Biology Reference
In-Depth Information
As the number of whooping cranes in captivity rose steadily, in 1992 scientists began to release them
into the wild on Florida's Kissimmee Prairie. Their goal was to create a nonmigratory flock containing
100 to 125 whoopers a year or more old.
Early releases were devastated by bobcats, which initially killed nearly two-thirds of the birds. In
1995, however, recovery experts changed tactics by switching from permanent to portable holding pens
placed in safer habitat— low grass and freshwater marsh, where it's much more difficult for bobcats to
stalk the cranes unseen until they're close enough to pounce. Once the cranes are properly acclimated,
the pens are removed, leaving the birds on their own. With this change, bobcat predation on new crane
releases has been reduced to a much more tolerable 30 percent.
The goal of one hundred whoopers age one and up in the Kissimmee flock now seems very feasible,
for there are currently seventy-five of them, with the number steadily increasing as more are released.
So far, none of those cranes has reproduced, but that all-important step seems to draw closer each year.
Last year there were nests, but no eggs were laid. This year two pairs of whoopers nested, and each
pair laid two eggs. Those eggs didn't hatch—possibly they weren't fertilized—but biologists are by no
means discouraged. Whooping cranes, which mate for life and are long-lived, often take several years
to settle into a routine of successful reproduction.
There are now 366 whooping cranes, 104 of them in captivity. In addition to the seventy-five wild
whoopers in the Kissimmee flock, there are now 183 in the migratory Aransas flock—the original flock
that was once reduced to only fifteen birds. This flock is growing at the rate of about 4 percent a year.
There are also four remaining whoopers from the unsuccessful experiment using sandhill crane parents.
Biologists would also like to start another migratory flock—an extremely difficult task, since mi-
gration is a learned behavior in whooping cranes. Experiments are under way with both whooping and
sandhill cranes to use ultralight aircraft as a means of leading young cranes to migrate.
With their present large population well distributed throughout North America, great blue herons
appear to be thriving in most areas. Still, biologists note that there are at least three things that could
reduce heron numbers in the future.
The first, ironically, is the return of the bald eagle, itself only recently taken off the endangered spe-
cies list. Although the eagles only occasionally kill adult great blues, they prey on their chicks. More
serious is the fact that they often frighten parents off the nests before their eggs hatch; as soon as a her-
on's nest is left unguarded, hordes of crows and other predators swoop in to seize the eggs. Although
eagles thus take a direct and indirect toll of herons, it seems doubtful that the big raptors, which require
a large territory, will become so numerous that they'll do serious harm to the herons. After all, they
previously coexisted successfully for countless millennia.
The second concern stems from the great blue's ability to catch fish. As aquaculture has expanded
dramatically in the past few years, great blues have discovered that these fish-filled ponds are pure lar-
gesse for a hungry heron. Naturally, owners of these commercial fish-raising ventures aren't thrilled at
the sight of their profits vanishing down those elongated gullets, and so they've sought and received
depredation permits to shoot as many as four thousand of the offending herons annually (great blue
