The diet of woodland caribou populations in west-central Alberta

The diet o f woodland caribou (Rangifer tarandus caribou) populations i n the foothills and R o c k y Mountains o f west-central Alberta was estimated by microhistological analyses o f feces collected i n winter and summer. In winter, terrestrial lichens averaged 60-83% o f fecal fragment densities i n both areas. In the mountains, decreasing proportions o f terrestrial lichens and increasing proportions o f conifer needles and moss indicated decreasing accessibility o f forage because o f deeper/harder snow. Apparent diets i n summer were dominated by Salix spp., sedges, and lichens. However , forb inflorescences and stems were largely undetected by the microhistological technique and results for summer samples must be interpreted accordingly. W e conclude that the conservation and management o f forest ecotypes o f caribou must include options o f l ichen-r ich habitats as a major component o f management plans. K e y words: a lp ine , borea l , co rd i l l e ra , forestry, subalpine , m i c r o h i s t o l o g y , Rangifer tarandus caribou Rangifer, Special Issue No. 9, 337-342 Introduction K n o w l e d g e o f d ie t is fundamenta l to d e f i n i t i o n o f a species n i c h e , habitat, and e c o l o g y . D i e t a r y i n f o r m a t i o n for w o o d l a n d c a r i b o u is scanty i n bo rea l and co rd i l l e r an forests o f wes te rn C a n a d a east o f the C o n t i n e n t a l D i v i d e . S u c h i n f o r m a t i o n is needed to he lp conserve c a r i b o u i n the sou the rn c o m m e r c i a l forest, w h i c h w i l l be p e r m a n e n t l y al tered b y fore stry and o ther deve lopments . T h e p r i m a r y habitat c o n c e r n is r e d u c e d p r o p o r t i o n s a n d sizes o f pos t r o t a t i o n forests a n d f ragmenta t ion . F u r t h e r m o r e , managers o f p ro tec t ed ecosystems, such as Jasper N a t i o n a l Pa rk , are responsible for vege ta t ion m a n a gemen t that affects f o o d supplies o f c a r i b o u and the e c o l o g y o f all species. W h a t sorts o f habitats s h o u l d be safeguarded? A r e l i chens essential to the v i a b i l i t y o f forest-alpine ecotypes o f c a r i b o u i n wes te rn Canada? O u r p r i m a r y objec t ive was to assess a n d c o m p a re the w i n t e r diet o f popu la t ions o f c a r i b o u i n wes t centra l A l b e r t a i n re la t ion to season, s n o w characteristics, and geographic l o c a t i o n . O n e g roup o f fecal samples came f r o m w i n t e r ranges o n the "east s lo pes" o f the R o c k y M o u n t a i n s and are t e r m e d the " footh i l l s" g r o u p . I n w i n t e r , there are t w o subpo¬ pula t ions w i t h i n each p o p u l a t i o n o f m o u n t a i n (forest-alpine) a n d w o o d l a n d (forest) ecotypes o f c a r i b o u i n the foothi l l s ( E d m o n d s , 1988) (F ig . 1). T h e forest-alpine eco type migrates i n t o a lp ine areas o f the W i l l m o r e W i l d e r n e s s , n o r t h e r n Jasper N a t i o n a l Pa rk , a n d adjacent B r i t i s h C o l u m b i a to calve a n d spend the summer . I n a d d i t i o n , c o m p o s i te samples w e r e ob t a ined f r o m a forest eco type that occup ies habitat y e a r r o u n d i n the bo rea l forest. T h e s e c o n d g r o u p o f samples came f r o m c a r i b o u w i n t e r i n g i n the R o c k y M o u n t a i n s , m o s t l y i n watersheds o f Jasper N a t i o n a l Pa rk . These ca r i bou , i n three subpopula t ions , traverse a lp ine , subalpine , a n d m o n t a n e regions o v e r short distances. W e also e x a m i n e d feed ing craters d u g i n the s n o w b y c a r i b o u i n b o t h areas. T h e purpose was to ob ta in i n d e p e n d e n t i n f o r m a t i o n o n diet b y e x a m i n i n g plant species present at f eed ing sites. A n o t h e r ob jec t ive was to o b t a i n insights i n to forage se lec t ion b y c a r i b o u b y c o m p a r i n g data f r o m the m i c r o h i s t o l o g i c a l t e chn ique w i t h the relat ive f requency o f p lant species f o u n d i n f eed ing craters. A d d i t i o n a l l y , w e c h e c k e d the accuracy o f the m i c r o h i s t o l o g i c a l t echn ique o n plant species m i x e d b y d r y w e i g h t i n p r o p o r t i o n s that s imula ted w i n t e r diet . W e also assessed the ab i l i ty o f the t e chn ique to detect plants i n the s u m m e r diet .


