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Quantifying long-term, low reproductive metrics indicative of an ungulate population’s low nutritional status can help spur action to manage for moderate densities in contrast to unsustainable, high densities. We previously ranked the moose (Alces alces gigas) population described here as having the lowest nutritional status among 14 moose populations in Alaska, USA, primarily using reproductive indices (1996– 2005) frommoose with ages estimated by counting cementum annuli. Here, we detailed lifetime reproductive metrics from a subset of known-age female moose initially radio-collared at 9–10 months of age (7 cohorts; 1996–2002); we renewed radio-collars as necessary. We radio-tracked and circled these moose via aircraft at 24- or 48-hour intervals to detect the presence of newborns during the 1998–2018 calving seasons, with meaningful annual sample sizes during 2000–2014. The number of snow-free days in the year preceding parturition had a subtle positive effect on parturition probability, but we found no evidence for effects of the preceding February and March immobilization, cohort affiliation, or the preceding winter’s snow cover on the probability of a female being parturient. The probability of twinning declined as the calving season progressed. Compared with moose production in populations with improved nutrition, our study population experienced low production primarily as a result of delayed maturation, occasional pauses in reproduction, and low twinning rates. Reproductive senescence occurred at normal advanced ages despite nutritional stress. We recorded a 28% parturition rate among 144 females 3 years of age (min. age of reproduction). Parturition rates were stable from 4 to 13 years of age (x̄ = 77%), declined at 14 years of age, and peaked at 15 years of age. Females first twinned at 5 years of age (5%), and the twinning rate increased with age, peaking at 13 years of age (25%). Overall, 136 radio-collared females with complete reproductive histories produced a mean of 5.3 calves/lifetime while being monitored a mean of 7.1 years at ages ≥3 years, although variability in individual production was high. Delaying or pausing reproduction increased the parturition rate at 4 and 5 years of age. However, females that delayed first reproduction produced fewer calves/lifetime on average compared with moose that first produced at 3 years of age. Virtually all moose regularly gave birth with occasional 1-year pauses that acted to enhance production the subsequent year; the incidence of 2 consecutive nonparturient years was 2.8% (24/844). Moose experienced relatively stable, low nutritional status during 2000–2014 based upon low population-wide twinning rates from annual aerial transect surveys (no telemetry) flown a few days after the median annual calving dates. Detailed understanding of low reproductive metrics encouraged empowered stakeholders to allow liberal harvests of female moose (2.0–4.4% of prehunt moose population numbers) and encouraged land managers to allow wildfires to burn 25% of the study area to improve moose carrying capacity. We helped manage a 31% decline in moose numbers during 2004–2012 by implementing liberal harvests of female moose. Elevated population-wide twinning rates in 2012, 2015, 2017, and 2018, similar to elevated levels prior to 1997, were likely a positive response to lower moose densities and improved browse after wildfires.

Where elevated harvest of ungulates is a priority, managers benefit by understanding how various sources of mortality affect the age and sex structure and trend of ungulate populations. Prior studies reported a long period (1997–2014) of moose (Alces alces gigas) nutritional stress from overabundance in our study area, an intentional 31% reduction in moose numbers using liberal harvests of females (2004–2012), and low bear (Ursus spp.) predation and high moose harvest densities relative to other largely roadless systems with moose, bears, and wolves (Canis lupus). In this paper, we detailed management findings after describing causes and rates of mortality from 226 female and 164 male moose radio-collared at 9 months of age (1997–2008) and followed through life (1997–2019) and throughout the population reduction. We listened for mortality signals on radio-collars 1–2 times/month when snow cover was complete and 2–4 times/month when snow cover was incomplete. Upon hearing a mortality signal, we investigated mortality sites usually within 24 hours via helicopter. Excluding hunter-caused mortality, we estimated 28% annual mortality for male yearlings versus 17% for female yearlings, then low annual mortality rates (0–4%) to 84 months of age for males and 96 months of age for females, and gradually increasing annual mortality rates thereafter. Most (83%) male moose ≥24 months of age died from hunters; minor causes included wolves (8%), malnutrition or disease (5%), grizzly bears (U. arctos; 2%), and accidents (2%). Most female moose ≥24 months of age died from wolves (37%) or hunters (33%); minor causes included malnutrition or disease (15%), grizzly bears (10%), and accidents (5%). The proportion of radio-collared females killed by hunters varied depending on numbers of permits issued to hunters; the kill rate of females ≥24 months of age was 58% during the initial 4 years of the 9-year reduction, moderated at 29% during the final 5 years of the reduction, and was only 7% for all other study years. We attributed 32% of hunter kills to illegal harvest and unrecovered hunter kills. Hunters played a key role in the intentional population reduction by harvesting prime-age and near prime-age male and female moose that rarely died from other sources of mortality compared with calf, yearling, and older moose. Restricting general season hunters to primarily harvesting prime-age and older male moose with antler spreads ≥127 cm did not appreciably reduce harvest of adult males. Male moose 2.0–5.3 years of age rarely died from non-hunter causes and were largely harvested at older, prime ages (5.3–8.3 yr of age). Yearling moose of both sexes died primarily from wolves, with wolves selecting more for males. By using liberal harvests of female moose to reduce the population, managers improved moose nutrition and reproduction, met mandates for elevated harvests, and may have avoided a reoccurrence of a previous precipitous decline in moose numbers that was initiated by overabundance and extreme snow depths.

