The Bald Eagle’s Reproductive Decline

This flow follows field observations suggesting that pesticide exposure was disrupting bald eagle reproduction.

increasingBearing stren­gth in each eventdecreasing

A Decade of Nest Counts

A Florida Record Broley’s Survey Charles Broley banded more than a thousand young bald eagles along Florida’s west coast. His long series of observations supplied a rare measure of nesting success over time. A Strong Starting Point He regularly found many occupied nests and banded about 150 young each year. The record later made falling reproduction visible against an established baseline.

Fewer Young Eagles

Nesting Output Falls Failed Nests The number of young began to decline. Some occupied nests held no eggs; others held eggs that failed to hatch. A Widening Pattern By the middle of the decade that followed, most nests in Broley’s study failed to produce young. The shift suggested a problem with reproduction, not simply the disappearance of adult birds.

Migration Counts Confirm Concern

Immature Birds Become Rare Hawk Mountain Observations At Hawk Mountain Sanctuary, Maurice Broun recorded a sharp decline in the proportion of immature eagles among migrants. Counts elsewhere also found few young birds. Independent Signals The observation aligned with Florida nest records and reports from riverside wintering areas. Several separate data sets pointed toward a broad failure to replace the adult population.

Experiments Suggest a Mechanism

Reproduction Under Exposure Controlled Evidence James DeWitt’s experiments showed that birds receiving DDT or related chemicals could survive while producing eggs that failed to hatch or chicks that died soon after. Residues in Eggs Studies of robins found pesticide residues in reproductive tissues, eggs, and embryos. Such findings offered a plausible mechanism for reproductive losses observed in eagles, though field causation remained under investigation.

A Suspected Coastal Link

Fish, Spraying, and Eagles Exposure Through Prey Coastal eagles ate fish from areas repeatedly sprayed with DDT against salt-marsh mosquitoes. Fish and crabs from these waters carried substantial residues. An Unresolved Threat Carson treats insecticides as compelling circumstantial evidence, not as a completed laboratory proof for eagles. The concern is that stored poison could impair reproduction and interrupt the continuity of the species.

1939–1949

Beginning in 1947

1955–1959

By the early 1960s

During the late 1950s field investigations