and Secord have discovered that female tree swallows living in the
Hudson River valley, where tree swallows are known to have abnormally
high levels of PCBs, develop plumage characteristics of adults significantly
earlier than females from uncontaminated areas.
tree swallows in the upper Hudson had an increased amount of adult-type
blue green color in their normally brown plumage. Females usually
reach their full adult, blue-green color in their second year. McCarty
and Secord present data showing that an unexpectedly high proportion
of first-year female tree swallows have more adult plumage than
places away from contamination.
is this important? It is an indication that endocrine disrupting
contaminants like PCBs can interfere with the timing of sexual maturity
in wildlife, perhaps analogous to changes in the timing of puberty
also find that within sub-adults, more adult-like plumage is linked
to breeding earlier in the nesting season. Normally, earlier breeding
in a season for tree swallows leads to greater reproductive success.
McCarty and Secord have reported elsewhere,
however, that tree swallows in this contaminated population have
lower reproductive success than other tree swallow popoulations.
strength of their conclusions are limited, however, by the fact
that their study is correlational and based upon comparisons among
locations that vary in PCB exposure, not upon variations among individuals
that vary in PCB contamination. Firm conclusions about the relationship
would require experimental manipulation of PCB contamination.