EFFECT OF FOOD-DEPRIVATION ON DOMINANCE STATUS IN BLUE-FOOTED BOOBY (SULA-NEBOUXII) BROODS

A pecking hierarchy is normally established in the usual two-chick bro od of the blue-footed booby (Sula nebouxii). The senior (first-hatched ) chick dominates its smaller sibling and receives a greater share of parentally provided food. Experimental broods were created by putting together two unrelated junior chicks of the same age in a vacated fost er nest. The state of the chicks was manipulated by a period of contro lled artificial feeding so that each chick underwent a different level of food deprivation. The resulting dominance relationship depended on the relative food deprivation level of the chicks: the hungrier chick normally became dominant. However, the effect of hunger was occasiona lly overruled by size difference: when the hungrier chick was much sma ller than its foster sibling, it was unable to gain dominance over its larger companion. Dominance status is likely to have greater value fo r the hungrier chick, while the cost of fighting should be lower for t he larger chick. These results conform to the evolutionarily stable st rategy predicted for games with asymmetric payoff and differences in r esource holding power.