And how does it know that?
The Boston Globe reports:
WESTBOROUGH, Mass.—Massachusetts wildlife officials are preparing to count bald eagles during the annual midwinter survey of the coast and major rivers, lakes and reservoirs.
The 33rd annual count is scheduled to go ahead Friday even though bad weather has forced a helicopter to cancel flights at the Quabbin Reservoir and Connecticut River, which together account for about two-thirds of the eagle population in Massachusetts.
The count is part of efforts to monitor the recovery of bald eagles after poisoning by pesticide DDT decimated their population.
Massachusetts’s first count in 1979 revealed 8 bald eagles. Last year, the state logged a record 107 bald eagles.
Division of Fisheries and Wildlife Assistant Director Thomas French says authorities changed the bird’s legal status in Massachusetts this year from endangered to threatened.
But DDT was banned in 1972. If the first bird count wasn’t until 1979, how do they know DDT was responsible?
As JunkScience.com readers know from “100 Things You Should Know About DDT“, bald eagles were “decimated” long before DDT came along:
66. Bald eagles were reportedly threatened with extinction in 1921 — 25 years before widespread use of DDT. [Van Name, WG. 1921. Ecology 2:76]
67. Alaska paid over $100,000 in bounties for 115,000 bald eagles between 1917 and 1942. [Anon. Science News Letter, July 3, 1943]
68. The bald eagle had vanished from New England by 1937. [Bent, AC. 1937. Raptorial Birds of America. US National Museum Bull 167:321-349]
69. After 15 years of heavy and widespread usage of DDT, Audubon Society ornithologists counted 25 percent more eagles per observer in 1960 than during the pre-DDT 1941 bird census. [Marvin, PH. 1964 Birds on the rise. Bull Entomol Soc Amer 10(3):184-186; Wurster, CF. 1969 Congressional Record S4599, May 5, 1969; Anon. 1942. The 42nd Annual Christmas Bird Census. Audubon Magazine 44:1-75 (Jan/Feb 1942; Cruickshank, AD (Editor). 1961. The 61st Annual Christmas Bird Census. Audubon Field Notes 15(2):84-300; White-Stevens, R.. 1972. Statistical analyses of Audubon Christmas Bird censuses. Letter to New York Times, August 15, 1972]
70. No significant correlation between DDE residues and shell thickness was reported in a large series of bald eagle eggs. [Postupalsky, S. 1971. (DDE residues and shell thickness). Canadian Wildlife Service manuscript, April 8, 1971]
71. Thickness of eggshells from Florida, Maine and Wisconsin was found to not be correlated with DDT residues.
Data from Krantz, WC. 1970. Pesticides Monitoring Journal 4(3):136-140.
State Thickness (mm) DDE residue (ppm) Florida 0.50 About 10 Maine 0.53 About 22 Wisconsin 0.55 About 4
72. U.S. Forest Service studies reported an increase in nesting bald eagle productivity (51 in 1964 to 107 in 1970). [U.S. Forest Service (Milwaukee, WI). 1970. Annual Report on Bald Eagle Status]
73. U.S. Fish and Wildlife Service biologists fed large doses of DDT to captive bald eagles for 112 days and concluded that “DDT residues encountered by eagles in the environment would not adversely affect eagles or their eggs.” [Stickel, L. 1966. Bald eagle-pesticide relationships. Trans 31st N Amer Wildlife Conference, pp.190-200]
74. Wildlife authorities attributed bald eagle population reductions to a “widespread loss of suitable habitat”, but noted that “illegal shooting continues to be the leading cause of direct mortality in both adult and immature bald eagles.” [Anon.. 1978. U.S. Fish and Wildlife Service, Endangered Species Tech Bull 3:8-9]
75. Every bald eagle found dead in the U.S., between 1961-1977 (266 birds) was analyzed by U.S. Fish and Wildlife Service biologists who reported no adverse effects caused by DDT or its residues. [Reichel, WL. 1969. (Pesticide residues in 45 bald eagles found dead in the U.S. 1964-1965). Pesticides Monitoring J 3(3)142-144; Belisle, AA. 1972. (Pesticide residues and PCBs and mercury, in bald eagles found dead in the U.S. 1969-1970). Pesticides Monitoring J 6(3): 133-138; Cromartie, E. 1974. (Organochlorine pesticides and PCBs in 37 bald eagles found dead in the U.S. 1971-1972). Pesticides Monitoring J 9:11-14; Coon, NC. 1970. (Causes of bald eagle mortality in the US 1960-1065). Journal of Wildlife Diseases 6:72-76]
76. U.S. Fish and Wildlife Service biologists linked high intake of mercury from contaminated fish with eagle reproductive problems. [Spann, JW, RG Heath, JF Kreitzer, LN Locke. 1972. (Lethal and reproductive effects of mercury on birds) Science 175:328- 331]
77. Shooting, power line electrocution, collisions in flight and poisoning from eating ducks containing lead shot were ranked by the National Wildlife Federation as late as 1984 as the leading causes of eagle deaths. [Anon. 1984. National Wildlife Federation publication. (Eagle deaths)]