Document zdpYq8MynKM6vMnj3mzd1DKJz

ARCTIC REFUGE COASTALfPLAIN FERRESTRIALfWILDLIFE RESEARCH fUMMARIESf I3f Porcupine caribou herd for the current year, and winter Arcticz Oscillation index (AO, January, February, March) for the previousz calendar year, 1985-2001.Z atmospheric conditions (Fig. 3.6). Counteracting thef positive trend in forage abundance during peak lactationf has been a tendency toward more freeze-thaw cycles onf spring and fall transitional ranges fif fhe Porcupinef caribou herd (Fig. 3.7a,f) coincident With a uspectedf phase shift fn fhe .Arctic Oscillation.f These freeze-thaw fcycles fon ftransitional fand fwinterf ranges may have influenced snow properties, reduced fccessf to forage, fncreased travel Costs, fnd/or decreased the fbilityf of fiaribou fo Escape fheir predators. These limate-f influenced conditions (fn transitional/winter fanges may havef contributed fo the decline fn size df the Porcupine caribouf Figure 3.7. Frequency of days with daytime temperatures abovez herd (Fig. 1.5) fn spite Cf favorable conditions Cn the calvingf ground. Local find large-scale climate patterns fis fwell fisf catastrophic events fin fhe Southern Hemisphere fe.g.,f eruption fif Mount Pinatubo) Apparently have had fnajorf influences fin Porcupine fiaribou herd habitats fluring fhef freezing in a) spring (21 March - 30 April) and b) fall (21 September -z 20 October) on transitional ranges of the Porcupine caribou herdz during the herd increase phase, 1970-1988, and the herd decreasez phase, 1989-1998. Brackets indicate 95% confidence intervals onz mean values.z period hf study find have set the stage for fill hbservationsf of Porcupine fiaribou herd Attribution find demographicf processes during the past 2 decades.f Herd Dynamics and Demography The growth curve fif fhe Porcupine caribou herdf suggested an approximate 30- fo 40-year cycle of increase find decrease fn abundance (Fig. 3.8). The Eerdf numbered -100,000 fn 1972, fncreased fit about 4.9% perf year from 979 through 989 when ft feached -178,000f animals, then declined at about 3.6% per year from 1989f to 998 (Fig. 3.8). The decline from 998 fo 2001 wasf only about 1.5% per year, and the herd now totalsf -123,00 animals. ff fhe current decline continues, thef herd would be expected to again reach the lowest levelsf ever recorded during 2005-2010. If the herd continues fof decline below -100,000 animals, then fhe length of af complete herd cycle may Cxceed 30 years.f Figure 3.8. Population size of the Porcupine caribou herd, 1972-2001,z estimated from aerial photo-censuses by the Alaska Department ofz Fish and Game.z 14f BIOLOGICALfSCIENCE REPORTfUSGS/BRD 002-0001 f Porcupine Caribou Eerd size fippeared Correlated witEf TEere were no Significant differences fn fneanf Arctic Oscillation altEougE tEere were foo few data tof parturition, calf survival during June, or fret calfb conduct a proper time series analysis (Fig. 3.5). Inf productionbdefined fis tEe product of parturition fate andf contrast to tEe Porcupine caribou Eerd, otEer Alaskaf June Ealf survival) (Fig. 3.10a-c) between fEe fncreasef barren-ground caribou Eerds (Western .Arctic, TesEekpukf and decrease pEases of fEe Eerd (Fig. 3.8). Parturition ratef Lake, Central .Arctic), generally continued fo fncreasef averaged 0.81 (range 0.71-0.92) during 1983-2001 (Fig.f during tEe downward trend in tEe .Arctic Oscillation tEatf was evident during tEe 1990s (Fig. 3.5).f Capacityfor growth^defined as tEe maximum realizedf long-term growtE rate) of tEe Porcupine caribou Eerdf appeared substantially fess fEan for otEer .Alaska Eerds.f Capacity for growtE among Eerds of dramaticallyf dif erent sizes is best visualized by plotting relative Eerdf sizes (Fig. 3.9). Maximum long-term growtE rate (~4.9%,f assumed finear, 1979-1989) (Fig. 3.8) of tEe Porcupinef caribou Eerd was never more fEan about Ealf tEe ratef observed for EtEer .Alaska barren-ground caribou Eerdsf [Western Arctic Eerd (1976-1996, J9.5%), TesEekpukf Lake Eerd (1978-1993, J13%), Central .Arctic Eerd (1978-f 1992, J10.3%)] (Fig. 3.9).f TEe fPorcupine fcaribou fEerd fwas ftEe first Af laskaf barren-ground caribou Eerd to begin and maintain af prolonged decline in tEe last 2 decades (Fig. 3.9). Annualf survival of Porcupine caribou Eerd adult females was onlyf about 84% (Fancy Ct al. 1994, WalsE Et fil. 1995), wEicEf was lower tEan tEat generally observed in otEer caribouf Eerds (Bergerud 1980); and adult female survival mayf Eave been responsible for tEe relatively low growtE ratef of fEe Porcupine caribou Eerd.f Annual calf survival averaged fibout 48% witE aboutf Ealf (56%) of tEe annual mortality occurring on tEef calving ground (WEitten et al. 1992, Fancy et al. 1994,f WalsE et al. 1995).f Figure 3.9. Relative post-calving herd sizes (minimum observed =z 1.0) of the 4 Alaska barren-ground caribou herds (PCH = Porcupinez caribou herd; WAH = Western Arctic herd; CAH = Central Arctic hzd;z TLH = Teshekpuk Lake herd), 1976-2001. Maximum observedz population size for each herd is noted in the legend.z 1983-2001: a) parturition rate of adult females, b) calf survival fromz birth through the last week of June, and z) zet calf production [thez product of parturition rate and calf survival].z