Habitat Use and Population Characteristics of the White-Tailed Ptarmigan in the Sierra Nevada, California ’

Home , Parker Peak (California), Uinta Mountains

The Condor94889-902 0 The CooperOrnithological Soaety 1992

HABITAT USE AND POPULATION CHARACTERISTICS OF THE WHITE-TAILED PTARMIGAN IN THE SIERRA NEVADA, CALIFORNIA ’

GLENN P. FREDERICKS AND R. J. GUTIBRREZ Department of Wildlife, Humboldt State University,Arcata, CA 95521

Abstract. We studied an introduced population of White-tailed Ptarmigan (Lagopus leucurus)during 1987 and 1988. Ptarmigan colonized alnine habitat 79 km north and 114 km south of their release site within 118years of their-liberation in the Sierra Nevada, California. Population densities were the lowest reported for the species.However, sex and age ratios were similar to native populations. Breeding seasonhabitats were in areasof tall (>30 cm) willow (Salix) shrubs and contained more subshrub, moss, and boulder cover than in unusedhabitats. In the postbreedingseason, ptarmigan usedtopographic depressions within breeding territories; brooding hens used moist meadows, while flocks occupied sites with abundantboulders. Ptarmigan primarily usedthe Salix anglorum antiplastavegetation alliance on rocky, north-facing slopes.Willow abundanceand proximity to water were the most discriminatory variables in logistic regressionanalyses between habitats used and unusedby ptarmiganduring the breedingand postbreedingseasons. Key words: White-tailedPtarmigan; Lagopusleucurus; demography; habitat use;limiting factors; colonization;logistic regression; Sierra Nevada.

INTRODUCTION low-growing alpine vegetation (Weeden 1959; White-tailed Ptarmigan (Lugopus leucurus) have Choate 1963; Jensenand Ryder 1965; Braun and been released in several alpine areas in western Pattie 1969; Braun 1970, 1971; Herzog 1977; North America, including the Wallowa Moun- Scott 1982). Extreme summer drought in the Si- tains, Oregon; the Sierra Nevada, California; erra Nevada restricts mesophytic alpine vege- Pike’s Peak, Colorado; and the Uinta Mountains, tation to protected slope exposures and topo- Utah. All transplants were apparently successful graphic depressions(Klikoff 1965, Pemble 1970, (Spencer 1976; DeSante and Gaines 1977; Braun Chabot and Billings 1972). In contrast, alpine et al. 1978; Hoffman and Giesen 1983; Gaines areas occupied by ptarmigan in the southern 1988; V. L. Coggins,Oregon Department of Fish Rocky Mountains experience a slight summer and Wildlife, LeGrande, pers. comm.; R. D. drought (Major and Bamberg 1967) and contain Thomas, California Department of Fish and large expanses of suitable habitat (Braun and Game, Sacramento, pers. comm.). The Sierra Rogers 197 1). Where suitable habitat is generally Nevada release was particularly noteworthy be- limited and population levels are low, habitat cause the mountain range is outside the species’ selection is likely to be most restricted (Hildtn historic distribution (Aldrich 1963). Successful 1965). The recent colonization of the Sierra Ne- transplants of ptarmigan in California and Or- vada by ptarmigan affords the uncommon op- egon were fortuitous becauseno objective means portunity to examine habitat factors that may for assessingptarmigan habitat characteristics limit ptarmigan abundance and influence range existed at the time of release(Braun et al. 1978). expansion. With one exception (Scott 1982), all analyses of In this paper, we provide a quantitative anal- White-tailed Ptarmigan habitat have been qual- ysis of ptarmigan habitat structure based on itative. Therefore, an objective method for eval- comparisons of habitats used and not used by uating habitat suitability for this ptarmigan was ptarmigan in the Sierra Nevada. We also provide needed. some demographic characteristicsof this intro- Summer habitats of White-tailed Ptarmigan in duced population. In addition, rates of range ex- the Rocky Mountains consistently include moist, pansion of White-tailed Ptarmigan transplanted outside their historic range have not been stud- I Received4 February 1992. Accepted 27 July 1992. ied. Therefore, we also assessptarmigan colo- ZPresent address:Arizona Game and Fish Depart- nizing abilities based on documented sightings ment, Tucson, AZ 85745. in the Sierra Nevada.

18891 890 GLENN P. FREDERICK AND R. J. GUTIFRREZ

a0 : I\ Carson 19g62< p_“:s \ Area Enlarged :::I g

- 380

-37O

BALPINE HABITAT $ STUDY AREAS 0 Km 0 120° 119O 1 18” I I

FIGURE 1. White-tailed Ptarmigan range expansion through alpine regions (redrawn from Kuchler 1977) of the SierraNevada showinglocation of 197l-l 972 White-tailed Ptarmigantransplant and subsequentdocumented sightingsduring 197l-1990. Dotted lines are furthest sightingfrom the releasesite reported in a particular year. Source of sighting records is described in text.

