INTER-BIRD DISTANCES AND BEHAVIORAL PRIORITIES IN LAYING HENS - THE EFFECT OF SPATIAL RESTRICTION

The aim of this experiment was to study the effects of spatial restric tion on the frequency with which different behaviour patterns were per formed. Hens (Gallus domesticus) were kept in groups of three in four different sized litter pens giving space allowances of 5630, 3000, 120 0 or 600 cm2 per bird. Using overhead time-lapse photography, the mean distance between the birds in the group when all birds were performin g the same activity and the mean frequency of that activity in the tim e budget, were determined. In the largest pen, the birds were furthest apart when they were walking (310 +/- 64 mm), closer together when th ey were standing (234 +/- 75 mm) or ground pecking (237 +/- 13 mm) and closest together when they were preening ( 154 +/- 98 mm). As pen siz e decreased, the frequency of walking and ground pecking decreased sig nificantly, the frequency of preening remained unchanged and the frequ ency of standing increased. A comparison of time-budget changes with t he average distances between birds while performing these different ac tivities indicated that the behaviour patterns which were performed at the largest inter-bird distances decreased in frequency as pen size g ot smaller. This suggested that the distance between birds when they w ere walking or ground pecking was sufficiently important so that when the available space decreased, the birds performed these activities le ss often rather than performing them at inappropriate inter-bird dista nces. Preening was performed when birds were close to each other and t he frequency of this behaviour was unaffected by the space restriction s used in the experiment. As the frequency of some behaviour patterns decreases, there must be a corresponding increase in the frequency of others. Standing appeared to be one such 'time-filler' behaviour patte rn. The results also suggest that the technique of reducing the space available to birds may be useful in experimentally assessing the resil ience of particular behaviour patterns and thus the importance birds a ttribute to performing them.