Aggressive behaviour and its relation to oviposition in the domestic fowl

Hens in battery cages behave differently from those housed in pens. A knowledge of the factors which govern the differences is important from both practical and theoretical viewpoints. Laying hens of two strains were housed in cages or pens and the incidence of aggression before and after laying was studied. In stable groups little aggression was seen, so a strange bird was introduced to stimulate aggressive behaviour. Under these circumstances the incidence in caged light hybrids rose considerably before oviposition and fell sharply afterwards. This pattern was not seen in light hybrids kept in pens, nor in medium hybrids, whether caged or penned. Other workers have shown that caged light hybrids may be in a state of frustration before laying, and it is postulated that pre-laying aggression is triggered by frustration rather than by hormonal changes.