STUDY AREAS Crest. The 1988 study area (10 km2, hereafter called HNA) was in the Harvey Monroe Hall Two study areas adjoining Tioga Pass, Mono Natural Area of the Inyo National Forest. Study County, California, were selectedin order to ob- areas were approximately 10 km apart and lo- tain an adequate number of independent habitat cated 4 l-22 km south of the transplant locations, samples (Fig. 1). The 1987 study site (13 km*, ranged in elevation from 3,200 to 3,840 m, and hereafter called Yosemite) extended from Mono were similar in vegetation and topography. The Passsouth to Parker Peak Passand west to Kuna study populations were apparently separatesince WHITE-TAILED PTARMIGAN HABITAT USE 891 no birds banded in Yosemite were observed in Birds were captured using a noose pole (Zwickel HNA. and Bendell 1967) and banded with numbered Moisture availability during the typically dry aluminum California Department of Fish and growing seasonis the principal factor controlling Game leg bands (size 10 and 12) and numbered, vegetation patterns in the Sierra Nevada alpine colored plastic bandettes (size 5 and 6; National (Klikoff 1965, Pemble 1970, Taylor 1984). Most Band and Tag Co., Newport, KY). Sex and age- cyclonic storms are diverted from the mountain classof each bird were estimated following Braun range in summer; consequently, average total and Rogers (1967). All ptarmigan observations summer rainfall is only 5.25 cm (U.S. Depart- were plotted on 7.5 minute US Geological Ser- ment of Commerce 1930-1964). Although oc- vice topographic maps and aerial photographs casional thunderstorms may temporarily replen- (scale 1: 10,000). We calculated total density (i.e., ish soil moisture (Klikoff 1965), melting snow is number of individuals on the entire study area) the major sourceof moisture during the growing and ecologicdensity (i.e., number of individuals season.Annual snowfall in the Sierra Nevada is within occupied habitat). Extent of occupied substantial (e.g., averaging 665 cm at Ellery Lake, habitat was estimated with a planimeter by mea- 3.2 km from the study area at 2,926 m elevation; suring the area enclosed by the boundaries of U.S. Department of Commerce 1930-l 964). outermost ptarmigan territories. This calculation Snow cover persists through mid-June in most assumed birds were located in the approximate areas, with few snowbanks remaining past mid- center of average-sized territories (i.e., 20 ha; July except on protected north- or east-facing Jensen and Ryder 1965, Schmidt 1969). slopes (Chabot and Billings 1972). Because the distribution and melting rate of snowbanks is HABITAT ANALYSIS uneven due to interaction of wind and topog- We analyzed habitat selection with a used/un- raphy, a distinct local vegetation pattern results usedcontrast rather than the more common used/ (Mooney et al. 1965). available approach because (1) the latter comparison can potentially contain unknown METHODS amounts of suitable habitat (Brennan et al. 1986), and (2) we were able to verify occupancy by the POPULATION CHARACTERISTICS conspicuous, persistent nature of ptarmigan Range expansion from the release sites was es- droppings and feathersand the reliable response timated from sightings of White-tailed Ptarmi- of ptarmigan to tape-recorded vocalizations gan reported to the California Department of (Braun et al. 1973). Unused habitats contained Fish and Game, Yosemite National Park Re- neither ptarmigan nor their feathers/feces. We searchLibrary records for 1971-1988, and from further reduced the probability of misidentifying personal observation. Two additional records unused habitats by locating unused study plots were obtained in 1990-1991 from knowledge- outside areas of ptarmigan concentrations. Al- able wildlife biologists. Only records with a re- though an unknown number of samples in the liable description of bird(s) plumage, behavior, unused habitat group may have received unde- and associatedhabitat were included in the doc- tected use, such infrequently used habitats prob- umentation of range expansion. ably were relatively unimportant to ptarmigan. Population characteristics were estimated by We recognized two seasonsin our study: (1) marking all previously unbanded birds encoun- breeding (early April to mid-July), defined by the tered during surveys of 1 km2 sections of the onset of molt of the winter plumage and by the study areas.Surveys began in early April to assess presence of both males and females on or im- breeding density. C. E. Braun (pets. comm.) not- mediately adjacent to defended territories; and ed that accurateestimates of ptarmigan breeding (2) postbreeding (mid-July to late August), rec- density can only be assessedduring the early ognized by the appearance of ptarmigan broods spring breeding period (April-early June). Using and flocks consisting of at least two mutually repeated, systematic searchesand tape-recorded non-aggressivemales. ptarmigan calls, we believe few individuals es- We measured habitat variables (seeAppendix) capeddetection; non-territorial males and brood- in 0.02-ha (15-m diameter) study plots in used less females were the most likely birds to have and unused habitats at approximately the same been missed during surveys (Braun et al. 1973). altitudes. For the used habitat sample, we cen- 892 GLENN P. FREDERICK AND R. J. GUTIBRREZ tered study plots on the first sighting of a bird Group covariance matrices were evaluated for (single or member of pair or flock) not sampled homogeneity of variance using Box’s M statistic previously during the same season.Thus, all hab- (Nie et al. 1975:460). We calculated chance cor- itat observationswere independent samples.Sites rected classification rates (Titus et al. 1984) for occupied by ptarmigan located with taped calls all discriminant and logistic regressionanalyses. were not sampled because birds may move in Classification matrices for SDA were based on a responseto calls. Unused habitats were sampled jackknife procedure (Dixon et al. 1985:5 19). following a completed survey of a 1 km2 section. We examined stability of model variables by Two to three study plots were randomly located comparing performance of SLR and SDA models in unoccupied areas of each section. From a ran- (Brennan et al. 1986). Model stability was further domly selected starting point within an unused evaluated through a cross-validation procedure section, we followed a randomly selected com- recommended by Capen et al. (1986). We de- passbearing approximately 30 m to the plot cen- rived a subset model from a random sample of ter. A plot was rejected if it contained previously 75% of the observations, and used the model to undetected evidence of ptarmigan use. Unused classify the remaining 25% of observations. We habitat plots established in the breeding season replicated this process 20 times for each com- were resampled the following seasonif they still parison and evaluated variable loading patterns did not contain ptarmigan, or their feathers or and stability of model coefficients. feces. We identified plant communities at the center RESULTS of each study plot using Pemble’s (1970) classi- PTARMIGAN COLONIZATION PATTERNS fication; the hierarchial classification ranks nine IN THE SIERRA NEVADA vegetation associationsin five alliances. We cal- Seventy-two adult White-tailed Ptarmigan from culated mean slope orientation (0) and its dis- Colorado were releasedin the central Sierra Ne- persion (r) for both used and unused sites vada at Eagle Peak and Twin Lakes, Mono Coun- (Batschelet 198 1:7); and we employed Rayleigh’s ty, during 1971-1972 in upper montane-subal- test (Zar 1984:442) to test if the sample was uni- pine forest below 3,000 m elevation (R. D. formly distributed. We used the Watson-Wil- Thomas, pers. comm.). Abandoning the release liams test (Batschelet 198 1:95) to examine dif- sites, the colonists dispersed 10 km to the Sierra ferencesin mean slope orientation between used Nevada crest. Within 18 years ptarmigan colo- and unused habitats, and chi-square contingency nized alpine habitats 114 km to the south and analysis to test for seasonalchanges in slope ori- 79 km to the north (Fig. 1). Movement must have entation (Batschelet 198 1: 109). been rapid becauseobservations 5 months, 1 year, We reduced the number of structural habitat and 4 years after releasewere 11, 27, and 41 km variables prior to multivariate analyses. Loga- from the release sites, respectively. The furthest rithmic and square-root transformations were southern observation was at Pine Creek Pass, used to normalize structural habitat data. We Mono County. The largestgap of unsuitable, low- first performed a one-way analysis of variance elevation (2,260 m) habitat (i.e., Middle Fork (ANOVA, Brown and Forsythe 1974) to deter- San Joaquin River) in their southward dispersal mine which variables had significant (P < 0.05) was 13.7 km. In their northward dispersal to between-group differences. Second, we used Carson Pass, Alpine County, ptarmigan crossed Spearman’s rank-correlation (Zar 1984:3 18) to similar areas of low-elevation forest lo-20 km eliminate one of a pair of statistically significant wide (Fig. 1). variables if r > 0.4. The variable with either the highest between-group significance or more POPULATION CHARACTERISTICS meaningful biological interpretation was re- We estimated the age-classof 140 of 141 ptar- tained. We then used stepwiselogistic regression migan banded on the two study areas. The com- (SLR, Dixon et al. 1985:330) to examine differ- bined population was 59.29% male and 40.71% encesbetween used and unused habitat structure. female; yearlings (i.e., first year birds) comprised We used step-wise discriminant analysis (SDA; 30% of the breeding seasonpopulation. Changes Klecka 1980) to examine differencesbetween used in sexand ageratios between seasonswere minor habitats (1) during the breeding and postbreeding and indicated little movement in or out of the season and (2) by flocks and hens with broods. study areas during summer (Table 1). WHITE-TAILED PTARMIGAN HABITAT USE 893

