Bimodal Distribution of Estimated Conception Dates in Rocky Mountain Elk

Squibb, Ronald C.; Kimball, Jonathan W.; Anderson, David R.

doi:10.2307/3801499

Cited by 8 publications

(5 citation statements)

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“…However, harvest data in Idaho suggests it is unlikely that age ratios would be skewed enough towards younger males for this to be the mechanism resulting in smaller calves. Alternatively, some studies have reported that human hunting pressure has the potential to disrupt breeding activities in elk resulting in a bimodal (Squibb et al ) or delayed (Davidson et al ) distribution of conception dates. In Idaho, archery seasons occur throughout the state during the rut, whereas rifle seasons generally occur after the rut.…”

Section: Discussionmentioning

confidence: 99%

Effects of wolf pack size and winter conditions on elk mortality

et al. 2019

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Elk (Cervus canadensis) are high‐profile game animals for many states in the western United States, yet over the past several decades some populations have experienced a persistent and broad‐scale decline in recruitment. Over this same period, gray wolves (Canis lupus) have become an integral component of many western landscapes and agencies are increasingly challenged to maximize hunting opportunities of ungulates via predator management while simultaneously ensuring wolf conservation. To better understand the implications of predator management on elk populations, we monitored survival of 1,244 adult female elk and 806 6‐month‐old calves from 29 populations distributed throughout Idaho, USA, from 2004 to 2016. We developed predictive models of mortality that related mortality risk to wolf pack size, winter conditions, and individual‐level characteristics. Annual mortality rates (excluding harvest) for adult females and calves were 0.09 and 0.40, respectively. Calf mortality was predicted best with a model that included additive effects of chest girth at time of capture, mean size of surrounding wolf packs, and snow depth. Adult female mortality was predicted best with a model that included female age, mean size of surrounding wolf packs, and snow depth. Based on a sensitivity analysis, chest girth had the largest effect on risk of mortality for calves followed by pack size and snow depth. Other than the effect of senescence in the oldest (>15 yr) individuals, pack size and snow depth had the largest effect on risk of mortality for adult females. We estimated cause‐specific mortality and predation was the dominant cause of known‐fate mortalities for adult females (35% mountain lion [Puma concolor] and 32% wolf) and calves (45% mountain lion and 28% wolf), whereas malnutrition accounted for 9% and 10% of adult female and calf mortalities, respectively. Wolves preferentially selected smaller calves and older adult females, whereas mountain lions showed little preference for calf size or age class of adult females. Our study indicates managers can increase elk survival by reducing wolf pack sizes on surrounding winter ranges, especially in areas where, or during years when, snow is deep. Additionally, managers interested in improving over‐winter calf survival can implement actions to increase the size of calves entering winter by increasing the nutritional quality of summer and early fall forage resources. Although our study was prompted by management questions related to wolves, mountain lions killed more elk than wolves and differences in selection of individual elk indicate mountain lions may have comparably more of an effect on elk population dynamics. Although we were unable to relate changes in mountain lion populations to elk survival in our study, future research should seek a better understanding of multi‐predator systems, including how management of one predator affect others and ultimately how these interactions affect elk survival. © 2019 The Wildlife Society

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Section: Discussionmentioning

confidence: 99%

Effects of wolf pack size and winter conditions on elk mortality

et al. 2019

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“…Possible mechanisms of stress-induced conception delays were reduced ovulation rate, suppression of behavioral estrus, and early death of embryos. Squibb et al (1986) also reported that stress from hunting did not reduce pregnancy rates, but did delay conception.…”

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confidence: 99%

“…Conception dates of female elk may be affected by mature male abundance (Noyes et al 1996(Noyes et al , 2002, female nutritional condition (Trainer 1971, Mitchell and Lincoln 1973, Hines and Lemos 1979, Albon et al 1986, Cook et al 2004a, and human activity during the rut (Squibb 1985). Squibb et al (1986) reported a sudden drop in conceptions coinciding with the opening of rifle elk seasons and speculated that the mechanism for the disruption of elk reproduction likely involved females, rather than males. Possible mechanisms of stress-induced conception delays were reduced ovulation rate, suppression of behavioral estrus, and early death of embryos.…”

