• Mook, L. J.
  Department of Forestry of Canada, Regional Laboratory, Fredericton, New Brunswick
  
• Marshall, G. W.
  Department of Forestry of Canada, Regional Laboratory, Fredericton, New Brunswick
  

To use gizzard analysis quantitatively, in the assessment of bird predation on insect populations, information is needed on the time that identifiable remains of the prey can be found in the gizzard and on the rate at which these remains disappear. The digestion rate measured by the disappearance of mandibles or cremasters, has been studied for larvae and pupae of the spruce budworm, Choristomeura fumiferana when eaten by the olive-backed thrush, Hylocichla ustulata swainsoni.