TABLE 1. Sex and age ratios of White-tailed Ptarmigan observed in the Sierra Nevada, in 1987-l 988. Only known age-classbirds were included.

Yearling male : Yearling female : adult male adult female Yearling :adult Male : female Breeding Entire Breeding Entire Breeding Entire Breeding Entire Study site season yGU S.%XSO” yeal. season year SGiSO” year

Yosemite 0.4: 1 0.5:1 O.l:l 0.4: 1 0.3:1 0.5:1 1.8:1 1.5:l (31) (37) (17) (25) (48) (62) (48) (62) HNA 0.3:1 0.4: 1 0.9:1 0.7:1 0.6:1 0.5:1 0.9: 1 1.4:1 (25) (46) (27) (32) (52) (78) (52) (78)

* Sample size.

Population density (ptarmigan per 100 ha) for (Fig. 3). The relatively moist Cassiope merten- the entire area surveyed ranged from 4.4 to 5.7 siana-Phyllodoce breweri association received in the breeding season, and from 4.7 to 7.1 in consistently high use both seasons.Females with the postbreeding season. Densities within occu- broods primarily used wet meadows; however, pied habitat (i.e., ecologicaldensity) were greater the frequency of occurrenceof plant associations than total densities and this relationship in- used by flocks and hens with broods was similar. creased two-fold (e.g., breeding = 10.5-14.2; Mean slope orientation of habitats used by postbreeding = 2 1.8-27.7) between seasons.The ptarmigan during the breeding and postbreeding number of breeding pairs per 100 ha was 1.8 and seasonswas 44 + 14 degrees(r = 0.64, n = 72) 2.8 in the Yosemite and HNA study sites, re- and 19 + 18 degrees(r = 0.59, n = 52), respec- spectively. tively. Used habitats showed significant slope We located 23 different broods in July and orientation during both seasons (Rayleigh’s August. Average annual brood size ranged from Z-test; breeding: Z = 29.49, P < 0.001; post- 2.6 to 2.8 chicks per brood (Table 2). breeding: Z = 18.10, P < 0.001). Distribution of slope orientations used by ptarmigan did not SEASONAL DISTRIBUTION differ between seasons(x2 = 12.42, df = 4, P > Ptarmigan distribution was closely associated 0.0 1). However, mean slope orientation differed with availability of mesic vegetation in spring between used and unused habitats in both sea- and summer. Edgesof snow-free patches on up- sons (Watson-Williams test; breeding: F = 9.24, land slopes were used extensively for foraging df = 1,151, P < 0.01; postbreeding: F = 3.94, and roosting during spring (n = 48 of 66 obser- df = 1,100, P < 0.01). Whereas 46% of used vations). As vegetation on these slopes became habitats had northeast to northwest slope ori- dry, ptarmigan moved to late developing plant entations, 28% of unused sites were on slopes communities in snow-free depressions.This pat- with northern orientations (x2 = 22.1, df = 8, P tern was reflected by a significant difference in < 0.001). use of vegetation alliances during the breeding season (x2 = 12.233, df = 3, P < 0.05; Fig. 2). TABLE 2. Number of broods and averagebrood size Moist plant communities, particularly with wil- of White-tailed Ptarmigan populations in the Sierra low (Salix spp.) and ericaceoussubshrubs as im- Nevada, California, 1987-l 988. Number of broodsdoes portant components, were used more often. The not include reobservation of individual broods during a sampling period. Salix anglorum antiplasta alliance was the most frequently occurring community in used breed- Average number of chicks ing and postbreeding season habitats sampled. per brood Conversely, drier plant alliances (e.g., Carex Date Yosemite HNA breweri-Calyptridium umbellatum and Arenaria July 1-15 2.0 (3) 6.0 (1) kingii-Senecio werneriaefolius) occurred pre- July 16-3 1 4.0 (2) 3.1 (7) dominantly in unused habitats (68.8%). August l-l 5 2.3 (3) 2.0 (4) August 16-3 1 2.0 (3) Ptarmigan also used a wider range of plant ND (0) associations, including drier types, during the Average 2.6 (8) 2.8 (15) breeding seasonthan in the postbreeding season il(n) = number of broods observed during the period. 894 GLENN P. FREDERICK AND R. J. GUTIERREZ

100

s 90 z 80

: 70 8 8 60

A il C D VEGETATION ALLIANCE m used breeding 0 used postbreeding fZ%j unused

FIGURE 2. Distribution of vegetation alliances between used and unused White-tailed Ptarmigan habitat in the Sierra Nevada, California. Alliance codes:A = Salix anglorumvar antiplasta,B = Saxifraga aprica-Gentiana newberryi,C = Carex breweri-Calyptridium umbellatum,D = Arenaria kingii-Seneciowerneriaefolius (Pemble 1970). Numbers atop bars are sample size.

2 2 mo -0 1 1 4 5 6 VEGETATION ASSOCIATION m used breeding 0 used postbreeding FIGURE 3. Distribution of vegetation associationsbetween White-tailed Ptarmigan habitat used during the breeding and postbreedingseason in the Sierra Nevada, California. Association codes: 1 = Carex subnigricans- Pedicularisattollens, 2 = Trtjolium monanthum-Phleumalpinum, 3 = Cassiopemertensiana-Phyllodoce breweri, 4 = Salix nivalis, 5 = Carex helleri-Poa suksdorfii,6 = Arabis platysperma-Penstemonheterodoxus (Pemble 1970). Numbers atop bars are sample size. Note associationsl-4 are within vegetation alliance ‘A’ and associations 5-6 are within alliance ‘C.’ WHITE-TAILED PTARMIGAN HABITAT USE 895

TABLE 3. Characteristicsof habitatsused and unusedby White-tailedPtarmigan during the breedingseason in the SierraNevada, California.

