BIRD FAT REDUCTIONS IN FORESTS TREATED WITH DIMILIN (R)
Environmental Toxicology & Chemistry. 12(11):2059-2064,
1993
Nov.
Abstract
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 control of gypsy moth (Lymantria
dispar) populations in Eastern forests. However,
Dimilin(R)
has
been implicated in mortality of nontarget insects, many of
which have been shown to be food for birds. This study
examined
the overall condition of birds breeding on
Dimilin(R)-treated
and untreated plots by determining the percentage of dry
weight
fat for a group of common forest songbirds. It was found that
seven of the nine tested bird species had significantly (p
<
0.05) lower fat reserves on treated plots than those on
nontreated plots. Although the two nonsignificantly different
bird species were permanent residents (black-capped chickadee
and tufted titmouse), all of the remaining seven species were
neotropical migrants. Possible causes of the fat reductions
center on (a) reduction in food, resulting in a decrease in
biomass of ingested food; (b) increase cost in obtaining food;
and (c) reduction in food quality. Whether or not the reduced
fat levels cause concomitant reductions in adult/juvenile
survival could not be demonstrated.
