Grit ingestion as a source of metal exposure in the spruce grouse, Dendragapus canadensis

The objective of this study was to determine if ingestion of grit was a sou rce of metal exposure to the spruce grouse, Dendragapus canadensis. A secon dary objective was to assess whether grit could provide a supplemental sour ce of essential minerals to their diet. Ca, P, Mg, S, Zn, Cu, Ni, Co, Cr, F e, Mn, Al, Pb and Cd of liver (adult, yearling, chicks), crop and gizzard c ontents (adults) were determined for grouse collected from a relatively pri stine boreal forest region of north-central Ontario, Canada. With the excep tion of Cd liver, concentrations were independent of age [one-way analysis of variance (ANOVA); p > 0.004). Zn liver concentrations tended to be great er in adults than yearlings and chicks tone-way ANOVA; p = 0.02). Liver con centrations of Cd increased with age (r = 0.99; p < 0.001). The contributio n of crop items to total gizzard elemental content was element specific; cr op contents contributed 90-100% of Mn and Zn, 70% for P and Ca, 60% for Pb, 50% for S, and 0-25% for Cu, Mg, Ni, Al, Fe, Co, Cr and Cd to the total el emental concentration of gizzard contents (crop plus grit). Incorporation o f grit by grouse could, therefore, constitute an important source of essent ial macro-(Ca, P, Mg, S) and trace elements (Cu, Fe) but not for Mn or Zn. However, in addition to providing nutrients to the bird, ingestion of grit results in exposure to toxic trace metals such as Cd which in turn is accum ulating in the liver. Research directed at determining grit turnover time, and hence metal exposure rates, in bird species which ingest grit to aid in food digestion is required. The toxicological significance of Cd exposure to grit-ingesting birds needs attention. (C) 1999 Elsevier Science Ltd. All rights reserved.