The decline of the Kalahari wildebeest

Advancing fence datasets: Comparing approaches to map fence locations and specifications in southwest Montana

Fencing is a major anthropogenic feature affecting wildlife distributions and movements, but its impacts are difficult to quantify due to a widespread lack of spatial data. We created a fence model and compared outputs to a fence mapping approach using satellite imagery in two counties in southwest Montana, USA to advance fence data development for use in research and management. The model incorporated road, land cover, ownership, and grazing boundary spatial layers to predict fence locations. We validated the model using data collected on randomized road transects (n = 330). The model predicted ~34,700 km of fences with a mean fence density of 0.93 km/km2 and a maximum density of 14.9 km/km2. We also digitized fences using Google Earth Pro in a random subset of our study area in survey townships (n = 50). The Google Earth approach showed greater agreement (K = 0.76) with known samples than the fence model (K = 0.56) yet was unable to map fences in forests and was significantly more time intensive. We also compared fence attributes by land ownership and land cover variables to assess factors that may influence fence specifications (e.g., wire heights) and types (e.g., number of barbed wires). Private land fences had bottom wires that were closer to the ground and top wires higher from the ground when compared to fences on public lands, with sample means at ~22 cm and ~26 cm, and ~115 cm and ~111 cm, respectively. Both bottom wire means were well below recommended heights for ungulates navigating underneath fencing (≥ 46 cm), while top wire means were closer to the 107 cm maximum fence height recommendation. We found that both fence type and land ownership were correlated (χ2 = 45.52, df = 5, p = 0.001) as well as fence type and land cover type (χ2 = 140.73, df = 15, p = 0.001). We provide tools for estimating fence locations, and our novel fence type assessment demonstrates an opportunity for updated policy to encourage the adoption of “wildlife-friendlier” fencing standards to facilitate wildlife movement in the western U.S. while supporting rural livelihoods.

Effects of fences and fence gaps on the movement behavior of three southern African antelope species

Globally, migratory ungulates are affected by fences. While field observational studies reveal the amount of animal–fence interactions across taxa, GPS tracking-based studies uncover fence effects on movement patterns and habitat selection. However, studies on the direct effects of fences and fence gaps on movement behavior, especially based on high-frequency tracking data, are scarce. We used GPS tracking on three common African antelopes (Tragelaphus strepsiceros, Antidorcas marsupialis, and T. oryx) with movement strategies ranging from range residency to nomadism in a semi-arid, Namibian savanna traversed by wildlife-proof fences that elephants have regularly breached. We classified major forms of ungulate–fence interaction types on a seasonal and a daily scale. Furthermore, we recorded the distances and times spent at fences regarding the total individual space use. Based on this, we analyzed the direct effects of fences and fence gaps on the animals’ movement behavior for the previously defined types of animal–fence interactions. Antelope-fence interactions peaked during the early hours of the day and during seasonal transitions when the limiting resource changed between water and forage. Major types of ungulate–fence interactions were quick, trace-like, or marked by halts. We found that the amount of time spent at fences was highest for nomadic eland. Migratory springbok adjusted their space use concerning fence gap positions. If the small home ranges of sedentary kudu included a fence, they frequently interacted with this fence. For springbok and eland, distance traveled along a fence declined with increasing utilization of a fence gap. All species reduced their speed in the proximity of a fence but often increased their speed when encountering the fence. Crossing a fence led to increased speeds for all species. We demonstrate that fence effects mainly occur during crucial foraging times (seasonal scale) and during times of directed movements (daily scale). Importantly, we provide evidence that fences directly alter antelope movement behaviors with negative implications for energy budgets and that persistent fence gaps can reduce the intensity of such alterations. Our findings help to guide future animal–fence studies and provide insights for wildlife fencing and fence gap planning.

