Smith, L., Wells, K., Marion, G., Swain, D.L. and Hutchings, M.R.
Animal Behaviour 80, 527-534.
fecal aversion; grazing, physiological state; lactation, parasitic state
||Animal behaviour is often a function of the animal's physiological state. Groups of animals will often
contain individuals with a range of physiological states and the grazing behaviour of herbivores is
affected by their physiological state. This study compared the grazing decisions of animals in groups of
single and mixed physiological states. Using a grazing model that simulated individual herbivore
behaviour in relation to environmental distributions of forage resource (grass) and parasites (faeces), we
tested the hypothesis that an animal's level of parasite exposure via the faecaleoral route is affected by
the composition of physiological states in the group. Four physiological states were considered: parasitenaïve,
parasitized, lactating and parasite-immune animals. Baseline parasite exposure levels for each
state were generated by simulating single-state groups and were compared to simulations of each of the
six two-state combinations. In single-state groups parasitized animals had the least and lactating animals
had the greatest levels of parasite exposure. When co-grazing with lactating animals, parasitized,
immune and naïve animals increased their parasite exposure, relative to single-state groups. When cograzing
with parasitized animals, lactating, immune and naïve animals reduced their parasite exposure,
relative to single-state groups. There was no difference in parasite exposure of the immune or naïve
animals co-grazing together when compared to the single-state groups. These results highlight the need
to recognize the impact of the individual when studying group-living animals.