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confidence: 99%

Effect of archer density on elk pregnancy rates and conception dates

et al. 2012

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Archery hunting in Oregon has increased dramatically over the past 2 decades. At the same time, spring juvenile to adult female ratios of Rocky Mountain elk (Cervus elaphus) have been declining. This has raised concern that archery seasons may be disrupting elk breeding and contributing to the decline in recruitment. Two mechanisms could contribute to reduced juvenile:female ratios: 1) reduced pregnancy rates, and 2) delayed conception dates because of human disturbance during the rut. We varied the number of archery hunters at the Starkey Experimental Forest and Range over 13 years to evaluate effects of archer density on reproduction of elk. Archer densities were maintained at high densities during 4 years ðx ¼ 1:09 tags sold=km 2 Þ, low densities during 3 years ðx ¼ 0:53 tags sold=km 2 Þ, and no archers during 6 years. We determined pregnancy status, age, kidney fat index (KFI), lactation status, and fetus conception dates for 622 female elk harvested in December. We found pregnancy rate differences of 0.105, 0.080, and 0.021 between high and no archer density years (P ¼ 0.004), high and low archer density years (P ¼ 0.054), and low and no archer density years (P ¼ 0.616), respectively. Conception dates were 4 days later for high archer density compared to low archer density (P ¼ 0.006), but did not differ between high and no archer years (2 days; P ¼ 0.136) or between low and no archer years (2 days; P ¼ 0.108). We compared generalized linear model estimates of pregnancy rates and determined pregnancy rates for 28% of the lactating female elk to be affected by high archer density, whereas archer densities had no significant affect on pregnancy rate estimates for non-lactating females. We found no difference in conception dates among archer densities when comparing model estimates. Our results suggest that archer density and its interaction with nutritional condition of elk influence pregnancy rates of lactating females with low KFI levels; however, the effect of archer density alone does not explain the magnitude of decline in juvenile to female ratios observed in Oregon. ß 2012 The Wildlife Society.

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“…Survival rates observed during the East Kootenay Trench studies in 1986–1993 and 2007–2010 were 0.92 and 0.81, respectively (Szkorupa & Mowat, 2010). Elk Valley cow pregnancy rates varied widely among years, possibly related to annual differences in cow elk health and fat reserves, or reduced breeding success (reduced pregnancy rates and/or delayed conception dates) as a result of continual harassment during the rut (Davidson et al, 2012; Squibb et al, 1986). Pregnancy rates also varied annually from 0.66 to 0.98 over 4 years in the Ya Ha Tinda elk population in eastern Alberta (Hebblewhite & Merrill, 2011).…”

Section: Discussionmentioning

confidence: 99%

Migration, movements, and survival in a partially migratory elk (Cervus canadensis) population

Poole,

Lamb,

Medcalf

et al. 2024

Conservat Sci and Prac

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Migration provides an adaptive strategy to improve fitness by allowing individuals to exploit gradients of resources and changes in predation risk. In recent decades, the extent and prevalence of migration has declined in numerous ungulate species including many populations of elk (Cervus canadensis). Resident elk are often more closely associated with human activity, are more readily involved in agricultural conflicts and may contribute to overgrazing on some ranges. We evaluated migratory trends, survival rates, and causes of mortality in a partially migratory elk population in southeastern British Columbia, Canada, and compared these parameters with data from a 1982–1996 study from the same area. Analysis of 201 animal‐years (n = 78 collared cow elk) between 2016 and 2022 showed a ratio of 52% migratory to 48% resident elk, similar to what was found during the 1982–1996 study (55% migratory to 45% resident; n = 40 cows). Among the migrants, 55% were standard migrants (traveling moderate to longer distances and changing little in elevation), 35% elevational, and 10% mixed/atypical. We detected a 14% yearly switching rate between migratory and resident strategies. We recorded 30 mortalities: 47% from human causes, predominantly elk‐vehicle/train collisions (33% of mortalities), apparent starvation/old age (17%), and predation (17%). Notably, while mortality from natural causes was similar between strategies, human‐caused mortality was nearly twice as high in resident elk. Signs of nutritional stress and lower pregnancy rates indicated potential forage limitations. Migrants had higher average survival rates (0.90) compared to residents (0.83), a shift from the 1982–1996 study that recorded higher resident survival rates (0.98), the same migrant survival rate (0.90), and fewer elk‐vehicle/train collisions. Cow elk in our study made fewer and shorter movements into upper mountain tributaries and greater use of mine properties than observed during the 1982–1996 study. Wildlife managers should consider opportunities to enhance elk forage within traditional high‐elevation summer ranges and mitigations to reduce elk‐vehicle/train collisions. Further research is needed to quantify reproductive success, monitor calf survival, and determine relative forage quality among summering areas between migratory strategies, and determine winter ranges of long‐distant migrants.

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Bimodal Distribution of Estimated Conception Dates in Rocky Mountain Elk

Cited by 8 publications

References 0 publications

Effects of wolf pack size and winter conditions on elk mortality

Effects of wolf pack size and winter conditions on elk mortality

Effect of archer density on elk pregnancy rates and conception dates

Migration, movements, and survival in a partially migratory elk (Cervus canadensis) population

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