Crane
Population Growth: Why So Slow?
By Tom Stehn
Whooping Crane Recovery
Team Co-Leader
Photo Joan Garland, ICF
The Whooping crane population needs every adult pair to do two things: live long lives, and try to raise a chick every year. The population has little capacity to increase in size rapidly. These are some reasons:
- Whooping cranes don’t even start nesting until they are at least 3 years of age, and they usually don’t lay eggs and hatch a chick until about age 5.
- Whooping cranes have to experience nesting to get it right. They must gain experience feeding and protecting a chick from predators to ensure its safety. Much of this parental behavior is instinctual, but the experience allows the cranes to do it the right way.
- Even though Whooping crane pairs lay 2 eggs every year, normally only the chick that hatches from the first egg survives. The eggs hatch 1-2 days apart, so the chick from the first egg is usually stronger. It will even peck at its sibling repeatedly to try to drive it off. That's how the stronger chick makes sure it gets most of the food brought by the parent cranes.
Limited
Ability to Have Young =
Slow Growth in Numbers
With
all the things that can go wrong with trying to hatch an egg and
then protecting the flightless youngster from
predators for 80
days
before
it learns to fly, a Whooping crane pair usually only
brings a chick to Aransas NWR every other year. I
know one male crane that
has nested
12 times
and only once successfully brought a chick
to Aransas.
Whooping cranes are not like mallard ducks that can lay and hatch 8 or more eggs. With this limited ability to have young, and the fact that Whooping cranes normally aren’t successful parents until they are about 5 years old, the population can only grow slowly.
Like the Tortoise Racing the Hare
Cranes
make up for this
slow reproduction by living long lives. Birds
that live 30 or more years
of age are very unusual in the bird kingdom.
Parrots are another bird that
can live many years, but most kinds of birds
live less than 10 years of age. Birds with short lives start
breeding at
age 1 or 2 and can
often produce several young every year. Think
of cranes like the story about
the tortoise racing the hare. The tortoise beat
the hare in a race, but only by continuing to plod forward
for
a long time. If you are
a crane
and reproduce slowly, you have to keep going
a long time in order for your species to survive.
Try This: Journal Questions
- It can be tough being the younger sibling! Can you relate to this? Is your older brother and sister allowed to do things you aren’t allowed to do? Why does it seem unfair?
- If only one chick usually survives, why do Whooping cranes lay that second egg? What reasons can you think of why a second egg might sometimes be important? After you list your ideas, see what Tom Stehn says: >>
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