Document x58qyRrpGYgOboragmeYZeDxm

ARCTIC REFUGE COASTALfPLAIN TERRESTRIALfWILDLIFE RESEARCH fUMMARIESf 23f Figure 3.20. Azrage percent of area in 4 exclusive snowcoverz classes for the aggregate extent of calving, annual calving grounds,z and concentrated calving areas of the Porcupine caribou herd, 1985-z 2001. Statistically significant selection or avoidance (P < 0.05, overallz xperiment) in comparison with the category to the left is indicated byz "+" or "-" above the bars. For example, female caribou on the annualz calving ground avoided areas of 0-25% snowcover and selected areasz of 26-50% and 51-75% snowcover when compared with availability inz the aggregate extent of calving. No significant selection of anyz snowcover class was detected for the concentrated calving area whenz compared with availability in the annual calving ground.z median) classes of a) daily rate of increase in the Normalizedz Difference Vegetation Index (NDVI_rate) b) NDVI at calvingz (NDVI_calving), and z) NDVI on 21 June (NDVI_621) for the aggregatez extent of calving, annual calving grounds, and concentrated calvingz areas of the Porcupine caribou herd, Alaska, 1985-2001. Statisticallyz significant selection or avoidance (P < 0.05, overall experiment) inz comparison with the category to the left is indicated by "+" or "-" abovez the bars. For example, female caribou on the annual calving groundz avoided low NDVI_rate and selected high NDVI_rate in comparisonz with availability in the aggregate zctent of calving. No significantz selection of NDVI_rate for the concentrated calving area whenz compared with the annual calving ground was detected.z (I.68x, Pfc 0.001), avoided alpine vegetation (0.34x, PhQf 0.001), and were non-responsive (Pb> 0.18) to thef remaining Vegetation types fFig. 3.21).f Although selection of vegetation types was scale-f independent, there was scale dependency in the selectionf of forage Quantity (NDVI_calving, NDVI_621) findf quality (NDVI_rate). Parturient Porcupine caribou herd females selected annual calving grounds with a highf proportion bf easily digestible forage (NDVI_rate), fhenf selected Concentrated Calving areas With relatively highf plant biomass at calving (NDVI_calving) and on 21 funef (NDVI_621).f The basis of habitat selection shifted from foragef quality to forage quantity between fhe fifth (ACG/EC) and sixth (CCA/ACG) orders. The Work of White et al.f (1975) and White and Trudell (1980f) at fhe fevels bf microhabitats (-seventh order, selection for biomass) andf plant species within microhabitats (-eighth order,f selection for digestibility) suggests that the basis of selection continues to be dynamic across successivelyf smaller scales.f Forage quality appears to be the basis of selection atf both relatively farge ffifth order) and relatively fmallf (eighth order) scales. Forage quantity appears to be thef basis of selection at intermediate scales of analysis withinf this range. Specification of the scale of analysis is criticalf to developing an understanding of the basis ff foragef selection by ungulates, and Porcupine herd baribouf demonstrated a variable functional response fo foragef (NDVI estimates) within the extent of calving.f 24f BIOLOGICALfSCIENCE REPORTfUSGS/BRD 2002-0001f aggregate extent of calving, annual calving grounds, and concentratedz calving areas of the Porcupine caribou herd, 1985-2001. Vzgetationz types: Wsedge = wet sedge; Msedge = moist sedge; HerbTT =z herbaceous tussock tundra; ShrubTT = shrub tussock tundra, Alpine,z and Riparian. Statistically significant selection or avoidance (P < 0.05,z overall experiment) in comparison with the category to the left isz indicated by "+" or "-" above the bars. For zxample, the female caribouz on the annual calving ground avoided the Alpine vegetation type andz selected the HerbTT vegetation type when compared with availabilityz in the aggregate extent of calving, and on the concentrated calvingz area the caribou showed similar selection when compared withz availability in the annual calving ground.z Figure 3.22. Estimated total intake of dietary nitrogen (g) from thez calving ground (25 May - 14 June) for 4 North American caribou herds.z Forage composition of diet and nutritional composition of forages werez stimated from locally collected samples. Intake rates were estimatedz from White et al. (1975).z ground s flid fhe Porcupine Caribou Eerd (Fig. 8.22). Ft fsf likely that the proportion of the annual nitrogen budgetf obtained from a calving ground is positively correlatedf with the relative value of fhe calving ground to thef nutrition of a herd Within its annual range.f There Were no Clear differences fn patterns of selection of any types of habitats between the increasef and decrease phases of fhe herd. This observation fsf tempered by the fact that habitat selection was assessed for only fhe fast 8 (ears (1985-1989) of the fncreasef phase, but has been fissessed for all 12 years of fhef current decline (1990-2001).f The shifting location of annual calving grounds withinf the extent of calving was apparently a functional responsef to annually variable landscape patterns in the quantity of easily digestible forage (NDVI_rate). The location of concentrated calving areas within annual calving groundsf was fin Apparent functional response fo forage biomassf (NDVI_calving, NDVI_621).f This functional response fo habitats allowedf Porcupine fcaribou fherd females fto fattain fsubstantialf intakes of nitrogen (Fig. 3.22) based on estimated dietf composition (Figs. 3.16a, 3.17a), estimated nitrogenf content Of consumed forages, and consumption fatesf presented by White et al (1975), White and Trudellf (1980a, b), and Trudell find White (1981). Thus, fhef Porcupine caribou herd calving ground was clearlyf important to the annual nitrogen budget of lactating females and was fikely Important fo the annual fnergyf budget.f The adjacent Central .Arctic herd Obtained only aboutf one-quarter s much dietary nitrogen from fts calvingf Effects pf Insect Harassment pn Habitat Usey Mosquitoes (Cuculidae) and flies of the familyf Oestridaebre known fo harass caribou, althoughf harassment by Oestrid flies may occur primarily afterf Porcupine herd caribou leave the calving ground.f Lactating females fhat are disturbed by insects mayf experience a negative energy balance due to increasedf movement Oates when frying fo escape harassment byf insects (White et al. 1975, Russell et al. 1993). 1 henf harassment causes lactating emales to substantiallyf reduce foraging time, calf growth may be reduced (Hellef and Tarvainen 1984, Fancy and White 1987, Russell et al.f 1993).f During warm and calm days fmean femperature B13Cf and mean wind speed Q6m/sec) when conditions weref such that caribou were likely harassed by insects (Nixonf 1990), Porcupine herd caribou preferred dry prostratef shrub vegetation types on ridge tops in the foothills andf mountains of the Brooks Range, elevated sites on thef coastal plain, and areas adjacent fo fhe Beaufort feaf coast, apparently to gain relief from mosquitoes (Walsh etf al. 1992).f Porcupine herd caribou did not display s strong af tendency to move to the coastline during potential insectf harassment fis has been Seen for fhe adjacent Centralf Arctic herd. Observations of movements of unmarkedf animals during Survey flights, however, Indicate fhatf