Patrick Valkenburg

Increases in moose, caribou, and wolves following wolf control in Alaska

Short-term studies in our study area and southeast Yukon have previously documented substantial increases in moose (Alces alces) and caribou (Rangifer tarandus) following wolf (Canis lupus) control. To provide long-term information, we present a 20-year history beginning autumn 1975 when precontrol wolf density was 14 wolves/1,000 km 2 . Private harvest and agency control kept the late-winter wolf density 55-80% (x = 69%) below the precontrol density during each of the next 7 years. Wolf numbers subsequently recovered in ≤ 4 years in most of the study area and increased further to between 15 and 16 wolves/1,000 km 2 during a period of deep snowfall winters. The post-hunt moose population increased rapidly from 183 to 481 moose/1,000 km 2 during the 7 years of wolf control (finite rate of increase, λ r = 1.15) and increased more slowly during the subsequent 12 years (λ r = 1.05) reaching a density of 1,020 moose/1,000 km 2 by 1994. The Delta caribou herd increased rapidly during wolf control (λ r = 1.16), more slowly during the subsequent 7 years (λ r = 1.06), then declined for 4 years (X r = 0.78) from a peak density of 890 caribou/ 1,000 km 2 . This decline coincided with declines in 2 adjacent, low-density herds (240-370 caribou/1,000 km 2 ). These caribou declines probably resulted from the synergistic effects of adverse weather and associated increases in wolf numbers. Reduced caribou natality and calf weights were associated with adverse weather. Wolf control was reauthorized to halt the Delta herds decline in 1993. Similar subarctic, noncoastal systems without effective wolf control have supported densities of 45-417 moose/l,000 km 2 (x = 148, n = 20), 100-500 caribou/1,000 km 2 , and 2-18 wolves/1,000 km 2 (x = 9, n = 15) in recent decades. In our 20-year history, 7 initial winters of wolf control and 14 initial years of favorable weather apparently resulted in 19 years of growth in moose, 14 years of growth in caribou populations, and a high average autumn wolf density after control ended (12 wolves/1,000 km 2 ). Benefits to humans included enjoyment of more wolves, moose, and caribou and harvests of several thousand additional moose and caribou than predicted if wolf control had not occurred. We conclude from historical data that controlling wolf populations, in combination with favorable weather, can enhance long-term abundance of wolves and their primary prey, and benefits to humans can be substantial.

Density estimation in a wolverine population using spatial capture–recapture models

ABSTRACT Classical closed-population capture—recapture models do not accommodate the spatial information inherent in encounter history data obtained from camera-trapping studies. As a result, individual heterogeneity in encounter probability is induced, and it is not possible to estimate density objectively because trap arrays do not have a well-defined sample area. We applied newly-developed, capture—recapture models that accommodate the spatial attribute inherent in capture—recapture data to a population of wolverines (Gulo gulo) in Southeast Alaska in 2008. We used camera-trapping data collected from 37 cameras in a 2,140-km2 area of forested and open habitats largely enclosed by ocean and glacial icefields. We detected 21 unique individuals 115 times. Wolverines exhibited a strong positive trap response, with an increased tendency to revisit previously visited traps. Under the trap-response model, we estimated wolverine density at 9.7 individuals/1,000 km2 (95% Bayesian CI: 5.9–15.0). Our model provides a formal statistical framework for estimating density from wolverine camera-trapping studies that accounts for a behavioral response due to baited traps. Further, our model-based estimator does not have strict requirements about the spatial configuration of traps or length of trapping sessions, providing considerable operational flexibility in the development of field studies.

Effects of Predator Treatments, Individual Traits, and Environment on Moose Survival in Alaska

ABSTRACT We studied moose (Alces alces) survival, physical condition, and abundance in a 3-predator system in western Interior Alaska, USA, during 2001–2007. Our objective was to quantify the effects of predator treatments on moose population dynamics by investigating changes in survival while evaluating the contribution of potentially confounding covariates. In May 2003 and 2004, we reduced black bear (Ursus americanus) and brown bear (U. arctos) numbers by translocating bears ≥240 km from the study area. Aircraft-assisted take reduced wolf (Canis lupus) numbers markedly in the study area during 2004–2007. We estimated black bears were reduced by approximately 96% by June 2004 and recovered to within 27% of untreated numbers by May 2007. Brown bears were reduced approximately 50% by June 2004. Late-winter wolf numbers were reduced by 75% by 2005 and likely remained at these levels through 2007. In addition to predator treatments, moose hunting closures during 2004–2007 reduced harvests of male moose by 60% in the study area. Predator treatments resulted in increased calf survival rates during summer (primarily from reduced black bear predation) and autumn (primarily from reduced wolf predation). Predator treatments had little influence on survival of moose calves during winter; instead, calf survival was influenced by snow depth and possibly temperature. Increased survival of moose calves during summer and autumn combined with relatively constant winter survival in most years led to a corresponding increase in annual survival of calves following predator treatments. Nonpredation mortalities of calves increased following predator treatments; however, this increase provided little compensation to the decrease in predation mortalities resulting from treatments. Thus, predator-induced calf mortality was primarily additive. Summer survival of moose calves was positively related to calf mass (&bgr; > 0.07, SE = 0.073) during treated years and lower (&bgr; = -0.82, SE = 0.247) for twins than singletons during all years. Following predator treatments, survival of yearling moose increased 8.7% for females and 21.4% for males during summer and 2.2% for females and 15.6% for males during autumn. Annual survival of adult (≥2 yr old) female moose also increased in treated years and was negatively (&bgr; = -0.21, SE = 0.078) related to age. Moose density increased 45%, from 0.38 moose/ km2 in 2001 to 0.55 moose/km2 in 2007, which resulted from annual increases in overall survival of moose, not increases in reproductive rates. Indices of nutritional status remained constant throughout our study despite increased moose density. This information can be used by wildlife managers and policymakers to better understand the outcomes of predator treatments in Alaska and similar environments.

