must swim to the
surface for their first breath of air. The mother dolphin often
dives under her baby to help steer it in the right direction.
Dolphins have one baby at a time, born about a year after
mating.
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Ice Babies
Like many seals in the Arctic, the Harp Seal is born on bare ice,
where its white fur helps it blend in. It receives milk from its mother
for only two weeks, but by that time it already weighs 100 pounds!
Baby Harp Seal on ice. ©
Barbara Gerlach - Visuals Unlimited
Pouch
Babies
Opossums are born long before they are able to survive on their
own. After birth, they crawl up the mother’s body and into a
pouch on her belly. Each baby latches onto a nipple and remains
in the pouch, attached to the mother, for at least two months.
The pouch protects the young while they grow.
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Virginia Opossum
young in mother’s pouch. © Gary Meszaros - Dembinsky Photo
Associates
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Hidden Babies
Pronghorns have their babies in a hidden spot on the open
plainsbut soon join a herd of other mothers and fawns. Females,
called does, have one fawn their first year but in following
years have twins or occasionally triplets.
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Pronghorns
© Michael Durham - Ellis Nature Photography
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