Date of Award:

1988

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Wildland Resources

Advisor/Chair:

Frederick Lindzey

Co-Advisor/Chair:

James Gessaman

Abstract

This study investigated relationships between blue grouse (Dendragapus obscurus) winter habitat and blue grouse adaptive strategies and overwinter survival. Blue grouse metabolism, physical characteristics of use-trees and roost sites , microclimatic parameters at roost sites, daily winter energy costs, and specific energy-saving behaviors were studied. Blue grouse have a relatively low standard metabolic rate (SMR; 0.835 ml o2 · g-1 · hr-1) and lower critical temperature in comparison to other northern tetraonids . Metabolic rate did not significantly increase from -5 to -20 C. Ambient temperature (Tal and the square root of wind speed were significantly correlated with metabolic rate.

Blue grouse selectively roosted in the largest Douglas-firs (Pseudotsuga menziesii) and subalpine firs (~ lasiocaroa) during the day and night, respectively. All roost sites were typically adjacent to tree trunks in the lower 2/3 of trees . Nocturnal roosts provided greater canopy coverage and were located in continuous stands more often than diurnal roosts . Wind speeds were reduced by 63 and 85% at diurnal and nocturnal roosts, respectively. Douglas-firs provided exposure to solar radiation , protection from wind, and a food source during the day. Subalpine firs increased protection from the wind and provided near maximum canopy coverage at night. Nocturnal subalpine roost sites provided a 10% net energy savings in comparison to diurnal Douglas-fir roost sites. The average T a at the study area was with in the thermoneutral zone of blue grouse.

The average field metabolic rate (FMR) of blue grouse measured with doubly-labeled water was about 1.4 times SMA, and was not influenced by weather. The proportion of FMR due to basal metabolism was twice that commonly assumed for other species, indicating the importance of microhabitat selection and relative inactivity by blue grouse in minimizing energy costs . Other energy saving behaviors included sunning , snow roosting, and walking uphill instead of flying. FMR measures (657 kJ·d-1) were within 12% of the energy costs estimated from average microclimatic values, and within 5% of the energy assimilation by captive blue grouse.

Habitat selection by blue grouse, particularly microhabitat selection of roost sites , reflects active choices designed to minimize energy costs imposed by winter weather. This selection indicates the importance of Douglas-fir and subalpine fir for overwinter survival.

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