Peregrine Falcons and Chemicals
Harm From DDT in Rural Populations and PBDEs in Urban Birds of Prey
Jul 2, 2008
In 1999 the peregrine falcon (Falco peregrinus) was officially removed from the Endangered Species list in the United States. These spectacular birds of prey had been nearly extirpated when contamination from the pesticide DDT resulted in the loss of many eggs and chicks. That recovery is now threatened by another chemical, Poly Brominated Diphenyl Ether (PBDE).
Urban Peregrine Falcons
As an alternative to poisoning to control feral pigeon populations, the peregrine falcon was introduced into cities where they have been thriving. But the pigeons and other small birds that make up the majority of their diet are contaminated with the flame retardant PBDE.
In 2003, peregrine falcon eggs in Sweden were found to have significant levels of PBDE, a flame retardant commonly used in furniture. Contamination of aquatic species such as the orca had been a concern previously but this was the first time that PBDEs were found in a terrestrial species.
Overall levels of PBDEs are higher in the US than in Europe. In California, where PBDE levels in human breast milk are the highest of any area studied worldwide, a survey of peregrine falcons in the Los Angeles and San Francisco urban belts showed that the birds there were also suffering from PBDE contamination.
Rural Peregrine Falcons
Meanwhile peregrine falcons monitored in more rural areas still show high levels of DDT (DichloroDiphenylTrichloroethane), most likely from residues of this long lasting chemical or from continuing use in some Latin American countries. Reduced reproductive success is a concern in these areas.
DDT and PBDEs
A neurotoxin, PBDE is known to delay brain development and cause behavioral and learning difficulties in laboratory animals. A study done on kestrels found changes in thyroid and Vitamin A concentration, which altered glutathione metabolism and caused oxidative stress. Peregrine falcons stoop dive at speeds up to 200mph to capture prey. It is feared that the ability to find and kill prey, as well as to effectively care for nestlings, is being compromised by exposure to PBDEs.
DDT causes thinning of eggshells and loss of chicks, as well as reducing breeding success. During the early stages of the recovery program for the peregrine falcon, eggs were taken from the nests and carefully brooded in incubators to prevent breakage. The hatchlings were then returned to the nests to be reared by the adults.
Today concerns about mosquito vector diseases are creating pressure to bring DDT back into regular use, increasing the potential threat to peregrine falcons and other birds.
The peregrine falcon has been hailed as a major success for the Endangered Species Act. Ongoing monitoring of peregrine populations is a part of the delisting process. The finding of a new contaminant problem and ongoing issues with the very chemical which nearly caused the extinction of the species highlight the value of these monitoring programs in preventing declines in these species.
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