Food Intake, Weight Changes and Egg Production in Captive Red Grouse before and during Laying: Effects of the Parasitic Nematode Trichostrongylus tenuis

Abstract

We investigated variations in egg production of captive hen Red Grouse Lagopus lagopus scoticus in relation to food intake, weight change, and parasitism by the nematode Trichostrongylus tenuis. Experimental infections of T. tenuis were used to mimic the relative effects on laying grouse of an adult worm burden, the resumed development of over-wintered worm larvae or no infection. Variations in egg production were significantly related to hen food intake and weight loss during laying but not to food intake or weight gained in the five weeks before laying. This supports the Thomas (1988) hypothesis that grouse produce eggs from 'income' rather than 'capital' reserves. There were no significant differences in the total weight, number or rate of eggs produced by hens from different treatment groups. However, hens infected with worms developing at the onset of laying lost significantly more weight while laying and, at the end of egg laying, were 13% lighter than other birds. In wild birds this could affect the quality of incubation and maternal care of chicks. The precise timing of the resumed synchronous development of previously arrested T. tenuis larvae may be a critical determinant of how this parasite affects egg production by wild Red Grouse.