Environmental complexity and group size: Immediate effects on use of space by domestic fowl

Current housing conditions for domestic fowl (Gallus gallus domesticus) offer little in the way of environmental features biologically relevant to the birds. More specifically there is a notable absence of protective cover, a fundamental element that influences how domestic fowl use space. The availability of cover could be more relevant to small, as opposed to larger groups, because large groups offer an individual natural protection. In this experiment we investigated the immediate effects of cover panels designed to increase environmental complexity (EC) and compared their effects across three group sizes (n = 8) of five (GS5), 10 (GS10), or 20 (GS20), broilers per group. Birds were tested under two different scenarios representing increasing EC, once with one long panel (single) once with four staggered small panels (quad) and once in an empty control arena (void). Each test lasted for 1 h. Core areas, or activity centers, were not affected by EC. EC had the greatest impact on the inter-individual distances of birds in smaller groups. Minimum and nearest neighbor distances in GS5 increased significantly with EC, whereas those in the GS10 and GS20 were not different across the EC treatments. Because GS were housed together in a home pen and moved from this common home pen into testing arenas, significant differences in minimum, maximum, and nearest neighbor inter-individual distances suggest that birds adjusted their use of space in response to immediate changes in group size and EC. Overall we found a significant impact of EC on the spacing behavior of domestic fowl, however the effects were not equal for all group sizes. As predicted, smaller groups were more affected by environmental features, and thus may experience the greatest benefit from increased EC.