BIRD FAT REDUCTIONS IN FORESTS TREATED WITH DIMILIN (R)

Indirect, nonacutely toxic, effects of pesticide applications on birds have been largely over-looked. Diflubenzuron (trade name Dimilin(R)) has extremely low toxicity to birds (LD50 > 3,762 mg/kg for red-winged blackbirds, Agelaiusphoeniceus). It has gained widespread use for con trol of gypsy moth (Lymantria dispar) populations in Eastern forests. However, Dimilin(R) has been implicated in mortality of nontarget inse cts, many of which have been shown to be food for birds. This study ex amined the overall condition of birds breeding on Dimilin(R)-treated a nd untreated plots by determining the percentage of dry weight fat for a group of common forest songbirds. It was found that seven of the ni ne tested bird species had significantly (p < 0.05) lower fat reserves on treated plots than those on nontreated plots. Although the two non significantly different bird species were permanent residents (black-c apped chickadee and tufted titmouse), all of the remaining seven speci es were neotropical migrants. Possible causes of the fat reductions ce nter on (a) reduction in food, resulting in a decrease in biomass of i ngested food; (b) increase cost in obtaining food; and (c) reduction i n food quality. Whether or not the reduced fat levels cause concomitan t reductions in adult/juvenile survival could not be demonstrated.