Modeling Wolverine Occurrence Using Aerial Surveys of Tracks in Snow

Abstract We designed a novel approach to determining extent of distribution and area of occupancy for wolverines (Gulo gulo) by using aerial surveys of tracks in snow and hierarchical spatial modeling. In 2005 we used a small, fixed-wing aircraft with pilot and one observer to search 575 of 588 survey units for wolverine tracks in approximately 60,000 km2 of boreal forest in northwestern Ontario, Canada. We used sinuous flight paths to scan open areas in the forest in the 100-km2 survey units. We detected tracks in 138 (24%) of the 575 sampled units. There was strong evidence of occurrence (probability of occurrence >0.80) in 30% of the 588 survey units, weak evidence of occurrence (0.50–0.80) in 12%, weak evidence of absence (0.20–0.50) in 15%, and strong evidence of absence (<0.20) in 43%. Wolverine range comprised 59% of the study area and area of occupancy was 33,400 km2. With information on probability of occurrence and core areas of occupation for wolverines in our study area, resource managers and others can examine factors that influence wolverine distribution patterns and use this information to formulate best management practices that will maintain wolverines on the landscape in the face of increasing resource development. Comparing future survey results with those of our 2005 survey will provide an objective way to assess the efficacy of management practices.

Integrating motion-detection cameras and hair snags for wolverine identification†

ABSTRACT We developed an integrated system for photographing a wolverines (Gulo gulo) ventral pattern while concurrently collecting hair for microsatellite DNA genotyping. Our objectives were to 1) test the system on a wild population of wolverines using an array of camera and hair-snag (C&H) stations in forested habitat where wolverines were known to occur, 2) validate our ability to determine identity (ID) and sex from photographs by comparing photographic data with that from DNA, and 3) encourage researchers and managers to test the system in different wolverine populations and habitats and improve the system design. Of the 18 individuals (10 M, 8 F) for which we obtained genotypes over the 2 years of our study, there was a 100% match between photographs and DNA for both ID and sex. The integrated system made it possible to reduce cost of DNA analysis by >74%. Integrating motion-detection cameras and hair snags provides a costeffective technique for wildlife managers to monitor wolverine populations in remote habitats and obtain information on important population parameters such as density, survival, productivity, and effective population size.

Calf mortality and population growth in the Delta caribou herd after wolf control

Abstract A program to control wolves (Canis lupus) in interior Alaska in 1993 and 1994 did not result in expected increases in calf survival in the Delta caribou (Rangifer tarandus) herd (DCH). Therefore, the Alaska Department of Fish and Game conducted a study to determine causes of calf mortality during 1995–1997 and monitored recruitment, mortality, and population size annually in the DCH for 6 years after wolf control ended. Despite removal of 60–62% of the autumn 1993 wolf population, wolves still killed 25% of 166 radiocollared calves between birth in mid- to late May and 30 September during 1995–1997. Although autumn calf:cow ratios in the DCH increased after wolf control, similar increases in calf:cow ratios occurred in the adjacent Denali Herd, where wolves were not controlled. Calf:cow ratios following wolf control in 1993 and 1994 were lower than ratios obtained in the same area after wolf control from 1976–1982. We identified 4 factors that contributed to continued low calf:cow ratios in the DCH following the 1993–1994 wolf control program: 1) other predators in combination (i.e., golden eagles [Aquila chrysaetos] and grizzly bears [Ursus arctos]) were the most significant mortality source for caribou calves, 2) the temporal and spatial extent for wolf removal was inadequate to effectively reduce wolf predation, 3) in 1987 the DCH shifted its main calving area, a move that may have increased predation by golden eagles and grizzly bears, and 4) natality rates and nutritional condition of caribou declined during the 5 years before wolf control coincident with a density-dependent population decline. We conclude that wolf control within the range of the DCH failed because the wolf trapping program did not remove enough wolves and was not conducted long enough to substantially reduce predation by wolves on caribou calves. In addition, wolves that lived outside the control area were responsible for about 40% of the wolf-caused mortality to collared caribou calves, and significant numbers of calves died from unknown, neonatal causes.

