Age-dependent changes in plasma and brain cholinesterase (ChE) activity were characterized in two altricial passerine species: eastern bluebirds (Sialia sialis) and European starlings (Sturnus vulgaris). Plasma acetylcholinesterase (AChE) activity declined rapidly immediately after hatching, while plasma butyrylcholinesterase (BChE) activity increased throughout the nestling period. These patterns continued after birds fledged, since the BChE: AChE ratio was higher in adult birds than fledglings. This is the first confirmation of age-dependent changes in plasma ChE activity in altricial species. Total plasma ChE activity increased with age in both species, which is the reverse of results previously reported for several precocial species. Brain ChE activity increased with age in both species, and did not reach asymptotic levels before young fledged. This corresponded with patterns previously documented in European starlings and three other altricial species. We propose that age and degree of precocity in young birds must be considered when examining sensitivity or evaluating field exposure of birds to ChE-inhibiting compounds.

Ecological risk assessments based on chemical residue analysis and species demographics tend to ignore the bioavailability and bioaccumulation of the chemicals of concern. This study describes the incorporation of mechanistically based biomarkers into an ecological risk assessment of a poly-cyclic aromatic hydrocarbon (PAH)-contaminated site. A combination of soil residue analysis, tissue residue analysis, biomarkers in one-site trapped animals and biomarkers in animals confined to enclosures was used. In particular, the use of captured deer mice (Peromyscus maniculatus) for these studies is compared to the use of laboratory-raised deer mice placed in enclosures. This study indicates that the higher degree of variability in the responses of wild deer mice make the use of enclosure studies advantageous. Positive control studies performed by dosing laboratory-raised deer mice with the same PAHs as found on the site were used to validate this approach. These studies indicate that immune suppression occurred at PAH concentrations an order of magnitude below those required for the induction of ethoxyresorufin-O-dealkylase activity.

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To study factors regulating clutch size in American Kestrels (Falco sparverius), brood manipulation experiments were performed on captive and wild birds in southwestern Quebec during 1986 and 1987. The largest normally occurring brood size was 5 young. Manipulations enlarged or decreased broods to 7 or 2 young, respectively. Significantly more young fledged from wild control and enlarged broods in 1987 than from comparable groups in 1986. The average number of young fledging from enlarged wild broods in 1987 was slightly higher than for control broods, but fledging weight was significantly depressed in enlarged broods. Growth rates and tarsal and antebrachial length at fledging were not affected by brood size, but development of primary feathers was slower in enlarged wild broods. Parental ability to adequately feed all young appears to be the major factor limiting brood size in American Kestrels.