Seasonal Foraging Rates of Free-Ranging Moose

Abstract

Foraging rates of free-ranging moose (Alces alces) in aspen (Populus spp.) boreal habitats were evaluated in summer, autumn, and winter. Consumption rates (g/min) increased asymptotically with biomass of potential forage, but both maximum rates and slopes varied seasonally. Maximum rates appeared related to forage quality since values declined from 23 g/minute in July to 11 g/minute in January. Slopes reflecting increments of foraging rate/unit increase in biomass seemed related to selectivity exercised by moose. The highest values were observed in winter when moose were least selective, the lowest in October when a mixture of green and cured forage offered the greatest opportunities for selective feeding. J. WILDL. MANAGE. 50(1): 143-147 Seasonal changes in the quality and availability of forage potentially limit daily food intake by moose throughout much of their biogeographical range. The ultimate constraint on dry matter intake for ruminants is rumen fill and hence rates of digestion and passage which are strongly influenced by physicochemical properties of forage. At another level, biomass and structure of vegetation influence feeding rates imposing an additional logistic constraint, particularly for large herbivores feeding in sparse habitats. Longer foraging times, higher biting rates, or greater bite sizes are tactics that herbivores can use to meet their daily forage requirements (Wickstrom et al. 1984). Total time devoted to feeding can be limited by search times and the need to ruminate while compensatory limits on bite rates and sizes are often dictated by vegetation characteristics. Following pioneering work on domestic animals (Allden and Whittaker 1970, Chacon and Stobbs 1976), several investigators have studied the intensity with which wild ungulates harvest food. The earliest of these considered feeding rates in relation to habitat type (Collins et al. 1978). This was followed by studies designed to determine how forage biomass and structure influenced feeding behavior of such species as caribou (Rangifer tarandus) (Trudell and White 1981), mule deer (Odocoileus hemionus) (Wickstrom et al. 1984), and elk (Cervus elaphus) (Nietfeld 1983, Wickstrom et al. 1984, Hudson and Nietfeld 1985). Comparable studies have not been conducted on large browsers such as moose. VivAs (in press) measured winter consumption rates of woody stems by moose in Norway, and Renecker and Hudson (1985) documented seasonal changes in dry matter intake by moose in central Alberta. But these measures have not been related to seasonal forage supplies. This study examined the logistics of foraging by moose in the aspen boreal environment and provided data on how seasonal changes in biomass of selected forages influenced feeding rates. Financial support was received from Alberta Rec., Parks and Wildl. Found., Agric. Res. Counc. Alberta, Alberta Envir. Trust, and Nat. Sci. and Eng. Res. Counc. We thank D. M. Renecker, D. M. Bayne, M. T. Nietfeld, C. D. Olsen, A. J. K ith, M. Young, and D. A. Welch for their skillful assistance in the field and R. G. Weingardt for help with statistical analysis.