Peregrine Falcons and DDT
Understanding "Bio-accumulation" of Toxins in the Environment
Even the youngest students that we talk to in the third and fourth grade seem to understand what it means to be listed as "endangered" and that the peregrine falcon and bald eagle were added to the endangered species list largely because of the impact of dichloro-diphenyl-trichloroethane (DDT).
DDT was considered to be a safe and effective insecticide in the 1940s and 1950s. It was used worldwide as an agricultural insecticide, and to combat lice and mosquitos responsible for the spread of human diseases such as typhus, and malaria. At the time, there were no known significant adverse effects to either animal or human health. Scientists later discovered the harmful effects of this pesticide and its derivatives in the environment. Select image at right to enlarge view.
When DDT was in wide and common use, daily doses of the chemical accumulated in the fatty tissue of the peregrine. The use of DDT was diminished and for some uses banned in 1972, however residual DDT in the environment today continues to contaminate peregrine falcons. Through a biological coincidence, the stored chemicals acted to "block" the movement of calcium during eggshell formation causing the shells to be "thin." Peregrine falcon eggs broke and embryos died at an alarming rate around the world, alerting biologists long-term to search for a cause.
DDT is an organochlorine, and is highly persistent in the environment. In soil DDT is reported to have a half life between 2-15 years. Its metabolic products (DDE, DDD) accumulate through the food chain, with top level predators such as raptors having a higher systemic concentration of the chemicals than other animals sharing the same environment. DDE (dichloro-diphenyl-ethylene) is the most stable and toxic of the DDT metabolites.
Because raptors and especially peregrine falcons exist at the top of food chains, regular surveys of their population status can reveal threats to environmental health before they become hazards to human beings. The Predatory Bird Research Group continues to study the peregrine falcon and monitor its breeding status because we believe it is an important indicator of ecosystem health. Our longterm studies of the peregrine falcon population in California could be very important to future assessments of the natural environment and have value for predicting future threats to human health.
Further Reading (JSTOR):
Bitman, J., Cecil, H.C., Fries, G.F. DDT-Induced Inhibition of Avian Shell Gland Carbonic Anhydrase: A Mechanism for Thin Eggshells Science, New Series, Vol. 168, No. 3931. (May 1, 1970), pp. 594-596.
Cade, T.J., Lincer, J.L., White C.M., Roseneau, D.G., Swartz, L.G. DDE Residues and Eggshell Changes in Alaskan Falcons and Hawks (in Reports). Science, New Series, Vol. 172, No. 3986. (May 28, 1971), pp. 955-957.
Fox, G.A. A Simple Method of Predicting DDE Contamination and Reproductive Success of Populations of DDE-Sensitive Species The Journal of Applied Ecology, Vol. 16, No. 3. (Dec., 1979), pp. 737-741.
Grier, J.W., Ban of DDT and Subsequent Recovery of Reproduction in Bald Eagles (in Reports). Science, New Series, Vol. 218, No. 4578. (Dec. 17, 1982), pp. 1232-1235.
Hickey, J.J., Anderson, D.W. Chlorinated Hydrocarbons and Eggshell Changes in Raptorial and Fish-Eating Birds (in Reports) Science, New Series, Vol. 162, No. 3850. (Oct. 11, 1968), pp. 271-273.
Lincer, J. L. DDE-Induced Eggshell-Thinning in the American Kestrel: A Comparison of the Field Situation and Laboratory Results. The Journal of Applied Ecology, Vol. 12, No. 3. (Dec., 1975), pp. 781-793.
Newton, I., Bogan, J.A., Rothery, P. Trends and Effects of Organochlorine Compounds in Sparrowhawk Eggs. The Journal of Applied Ecology, Vol. 23, No. 2. (Aug., 1986), pp. 461-478.
Peakall, D.B. DDE: Its Presence in Peregrine Eggs in 1948 (in Reports) Science, New Series, Vol. 183, No. 4125. (Feb. 15, 1974), pp. 673-674.
White, C.M., Emison, W.B., Williamson, F.S.L. DDE in a Resident Aleutian Island Peregrine Population. The Condor, Vol. 75, No. 3. (Autumn, 1973), pp. 306-311.
Wiemeyer SN, Porter RD. DDE thins eggshells of captive American kestrels*. Nature. 1970 Aug 15;227(5259):737-8.