Dewaine H. Jackson

Neonatal mortality of elk driven by climate, predator phenology and predator community composition

1. Understanding the interaction among predators and between predation and climate is critical to understanding the mechanisms for compensatory mortality. We used data from 1999 radio-marked neonatal elk (Cervus elaphus) calves from 12 populations in the north-western United States to test for effects of predation on neonatal survival, and whether predation interacted with climate to render mortality compensatory. 2. Weibull survival models with a random effect for each population were fit as a function of the number of predator species in a community (3-5), seven indices of climatic variability, sex, birth date, birth weight, and all interactions between climate and predators. Cumulative incidence functions (CIF) were used to test whether the effects of individual species of predators were additive or compensatory. 3. Neonatal elk survival to 3 months declined following hotter previous summers and increased with higher May precipitation, especially in areas with wolves and/or grizzly bears. Mortality hazards were significantly lower in systems with only coyotes (Canis latrans), cougars (Puma concolor) and black bears (Ursus americanus) compared to higher mortality hazards experienced with gray wolves (Canis lupus) and grizzly bears (Ursus horribilis). 4. In systems with wolves and grizzly bears, mortality by cougars decreased, and predation by bears was the dominant cause of neonatal mortality. Only bear predation appeared additive and occurred earlier than other predators, which may render later mortality by other predators compensatory as calves age. Wolf predation was low and most likely a compensatory source of mortality for neonatal elk calves. 5. Functional redundancy and interspecific competition among predators may combine with the effects of climate on vulnerability to predation to drive compensatory mortality of neonatal elk calves. The exception was the evidence for additive bear predation. These results suggest that effects of predation by recovering wolves on neonatal elk survival, a contentious issue for management of elk populations, may be less important than the composition of the predator community. Future studies would benefit by synthesizing overwinter calf and adult-survival data sets, ideally from experimental studies, to test the roles of predation in annual compensatory and additive mortality of elk.

Survival of Columbian white-tailed deer in western Oregon

Columbian white-tailed deer (Odocoileus virginianus leucurus; CWTD) are an endangered subspecies on which little demographic information exists. We determined survival rates and causes of mortality for 64 radiocollared adults from 1996 to 1998, and for 63 radiocollared neonatal fawns during the summer and fall months of 1996-2001 in Douglas County, Oregon, USA. Annual adult survival rates averaged 0.74 over 3 years, and most mortality (73%) occurred between fall and winter. Seasonal survival was lowest (0.75) for the fall-winter 1997-1998, and was ≥0.90 during all spring-summer periods. Annual and seasonal survival rates did not differ by gender. Average annual survival was 0.77 for deer in wildland areas compared with 0.66 for deer in suburban areas, but these differences were not consistent between years and seasons. Survival over the entire 3-year study was low (0.38). Eight deer died from a combination of emaciation and disease, and almost all (92%) necropsied deer were in poor body condition. Fawn survival to 7 months was low (0.14, 95% CI = 0.02-0.26) and declined most rapidly during the first 1.5 months of life. Predation (n = 21) and abandonment (n = 6) were the most frequent known causes of death for fawns. Our results suggest that CWTD may have responded to density-dependent factors during this short-term study, although the effects of other environmental or intrinsic factors cannot be ignored. Fawn survival may be insufficient to produce enough recruits for population growth and eventual range expansion.

Evaluation of transmitter attachment techniques on growth of wild turkey poults

We compared the effects on growth of backpack-mounted and surgically implanted radiotransmitters used as marking techniques in studies of wild turkey (Meleagris gallopavo) poult survival. We applied repeated-measures analysis of variance (ANOVA) and Bayesian analysis to evaluate the null hypothesis that marking technique did not affect growth. Growth in body mass was similar among treatment groups. We did, however, find differences in wing-growth rates among treatment groups. The control group had the highest wing-growth rate, the backpack group had the lowest growth rate, and the surgical implant group was intermediate. Latex backpack harnesses also caused physical developmental problems that would have negatively biased wild poult survival estimates in the field. Surgically implanted transmitters affected wing growth less than the backpack harnesses and are therefore recommended for attaching transmitters to wild turkey poults.

An Expandable Drop-off Transmitter Harness for Young Bobcats

Our data also rasied the question on the usefulness of CB data. We feel that only as more data become available of this size range and number of years, in a variety of geographic locations, will a clear picture of the bobcats reproductive potential be defined. In conclusion, the realized productivity of Kansas bobcats is largely controlled by the average number of embryos carried to term by pregnant females and by the percentage of barren females.

