AN EXPLORATORY ANALYSIS OF LIVER ELEMENT RELATIONSHIPS IN A CASE SERIES OF COMMON LOONS (GAVIA IMMER)

To examine the relationships among liver element concentrations, princ ipal component analysis (PCA) was performed on data from a case series of 54 common loons collected in Michigan during the period from July 1988 to February 1993. Data available for each bird included season an d district of collection, age, sex, necropsy findings, and liver conce ntrations of twelve elements as determined by spectrophotometry. The f irst three principal components (PC) accounted for 86% of the total va riability of the data, which made possible a substantial reduction in dimensionality. Within PC1-PC3, calcium, iron, mercury and lead were t he most influential elements in accounting for variation. The possibil ity of a competitive interaction between mercury and lead for selenium is suggested, with consideration given to possible alterations in bio availability due to environmental acidification. PCA can generate hypo theses that subsequently can be investigated under conditions which al low causal inference and better control of confounding factors. Conseq uently, sparse field data can be used efficiently to generate informat ion on risk factors for environmental diseases, and to provide bases f or intervention strategies.