Eric M. Rominger

Winter foraging ecology of woodland caribou in northeastern washington

To better understand late winter foraging ecology of woodland caribou (Rangifer tarandus caribou) feeding on arboreal lichens, we used bottle-raised caribou in experimental arena trials with artificial trees, and in field trials within historical late-winter habitat. Factors with the greatest influence on intake rate differed between experimental arena and field trials. Bite size was the most important variable in experimental arena trials; bite rate was the most important in field trials. During late winter field trials, caribou foraged on lichen primarily on standing subalpine fir (Abies lasiocarpa) and dead trees. Bite size, bite rate, intake rate, tree resident time, and amount of lichen eaten per tree were included in a general linear model with tree species, tree size class, and tree lichen class ( average) as the independent variables. Tree lichen class was the most important variable in the model and 76% of all bites occurred on >average lichen class trees. Compared to theoretical maximums, intake rate was low on all lichen class trees (range = 1.4-2.1 g/min). At these intake rates caribou would have to forage 14-21 hours to meet predicted daily requirements. Tree resident time and time between trees varied inversely with tree density. In cafeteria style preference trials with the 2 primary arboreal lichen genera, caribou strongly preferred Bryoria spp. (92%) compared to Alectoria sarmentosa (8%). Apparent dry matter digestibility of this diet was 82%. Timber stands must be substantially older than traditional harvest rotation lengths to provide the high lichen biomass found on >average lichen class trees. Caribou remained in habitats where Bryoria was the predominant genus of arboreal lichen and would not forage in A. sarmentosa dominated valley bottom habitat.

THE INFLUENCE OF MOUNTAIN LION PREDATION ON BIGHORN SHEEP TRANSLOCATIONS

Abstract We studied the effects of mountain lion (Puma concolor) predation on 2 translocated populations of bighorn sheep (Ovis canadensis) in New Mexico, USA. During 1993, 32 Rocky Mountain bighorn sheep (O. c. canadensis) were translocated to Wheeler Peak Wilderness Area in northern New Mexico, and during 1992–1993, 31 desert bighorn sheep (O. c. mexicana) were translocated to Sierra Ladron in central New Mexico. We monitored both populations from release through 2000 using fixed-wing aircraft and ground and/or helicopter surveys. We determined cause of mortality for radiomarked individuals (n = 26) and calculated survival rates, cause-specific mortality rates, exponential growth rates, and lamb:ewe ratios. The post-lambing population estimates in 2000 were 180 in Wheeler Peak and 21 in Sierra Ladron. Annual adult survival was higher (P < 0.005) in the Wheeler Peak population (0.955) than in the Sierra Ladron population (0.784). Annual lamb:ewe ratios also were higher (P < 0.001) in the Wheeler Peak population (66.7 vs. 29.8). Mean annual exponential growth rate (r) in the Wheeler Peak population was 0.25 compared to −0.01 for the Sierra Ladron population. Predation by mountain lions was the primary proximate cause (75%) of 16 known-cause mortalities of radiomarked bighorn sheep in the Sierra Ladron population, while we did not document any predation in Wheeler Peak. The annual cause-specific mortality rates due to mountain lion predation in Sierra Ladron were 0.13 for males, 0.09 for females, and 0.11 for all adult bighorn sheep. Mountain lion predation may have limited the Sierra Ladron bighorn sheep population and could be imposing a destabilizing inverse density-dependent mortality. Mountain lions preyed on domestic cattle in the Sierra Ladron area and throughout desert bighorn sheep habitat in New Mexico; we therefore hypothesize that cattle “subsidized” the diets of mountain lions (i.e., reduced or eliminated natural starvation). The ultimate cause of mortality for these desert bighorn sheep may be related to subsidized mountain lion populations that do not appear to decline following native ungulate population decreases. In addition, the encroachment of woody vegetation may increase the hunting success of ambush predators like mountain lions. High mountain lion predation may require mitigation for the successful restoration of bighorn sheep.

Autumn foraging dynamics of woodland caribou in experimentally manipulated habitats, northeastern Washington, USA.

Foraging options of woodland caribou (Rangifer tarandus caribou) in the high snowpack ecosystems of western North America become narrowed after freezing temperatures in antumn precipitate leaf-drop in deciduous shrubs. The objectives of this research were to determine the influence of (1) removing arborca lichen (Ascompecytes) on windthrown trees and myrtle boxwood (Pachistime myrsinites) and (2) stand type (oldgrowth versus clearcnt) on woodland caribou foraging dynamics during autum. Foraging trials were conducted with 3 tame woodland caribou in 6 0.5-ha pens. In 3 treatment pens all windthrown arboreal lichen-bearing trees were removed from the old-growth portion of the pen and extant invrtle hoxwood plants were removed from the entire pen. In the 3 control pens all extant windthrown trees and invrtle boxwood plants were retained In addition, pens were constructed such that half of each pen was in an old-growth stand of western red-cedar (Thuja plicata)-western hemlock (Tsuga heterophylla) and half was in an adjacent clearent. Arboreal hcher had the greatest influence on dry-matter intake rate (DMIR) because of the large bite size provided by this forage. In control pens, caribou had higher DMIR (P = 0.006) and crude protein intake rate (CPIR) (P = 0.007) than in treatment pens where lichen-bearing windthrown trees had been removed. Arboreal lichen from windthrown trees was 52% (range 43-61) of the total DMI in the old-growth portious of control pens Arboreal lichen from windthrown trees comprised 81% (range = 75-92) of the arboreal lichen bites (i.e., 19% of arboreal lichen bites were from litterfall and standing trees), and 28% range = 16-48) of total bites in the timbered portion of control peus. The DMIR (P = 0.004) and CPIR (P = 0.004) of caribou was also greater in old-growth than in clearcat portions of pens. Search time was greater (P = 0.008) in clearent portions or pens than in old-growth portions. Myrtle boxwood comprised <0.4% of caribou diets. These data suggest that arboreal lichen is an important dietary component earlier in antamn than previously reported.

Biological and Statistical Errors Make Inferences Circumspect: Response to Bender and Weisenberger

Abstract Bender and Weisenberger (2005) reported that desert bighorn sheep (Ovis canadensis) on San Andres National Wildlife Refuge (SANWR), New Mexico, USA, were primarily limited by rainfall. However, they failed to mention, or were unaware, that persistent long-term predator control was used to enhance population growth at SANWR. Additionally, lamb:female ratios were collected throughout the year, rather than dates typically associated with assessing recruitment, and therefore influence of precipitation on lamb recruitment was unknown. Finally, model predictions forwarded by Bender and Weisenberger (2005), that carrying capacity of SANWR is zero when annual rainfall is <28.2 cm, were not supported by data, nor were their model results properly interpreted. The coefficient of determination value of 88.9% for the relationship between population size and current years precipitation was primarily a function of serial correlation between successive years in population data, with current years precipitation accounting for only 3.8% of this value. This suggests that precipitation was a weak predictor of population increase. These errors in concert make biological inferences reported in Bender and Weisenberger (2005) of limited value.

Generic preference and in-vivo digestibility of alectorioid arboreal lichens by woodland caribou

All caribou exhibited a strong preference (92%) for lichen in the multi-species Bryoria complex (range=87-99%).Preference for Bryoria may be a function of higher protein content, lower tensile strength, or differences in concentrations of secondary plant constituents.