The importance of invertebrate food to chicks of gallinaceous species

Abstract

In the wild, the precocious young of gallinaceous birds are omnivorous, and proportions of plant and animal food in their diets vary greatly between and within species (Cramp & Simmons, 1980; Johnsgard, 1983). The animal food consists almost entirely of invertebrates (mainly arthropods), and the purpose of the present paper is to examine factors that cause its consumption to vary, and its importance relative to plant food in terms of meeting nutritional requirements for growth and survival. A search of the literature revealed detailed quantitative information on the diets of twenty-one species of Galliformes, in two families (Tetraonidae and Phasianidae), in their first month or two of life. Most of the published accounts referred to in Table 1 allowed mean percentages of invertebrate food (IF), based on volumes or dry weights of crop contents, or in a few cases on analyses of faecal droppings, to be assigned to one of four categories (>90%, 50-!20%, 10-50% or 90% IF, and only two, red grouse and Caucasian snowcock (Tetraogul-lus caucusicw), as not eating >lo% (Table 1). In the second 2 weeks, only eight species ate >50% and six species 50%. As a general rule, therefore, consumption of IF is highest in the first 2 weeks and declines thereafter, and, at any given age, variation in this consumption appears to be greater between than within species. Conclusions based on knowledge of proportions of different dietary constituents alone must necessarily be qualified, since ultimately growth depends on total intake of each constituent. In none of the accounts referred to in Table 1, however, were estimates made of food consumption of wild chicks at any age. Reasons for variation in consumption of IF with age