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 source of metal exposure to the spruce grouse, Dendragapus canadensis. A secondary objective was to assess whether grit could provide a supplemental source of essential minerals to their diet. Ca, P, Mg, S, Zn, Cu, Ni, Co, Cr, Fe, Mn, Al, Pb and Cd of liver (adult, yearling, chicks), crop and gizzard contents (adults) were determined for grouse collected from a relatively pristine boreal forest region of north-central Ontario, Canada. With the exception of Cd liver, concentrations were independent of age one-way analysis of variance (ANOVA); p>0.004). Zn liver concentrations tended to be greater in adults than yearlings and chicks (one-way ANOVA; p=0.02). Liver concentrations of Cd increased with age (r=0.99; p<0.001). The contribution of crop items to total gizzard elemental content was element specific; crop 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 elemental concentration of gizzard contents (crop plus grit). Incorporation of grit by grouse could, therefore, constitute an important source of essential 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 accumulating 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.