Population decline in the Delta caribou herd with reference to other Alaskan herds

After growing continuously for nearly 15 years, the Delta caribou herd began to decline in 1989. Most other Interior Alaskan herds also began declining. In the Delta herd, and in other herds, the declines were caused primarily by high summer mortality of calves and increased natural mortality of adult females. Other minor causes included increased winter mortality of calves, and reduced parturition rates of 3-year-old and older females. The decline in the Delta herd also coincided with increased wolf (Canis lupus) numbers, winters with deeper than normal snow, and warm summers. Mean body weight of annual samples of 10-month-old female calves was consistently low during the decline. Except in some of the smallest Interior Alaskan herds, we conclude that evidence for population regulation in Alaskan caribou is weak, and that herds are likely to fluctuate within a wide range of densities due to complex interactions of predation and weather. Unless wolf numbers are influenced by man, the size of a caribou herd in a given year is likely to be largely a function of its size during the previous population low and the number of years of favorable weather in the interim.

Stochastic and Compensatory Effects Limit Persistence of Variation in Body Mass of Young Caribou

Abstract Nutritional restriction during growth can have short- and long-term effects on fitness; however, animals inhabiting uncertain environments may exhibit adaptations to cope with variation in food availability. We examined changes in body mass in free-ranging female caribou (Rangifer tarandus) by measuring mass at birth and at 4, 11, and 16 months of age to evaluate the relative importance of seasonal nutrition to growth, the persistence of cohort-specific variation in body mass through time, and compensatory growth of individuals. Relative mean body mass of cohorts did not persist through time. Compensatory growth of smaller individuals was not observed in summer; however, small calves exhibited more positive change in body mass than did large calves. Compensation occurred during periods of nutritional restriction (winter) rather than during periods of rapid growth (summer) thus differing from the conventional view of compensatory growth.

Spatio-temporal patterns of predation among three sympatric predators in a single-prey system

Abstract The manner in which species partition space and time to minimize competition for shared, limited resources has been a major focus of theoretical and empirical ecology. Although numerous examples exist of intra-guild dietary separation among coexisting species, studies of spatio-temporal partitioning among species sharing a single food type are rare. We investigated spatio-temporal patterns of multi-species predation on individually-marked moose Alces alces calves in an Alaskan boreal forest community where moose are the only large herbivore, and constitute the primary prey of coexisting black bears Ursus americanus, brown bears U. arctos and gray wolves Canis lupus. The two most closely related predators, black bears and brown bears, overlapped temporally and spatially in their consumption of moose calves, as indicated by univariate analyses. Moreover, both bear species segregated spatially from wolves when killing moose calves. Hence, our study appears to support key predictions of predator coexistence on a shared resource: namely, that bears and wolves differentiate spatially or temporally in their use of a pulsed prey, presumably to minimize competition.

Population dynamics of caribou herds in southwestern Alaska

The five naturally occurring and one transplanted caribou (Rangifer tarandus granti) herd in southwestern Alaska composed about 20% of Alaskas caribou population in 2001. All five of the naturally occurring herds fluctuated considerably in size between the late 1800s and 2001 and for some herds the data provide an indication of long-term periodic (40-50 year) fluctuations. At the present time, the Unimak (UCH) and Southern Alaska Peninsula (SAP) are recovering from population declines, the Northern Alaska Peninsula Herd (NAP) appears to be nearing the end of a protracted decline, and the Mulchatna Herd (MCH) appears to now be declining after 20 years of rapid growth. The remaining naturally occurring herd (Kilbuck) has virtually disappeared. Nutrition had a significant effect on the size of 4-month-old and 10-month-old calves in the NAP and the Nushagak Peninsula Herd (NPCH) and probably also on population growth in at least 4 (SAP, NAP, NPCH, and MCH) of the six caribou herds in southwestern Alaska. Predation does not appear to be sufficient to keep caribou herds in southwestern Alaska from expanding, probably because rabies is endemic in red foxes (Vulpes vulpes) and is periodically transferred to wolves (Canis lupus) and other canids. However, we found evidence that pneumonia and hoof rot may result in significant mortality of caribou in southwestern Alaska, whereas there is no evidence that disease is important in the dynamics of Interior herds. Cooperative conservation programs, such as the Kilbuck Caribou Management Plan, can be successful in restraining traditional harvest and promoting growth in caribou herds. In southwestern Alaska we also found evidence that small caribou herds can be swamped and assimilated by large herds, and fidelity to traditional calving areas can be lost.