Contrasting capabilities of two ungulate species to cope with extremes of aridity

Southern Africa is expected to experience increased frequency and intensity of droughts through climate change, which will adversely affect mammalian herbivores. Using bio-loggers, we tested the expectation that wildebeest (Connochaetes taurinus), a grazer with high water-dependence, would be more sensitive to drought conditions than the arid-adapted gemsbok (Oryx gazella gazella). The study, conducted in the Kalahari, encompassed two hot-dry seasons with similar ambient temperatures but differing rainfall patterns during the preceding wet season. In the drier year both ungulates selected similar cooler microclimates, but wildebeest travelled larger distances than gemsbok, presumably in search of water. Body temperatures in both species reached lower daily minimums and higher daily maximums in the drier season but daily fluctuations were wider in wildebeest than in gemsbok. Lower daily minimum body temperatures displayed by wildebeest suggest that wildebeest were under greater nutritional stress than gemsbok. Moving large distances when water is scarce may have compromised the energy balance of the water dependent wildebeest, a trade-off likely to be exacerbated with future climate change.

The Shrinking Resource Base of Pastoralism: Saami Reindeer Husbandry in a Climate of Change

The productive performance of large ungulates in extensive pastoral grazing systems is modulated simultaneously by the effects of climate change and human intervention independent of climate change. The latter includes the expansion of private, civil and military activity and infrastructure and the erosion of land rights. We used Saami reindeer husbandry in Norway as a model in which to examine trends in, and to compare the influence of, both effects on a pastoral grazing system. Downscaled projections of mean annual temperature over the principal winter pasture area (Finnmarksvidda) closely matched empirical observations across 34 years to 2018. The area, therefore, is not only warming but seems likely to continue to do so. Warming notwithstanding, 50-year (1969–2018) records of local weather (temperature, precipitation and characteristics of the snowpack) demonstrate considerable annual and decadal variation which also seems likely to continue and alternately to amplify and to counter net warming. Warming, moreover, has both positive and negative effects on ecosystem services that influence reindeer. The effects of climate change on reindeer pastoralism are evidently neither temporally nor spatially uniform, nor indeed is the role of climate change as a driver of change in pastoralism even clear. The effects of human intervention on the system, by contrast, are clear and largely negative. Gradual liberalization of grazing rights from the 18th Century has been countered by extensive loss of reindeer pasture. Access to ~50% of traditional winter pasture was lost in the 19th Century owing to the closure of international borders to the passage of herders and their reindeer. Subsequent to this the area of undisturbed pasture within Norway has decreased by 71%. Loss of pasture due to piecemeal development of infrastructure and to administrative encroachment that erodes herders' freedom of action on the land that remains to them, are the principal threats to reindeer husbandry in Norway today. These tangible effects far exceed the putative effects of current climate change on the system. The situation confronting Saami reindeer pastoralism is not unique: loss of pasture and administrative, economic, legal and social constraints bedevil extensive pastoral grazing systems across the globe.

Long-term persistence of wildlife populations in a pastoral area

Facilitating coexistence between people and wildlife is a major conservation challenge in East Africa. Some conservation models aim to balance the needs of people and wildlife, but the effectiveness of these models is rarely assessed. Using a case-study approach, we assessed the ecological performance of a pastoral area in northern Tanzania (Manyara Ranch) and established a long-term wildlife population monitoring program (carried out intermittently from 2003 to 2008 and regularly from 2011 to 2019) embedded in a distance sampling framework. By comparing density estimates of the road transect-based long-term monitoring to estimates derived from systematically distributed transects, we found that the bias associated with nonrandom placement of transects was nonsignificant. Overall, cattle and sheep and goat reached the greatest densities and several wildlife species occurred at densities similar (zebra, wildebeest, waterbuck, Kirk's dik-dik) or possibly even greater (giraffe, eland, lesser kudu, Grant's gazelle, Thomson's gazelle) than in adjacent national parks in the same ecosystem. Generalized linear mixed models suggested that most wildlife species (8 out of 14) reached greatest densities during the dry season, that wildlife population densities either remained constant or increased over the 17-year period, and that herbivorous livestock species remained constant, while domestic dog population decreased over time. Cross-species correlations did not provide evidence for interference competition between grazing or mixed livestock species and wildlife species but indicate possible negative relationships between domestic dog and warthog populations. Overall, wildlife and livestock populations in Manyara Ranch appear to coexist over the 17-year span. Most likely, this is facilitated by existing connectivity to adjacent protected areas, effective anti-poaching efforts, spatio-temporal grazing restrictions, favorable environmental conditions of the ranch, and spatial heterogeneity of surface water and habitats. This long-term case study illustrates the potential of rangelands to simultaneously support wildlife conservation and human livelihood goals if livestock grazing is restricted in space, time, and numbers.

