Biology Reference
In-Depth Information
After mating, the female whooper lays only two eggs. This number alone would represent a low re-
productive rate, but that's only half of the crane's problem. Assuming that both eggs hatch, only the
larger, stronger chick survives. Either the parents feed the larger one nearly to the exclusion of its smal-
ler sibling, or the larger one pecks the smaller one to death or drives it out of the nest. Once outside the
protection of the nest, of course, the chick quickly becomes prey for one predator or another.
This minuscule reproductive rate, combined with relentless hunting for its feathers and even more
deadly habitat loss, caused the whooping crane population to dwindle steadily. Whoopers' numbers
were probably never very high, but by 1941 only fifteen whooping cranes remained alive in the
wild—all that stood between their species and extinction! Incidentally, some sources list the wild pop-
ulation of whooping cranes in 1941 as either fourteen or sixteen, but the official count at the Aransas
National Wildlife Refuge in Texas, where the whoopers winter, was fifteen.
Efforts to save the whooping crane began at that point—efforts fraught with all manner of diffi-
culties, not the least of which is the whooper's extraordinarily low reproductive rate. No one knew
where the cranes nested, so until 1954 little could be done except give the remaining whoopers total
protection and hope that they might eventually rebuild their shattered population, albeit at an excruci-
atingly slow pace.
Then serendipity struck. In that year, a pilot who was flying over Wood Buffalo National Park in
Canada's Northwest Territories saw a pair of whooping cranes and what he believed might be a chick.
He was right, and scientists now held the key to accelerated whooping crane reproduction.
After much study and debate, biologists decided in 1975 to remove one egg from some of the whoop-
ers' nests. This had no adverse effect on whooping crane reproduction, since only one chick survives
anyway. The pilfered eggs were then placed in the nests of the whooper's slightly smaller relative, the
sandhill crane. This technique seemed to work well at first, as the sandhill cranes successfully hatched
and raised the young whoopers. Then a major flaw became apparent.
Much of what whooping cranes do appears to be learned, rather than instinctive, behavior. Un-
fortunately, this happens to include mating behavior. Raised by sandhill cranes, the whoopers simply
wouldn't mate and raise chicks when they reached maturity. Thus it was back to the drawing board for
the scientists overseeing the whoopers' recovery.
Whooper eggs could readily be incubated artificially, but a major obstacle arose after the chicks
hatched: How could they be raised without becoming imprinted on humans, which they would then re-
gard as their parents? As biologists knew all too well from the sandhill crane experiment, cranes raised
in this fashion would fail to reproduce.
The solution was to feed the whooper chicks using hand/arm puppets that resemble a crane's head
and neck. Workers also donned crane costumes when caring for the chicks or carrying out other activ-
ities with them. The chicks and young adults are never allowed to see a human except under unpleas-
ant circumstances, such as having a veterinarian catch and examine them. These techniques have been
much more successful than the experiment with the foster-parent sandhill cranes.