Given recent actions to increase sustained yield of moose (Alces alces) in Alaska, USA, we examined factors affecting yield and moose demographics and discussed related management. Prior studies concluded that yield and density of moose remain low in much of Interior Alaska and Yukon, Canada, despite high moose reproductive rates, because of predation from lightly harvested grizzly (Ursus arctos) and black bear (U. americanus) and wolf (Canis lupus) populations. Our study area, Game Management Unit (GMU) 20A, was also in Interior Alaska, but we describe elevated yield and density of moose. Prior to our study, a wolf control program (1976–1982) helped reverse a decline in the moose population. Subsequent to 1975, moose numbers continued a 28-year, 7-fold increase through the initial 8 years of our study (λB1 = 1.05 during 1996–2004, peak density = 1,299 moose/1,000 km2). During these initial 8 hunting seasons, reported harvest was composed primarily of males (x̄ = 88%). Total harvest averaged 5% of the prehunt population and 57 moose/1,000 km2, the highest sustained harvest-density recorded in Interior Alaska for similar-sized areas. In contrast, sustained total harvests of <10 moose/1,000 km2 existed among low-density, predator-limited moose populations in Interior Alaska (≤417 moose/1,000 km2). During the final 3 years of our study (2004–2006), moose numbers declined (λB2 = 0.96) as intended using liberal harvests of female and male moose (x̄ = 47%) that averaged 7% of the prehunt population and 97 moose/1,000 km2. We intentionally reduced high densities in the central half of GMU 20A (up to 1,741 moose/1,000 km2 in Nov) because moose were reproducing at the lowest rate measured among wild, noninsular North American populations. Calf survival was uniquely high in GMU 20A compared with 7 similar radiocollaring studies in Alaska and Yukon. Low predation was the proximate factor that allowed moose in GMU 20A to increase in density and sustain elevated yields. Bears killed only 9% of the modeled postcalving moose population annually in GMU 20A during 1996–2004, in contrast to 18–27% in 3 studies of low-density moose populations. Thus, outside GMU 20A, higher bear predation rates can create challenges for those desiring rapid increases in sustained yield of moose. Wolves killed 8–15% of the 4 postcalving moose populations annually (10% in GMU 20A), hunters killed 2–6%, and other factors killed 1–6%. Annually during the increase phase in GMU 20A, calf moose constituted 75% of the predator-killed moose and predators killed 4 times more moose than hunters killed. Wolf predation on calves remained largely additive at the high moose densities studied in GMU 20A. Sustainable harvest-densities of moose can be increased several-fold in most areas of Interior Alaska where moose density and moose:predator ratios are lower than in GMU 20A and nutritional status is higher. Steps include 1) reducing predation sufficient to allow the moose population to grow, and 2) initiating harvest of female moose to halt population growth and maximize harvest after density-dependent moose nutritional indices reach or approach the thresholds we previously published.