Used (n = 72) Unused (n = 82) Variablea R SE R SE P Altitude (m) 3,303.9 11.99 3,319.l 13.53 0.401 Slope( “) 15.7 0.69 15.3 0.76 0.759 Shrubheight (cm) Maximum 61.9 9.43 137.8 22.76 0.075 Minimum 9.8 1.53 12.9 2.13 0.879 Distance(m) to Snow 16.1 5.87 28.9 3.72 0.596 Water 8.1 1.77 53.5 6.84

a See Appendix for explanation of habitat variables. b One-way ANOVA; df = I, 152.

BREEDING SEASONHABITAT STRUCTURE models and consistently ranked first. All vari- We measured habitat characteristicsat 72 ptar- ables, except boulder cover and subshrub cover, migan locationsduring the breeding seasons.Each entered 2 12 of 20 subsetmodels. Moreover, signs location was an independent sample (i.e., a color- of coefficients were consistent and their values marked bird). Thirteen structural habitat vari- similar for the subset and full models (Table 4). ables differed (P < 0.05) between used and un- Mean correctclassification was 62.8% (SE = 2.38, used breeding habitat (Table 3). Our data fit the P < 0.001). All variables, except subshrub cover logistic model (x2 = 83.6, df = 147, P = 1.0) and boulder cover, had structure coefficients and stepwise inclusion of each variable, except >0.52 in the SDA model. percent boulder cover, improved the predictive power of the model (P 5 0.05).The probability POSTBREEDING SEASONHABITAT of a habitat being used increased with increasing STRUCTURE cover by dwarf willow, subshrubs, moss, and We measured habitat characteristicsat sites oc- boulders, and with decreasingdistance from wa- cupied by 52 different, color-marked ptarmigan ter and willow shrubs. Based on a logistic cut- during the postbreeding seasons.Fourteen vari- point of 0.435, the full model correctly classified ables differed (P < 0.05) between habitats used 75.4% of habitats (Z = 9.34, P c 0.001). and not used by ptarmigan (Table 5). Although Although group covariance matrices were un- boulder cover was not statistically different, it equal(Box’sM= 525.24, F= 23.95, P < 0.001) was retained for further analyses for biological we inferred from the cross validation analyses reasons(i.e., the birds will use bouldersfor cover). that this did not seriously affect model perfor- Mean distance to snow was probably too great mance. The same six predictor variables entered for snow to be an important factor in habitat the full model and subsetmodels in similar order selection(X = 124.2 m). However, snowmelt from (Table 4). Percent dwarf willow cover entered all adjacent slopesand higher elevations facilitated 896 GLENN P. FREDERICK AND R. J. GUTIERREZ

TABLE 4. Step-wise order of variable selection,regression coefficients, and error terms in subsetand full data logistic regressionanalyses of White-tailtid Ptarmigan habitat in the Sierra Nevada.

step Regression coefficient Full model Regression Season variable RI SE X’ SE ster, coeficient SE of coetlicient

Breeding Dwarf willow cover 1.0 0.00 0.0538 0.002 0.0513 0.014 Subshrubcover 2.6 0.05 0.0209 0.002 0.0095 0.006 Moss cover 2.8 0.31 0.2019 0.008 0.1863 0.083 Dist. to water 3.4 0.28 -0.0444 0.002 -0.0342 0.016 Dist. to willow 3.4 0.23 ~1.1310 0.084 -0.9433 0.422 Boulder cover 4.3 0.53 0.060 1 0.004 0.0409 0.028 Constant -0.9467 0.235 -0.6876 0.759

Dwarf willow cover 1.2 0.01 0.8548 0.046 1 0.038 1 0.012 Dist. to water 1.9 0.02 PO.7577 0.042 2 -0.0345 0.103 Soil cover 2.9 0.02 3.8877 2.633 3 0.1813 0.093 Constant -8.4021 5.363 - 1.2134 0.768

I + = mean entry of variable into model, SE = standard error. 2x = mean regression coellicient, SE = standard error of the man regression coefficient. development of greater vegetation cover in used boulders (P < 0.001) while having less turf (P = (X = 45.0%, SE = 2.5) than in unused (K = 29.2%, 0.0 18) than brood habitats. Covariance matrices SE = 3.8) habitats (F = 19.73; df = 1,100; P < were equal for these analyses (Box’s A4 = 1.49, 0.00 1). A logistic model was appropriate for our F = 1.45, P = 0.229). data (x2 = 43.3, df = 98, P = 1.0) and its pre- COMPARISON OF BREEDING AND dictive power was improved by inclusion of each POSTBREEDING SEASON HABITAT variable (P 5 0.05). The probability of a habitat STRUCTURE being used by ptarmigan increased with increas- Ptarmigan moved into lesssteep topographic de- ing cover of dwarf willow and soil, and with depressions with more dwarf willow (P < 0.001) creasing distance to water. Based on a logistic and gravel cover (P = 0.003) after the breeding cutpoint 0.046, the full model correctly classified seasonhad ended. The SDA model did not re- 86.2% of habitats (Z = 8.70, P < 0.001); mean liably distinguish used ptarmigan habitats be- correct classification rate was 78.6% (SE = 2.64, tween seasons;correct classification rates of most P 5 0.004). (70%) subset models were not significantly (P > Although covariance matrices were unequal 0.01) better than a classification based solely on (Box’s M = 347.3, F = 15.47, P < 0.001) high prior probabilities of group membership. Co- correct classification rates and cross-validation variance matriceswere unequal (Box’sM= 11.83, results indicated the models were stable. Percent F = 3.87, P < 0.01). dwarf willow cover and distance to water were most consistent in their contribution to subset DISCUSSION models, entering 19 and 17 times, respectively. Additionally, percent soil cover entered the sub- POPULATION CHARACTERISTICS set models 14 times; however, its low structure Documented sightings of White-tailed Ptarmi- coefficient (-0.33) from SDA indicated it was gan in the Sierra Nevada indicated a rapid rate not a highly discriminatory variable; structure of range expansion (Fig. 1). Within 18 years of coefficients of remaining variables were >0.70. their release, ptarmigan had colonized over 190 While signs of coefficients were consistent be- km of alpine habitat. In comparison, range ex- tween the subset and full models, their values pansion following transplants and experimental were relatively unstable (Table 4). removals of ptarmigan in the Rocky Mountains Boulder cover distinguished ptarmigan flock was considerably slower. For example, ptarmi- and brood habitat in the SDA model (Z = 4.6 1, gan transplanted to Pike’s Peak, Colorado, re- P < 0.001). Flocking habitats contained more quired four years to colonize all suitable habitats WHITE-TAILED PTARMIGAN HABITAT USE 897

TABLE 5. Characteristicsof habitats used and unused by White-tailed Ptarmigan during the postbreeding seasonin the Sierra Nevada, California.

