Experimental Analysis of Winter Food Selection by Spruce Grouse

Abstract

Three feeding trials were conducted to test the ability of captive spruce grouse (Dendragapus canadensis) to select between and random of lodgepole pine (Pinus contorta) and Engelmann spruce (Picea engelmannii) and between random lodgepole pine and Engelmann spruce. Nutritional analyses of needles were conducted to assess the importance of crude protein, neutral detergent fiber (NDF), and essential oil in selection of trees. Birds selected branches from in both the lodgepole pine and Engelmann spruce feeding trials (P 0.05). Engelmann spruce and random did not differ in crude protein, NDF, or total essential oil (P > 0.05). Lodgepole pine had more crude protein and NDF (P = 0.001) and slightly less total oil (P = 0.057) than Engelmann spruce. Although, Engelmann spruce were heavily used as roost trees, birds were feeding mainly in lodgepole pine. J. WILDL. MANAGE. 51(1):159-167 The winter diet of spruce grouse consists entirely of conifer needles (Crichton 1963, Ellison 1966, Robinson 1969, Pendergast and Boag 1970, Pietz and Tester 1982). However, variation in chemical characteristics among (Lowry 1970, von Rudloff 1975) may influence food quality. Spruce grouse repeatedly browse or roost in individual while ignoring adjacent of similar physical characteristics (Gurchinoff and Robinson 1972, Ellison 1976, Paterni 1979, Ratti et al. 1984). These trees, termed activity trees (Ratti et al. 1984), may be repeatedly used for feeding and/or roosting for up to 5 years (Ellison 1976). In northcentral Washington spruce grouse used lodgepole pine and Engelmann spruce as (Ratti et al. 1984); however, birds may feed exclusively on lodgepole pine (Pendergast and Boag 1970). Previous studies have indicated that spruce grouse may select based on chemical or morphological characteristics of the needles, as opposed to cover characteristics of the (Gurchinoff and Robinson 1972, Ellison 1976, Ratti et al. 1984). Selective browsing by other grouse species has been correlated with chemical characteristics of the forage (Hoffman 1961, Seiskari 1962, Gardarsson and Moss 1970, Pulliainen 1970, Moss 1972, Svoboda and Gullion 1972, Remington and Braun 1985). Food selection by spruce grouse may be influenced 'Present address: Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID 83843. 2 Send reprint requests to this author. This content downloaded from 207.46.13.77 on Tue, 17 May 2016 06:33:32 UTC All use subject to http://about.jstor.org/terms 160 SPRUCE GROUSE FOOD SELECTION * Hohf et al. J. Wildl. Manage. 51(1):1987 by plant secondary compounds, such as monoterpenes and phenolics, in addition to nutrient or energy content (Bryant and Kuropat 1980). Monoterpenes inhibit digestive microbes of mule deer (Odocoileus hemionus) (Oh et al. 1967, 1968; Radwan and Crouch 1974, 1978; Schwartz et al. 1980) and also may be important digestive inhibitors of cecal microbes in grouse (Moss 1973, 1974; Bryant and Kuropat 1980). These compounds are among several forms of reported plant defense mechanisms. The volatile nature of monoterpenes may make these compounds readily detectable by grouse, enabling birds to avoid individual plants or species high in such compounds. Although previous work has demonstrated that spruce grouse select specific trees, it has not been demonstrated experimentally whether selection is based on traditional and learned behavior, or environmental conditions associated with location of the tree. Objectives of this study were to test 4 hypotheses: (1) spruce grouse can distinguish between branches from and randomly selected trees; (2) selected by spruce grouse are higher in nutritional content than random trees; (3) selected by spruce grouse contain less monoterpenes (potent digestive inhibitors) than random trees; and (4) spruce grouse select lodgepole pine over Engelmann spruce for