3.11 Banning of a toxin and captive breeding brought peregrine falcons back from the brink of extinction

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Using what you learned about population growth earlier in the chapter, predict how the pattern of growth shown in Figure 3.28 will or will not change over the long term. (Hint: Consider Figure 3.11.)

After the peregrine falcon was declared an endangered species in the United States in 1970, the greatest threat to its survival needed to be eliminated. In 1972 the United States banned the insecticide DDT, which had caused eggshell thinning. As a result of decreased DDT use in the United States, Canada, and Latin America, the amount of DDE, the breakdown product of DDT associated with eggshell thinning, has gradually decreased in the tissues of peregrine falcons (Figure 3.27). However, that was only the first step toward a solution.

CONCENTRATION OF DDE IN BLOOD PLASMA OF MIGRATORY PEREGRINE FALCONS
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FIGURE 3.27 The concentration of DDE, a breakdown product of DDT, in the blood plasma of peregrine falcons captured at Padre Island, Texas, during spring migration declined rapidly between 1979 and 2004. (Data from Henny et al., 2009)

To restore falcon populations, the U.S. Fish and Wildlife Service entered into a partnership with state natural resource agencies and nongovernmental organizations to establish captive rearing programs. From 1974 to 1997, these programs released more than 6,000 peregrine falcons to their historic range in 34 states. In addition, critical habitat for the peregrine falcon was identified and protected.

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How would reduced genetic diversity among North American peregrine falcons between 1985 and 2007 have made the population less able to adapt to future environmental challenges?

The initial goal of the captive rearing and release program was to build the population back up to 631 nesting pairs in the United States. By the mid-1990s, the population had grown well beyond this target (Figure 3.28), and the U.S. Fish and Wildlife Service announced its intention to remove the American peregrine falcon from the endangered species list.

PEREGRINE FALCONS NESTING IN THE LOWER 48 UNITED STATES
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FIGURE 3.28 The number of pairs of nesting peregrine falcons in the lower 48 (contiguous) United States grew rapidly following the banning of DDT, as did the release of falcons produced by the captive breeding program. (Data from U.S. Fish and Wildlife Service 2003, 2006)

The American peregrine falcon was removed from the endangered species list on August 25, 1999, and the population continued to grow. By 2003 the American peregrine falcon population in the United States, Canada, and Mexico reached an estimated 3,005 breeding pairs. Follow-up genetic studies of migratory peregrine falcons have shown no reductions in genetic diversity from 1985 to 2007, indicating that the restored peregrine falcon populations of North America are not in decline.

Think About It

  1. Why was a captive rearing program necessary? Why was a ban on DDT alone not sufficient for the peregrine falcon to recover on its own?

  2. What were some advantages of having a cooperative breeding program for the peregrine falcon, involving federal and state scientists along with private foundations and citizens?