Introduction
Knowledge of diet is fundamental to definition of a species niche, habitat, and ecology.Dietary information for woodland caribou is scanty in boreal and cordilleran forests of western Canada east of the Continental Divide.Such information is needed to help conserve caribou in the southern commercial forest, which will be permanently altered by forestry and other developments.The primary habitat concern is reduced proportions and sizes of postrotation forests and fragmentation.
Furthermore, managers of protected ecosystems, such as Jasper National Park, are responsible for vegetation management that affects food supplies of caribou and the ecology of all species.What sorts of habitats should be safeguarded?Are lichens essential to the viability of forest-alpine ecotypes of caribou in western Canada?
Our primary objective was to assess and compare the winter diet of populations of caribou in westcentral Alberta in relation to season, snow characteristics, and geographic location.One group of fecal samples came from winter ranges on the "east slopes" of the Rocky Mountains and are termed the "foothills" group.In winter, there are two subpo¬ pulations within each population of mountain (forest-alpine) and woodland (forest) ecotypes of caribou in the foothills (Edmonds, 1988) (Fig. 1).
The forest-alpine ecotype migrates into alpine areas of the Willmore Wilderness, northern Jasper National Park, and adjacent British Columbia to calve and spend the summer.In addition, composite samples were obtained from a forest ecotype that occupies habitat year-round in the boreal forest.
The second group of samples came from caribou wintering in the Rocky Mountains, mostly in watersheds of Jasper National Park.These caribou, in three subpopulations, traverse alpine, subalpine, and montane regions over short distances.
We also examined feeding craters dug in the snow by caribou in both areas.The purpose was to obtain independent information on diet by examining plant species present at feeding sites.Another

Methods
Pellets were obtained throughout the year from several locations on the ranges of the caribou populations.
Fresh pellets from 5-30 groups were pooled into a composite sample by taking about equal amounts (2-Rangifer, Special Issue No. 9, 1996 * indicates significant variation in row (Chi-square p<0.05).
for months, years, and locations were pooled where there was no statistical difference (p>0.05) between or among them.Comparisons between the two major study areas were made after results were adjusted by the amount of conifer needles and moss.We assumed that both of those plant groups were ingested incidentally with lichens and diet comparisons were best made on species selected by caribou.

Apparent Winter Diet in the Foothills
Seventy-nine composite fecal samples were obtained from the A la Peche, Prairie Creek, and Little Smoky River drainages (Fig. 1) throughout the winters (October-April) of 1979/80 through 1982/83 (Edmonds & Bloomfield, 1984).The apparent diets were almost identical for all three areas and winter months.Therefore, data were pooled.The apparent diet of caribou on winter ranges in the foothills varied little over four winters in spite of pronounced differences in snow depth (Table 1).

Winter diet in the Rocky Mountains
Apparent diets were similar among years within watersheds (Thomas, 1993) but species composition Variations in apparent diets were slight in early winter among three regions in the mountains: Maligne, Astoria, and Sunwapta watersheds (Fig. 1).
In late winter, plant species compositions were similar in caribou feces from those watersheds.However, That protein-poor diet (Nieminen & Heiskari, 1989) was supplemented with E. scirpoides.
The two species of horsetails that were eaten by caribou in winter were winter-green forms.
Samples of E. variegatum and E. scirpoides obtained in

Apparent diet in the foothills and the Rocky Mountains
There was no statistical difference in the results for major forage groups between the two major wintering areas (Table 3).There were significant differences within plant types, such as less Cladonia-type lichens and more Cetraria spp.and conifer needles in the foothills samples.Other differences not reflected in Table 3 were more Vaccinium/Empetrum and less Ledum spp. in fecal samples from the foothills compared with those from the mountains.

Frequency of occurrence of plant species in craters
Frequency of occurrence (presence-absence data) in craters revealed high occurrences of Cladonia spp., Rangifer, Special Issue No. 9, 1996 * 50% means that the plant was detected in half of the craters examined.These are presence-absence data.
Cladina mitis, Peltigera spp., moss, Ledum spp., and Vaccinium vitis-idaea (Table 4).There was significant regional variation in the proportion of Cladoniatype lichens and a major component, C. mitis.The consistency of winter diet (Table 3) in contrast to the significant variation in major vegetation species in the craters (Table 4) indicated that caribou were selecting for Cladina-type lichens and selecting against low shrubs and moss.
The only data for the population that wintered in the foothills was for August in alpine areas north and northwest of Jasper National Park.There, the apparent diet was 54% terrestrial lichens, 38% shrubs, 5% graminoids, 2% forbs, and 1% arboreal lichens (Edmonds & Bloomfield, 1984).By late September and October, in the same area, the lichen component increased to 73% and shrubs decreased to 16%.

Plant proportions versus fragment relative densities
The microhistological results for two non-digested mixtures that simulated diet revealed close correspondence except for Pinus contorta needles and Bryoria spp.(Table 6).