We focused on describing low nutritional status in an increasing moose (Alces alces gigas) population with reduced predation in Game Management Unit (GMU) 20A near Fairbanks, Alaska, USA. A skeptical public disallowed liberal antlerless harvests of this moose population until we provided convincing data on low nutritional status. We ranked nutritional status in 15 Alaska moose populations (in boreal forests and coastal tundra) based on multiyear twinning rates. Data on age-of-first-reproduction and parturition rates provided a ranking consistent with twinning rates in the 6 areas where comparative data were available. Also, short-yearling mass provided a ranking consistent with twinning rates in 5 of the 6 areas where data were available. Data from 5 areas implied an inverse relationship between twinning rate and browse removal rate. Only in GMU 20A did nutritional indices reach low levels where justification for halting population growth was apparent, which supports prior findings that nutrition is a minor factor limiting most Alaska moose populations compared to predation. With predator reductions, the GMU 20A moose population increased from 1976 until liberal antlerless harvests in 2004. During 1997–2005, GMU 20A moose exhibited the lowest nutritional status reported to date for wild, noninsular, North American populations, including 1) delayed reproduction until moose reached 36 months of age and the lowest parturition rate among 36-month-old moose (29%, n = 147); 2) the lowest average multiyear twinning rates from late-May aerial surveys (x̄ = 7%, SE = 0.9%, n = 9 yr, range = 3–10%) and delayed twinning until moose reached 60 months of age; 3) the lowest average mass of female short-yearlings in Alaska (x̄ = 155 ± 1.6 [SE] kg in the Tanana Flats subpopulation, up to 58 kg below average masses found elsewhere); and 4) high removal (42%) of current annual browse biomass compared to 9–26% elsewhere in boreal forests. When average multiyear twinning rates in GMU 20A (sampled during 1960–2005) declined to <10% in the mid- to late 1990s, we began encouraging liberal antlerless harvests, but only conservative annual harvests of 61–76 antlerless moose were achieved during 1996–2001. Using data in the context of our broader ranking system, we convinced skeptical citizen advisory committees to allow liberal antlerless harvests of 600–690 moose in 2004 and 2005, with the objective of halting population growth of the 16,000–17,000 moose; total harvests were 7–8% of total prehunt numbers. The resulting liberal antlerless harvests served to protect the moose population's health and habitat and to fulfill a mandate for elevated yield. Liberal antlerless harvests appear justified to halt population growth when multiyear twinning rates average ≤10% and ≥1 of the following signals substantiate low nutritional status: <50% of 36-month-old moose are parturient, average multiyear short-yearling mass is <175 kg, or >35% of annual browse biomass is removed by moose.

During June 1993 and 1994, 11 radiocollared and 7 unmarked grizzly bears (Ursus arctos) were monitored visually (observation) from fixed-wing aircraft to document predation on calves of the Porcupine Caribou (Rangifer tarandus) Herd (PCH) in northeastern Alaska. Twenty-six (72%) grizzly bear observations were completed (≥60 min) successfully (median duration = 180 min; ±95% CI = 136-181 min; range = 67-189 min) and 10 were discontinued (duration ≤24 min) due to disturbance to the bear, or unfavorable weather conditions. Of the 26 successfully completed observations, 15 (58%) included predatory activity (encounter) directed at caribou calves and 8 (31%) included kills. Of 32 encounters, 9 resulted in kills, for a success rate of 28%. The median duration of encounters was 1 minute (±95% CI = 1-2 min; range = 1-6 min; n = 32;), and the median time spent at a kill was 14 minutes (±95% CI = 9-23 min; range = 6-56 min; n = 9). Sows with young (n = 4) killed more frequently (75%; P = 0.0178) than barren sows, boars, and consorting pairs combined (17%; n = 18). Estimated kill rate was highest for sows with young (6.3 kills/bear/day; n = 4), followed by barren sows (4.6 kills/bear/day; n = 5), boars (1.9 kills/bear/day; n = 5), and, finally, consorting pairs (1.0 kills/bear/day; n = 8). Estimated kill rate obtained via conventional radiotracking point surveys (4.8 kills/bear/day) was higher than that obtained via concurrent bear observations (3.1 kills/bear/day). Our research provides baseline estimates of predation rates by grizzly bears on caribou calves that will enhance the capability of wildlife professionals in managing populations of both predators and their prey.