Used (n = 52) Unused (n = 50) Variable x SE x SE P

Altitude (m) 3,311.0 10.83 3,359.2 15.34 0.011 Slope (“) 11.4 0.76 14.9 1.02 0.006 Shrub height (cm) Maximum 24.2 3.95 92.1 21.08 0.031 Minimum 7.1 1.24 11.5 2.78 0.693 Distance (m) to Snow 124.2 12.42 177.4 15.33 0.018 Water 13.5 3.3 88.2 10.01

“See Appendix for explanatmn of habitat variables. h One-way ANOVA; df = I, 100. within 5 km of the release site (Hoffman and in Colorado (Choate 1963, Braun and May 197 1, Giesen 1983). Breeding territories in the Uinta respectively). Mountains, Utah, establishedthe year following Breedingsuccess (i.e., ratio ofyearlings to adults a releasewere located within 5 km of the release during postbreeding season) in our study sites site (Braun et al. 1978). Ptarmigan repopulated was less than reported for native populations in an isolated 5 km* area in northern Colorado the Rocky Mountains (Choate 1963, Braun and within two years of an experimental removal of Rogers 197 1). However, the proportion of year- all birds; the nearest colonization sourcewas 3.2 lings in the breeding seasonpopulation was com- km away (Braun 1975). parable to Rocky Mountain populations and in- Our estimated population densities were with- dicatedadequate over-winter survival. Clarke and in the range of values (3.71-6.57 birds per 100 Johnson (1990) reported that breeding successin ha) reported by Clarke and Johnson (1992) the Sierra Nevada varied between years but did for the south-half of our HNA study area during not differ significantly from breeding successof the previous six years. These are the lowest den- naturally occurring populations. Average brood sities reported for White-tailed Ptarmigan. Over- size in our study areas also was below reported all breeding seasondensity (birds per 100 ha) at values. Average annual brood size for five study Logan Pass, Montana, was 6.8, while density areasin southern Colorado during four years was within suitable habitats was 19.3 (Choate 1963). 3.6 (range 3.2-4.5; Braun and Rogers 1971). Breeding density of three unhunted populations Brood size at flight age in Montana ranged from in Colorado ranged from 9.6 to 11.9 and aver- 3.25 to 3.47 (Choate 1963). aged 10.8 over a five year period (Braun and May Below averagepopulation density, small brood 197 1, Braun and Rogers 197 1). Postbreeding size, and variable breeding successin Sierra Ne- ptarmigan density for thesepopulations was 10.6 vada ptarmigan may be attributable to the lim- in Montana and averaged 19.3 (range 15.7-23.4) ited availability and quality of ptarmigan habi- 898 GLENN P. FREDERICK AND R. J. GUTICRREZ tat. White-tailed Ptarmigan are closely associated banks, protected from direct solar radiation, pro- with mesic, low-growing alpine vegetation in our vide moisture. In contrast, south-facing slopes, study sites as well as throughout the Rocky ridges,and exposedsummits which are dryer are Mountains (Weeden 1959; Choate 1963; Jensen rarely used by these grouse. andRyder 1965;Braun 1969,1970,1971;Braun Ptarmigan distribution was most patchy in and Pattie 1969; Herzog 1977; Scott 1982). Me- summer when few snowbanksremained and most sic vegetation in the Sierra Nevada is limited to alpine habitats were dry. During this season, topographic lows and protected slope exposures flocks and hens with broods concentrated use in where late-lying snowbanks provide moisture topographic depressionswhere mesic vegetation throughout the otherwise dry growing season cover was most extensive. As the breeding season (Klikoff 1965, Pemble 1970, Chabot and Billings progressed into summer, amount of occupied 1972). Consequently, total plant cover, especial- habitat declined from 42% to 25% of the study ly the coverage of mesic communities, is lower sites.Moreover, the increasein density following and more patchy in the Sierra Nevada alpine the breeding seasonwas greaterthan reported for than in the Rocky Mountains (Chabot and Bill- populations occupying large expansesof suitable ings 1972, Billings 1978). In yearswith high spring habitat in the Rocky Mountains (Choate 1963). snow depth, snow cover further reduces avail- White-tailed Ptarmigan have high energy and ability of ptarmigan nesting and foraging sites nutrient requirements due to an unusually high required for breeding (Clarke and Johnson 1990). metabolic rate (Johnson 1968, May 1975) and Deep spring snowpack in the Sierra Nevada in- nearly continuous molt. Consequently, they must hibits ptarmigan breeding activity (i.e., delays maximize their use of plant productivity by nesting and hatching dates)and reducesbreeding closely tracking plant phenology. Willow is a nu- success(Clarke and Johnson 1992). In addition, tritious and important food item for White-tailed we suggestthat breeding density may decline with Ptarmigan (Weeden 1967, May and Braun 1972, greater snow depth if birds must search a larger May 1975). Previous investigators have sug- area for snow-freeterritories. In contrastto Clarke gested that willow availability is the principal and Johnson (1992) several years of low spring factor controlling ptarmigan distribution (Braun snow depth potentially may affect breeding suc- and Pattie 1969; Braun 1970, 1971, 1975). Our cessby reducing productivity of plant forage. If comparisons of used and unused habitats sup- soil drought occurs during the period following port the importance of dwarf willow (Salix an- plant emergence,plant growth is curtailed (Bill- gbrum) for predicting suitable ptarmigan habi- ings and Bliss 1959, Klikoff 1965) which may tat. However, the best predictive models also directly or indirectly (i.e., through its effect on included cover of ericaceoussubshrubs and moss- insect populations) influence ptarmigan chick like plants which may be an indication of the growthand development. The effectsof low spring importance of the plant community in general. snow depth may not be evident for several years, Similarly, Choate (1963) reported that all habitat whereas Clarke and Johnson (1992) detected an samples in his Rocky Mountain study area con- immediate correlation between high spring snow tained dwarf willow, heath, and mosses. depth and ptarmigan reproduction. While vegetation