Resource Partitioning between Sympatric Columbian White-Tailed and Black-Tailed Deer in Western Oregon

ABSTRACT We studied resource partitioning between sympatric populations of Columbian white-tailed (CWTD; Odocoileus virginianus leucurus) and black-tailed (BWTD) deer (O. odocoileus hemionus columbianus) in western Oregon to understand potential mechanisms of coexistence. We used horseback transects to describe spatial distributions, population overlap, and habitat use for both species, and we studied diets with microhistological analysis of fecal samples. Distribution patterns indicated that white-tailed and black-tailed deer maintained spatial separation during most seasons with spatial overlap ranging from 5%–40% seasonally. Coefficients of species association were negative, suggesting a pattern of mutual avoidance. White-tailed deer were more concentrated in the southern portions of the study area, which was characterized by lower elevations, more gradual slopes, and close proximity to streams. Black-tailed deer were more wide ranging and tended to occur in the northern portions of the study area, which had higher elevations and greater topographical variation. Habitat use of different vegetative assemblages was similar between white-tailed and black-tailed deer with overlap ranging from 89%–96% seasonally. White-tailed deer used nearly all habitats available on the study area except those associated with conifers. White-tailed deer used oak-hardwood savanna shrub, open grassland, oak-hardwood savanna, and riparian habitats the most. Black-tailed deer exhibited high use for open grassland and oak-hardwood savanna shrub habitats and lower use of all others. The 2 subspecies also exhibited strong seasonal similarities in diets with overlap ranging from 89% to 95%. White-tailed deer diets were dominated by forbs, shrubs, grasses, and other food sources (e.g., nuts and lichens). Columbian black-tailed deer diets were dominated mostly by forbs and other food sources. Seasonal diet diversity followed similar patterns for both species with the most diverse diets occurring in fall and the least diverse diets in spring. High overlap in habitat use and diets resulted in high trophic overlap (81–85%) between white-tailed and black-tailed deer; however, the low spatial overlap reduced the potential for exploitative competition but may have been indicative of inference competition between the species. Diverse habitat and forage opportunities were available on the study area due to heterogeneous landscape characteristics, which allowed ecological separation between white-tailed and black-tailed deer despite similarities in diets and habitat use. We make several recommendations for management of CWTD, a previously threatened species, based on the results of our study.

Denning ecology of American black bears in the Cascade Mountains of western Oregon

Abstract Little is known about the denning ecology of American black bears (Ursus americanus) in the Cascade Mountains of western Oregon. Extensive logging during the late 20th century altered the landscape significantly and may have affected the availability and quality of denning habitat. We visited 104 dens of 54 radiocollared bears during 1993–98 to document den-site characteristics and bear behavior in the Cascade Mountains of western Oregon. We also monitored bears in the spring and fall to estimate denning chronology. In addition, we randomly selected 5-ha quadrats to search for fungal activity and potential den sites. Eighty percent of dens we located were in trees that had cavities created by fungal activity. The remaining dens were located in rocky outcroppings and caves, under logs, or on the ground. We found no selection of dens based on micro- or macro aspect, elevation, or slope. Bears denned more than expected in mature timber with trees that averaged >50.8 cm diameter at breast height (dbh). Mean den entry date for bears in our study was November 20, and mean den emergence date was April 15. Pregnant females entered dens earlier and emerged later than barren females, females with yearlings, and all male age classes. Bears were more likely to abandon dens at lower elevations with little snow accumulation and less secure den structures. Fungal activity was randomly distributed throughout the study area. Fifty-one potential tree and log den structures were found in 27 of 64 quadrats we sampled. This information can help federal and state foresters schedule and design management activities within stands of timber containing denning habitat, aid wildlife managers in setting bear hunting seasons, and help timber cruisers and biologists detect and avoid disturbance of active dens.

Monthly and Annual Survival Rates of Cougar Kittens in Oregon

Abstract Cougar (Puma concolor) kittens are a substantial proportion of resident cougar populations and their survival has important implications for population dynamics of the species. To better understand effects of age and sex on cougar kitten survival, we estimated age specific (mo.) survival rates of cougar kittens (n = 72) radiocollared during three studies conducted in Oregon from 1989–2011. Cougar kittens were entered into the dataset based on age (mo.) at capture and fates were determined at monthly intervals. We analyzed survival in Program MARK using known-fate models of radiocollared individuals. We tested for effects of sex and linear, log-linear, and quadratic effects of age. Our best model indicated survival rates of cougar kittens were similar between sexes and increased in a linear manner with age. Annual survival estimates of cougar kittens were 0.66 (95% CI = 0.42–0.84). Our second ranked model was the null model, that indicated constant survival over time and between sexes with an annual survival rate of 0.78 (95% CI = 0.62–0.88). All other models in our candidate model set were not considered further because they ranked below the null model and contained non-informative parameters where the estimated effect broadly overlapped zero. Fates of littermates were dependent due to high levels of mortality at nursery sites which likely reduced the potential importance of sex on survival rates. We expect patterns of increased kitten survival with age and lack of differences between sexes to be consistent across the geographic range of cougars.

HOME-RANGE SIZE AND SUBADULT DISPERSAL OF BLACK BEARS IN THE CASCADE RANGE OF WESTERN OREGON

Abstract. Knowledge of home-range size and subadult dispersal activity of American black bears (Ursus americanus) is essential for understanding the complexity of how bears interact within populations and the environment. During 1993–1998, we monitored 95 radio-collared black bears in the Cascade Range of western Oregon to estimate homerange sizes and dispersal movements. Composite fixed-kernel home ranges were calculated for 37 bears. Mean home-range size differed between genders (189.7 km2 for males and 33.6 km2 for females); however, there was no difference in mean home-range size between subadult and adult males or subadult and adult females. We monitored 40 subadult bears (29 M, 11 F) to detect dispersal activity. We did not detect any dispersal of subadult females. One subadult male dispersed as a 2 year old, one dispersed as a 3 year old, and one as a 4 year old. The greatest dispersal distance of any subadult was 34 km by a 2-year-old male.