The DDT Debate Continues

To the Editor,

In my September 3 letter, I stated that bald eagles increased by 25 percent during the years of heavy DDT use. My source was the annual Audubon Christmas counts, except that I erred in typing Hawk Mountain instead of Audubon, begetting dissatisfaction from Craig Fosdick, assistant naturalist at Hawk Mountain (October 1). He doesn’t deny the 25-percent increase was Audubon’s Christmas count.

Even Hawk Mountain data show increases in ospreys, peregrine falcons, and hawks. The peregrine falcon fluctuated from 14 in 1965 to 32 in 1969. The osprey increased regularly from, in 1946, 191 to 600 in 1970. (Source: Hawk Mountain Sanctuary Newsletter, May, 1977.)

Mr Fosdick’s data are from the East Coast. Entomologist J. Gordon Edwards, professor at San Jose State University, noted that in November, 1969, in Montana, a record number of 373 bald eagles were sighted on a single day, of which 120 were young, suggesting successful mating and nesting during the years of heavy use of DDT.

Mr Fosdick’s chief point is the long-lived claim that DDT caused eggshell thinning of bald eagles, decreasing their number. (Even if so, does it follow that it was right to ban DDT, that boon to mankind that controlled malaria, encephalitis, and a dozen other diseases, and gypsy moths and dozens of other insects?)

Not everyone agreed eggshells thinned. Researcher Postupalsky found no correlation between DDT or DDE residues and shell thickness in a large series of bald eagle eggs in 1971. Likewise, scientists working with bald eagles, brown pelicans, ospreys, and other birds reported no correlation or a negative correlation between thickness of shells and levels of DDT residues in the eggs, according to Professor Edwards.

But there are also numerous accounts of decrease of raptor populations for which there were many causes: a widespread loss of suitable habitat; illegal shooting; powerline execution; collisions in flight; poisoning from eating ducks that contained lead shot; oil, lead, mercury, cadmium, lithium, manganese, selenium, and certain sulfur compounds.

Zoologist Dixy Lee Ray cites many causes in “Trashing the Planet,” not enough calcium or vitamin D, fright, high nocturnal temperatures, and diseases like Newcastle’s disease. Quail that were fed huge quantities of DDT hatched 80 percent of their chicks compared with 84 percent for the control group.

Professor Edwards says the chief cause of thinning was not enough calcium. Anti-DDT players sometimes withheld calcium from birds’ diets. At Patuxent, for instance, they deliberately fed their birds only calcium-deficient food (0.5 percent rather than the needed 2.5 percent calcium) and then attributed eggshell problems to DDT.

In another case, one Peakall abruptly reduced the illumination in his dove cages from 16 to 8 hours a day and at the same time started feeding the birds high levels of DDT in all their food. He then claimed DDT had inhibited shell formation.

Professor Edwards says the frauds were exposed (probably by him) but the media refused to publicize them, and the public remained misinformed.

Damage to eagles, no matter what the cause, was generally attributed to DDT, but there was much misidentification, some honest, as by Mr Fosdick’s source, Risebrough and his associates. In 1965 they reanalyzed the samples. Three had no DDT and the other two had only a fraction as much as they originally reported.

One point is worth recalling: The charge that DDT thinned eggshells of bald eagles was made during the seven-month hearing on DDT before EPA’s Administrative Law Judge Edmund Sweeney, who found that DDT does “not have a deleterious effect on… wild birds, or other wildlife.”

Natalie Sirkin

44 Big Trail, Sherman                              October 19, 1999