cover featuresand proximity of water were important discriminators of ptar- HABITAT ECOLOGY migan habitat, most occupied habitats also con- Ptarmigan distribution in the Sierra Nevada is tained boulders. Boulders were used extensively influenced primarily by distinct vegetation pat- by ptarmigan as cover; we recorded 66 obser- terns resulting from limited, uneven water dis- vations of birds using boulders as roosting or tribution. Our analyses indicate that distance to escapecover and 42 observations of flocks using water is an important predictor of suitable ptar- boulders for shelter. White-tailed Ptarmigan are migan habitat in the Sierra Nevada. Plant com- poorly adapted to high ambient temperatures munities most commonly used by ptarmigan are (Johnson 1968, May 1975) and apparently re- restricted to the wettest habitats above timber- quired boulder cover to reduce thermoregulatory line. In general, these communities occur along energy demands, particularly on hot or windy borders of lakes and streams and in topographic days. Protection from direct solar radiation was depressions (Pemble 1970). In addition, ptar- possibly a critical factor in the Sierra Nevada migan select north-facing slopes where snow- where cloud cover and humidity in summer were WHITE-TAILED PTARMIGAN HABITAT USE 899 substantially less than in the Rocky Mountains parison, the Sierra Nevada is among the largest (Major and Bamberg 1967, Chabot and Billings mountain rangesin North America and contains 1972). Despite a frequent association of ptar- over 3,000 km2 of alpine vegetation. The key to migan and boulders, boulder cover was a poor thesesuccessful transplants is the ability of White- discriminator of used habitats. This was partly tailed Ptarmigan to exploit patchy alpine envi- due to the abundance of exposedbedrock in our ronments while sustaining populations at low heavily glaciated study areas. Ptarmigan pri- densities. Furthermore, this speciesis long-lived marily used rock fragments > 30 cm in diameter (2 15 years; Choate 1963) and capable of main- and fractured rock-shelves. taining populations during occasional years of poor reproduction (Clarke and Johnson 1990). COLONIZATION OF THE SIERRA NEVADA Range expansion by White-tailed Ptarmigan Dispersal abilities of White-tailed Ptarmigan are in the Sierra Nevada indicates that the speciesis well documented (Braun 1969, Schmidt 1969, a better colonizer than has been suggestedby Braun 1975, Hoffmanand Braun 1975, Hoffman previous studies of ptarmigan in the Rocky and Giesen 1983). The rate of range expansion Mountains (Schmidt 1969, Braun 1975, Hoff- is controlled primarily by yearling dispersalfrom man and Giesen 1983). Ptarmigan crossed lo- wintering areas to breeding territories (Schmidt to 20-km wide gapsof unsuitable vegetation and 1969, Braun 1975, Hoffman and Braun 1975). colonized alpine habitats over 100 km from the Yearling males unsuccessfulin obtaining terri- release sites within 18 years of their liberation. tories on natal areas commonly disperseover 10 Clarke and Johnson (1990) assessedthe ability km in search of a suitable territory; yearling fe- of White-tailed Ptarmigan to naturally colonize males may traverse longer distances (> 20 km) the Sierra Nevada during prehistorictimes. Based in search of unmated territorial males (Braun on paleoecologicevidence and measurements of 1975, Hoffman and Braun 1975). Suitable breed- current treeline in the South CascadeMountains, ing and flocking areas in the Sierra Nevada are they concluded that White-tailed Ptarmigan nev- limited and widely distributed (pers. observ.). er successfullycolonized the Sierra Nevada. We Habitat availability is further reduced during do not agree that measurement of current tree years with deep spring snow depth (Clarke and line is an accurate measure of past alpine habitat Johnson 1992). Consequently, ptarmigan must distribution. Our data from the Sierra Nevada dispersefurther to colonize new areas in the Si- indicates that ptarmigan are strongdispersers and erra Nevada than in alpine systems with more probably were capable of exploiting isolated continuous expansesof suitable habitat. Patchy patchesof suitable alpine habitat as they became distribution of suitable habitat apparently pro- available. In early postglacial times, tempera- motes greater dispersalbehavior and more rapid tures were considerably cooler and alpine regions range expansionin Sierra Nevada ptarmigan than with mesic vegetation more extensive than today in previously studied populations. Strong dis- (Hoffmann and Taber 1967, Chabot and Billings persal behavior by birds occupying a patchy en- 1972). A southernrange extension of White-tailed vironment is advantageous since it may lead to Ptarmigan in westernNorth America would have colonization of unoccupied but favorable habitat been possible at this time. During successivepe- patches (Wiens 1976). riods of warm climate, alpine areas were greatly Additional transplants of White-tailed Ptar- restricted, likely isolating or extirpating some migan have occurred in Pike’s Peak, Colorado; southern ptarmigan populations. A period of ex- Uinta Mountains, Utah; and Wallowa Moun- treme climatic warming, the Hypsithermal, se- tains, Oregon. Although these alpine systems verely limited mesic alpine vegetation (La- contain different conditions for ptarmigan col- Marche and Mooney 1967) and probably onization and dispersal,all transplants were suc- eliminated ptarmigan from the Sierra Nevada if cessful.Pike ’s Peak is a 39 km2 “island” of alpine they occurred in the range. This warming trend habitat isolated from the nearest alpine area by terminated about 2,900 years ago with the Little 60 km of unsuitable habitat (Hoffman and Gie- Ice Age (Adam 1967) a period which favored sen 1983). The Uinta and Wallowa Mountains development of a sufficient amount of alpine are similarly isolated from more extensive alpine vegetation to support White-tailed Ptarmigan in systemsand contain limited amounts of habitats the Sierra Nevada, as the current introduced suitable for colonization by ptarmigan. In com- population demonstrates. White-tailed Ptarmi- 900 GLENN P. FREDERICK AND R. J. GUTIfiRREZ