Discussion
The winter diet of caribou in west-central Alberta did not change appreciably, either spatially or temporarly, provided the snow cover was soft, regardless of depth.The differences in apparent diet among locations in the mountains reflected, for the most part, variations in relative forage availability caused by deep snow containing hard layers, including ice.High evergreen shrub and moss content in the winter diet were indicators of poor range condition or poor availability, as found in Alaska (Boertje, 1984).
The diet of three subspecies of caribou that winter in boreal and cordilleran forests, where soft snow generally is <60 cm deep, were remarkably similar (Thomas & Barry, 1991;Russell et al, 1993, this study).This similarity points to caribou "lichenophilia" and a high degree of consistency in surface vegetation under mature and old-growth pine forests over wide geographic areas.occurred more frequently in caribou craters than in random snowplots used as controls (Edmonds & Bloomfield, 1984).Paradoxically, the other lichen genus with high protein content, Stereocaulon, is eschewed by caribou where it is abundant (Thomas, 1994).
Terrestrial lichens, when damp and where available, are consumed in summer by caribou (rev.by Boertje, 1984;Thomas, 1993).They are a high energy source and their continued use in summer may be necessary to maintain a microflora that is efficient at digesting them.
Winter-green forms of Equisetum spp.are selected by caribou in winter as indicated by high use of E. variegatum on the Medicine Lake delta and cratering for the sparse, wiry E. scirpoides.Moose (Alces alces) also cratered for the same species.Equisetum spp.generally have protein levels of 8% to 10% (range 5% to 15%) and are rich in minerals (Nieminen & Heiskari, 1989).Winter-green grasses and sedges are also important sources of protein in winter.

Management implications
Caribou

Conclusions
The apparent winter diet of caribou populations was similar among foothills and Rocky Mountain regions in spite of significant regional variation in the vegetation at feeding sites.Diet changed involuntarily as vegetation became increasingly inaccessible because of thick snow containing icy layers.Rangifer, Special Issue No. 9, 1996 objective was to obtain insights into forage selection by caribou by comparing data from the microhistological technique with the relative frequency of plant species found in feeding craters.Additionally, we checked the accuracy of the microhistological technique on plant species mixed by dry weight in proportions that simulated winter diet.We also assessed the ability of the technique to detect plants in the summer diet.
of terrestrial lichens were lower in two watersheds (Miette & Whirlpool, Fig. 1), near the Continental Divide, and in areas south of Jasper National Park.Increased proportions of Ledum spp.and moss accounted for most of the difference.Winter dietary information for the Rocky Mountains (Table 2) excluded results from two areas where atypical foraging occurred in winter.Caribou foraged on the Medicine Lake drawdown delta, where fresh pellets collected during the winter contained mostly fragments of Equisetum variegatum.At a second location of the Maligne Valley, caribou fed mostly on arboreal lichens (Bryoria spp.and Alectoria spp.) in forests older than 400 years and with an easterly exposure.Long-strand lichens grew on widely spaced large and tall fir (Abies lasiocarpa) and spruce (Picea englemanni).
dietary information and field observations in the study areas indicated the need for winter habitats where terrestrial lichens were relatively abundant.These generally were open, pine-dominated forests older than 80 and 100 years in the Foothills and Rocky Mountains, respectively.In winters with deep and crusted snow, some caribou moved to areas of more-favourable snow.Those were old spruce/fir dominated forest (>130 years in the Foothills and >200 years in the mountains) with high arboreal lichen biomass; alpine ridges with little snow cover; or subalpine and montane valleys with relatively shallow snow.Alternative wintering areas may become important or critical to caribou in only 1 winter of 10 or 20.There are at least three reasons why caribou need optional areas to forage at regional and local scales.(1) They need optional regions to travel to when environmental conditions are unfavourable in parts of the traditional winter range.(2) They need alternate areas to prevent overgrazing and to allow grazed areas to recover lichen biomass.Caribou appear to rotate use of winter range by using one area for several winters and then shifting to another area.(3) They need optional habitat types locally when snow precludes them from using other types.These options must be left open for caribou in planning their habitat needs in managed forests.
Summer diet was dominated by graminoids, Salix spp.(leaves), terrestrial lichens, and an unknown proportion of forbs that went undetected by the microhistological technique.

Table 1 .
Plant fragment densities in caribou fecal pellets 119° 119° Fig. 1.Locations where fecal samples were obtained for this study of caribou diet.5 pellets depending on size) from each group.All comparisons of plant species composition in fecal samples among seasons, areas, and years were tested using Chi-square and Kruskal-Walks tests.Data 1 A la Peche, Prairie Creek, and Little Smoky River regions.b Cladonia-type, Cetraria-type, and Peltigera spp.lichens. 1 Data not available.

Table 3 .
Mean relative densities of plant fragments in winter feces of two populations of caribou in Alberta and the densities adjusted by the proportion of conifer needles and moss.
b Maligne, Astoria, and Sunwapta valleys (n=53 composite samples).c Adjusted by the proportion of conifer needles and moss to reflect forages selected by caribou and not consumed incidentally with lichens.Significant difference (Chi-square and t test).Alpine areas with adequate food supplies were used in the foothills and the mountains in winters when the slopes were windswept.Dryas spp. was the most consistent item in the diet.In a sample from northern Jasper National Park, Vaccinium spp.(mostly berries) and Dryas spp.comprised 88% of the fecal fragments.

Table 4 .
Frequency of occurrence of abundant plant species in snow craters dug by caribou throughout winter in the foothills and Rocky Mountains.

Table 5 .
Plant fragment densities in caribou feces collec- 1 Cladonia, Cetraria, and Peltigera types.Note: These data are biased by absence of forbs (see text).