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Reproductive phenology is a critical element of how animals persist in their environment and affects survival of young, especially in seasonal environments. We investigated the correlation between fetal eye diameter and birth timing to determine if birthdates could be predicted by a prenatal metric. We used ultrasonography to measure eye diameters of fetuses and vaginal implant transmitters to determine birthdates of Rocky Mountain Bighorn Sheep (Ovis canadensis canadensis) in Wyoming, United States, from 2019 to 2023. Fetal eye diameter strongly predicted days until birth (β = −2.8; pseudo- R 2 = 0.88). Effective prediction of birthdates via ultrasonography can yield opportunities for logistical planning in neonatal studies, monitoring changes in reproductive phenology, and evaluating questions of resource allocation relative to reproductive processes. [ABSTRACT FROM AUTHOR]

Though far less obvious than direct effects (clinical disease or mortality), the indirect influences of pathogens are difficult to estimate but may hold fitness consequences. Here, we disentangle the directional relationships between infection and energetic reserves, evaluating the hypotheses that energetic reserves influence infection status of the host and that infection elicits costs to energetic reserves. Using repeated measures of fat reserves and infection status in individual bighorn sheep (Ovis canadensis) in the Greater Yellowstone Ecosystem, we documented that fat influenced ability to clear pathogens (Mycoplasma ovipneumoniae) and infection with respiratory pathogens was costly to fat reserves. Costs of infection approached, and in some instances exceeded, costs of rearing offspring to independence in terms of reductions to fat reserves. Fat influenced probability of clearing pathogens, pregnancy and over-winter survival; from an energetic perspective, an animal could survive for up to 23 days on the amount of fat that was lost to high levels of infection. Cost of pathogens may amplify trade-offs between reproduction and survival. In the absence of an active outbreak, the influence of resident pathogens often is overlooked. Nevertheless, the energetic burden of pathogens likely has consequences for fitness and population dynamics, especially when food resources are insufficient. [ABSTRACT FROM AUTHOR]

Bighorn sheep (Ovis canadensis) across North America commonly experience population-limiting epizootics of respiratory disease. Although many cases of bighorn sheep pneumonia are polymicrobial, Mycoplasma ovipneumoniae is most frequently associated with all-age mortality events followed by years of low recruitment. Chronic carriage of M. ovipneumoniae by adult females serves as a source of exposure of naïve juveniles; relatively few ewes may be responsible for maintenance of infection within a herd. Test-and-remove strategies focused on removal of adult females with evidence of persistent or intermittent shedding (hereafter chronic carriers) may reduce prevalence and mitigate mortality. Postmortem confirmation of pneumonia in chronic carriers has been inadequately reported and the pathology has not been thoroughly characterized, limiting our understanding of important processes shaping the epidemiology of pneumonia in bighorn sheep. Here we document postmortem findings and characterize the lesions of seven ewes removed from a declining bighorn sheep population in Wyoming, USA, following at least two antemortem detections of M. ovipneumoniae within a 14-mo period. We confirmed that 6/7 (85.7%) had variable degrees of chronic pneumonia. Mycoplasma ovipneumoniae was detected in the lung of 4/7 (57.1%) animals postmortem. Four (57.1%) had paranasal sinus masses, all of which were classified as inflammatory, hyperplastic lesions. Pasteurella multocida was detected in all seven (100%) animals, while Trueperella pyogenes was detected in 5/7 (71.4%). Our findings indicate that not all chronic carriers have pneumonia, nor do all have detectable M. ovipneumoniae in the lung. Further, paranasal sinus masses are a common but inconsistent finding, and whether sinus lesions predispose to persistence or result from chronic carriage remains unclear. Our findings indicate that disease is variable in chronic M. ovipneumoniae carriers, underscoring the need for further efforts to characterize pathologic processes and underlying mechanisms in this system to inform management. [ABSTRACT FROM AUTHOR]

Animals are inherently tied to nutritional resources of the landscape. Added cost of coping with environmental stressors, like disease, can exacerbate nutritional limitations. Pneumonia, a respiratory disease caused primarily by bacterial pathogens, has caused massive declines in populations of bighorn sheep (Ovis canadensis) throughout western North America. Nevertheless, population dynamics following a pneumonia epizootic vary across populations, which has spawned the idea that ecological conditions may play a role in regulating populations after a die‐off. We used 2 bighorn sheep populations with contrasting dynamics to test the hypothesis that habitat quality on summer range affects population dynamics following a pneumonia epizootic. We sampled over 700 vegetation transects and quantified nutrient content of 2,093 forage samples of 127 genera on summer ranges to compare habitat quality (macro‐ and micronutrients in forage, biomass, plant cover, and species diversity) between the ranges. The population exhibiting growth, higher recruitment, and better nutritional condition had over double the herbaceous biomass in their core foraging areas in summer than the population exhibiting decline, lower recruitment, and poorer nutritional status. The population experiencing growth also had more macro‐ and micronutrients available on their summer range as a function of higher biomass along with higher species diversity. Although winter range often is considered the nutritional bottleneck for ungulates, we demonstrate that the conditions of summer range can have consequences for population dynamics. Habitat quality should be incorporated when considering management objectives and population recovery of large herbivores in the presence of disease; interactions between habitat quality and population dynamics still apply and likely are amplified with additional stressors like disease. [ABSTRACT FROM AUTHOR]

Capture and handling techniques for individual‐based, long‐term research that tracks the life history of animals by recapturing the same individuals for several years has vastly improved study inferences and our understanding of animal ecology. Yet there are corresponding risks to study animals associated with physical trauma or capture myopathy that can occur during or following capture events. Rarely has empirical evidence existed to guide decisions associated with understanding the magnitude of capture‐related risks, how to reduce these risks when possible, and implications for mortality censoring and survival estimates. We used data collected from 2,399 capture events of mule deer (Odocoileus hemionus) via helicopter net‐gunning to compare daily survival probabilities within a 10‐week period centered on a capture event and evaluated how animal age, nutritional condition (body fat), and various handling methods influenced survival before, during, and following a capture event. Direct mortality resulting from capture efforts was 1.59%. Mean daily survival was 0.9993 ± 0.0001 (SE) during the 5‐week pre‐capture window, was depressed the day of capture at 0.9841 ± 0.0004, and rebounded to 0.9990 ± 0.0008 during the 5‐week post‐capture window. Neither capture nor handling had a detectable effect on post‐capture survival, including handling time (x¯ $\bar{x}$ = 13.30 ± 1.87 min), capture time of year (i.e., Dec or Mar), tooth extraction, and the number of times an animal had been recaptured (2–17 times). Although mortality rate was slightly elevated during capture (resulting from physical trauma associated with capture), age and nutritional condition did not influence the probability of mortality during a capture event. Following a capture event, nutritional condition influenced survival; however, that relationship was consistent with expected effects of nutritional condition on winter survival and independent of capture and handling. Overall survival rates 5 weeks before capture and 5 weeks after capture were not different. A specified window of time with depressed survival following capture and handling was not evident, which contradicts the implementation of a predetermined window often used by researchers and managers for censoring mortalities that occur after capture. Previous notions that censorship of all mortality data in the 2 weeks following capture is unwarranted and risks removal of meaningful data. With previous evidence guiding our protocols for capture (e.g., reduced chase time) and handling (e.g., temperature mitigation), low direct mortality and almost undetectable indirect mortality post capture reinforces the efficacy of helicopter net‐gunning for capture and recapture of mule deer in long‐term, individual‐based studies. [ABSTRACT FROM AUTHOR]