In his book On the Wing, Alan Tennant chronicles his efforts to track the migration of the peregrine falcon. Valued for their beauty, swiftness, and power, these amazing birds of prey were favorite hunting companions of emperors and nobility. Sadly, the wide use of the pesticide DDT in the 1950s interfered with their reproductive cycle and placed them on the endangered species list.

Interested in the recovery of this species, Tennant attached transmitters to a select number of falcons to track their migration patterns. But when he and his pilot flew their Cessna behind the birds, they repeatedly lost signal from the…