Large herbivore conservation in a changing world: Surface water provision and adaptability allow wildebeest to persist after collapse of long-range movements

Large herbivores, particularly wide-ranging species, are extensively impacted by land use transformation and other anthropogenic barriers to movement. The adaptability of a species is, therefore, crucial to determining whether populations can persist in ever smaller subsets of their historical home ranges. Access to water, by drinking or from forage moisture, is an essential requirement, and surface water provision is thus a long-established, although controversial, conservation practice. In the arid Kgalagadi Transfrontier Park (KTP), South Africa, surface water provision in the 1930s facilitated the establishment of a sedentary wildebeest (Connochaetes taurinus) population in a region historically accessed only in the wet season, via now collapsed long-distance movements. Here, we investigate the behaviour and diet of this wildebeest population, and how these relate to water in the landscape, to better understand the process of transitioning from a mobile to sedentary population. Data from 26 monthly surveys reveal that wildebeest distributions are shaped by water availability and salinity, shade, forage, season and possibly predator detectability. Areas with saline or no water are used predominantly in the wet season when forage moisture is high. Wet season movements beyond the study area mean the timing of wildebeest grazing in these regions matches historical timing. Grass utilization field data suggest that the KTP grazer population experiences forage deficits during the dry season, when ~80% of grass tufts are grazed and C:N and crude protein levels decline. Nonetheless, dung isotope data show that wildebeest meet their crude protein intake requirements during the dry season, likely by consuming unprecedentedly high levels of browse (>33%). While restoring the full historical range and movements of most large herbivore populations is not possible, these findings highlight that understanding the behavioural and dietary adaptability of a species can augment 'next best' efforts to conserve viable populations while home ranges contract.

How free-ranging ungulates with differing water dependencies cope with seasonal variation in temperature and aridity

Large mammals respond to seasonal changes in temperature and precipitation by behavioural and physiological flexibility. These responses are likely to differ between species with differing water dependencies. We used biologgers to contrast the seasonal differences in activity patterns, microclimate selection, distance to potential water source and body temperature of the water-independent gemsbok (Oryx gazella gazella) and water-dependent blue wildebeest (Connochaetes taurinus), free-living in the arid Kalahari region of Botswana. Gemsbok were more active nocturnally during the hot seasons than in the cold-dry season, while wildebeest showed no seasonal difference in their nocturnal activity level. Both species similarly selected shaded microclimates during the heat of the day, particularly during the hot seasons. Wildebeest were further than 10 km from surface water 30% or more of the time, while gemsbok were frequently recorded >20 km from potential water sources. In general, both species showed similar body temperature variation with high maximum 24-h body temperature when conditions were hot and low minimum 24-h body temperatures when conditions were dry, resulting in the largest amplitude of 24-h body temperature rhythm during the hot-dry period. Wildebeest thus coped almost as well as gemsbok with the fairly typical seasonal conditions that occurred during our study period. They do need to access surface water and may travel long distances to do so when local water sources become depleted during drought conditions. Thus, perennial water sources should be provided judiciously and only where essential.

Connectivity and bottlenecks in a migratory wildebeest Connochaetes taurinus population

Surprisingly little is known about the spatial dimensions of most tropical ungulate migrations, including that of wildebeest Connochaetes taurinus, a species famous for long-distance movements. Using non-invasive photographic identification of 834 adult wildebeest from 8,530 images collected over 4 years we characterize patterns of migratory connectivity throughout the northern Tarangire–Manyara Ecosystem, Tanzania. We document movements between Tarangire and Lake Manyara National Parks and northwards to the shore of Lake Natron, a straight-line distance of > 130 km. Fifty-six percent of observed movements occur outside the ecosystem's three main protected areas. We supplement photographic data with fine-scale movement data from two individuals with global positioning system collars, and identify three narrow bottlenecks, each vulnerable to human development. We discuss the possible consequences for the wildebeest population if these bottlenecks become impeded. Persistence of this migration alongside a growing human population and proposed road improvement will require additional measures to ensure that pathways remain open to wildlife movement and protected from illegal hunting.