gan were unable to colonize the Sierra Nevada tailed Ptarmigan in Colorado and New Mexico. in recent times because of geographic and eco- Annu. Meet. Southwest. and Rocky Mtn. Div., Am. Assoc. Advance. Sci. 46:35. logic barriers to ptarmigan dispersal between the BRAUN,C. E. 1971. Habitat requirements of Colo- Sierra Nevada and the nearest naturally occur- rado White-tailed Ptarmigan. Proc. West. Assoc. ring populations in the North Cascade Moun- State Game and Fish Comm. 5 1:284-292. tains (Clarke and Johnson 1990). BRAUN,C. E. 1975. Experimental removal of a breeding population of White-tailed Ptarmigan. Colo. Studies of introduced populations may allow Div. Wildl. Game Res. Rep. Fed. Aid Proj. inferences about that species in its natural hab- W-37-R-28. itat. For example, the ability of White-tailed BRAUN,C. E., AND T. A. MAY. 1971. Inventory of Ptarmigan to locate suitable habitat, disperse, selectedptarmigan populations.Colo. Div. Game, and colonize habitat, as well as to exploit a patchy Fish, and Parks. Game Res. Rep., Fed. Aid Proj. W-37-R-24. environment, widens our perceptions of this bird BRAUN,C. E., D. H. NISH, AND K. M. GIESEN. 1978. that were not apparent from studies conducted Release and establishment of White-tailed Ptar- in its native range. The adaptability demonstrat- migan in Utah. Southwest.Nat. 23:66 l-668. ed by White-tailed Ptarmigan in the Sierra Ne- BRAUN,C. E., AND D. L. PATTIE. 1969. A comparison of alpine habitats and White-tailed Ptarmigan oc- vada also suggests that conservation and resto- currence in Colorado and northern Wyoming. ration of the species could be enhanced by Annu. Meet. Southwest. Rocky Mtn. Div., Am. protecting critical zones which are distributed Assoc. Advance. Sci. 45:50. throughout key parts of degraded range. BRAUN.C. E.. AND G. E. ROGERS. 1967. Determi- naiion ofage and sex of the southernWhite-tailed ACKNOWLEDGMENTS Ptarmigan. Colo. Div. Game, Fish and Parks. Game Info. Leaflet 54. Financial assistancewas provided in part by the Yo- BRAUN,C. E., AND G. E. ROGERS. 1971. The White- semite Association and California Deuartment of Fish tailed Ptarmigan in Colorado. Colo. Div. Game, and Game. J. Van Wagtendonk, L. M&ibben, J. Mas- Fish and Parks. Tech. Publ. 27. sie, and T. Hargaswere instrumental in obtaining fund- BRAUN, C. E., R. K. SCHMIDT,AND G. E. ROGERS. ing or logistic support.The CarnegieInstitute of Wash- 1973. Census of Colorado White-tailed Ptarmi- ington and Yosemite National Park, U.S. Interior gan with tape-recordedcalls. J. Wildl. Manage. 37: Department, provided housing during the field sea- 90-93. sons. We thank S. Garton and T. L. Moore for their BRENNAN,L. A., W. M. BLOCK,AND R. J. GUTIBRREZ. field assistance,and B. R. Noon, C. E. Braun, C. 1986. The use of multivariate statistics for de- McKarthy, and J. 0. Sawyer for suggestionson study veloping habitat suitability index models, p. 177- design and statisticalanalyses. We gratefully acknowl- 182. In J. Vemer, M. L. Morrison, and C. JI Ralph edge C. E. Braun, T. L. Moore, B. R. Noon, J. 0. leds.1.Wildlife 2000: modeline. habitat relation- Sawyer, and one anonymous reviewer for suggesting shipsofterrestrial vertebrates.&iv. of Wisconsin improvements to previous drafts of this paper. Press, Madison, WI. BROWN,M. B., ANDA. B. FORSYTHE.1974. The small LITERATURE CITED sample behavior of some statisticswhich test the equality of severalmeans. Technometrics 16:129- ADAM, D. P. 1967. Late-Pleistoceneand Recent pal- 132. ynology in the Central Sierra Nevada, California, CAPEN,D. E., J. W. FENWICK,D. B. INKLEY,AND A. p. 275-301. In E. J. Cushingand H. E. Wright, Jr. C. BOYNTON.1986. Multivariate models ofsong- [eds.],Proc. VII Congr. Int. Assoc.Quat. Res. Yale bird habitat in New England forests, p. 17l-l 76. Univ. Press, New Haven, CT. In J. Vemer, M. L. Morrison, and C. J. Ralph ALDRICH, J. W. 1963. Geographic orientation of [eds.], Wildlife 2000: modeling habitat relation- American Tetraonidae. J. Wildl. Manage. 27:529- shipsof terrestrialvertebrates. Univ. of Wisconsin 545. Press, Madison, WI. BATSCHELET,E. 1981. Circular statistics in biology. CHABOT,B. F., AND W. D. BILLINGS. 1972. Origins Academic Press, San Francisco, CA. and ecology of the Sierran alpine flora and vege- BILLINGS,W. D. 1978. Alpine phytogeographyacross tation. Ecol. Monogr. 42: 163-199. the Great Basin. Great Basin Nat. Mem. 2:105- CHOATE,T. S. 1963. Habitat and population dynam- 117. ics of White-tailed Ptarmiganin Montana. J. Wildl. BILLINGS,W. D., AND L. C. BLISS. 1959. An alpine Manage. 27:684-699. - snowbank environment and its effects on vegeta- CLARKE,J. A., AND R. E. JOHNSON.1990. Biogeog- tion, plant development, and productivity. Ecol- raphy of White-tailed Ptarmigan (Lanopus leu- ogy 40:388-398. c&11$: implications from an introduced-popula- BRAUN,C. E. 1969. Population dynamics, habitat, tion in the Sierra Nevada. J. Bioe. 17:649-656. and movements of White-tailed Ptarmigan in Col- CLARKE,J. A., AND R. E. JOHNSON.i$92. The influ- orado. Ph.D.diss. Colorado State Univ., Fort Col- ence of spring snow depth on White-tailed Ptar- lins, CO. migan breedingsuccess in the SierraNevada. Con- BRAUN,C. E. 1970. Distribution and habitat of White- dor 94~622-627. WHITE-TAILED PTARMIGAN HABITAT USE 901

