Browsing by Author "Mesa Cruz, Jose Bernardo"
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- Assessment of Physiological Challenges in Overwintering Black Bears (Ursus americanus): Active Gestation, Neonatal Growth, and Skeletal Muscle ConservationMesa Cruz, Jose Bernardo (Virginia Tech, 2018-06-29)The American black bear (ABB) (Ursus americanus) exhibits physiological strategies highly synchronized with the environment. Such strategies enable bears to exploit food resources when available and survive the winter months by hibernating without ingesting food or water. However, there are multiple aspects of ABB hibernation physiology that remain unknown. For instance, there is conflicting evidence on the occurrence of ABB pseudopregnancy (a physiological state in which a non-pregnant bear exhibits progesterone levels similar to gravid bears in the absence of an actual pregnancy). Also, there is little known about postnatal development of cubs or the influence of maternal traits on embryonic implantation and cub growth. Finally, the role of satellite cells (SCs – stem cells able to regenerate muscle fibers) play in maintaining muscle functionality during hibernating remains understudied. Therefore, I aimed to assess these four aforementioned aspects using wild ABBs held temporarily captive at Virginia Tech's Black Bear Research Center (VT-BBRC). The major findings of this dissertation are: 1) I suggest that wild ABBs do not experience pseudopregnancy as a reproductive strategy; 2) interactions between litter size and cub age best described postnatal cub weight dynamics and organ development. Twin cubs were heavier than single and triplet cubs, yet cubs from all litter sizes reached similar weights after mothers began consuming food post hibernation. Single cubs experienced delayed timing in ear, eye, and teeth development compared to other litter sizes; 3) maternal traits such as higher body weight and higher ability to gain weight in the fall are closely associated with earlier timing of embryonic implantation than in leaner females, which gained less weight per day in the fall; and 4) SC ability to generate muscle fibers is increased during ABB hibernation. I propose that maintaining the SCs are an important potential pathway for limiting muscle atrophy during bear hibernation. Understanding pre and postnatal development of ABBs is important for exploring factors related to climate, maternal characteristics, which possibly affect birthing phenology, and fitness of bears experiencing rapid anthropogenic environmental change. Functional aspects of bear muscle conservation are interesting for potentially for elucidating avenues to improve treatments for human metabolic disorders such as muscular dystrophy, sarcopenia, and disuse atrophy.
- A Bear's Eye View: Insight on American Black Bear (Ursus americanus) Hibernation and Foraging Ecology in Virginia's Central Appalachian MountainsHolcombe, Brogan Elizabeth (Virginia Tech, 2024-06-07)Following mass agricultural expansion and deforestation in the late 1800s and early 1900s, American black bear populations (Ursus americanus, hereafter black bear) were low across most of Virginia. The Department of Wildlife Resources (VADWR) and the United States Forest Service worked to rebuild wildlife habitat in the state, leading to recovery of bears. While some aspects of black bear hibernation and foraging ecology have been studied, there remain knowledge gaps on key aspects of black bear biology. Hibernation behavior, for example, is understudied with most knowledge stemming from post-hibernation emergence studies. We used a unique dataset with continuous monitoring of mother bears and their cubs from Virginia Tech's Black Bear Research Center in 2015-2016, to better understand hibernation ecology, mother-cub dynamics, and biological-foster cub dynamics. We found that increased black bear activity levels were driven by both higher temperature and photoperiod, but the onset of hibernation was primarily driven by only temperature. Temperature is projected to rise in VA and rising temperatures regionally could be responsible for increased active behaviors in bears, which could lead to increased human-black bear interactions on the landscape, especially during hibernation onset. We also found that mother bears spend similar amounts of time with biological and foster cubs. Biological cubs did not show more dominance behaviors toward fosters than biological siblings, which we also observed with foster, where they did not continuously display these behaviors towards biological cubs. These results are promising for orphan cub fostering programs in VA and other states and indicate that foster cub litter integration can be successful. Foraging ecology also is challenging to study in black bears because direct observation is generally not possible due to their cryptic nature, closed habitat, or potential danger in observing. We used a dataset from camera collars deployed on 15 bears (8 males, 7 females) in Bath County Virginia in 2018 and 2019 to better understand diet seasonality and to determine habitat and environmental drivers of black bear foraging patterns, particularly on white-tailed deer (Odocoileus virginianus) and invasive plant species. We identified 178 unique diet items to family, genus, or species in videos, much higher numbers than previously reported in the literature, and we found high diet overlap between sexes. Diet composition was primarily influenced by season with higher levels of consumption of herbaceous soft mast in spring, fruit and seed soft mast in summer, and hard mast in fall. Females exhibited more hunting events on deer fawns in spring than males, but males and females consumed similar numbers (28 vs. 24, respectively) via hunting and scavenging combined. Males consumed anthropogenic foods more often than females, particularly when closer to human settlements and males more commonly consumed invasive plant species in spring while females more often consumed insect in spring invasive species in summer. Our results highlight strong seasonally- and subtle sex-mediated differences in black bear diets. We provide information on drivers of diet choices by bears, as well as identify where foraging hotspots on species of interest occur, providing information useful to VADWR in managing increased human-wildlife interactions (and mitigating potential for negative interactions), predator-prey relations, and invasive species spread across the landscape.
- Non-invasive assessment of stress hormones, parasites, and diet, using scat of five felid species in Belize, Central AmericaMesa Cruz, Jose Bernardo (Virginia Tech, 2014-06-02)Many Neotropical felid species, such as jaguars, are threatened with extinction due to habitat fragmentation and/or human persecution. Human activities around protected areas in Belize, Central America, are increasing and so are levels of human-felid conflict. Potential consequences of this conflict are an increase in stress impacting health, diet shifts, or heightening of animal aggression. The goal of this work was to assess the effects of human-modified habitats on native felids by comparing fecal glucocorticoid metabolite (FGM) concentrations, endoparasite species richness (ESR), and diet using non-invasive scat sampling in a protected forest vs. surrounding non-protected areas in Belize. Field studies relying on non-invasive fecal hormone monitoring are subject to potential hormone degradation in samples exposed to the environment. Therefore I conducted immunoassay and environmental validations for measuring FGM in jaguars (Panthera onca). In the field, I collected scat using a detector dog, identified samples using DNA, retrieved parasite propagules with a flotation technique, and identified prey remains by morphology. I detected five felids: jaguar, puma, ocelot, jaguarundi and domestic cat. FGM concentrations were higher in pumas and jaguarundis than in the other felids. I found no livestock remains in felid scats. ESR was similar across felid species. Domestic cats were found only in human-modified areas. This results provide a baseline on adrenal activity, prey consumption, and endoparasites in felids of Belize. These findings could be used for comparisons to populations thought to be affected by human activities across Belize and in neighboring countries.