Researchers have debated the effect of the Trans-Alaska Pipeline (TAP) and associated developments to caribou (Rangifer tarandus) of the central Arctic herd (CAH) since the 1970s. Several studies have demonstrated that cows and calves of the CAH avoided the TAP corridor because of disturbance associated with the pipeline, whereas others have indicated that female caribou of the CAH avoided riparian habitats closely associated with the pipeline. This avoidance was explained as a predator-avoidance strategy. We investigated the relation between female caribou and grizzly bear (Ursus arctos) use of river corridors on the yet undisturbed calving grounds of the Porcupine caribou herd (PCH) in northeastern Alaska. On the coastal plain, caribou were closer to river corridors than expected (P = 0.038), but bear use of river corridors did not differ from expected (P = 0.740). In the foothills, caribou use of river corridors did not differ from expected (P = 0.520), but bears were farther from rivers than expected (P = 0.001). Our results did not suggest an avoidance of river corridors by calving caribou or a propensity for bears to be associated with riparian habitats, presumably for stalking or ambush cover. We propose that PCH caribou reduce the risks of predation to neonates by migrating to a common calving grounds, where predator swamping is the operational antipredator strategy. Consequently, we hypothesize that nutritional demands, not predator avoidance strategies, ultimately regulate habitat use patterns (e.g., use of river corridors) of calving PCH caribou.

We used a distance-based test of independence to measure the association between concurrent distributions of radio-collared grizzly bears (Ursus arctos) and calving caribou (Rangifer tarandus) of the Porcupine caribou herd (PCH) on the Arctic National Wildlife Refuge (ANWR), Alaska. The analysis utilized 552 grizzly bear and 585 caribou radio relocations recorded during 5 consecutive time intervals between 29 May and 22 June, 1988-90. Correlation coefficients of bear and caribou distributions tended to be positive in 1988 and negative in 1990. Those trends corresponded with annual variations in snowmelt in the Alaska portion of the PCH calving grounds and mortality for calves of radio-collared PCH cows. Concurrent distributions of bears and caribou were positively correlated (P < 0.05) during time intervals 29 May-2 June and 8-12 June 1989. We hypothesize that positive correlations were the result of extensive overlap and a high degree of interspersion between bear and caribou distributions. The majority (13/15) of concurrent distributions of bears and calving caribou were not significantly correlated. We hypothesize this occurred because the ANWR bear population did not respond to the availability of calving caribou in a homogeneous manner. The distance-based test of independence appeared to be an acceptable technique for quantifying associations between discrete, but interacting, populations of wildlife.

Twenty-two Golden Eagle (Aquila chrysaetos) nesting territories and 31 occupied eagle nests were documented on the north slope of the Brooks Range in northeastern Alaska, 1988-1990, in an area previously thought to be marginal breeding habitat for eagles. The mean number of young/successful nest was 1.25 in 1988, 1.27 in 1989, and 1.13 in 1990; means did not differ significantly among years. Eighty percent (20/25) of the nestlings for which age was estimated were assumed to have successfully fledged. Nesting success was 79% (11/14) in 1989, the only year nesting success could be determined. Laying dates ranged from 23 March (1990) to 11 May (1989) with mean estimated laying dates differing significantly among years. Annual variation in nesting phenology coincided with annual differences in snow accumulations during spring. These results indicate that Golden Eagles consistently and successfully breed at the northern extent of their range in Alaska, although, productivity may be lower than that for eagles at more southern latitudes. /// Se documentaron 22 territorios de anidaje y 31 nidos ocupados de Aquila chrysaetos en la pendiente norte de la extensión Brooks en el noreste de Alaska entre 1988 y 1990, en un área considerada previamente como habitat reproductivo marginal para águilas. El número promedio de juveniles/nido exitoso fue de 1.25 en 1988, de 1.27 en 1989 y de 1.13 en 1990; los promedios fueron similares entre años (P = 0.74). Ochenta por ciento (20/25) de los anidantes para los cuales se estimó la edad se asume que fueron exitosos en dejar el nido. El éxito en anidar fue de 79% (11/14) en 1989, el único año en que se pudo determinar el éxito en anidar. Las fechas de anidaje fluctuaron entre el 23 de marzo (1990) y el 11 de mayo (1989) con el promedio estimado de fechas de ovoposición difiriendo entre años (P = 0.0047). La variación anual en la fenología de anidaje coincidió con con diferencias anuales en acumulaciones de nieve durante la primavera. Estos resultados indican que parejas de Aquila chrysaetos anidan consistentemente y exitosamente en el límite norte de su extensión en Alaska, aunque la productividad puede ser menor que la de águilas en latitudes más al sur.