McCarty 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.

"Subadult" 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.

Why 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 in people.

They 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.

The 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.

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