ALTERNATIVE FORAGING STRATEGIES AND RESOURCE-ALLOCATION BY MALE AND FEMALE WANDERING ALBATROSSES

Allocation processes play a central role in life history theories. Yet very few studies have been carried out on the link between foraging a nd life history in the context of allocation of resources. Here we rep ort a study examining the relationship between foraging and allocation of resources in the Wandering Albatross Diomedea exulans of Crozet Is lands. We simultaneously studied individual foraging strategies at sea and differential allocation to reproduction and storage by measuring the energy supplied to chicks and the variation of body mass of the ad ult. Satellite tracking and continuous monitoring of nest attendance b y adults showed that while rearing a chick Wandering Albatrosses have two specific alternative foraging strategies. They either forage in sh ort trips, short in duration and close to the colony over the southeas tern slope of the peri-insular shelf, or in long trips far from the co lony in the oceanic waters north of Crozet. On average, birds made fiv e successive short trips before making a long trip. Chicks received a meal every 1.8 d and were fed with fresh prey, 72% squid and 24% fish, and a liquid fraction composed of oil and water. During short trips b irds appear to rely to a great extent on Moroteuthis ingens, a squid s pecies probably available in large numbers at the southeastern edge of the Crozet shelf. The measure of energy flows indicates that 74% of t he energy delivered to the chick comes from short trips, whereas only 33.8% of the total energy is gained at sea during these trips. Males s pent a greater proportion of their time foraging in short trips than f emales, and consequently chicks received 61.3% of their meals from mal es and 38.7% from females. Adult birds tended to lose mass after short trips and to lose more mass with increased duration of short trips, w hereas they gained mass after long trips. They initiated long trips wh en their body mass was low. Although Wandering Albatrosses are able to provision their chicks at a rapid rate because of the proximity of an abundant resource, birds still have to forage far from the colony to restore their body condition. Estimates of energy yield explain this p aradox, as they suggest that the rate at which prey is caught during s hort trips in shallow waters is half that during long trips in oceanic waters. The significance of the twofold foraging strategy in relation to food availability and foraging efficiency is discussed.