DESANTE,D., AND D. GAINES. 1977. The nestingsea- MAY, T. A., ANDC. E. BRAUN. 1972. Seasonalfoods son: middle Pacific Coast’ region. Am. Birds 31: of adult White-tailed Ptarmigan in Colorado. J. 1184. Wildl. Manage. 36:1180-l 186. DIXON,W. J., M. B. BROWN,L. ENGELMAN,J. W. FRANE, MONEY H. A., R. D. HILLIER,AND W. D. BILLINGS. M. A. HILL, R. I. JENNRICH,AND J. D. TOPOREK. 1965. Transpiration rates of alpine plants in the 1985. BMDP statistical software. Univ. of Cali- Sierra Nevada of California. Am. Midl. Nat. 74: fornia Press, Los Angeles. 374-386. GAINES,D. 1988. Birds of Yosemite and the east NIE, N. H., C. H. HULL, J. G. JENKINS,K. STEINBR- slope. Artemisia Press, Lee Vining, CA. ENNER,AND D. H. BENT. 1975. Statistical pack- HERZOG,P. W. 1977. Summer habitat use by White- age for the social sciences.2nd ed. McGraw Hill, tailed Ptarmigan in southwestern Alberta. Can. New York. Field Nat. 9 1:367-37 1. PEMBLE,R. H. 1970. Alpine vegetation in the Sierra HILDBN,0. 1965. Habitat selectionin birds: a review. Nevada of California as lithosequencesand in re- Ann. Zool. Fenn. 2~53-75. lation to local site factors.Ph.D.diss. Univ. of Cal- HOFFMAN,R. W., AND C. E. BRAUN. 1975. Migration ifornia. Davis, CA. of a wintering population of White-tailed Ptar- SCHMIDT,R. K., JR. 1969. Behavior of White-tailed migan in Colorado.J. Wild]. Manage. 39:485490. Ptarmiean in Colorado. M.Sc. thesis. Colorado HOFFMAN,R. W., ANDK. M. GIESEN. 1983. Demog- State Univ., Fort Collins, CO. raphy of an introduced population of White-tailed SCOTT,M. D. 1982. Distribution and habitat use of Ptarmigan. Can. J. Zool. 61:1758-1764. White-tailed Ptarmigan in Montana. Proc. Mon- HOFFMANN,R. S., AND R. D. TABER. 1967. Origin tana Acad. Sci. 4 1:5?-66. and history of holarctic tundra ecosystemswith SPENCER.C. 1976. In searchof the White-tailed Ptar- specialreference to their vertebratefaunas, p. 143- migan. Outdoor Calif. 37(6):18-19. 170. In H. E. Wright and W. H. Osbum [eds.] TAYLOR,D. W. 1984. Vegetation ofthe Harvey Mon- Arctic and alpine environments. Indiana Univ. roe Hall Research Natural Area, Inyo National Press, Bloomington, IN. Forest, California. Unpubl. rep. U.S. For. Serv. JENSEN,L., AND R. A. RYDER. 1965. Breeding be- Pacific Southwest For. and Range Exp. Stn., havior of the White-tailed Ptarmigan near Aspen, Berkeley, CA. Colorado. J. Colorado-Wyoming Acad. Sci. 5:52- TITUS, K., J. A. MOSHER,AND B. K. WILLIAMS. 1984. 53. Chance-correctedclassification for usein discrim- JOHNSON,R. E. 1968. Temperature regulation in the inant analysis:ecological applications. Am. Midl. White-tailed Ptarmigan, Lagopusleucurus. Comp. Nat. 11l:l-7. Biochem. Physiol. 24:1003-1014. U.S. DEPARTMENTOF COMMERCE.1930-1964. Cli- KLECKA,W. R. 1980. Discriminant analysis. Sage matic summary of the United States, Section 18, Publishing, Beverly Hills, CA. southern California. U.S. Dept. Commerce, KLIKOW, L. G. 1965. Microenvironmental influence Washington, DC. on vegetationalpattern near timberline in the cen- WEEDEN,R. B. 1959. The ecology and distribution tral Sierra Nevada. Ecol. Monogr. 35: 187-2 11. ofptarmigan in westernNorth America. Ph.D.diss. KUCHLER,A. W. 1977. The map of the natural veg- Univ. of British Columbia, Vancouver, BC, Can- etation of California. Univ. of Kansas Press,Law- ada. rence, KS. WEEDEN,R. B. 1967. Seasonaland geographicvari- LAMARCHE,V. C., AND H. A. MOONEY. 1967. Al- ation in the foods of adult White-tailed Ptarmigan. tithermal timberline advance in western United Condor 69:303-309. States. Nature 2 13:980-982. WIENS,J. A. 1976. Population responsesto patchy MAJOR.J.. AND S. A. BAMBERG.1967. Comparison environments. Ann. Review of Ecol. and Syst. 7: of some North American and Eurasianalpine eco- 81-120. systems, p. 89-l 18. In H. E. Wright and W. H. ZAR, J. H. 1984. Biostatisticalanalysis. Prentice-Hall Osbum leds.1. Arctic and alpine environments. Inc., Englewood Cliffs, NJ. Indiana &iv: Press, Bloomington, IN. ZWICKEL,F. C., AND J. F. BENDELL. 1967. A snare MAY. T. A. 1975. Phvsioloeical ecoloev of White- for capturing Blue Grouse. J. Wildl. Manage. 3 1: tailed Ptarmigan in Colorido. Ph.D.&s. Univ. of 202-204. Colorado, Boulder, CO. 902 GLENN P. FREDERICK AND R. J. GUTIFRREZ

APPENDIX. Habitat variables measured on 0.02-ha plots. Cover values were measuredalong two 15-m line intercepts that crossedat plot center.

Variable Explanation

Elevation Elevation above sea level measuredwith an altimeter or estimated from a topographic map. Slope Slope angle measured in degreeswith a clinometer. Aspect General slope orientation measured to nearest 10 degreeswith hand-held compass. Distance to snow Meters to nearest snow measuredwith a tape or estimated with range- finder. Distance to water Meters to nearest water measuredwith a tape or estimated with range- finder. Distance to shrub Meters to nearest shrub > 30 cm tall measuredwith a tape or estimated with range-finder. Distance to willow shrub Meters to nearest willow (S&x) shrub > 30 cm tall measured with a tape or estimated with range-finder. Maximum shrub height Height (cm) of tallest shrub in plot. Minimum shrub height Height (cm) of shortest shrub in plot. Percent soil cover Average percentageof line intercepts covered by mineral soil. Percent gravel cover Average percentageof line intercepts covered by stones < 10 cm in diameter. Percent rock cover Average percentageof line intercepts covered by stones lo-30 cm in diameter. Percent boulder cover Average percentageof line intercepts covered by bedrock and stones > 30 cm in diameter. Percent snow cover Average percentageof line intercepts covered by snow. Percent shrub cover Average percentageof line intercepts covered by shrubs > 30 cm tall. Percent subshrubcover Average percentageof line intercepts covered by ericaceousshrubs 530 cm tall. Percent dwarf willow cover Average percentageof line intercepts covered by dwarf willow (S&x anglorum and S. nivalis). Percent turf cover Average percentageof line intercepts covered by graminoids. Percent forb cover Average percentageof line intercepts covered by perennial forbs. Percent herb cover Average percentageof line intercepts covered by sum of turf and forb cover. Percent moss cover Average percentageof line intercepts covered by moss and moss-like plants.