INTERACTIONS BETWEEN GREATER SNOW GEESE AND THEIR REARING HABITAT

For herbivores, food quality is a major component of habitat quality. However, food quality is complex to assess because it must integrate not only the availability of nutrients but also their digestibility and the requirements of the animal. To evaluate the quality of food and to determine the feeding constraints faced by young herbivores, we compared two brood-rearing habitats used by the Greater Snow Goose (Chen caerulescens atlantica) in the High Arctic using three levels of investigation. The first was based on a quantitative and qualitative analysis of the plants; the second was behavioral, and compared the feeding effort of human-imprinted goslings; and the third was physiological and compared food selection and plant nutrient metabolizability by the goslings. The two habitats grazed by goslings were a sedge meadow (dominated by Carex aquatilis and Dupontia fisheri) and a grass meadow (dominated by Dupontia fisheri and Eriophorum spp.). Plant biomass was higher in the sedge than in the grass meadow. Plant quality declined during the summer but Eriophorum spp. had a significantly higher nitrogen and lower fiber content than the other two species at all times. However, when combining data on quality and relative abundance, the overall plant quality was similar in both meadows. Goslings spent more time feeding and had a higher pecking rate in the grass than in the sedge meadow. Comparison of diet quality to overall plant quality indicated a higher nitrogen and lower fiber content of the diet in the grass meadow but not in the sedge meadow, probably because goslings fed selectively on Eriophorum in the former habitat. Apparent metabolizability of organic matter and nitrogen, and nitrogen assimilation efficiency by goslings were lower in the sedge than in the grass meadow at some periods. However, goslings did not compensate by an increased rate of food intake when their nitrogen intake was low which suggests that they had reached their gastrointestinal capacity. Under some circumstances, food quality is therefore more important than food abundance for herbivores. We show that integration of our three levels of investigation (plant food, animal behavior, and physiology) is essential to fully evaluate habitat quality for an herbivore.