Modeling fence location and density at a regional scale for use in wildlife management

Barbed and woven wire fences, common structures across western North America, act as impediments to wildlife movements. In particular, fencing influences pronghorn (Antilocapra americana) daily and seasonal movements, as well as modifying habitat selection. Because of fencing's impacts to pronghorn and other wildlife, it is a potentially important factor in both wildlife movement and habitat selection models. At this time, no geospatial fencing data is available at regional scales. Consequently, we constructed a regional fence model using a series of land tenure assumptions for the Hi-Line region of northern Montana – an area consisting of 13 counties over 103,400 km². Randomized 3.2 km long transects (n = 738) on both paved and unpaved roads were driven to collect information on habitat, fence densities and fence type. Using GIS, we constructed a fence location and a density model incorporating ownership, size, neighboring parcels, township boundaries and roads. Local knowledge of land ownership and land use assisted in improving the final models. We predict there is greater than 263,300 km of fencing in the Hi-Line region, with a maximum density of 6.8 km of fencing per km² and mean density of 2.4 km of fencing per km². Using field data to assess model accuracy, Cohen's Kappa was measured at 0.40. On-the-ground fence modification or removal could be prioritized by identifying high fence densities in critical wildlife areas such as pronghorn migratory pathways or sage grouse lekking habitat. Such novel fence data can assist wildlife and land managers to assess effects of anthropogenic features to wildlife at various scales; which in turn may help conserve declining grassland species and overall ecological functionality.

Leadership, collective motion and the evolution of migratory strategies

Migration is a hallmark life history strategy of a diverse range of organisms, and also ubiquitous in ontogenic processes including normal embryonic development as well as tumor progression. In such scenarios, individual organisms/cells typically respond to long range (and often noisy) environmental cues. In addition, individuals may interact socially with one another leading to emergent group-level navigational abilities. Although much progress has been made in understanding the mechanisms of taxis, there is a lack of theoretical and quantitative understanding of how individuals trade-off information obtained through their own migratory ability and that via social interactions. Here, we discuss results and insights from a recent computational model developed to investigate the evolution of leadership and collective motion in migratory populations. It is shown that, for a broad range of parameter values, only a small proportion of the population gather directional information while the majority employ social cues alone. More generally, ecological conditions for the evolution of resident, solitary and collective migratory strategies are obtained. We discuss how consideration of both proximate and ultimate factors within the same framework may provide insights into preserving migratory patterns that are in grave danger due to anthropogenic pressures.

The need for integrative approaches to understand and conserve migratory ungulates

Over the last two centuries overhunting, anthropogenic barriers and habitat loss have disrupted many ungulate migrations. We review the literature on ungulate migration disruptions and find that for many species the disruption of migratory routes causes a rapid population collapse. Previous research has focused on the proximal ecological factors that might favour migration, particularly spatiotemporal variation in resources and predation. However, this does not provide an adequate basis for understanding and mitigating anthropogenic effects on migratory populations. Migration is a complex behaviour and we advocate an integrative approach that incorporates population dynamics, evolution, genetics, behaviour and physiology, and that borrows insights and approaches from research on other taxa. We draw upon research on avian migration to illustrate research approaches that might also be fruitful in ungulates. In particular, we suggest that the migratory cycle should be evaluated in the context of seasonal population limitation, an approach we highlight with a preliminary demographic perturbation analysis of the Serengeti wildebeest (Connochaetes taurinus) population. We provide suggestions for avenues of future research and highlight areas where we believe rapid progress can be made by applying recent advances in theory, technology and analytical approaches.