Importance of insect prey quality for grey partridge chicks Perdix perdix:: a self-selection experiment

1. The proportion of aphids in the cereal arthropod fauna has increased since the introduction of herbicides in the 1950s. In order to examine whether this increase has negative consequences for partridge chicks, a controlled experiment was carried out. Four groups of partridge chicks were fed different diets of fixed mixtures of grasshoppers and aphids, with aphid contents ranging from 0% to 45% wet weight. One additional group was allowed to select how much to eat of aphids and grasshoppers (self-selection). 2. Over the run of the 5-day experiment the self-selecting chicks ate 7% wet weight of aphids and showed a higher growth rate than all groups on fixed diets. 3. Increasing the proportion of aphids in the chick diet above the self-selected level had negative consequences for chick growth and flight feather development. 4. Food consumption and growth efficiency were markedly lower when chicks were fed a diet with a high proportion of aphids. 5. It is concluded that high densities of aphids cannot substitute for a diverse insect fauna as food for partridge chicks. Changes in the composition of the cereal arthropod fauna towards aphids constituting a greater proportion of available chick food may be detrimental to chick survival.