Answers from the Whooping Crane Expert
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Answers from the Whooping Crane Expert
Special thanks to ornithologist Laura Erickson for providing her time and expertise in responding to your questions below.
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From:
Lincoln, Nebraska
Q: How many Whooping Cranes migrate from the Aransas/Wood Buffalo
preserve to Canada on an annual basis? What percentage of the cranes that
migrated from the Aransas/Wood Buffalo Flock typically stop in Nebraska
on their way north?
A: This past
winter a record number of Whooping Cranes wintered in Aransas National
Wildlife Refuge: 194. These are the birds that breed in Wood Buffalo National
Park in Canada. Only a very small percentage of them stop in Nebraska
on their way north. They cover very long distances on migration, choosing
to move on days with perfect migrating conditions--lots of thermals to
carry them aloft with minimal effort.
Q:
What time of year do they typically stop? How long do they usually stay?
Where (I assume somewhere along the Platte River) do they prefer to stop?
A: Ones that
drop in on the Platte River stay for several days or up to a few weeks.
Q:
How many Whooping Cranes are there in all the known populations?
A: As of
Feb. 2004, there were 194 in the Wood Buffalo/Aransas wild flock, at least
83 in the non-migratory Florida flock, and 36 in the Wisconsin/Florida
migratory flock, making a total of 313 wild cranes. There are also 119
captive cranes, making a total world population of 432. You can keep track
of crane numbers by clicking
here.
Q:
What are the best estimates of how many Cranes there were before they
began to be adversely impacted by anthropogenic activities?
A: Whooping
Cranes were never abundant, as far as we can determine. The population
in the 1850s was probably somewhere between 1300 and 1500 birds.
Q:
What is the number (the restoration goal) of Whooping Cranes in the population
that is needed before the USFWS can downlist them from endangered to threatened?
A: The Whooping
Crane restoration team has decided that in addition to the Aransas/ Wood
Buffalo flock, two additional flocks of 25 breeding pairs each (the Wisconsin/Florida
migratory flock and the non-migratory Florida flock) will be needed to
improve population health to the point that whooping cranes could be downlisted
from endangered to threatened under the Endangered Species Act.
Q:
Are there any critical habitat limitations that are adversely impacting
population recovery? If so what are the limitations and how many birds
could the known habitat sustain if something is not done to improve it?
A: Whooping Cranes require extensive wetlands for breeding, wintering, and migratory stopovers. The blue crab population where they winter is critical to their breeding success the following summer. They suffer when the rivers feeding into their wintering estuary are depleted of water as a result of droughts and from people diverting the water for other uses.
From: Marilyn Beale
Q: What caused the depletion in the numbers of whooping cranes
so that we need to help them?
A: During
the 1800s, Whooping Cranes were over-hunted. At the same time, wetlands
were being drained for agriculture. During the mid- and late-1900s, even
as more wetlands were being drained and developed, pollutants were increasing,
and more water was being taken from rivers feeding into the estuary waters
where the Whooping Cranes spend the winter. This caused their population
to crash to a critical level.
From:
White Bear Lake, Minnesota
Q:
It is amazing that the whooping cranes seem to leave their wintering grounds
at almost the same time each year. Why is this? What factors signal the
cranes that it is time to leave?
A: Birds
become increasingly restless during their migration season as a response
to day length, which changes the same from one year to the next. But to
actually act on this restlessness and head north, Whooping Cranes take
advantage of certain weather conditions--little or no wind, or tail winds
along with enough sun to produce thermal air currents, which happen on
only a few days. And they're social birds, taking their cues from others
in their flock. On average, these happen pretty much at the same time
each year.
From:
Victoria, Minnesota
Q:
Why do you think that the groups continue to split up during migration?
(After all, didn't they all fly south together and stay together on the
wintering grounds?)
A: Whooping
Cranes are not gregarious birds like finches that like to flock in huge
groups. They are sociable, so we almost always encounter family units,
pairs, and small groups of unpaired young. There is probably something
in their genes that makes cranes most comfortable in these small groups.
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Lobstick
Family at Aransas NWR Photo Diane Loyd |
Q:
Do these families usually migrate together? What advantages or disadvantages
might there be if they migrate together? Or migrate apart?
A: The family group stays together for all of autumn migration and then much of spring migration, before the parents push on without last year's young. More eyes make it more likely that at least one of them will spot a predator in time for the whole group to escape. The parents are warier and more experienced than last year's young, and the chick will benefit from staying with them as long as possible. And the migration route experience of the parent birds gives an advantage to last year's chick, too; the parents are more likely to know good resting and feeding places, which is especially important for inexperienced young birds when they're following a different route in spring than they did in fall. But as a pair gets closer and closer to its breeding ground, its need for isolation becomes greater than its concern for its young, and the parents move on without them. One disadvantage of being in a group is the greater competition for food. In non-related groups, there is even--to some degree--competition for mates, which could lead to the breakups of established pairs, or a waste of energy in extra displays to show which birds are mated pairs. It will be fascinating to see how the young cranes in the Wisconsin/Florida flock break up and form pairs as they mature in the coming years.
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Q:
Before in one of your updates there was something on how experts tried
to raise the whoopers with sandhill cranes, but they imprinted and would
only mate with sandhills. There was also something on how one whooper
imprinted on a human and that person had to jump up and down and flap
his arms every year to get it to lay eggs. If I'm correct on this, does
that mean that the whooping cranes don't do any physical contact when
breeding like we do? Is it more of a mental thing? I'd like to know more;
I don't understand. I know they do the dance with each other, but is that
it?
A: Crane pairs dance to prepare for mating, in the way that human couples date and have romantic evenings before they marry. Dancing helps each crane pair to be in perfect physiological synchrony so the females will ovulate and be receptive to mating right when the males are most capable of producing sperm. But to actually mate, the cranes must come into physical contact.
From:
Montrose, Minnesota
Q:
How could it be that we saw a pair of whooping cranes here in Montrose,
Minnesota? Could they possibly be nesting nearby or are they migrating?
A: These
birds were seen in April, which is migratory season, and were confirmed
as wanderers from the Wisconsin flock. In spring or fall, they could also
be birds passing through between Aransas and Wood Buffalo.
Q:
Could they be part of the Wisconsin flock and only here for the day? What
is this dancing, soaring thing they were doing? It was magnificent.
A: The Wisconsin
flock has been doing a bit of wandering, which is normal for subadults.
The dancing cranes do is partially a part of their mating behavior, and
since you were seeing a pair, it's possible they were a breeding pair.
But young birds often dance, and in migration, as hormones are revving
up, often birds seem to dance as an aggressive behavior. To see photos
and a video of a pair of cranes dancing at the Patuxent Wildlife Center,
click
here.
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