Natural Selection Image Map

Case Study #1: The Bald Eagle

The bald eagle, an American symbol, has become a model for the successful recovery of an endangered species.  Once, only a little over 400 nesting pairs of these predatory birds existed in the lower United States.  Today, under the protection of the Endangered Species Act,  that number is almost 6,000.  Although promising, one would wonder how over 200,000 of these birds came to be on the brink of extinction in just a few centuries.  

During the mid-1800ís, hunters began killing large numbers of prey species, like waterfowl, that support the bald eagle in its ecological niche.  Along with this, the bird itself also became a target. 

These events led to governmental intervention in the form of laws protecting bald eagles from hunters and merchants.  But other unseen threats were even more serious. Pesticides, specifically DDT, caused the shells of eggs to thin and prevented reproduction (see Story Time about Rachel Carson). Once again, the actions of humankind upset the delicate ecological balance of the bald eagle population.  After DDT was banned, the population of these magnificent predators began to rise. 

Case Study #2: A Look at Whooping Cranes

Aransas National Wildlife Refuge, located on the Texas Gulf Coast, is home to some of the best bird watching our nation has to offer.  Perhaps this same place is also the birthplace one of our nation's most unique efforts to rescue an endangered species.  About sixty years ago, ecologists estimated that only 15 whooping cranes remained alive.  Their numbers had been decimated by the human activities of hunting and farming. So the Wildlife Refuge was created where no hunting was allowed. Today the Aransas population is estimated to include 174 whooping cranes, which has inspired other notable efforts to save this species.

The ecosystem at Aransas cannot support infinite numbers of whoopers. So, ecologists came up with a clever idea of training young whoopers to migrate to another safe winter haven, in Florida.

In fall 2001, a group of 5 whooping cranes literally took off from Necedah Wildlife Refuge in Wisconsin in what was to become one of the most unique attempts to rescue an endangered species to date.  These birds, guided by an ultralight plane, were led to Chassahowitzka National Wildlife Refuge in Florida.  As everyone had hoped, they returned back to Wisconsin on their own the following spring. We hope they now know how to get to Florida and will set up the nucleus of a new wintering place in Florida. Efforts are currently underway to introduce at least ten more birds into this program. 

Still interested about learning about whooping cranes?  Track their migration progress at

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