New research shows that for antelope populations in East Africa, it is not just about the weather but where they can roam. This highlights why we need big, connected spaces for conservation.
Environmental changes threaten naturally heterogeneous and dynamic ecosystems that are essential in creating and maintaining a rich, resilient, and adaptable biosphere. In East Africa’s savanna, antelope populations are vital for a healthy and functioning ecosystem. They shape the vegetation, disperse seeds, cycle nutrients, and provide food for other animals. A natural dynamic mosaic of vegetation types, water sources, and weather forms a delicate balance with the antelopes that is more and more disrupted by human influences and climatic changes. To protect these hotspots of biodiversity and enable the ecosystem to work properly, it is vital to maintain healthy antelope populations.
Previous studies have shown that densities of savanna antelopes vary based on location, season, and year, but no empirical studies had ever examined all these effects together. Simultaneously studying how environmental variation over space and time affects the local densities of antelope species could resolve whether location, or seasonal or annual variation is the most important factor driving local densities of these wildlife.
Using seven years of antelope monitoring data from the Tarangire Ecosystem in Tanzania, an international collaboration between the University of Zurich and the Wild Nature Institute examined this question. They found spatial factors explained the largest proportion of variation in density for four of the five antelope species they studied. These spatial covariates included proximity to water and human activities as well as vegetation community—suggestive of both bottom-up (resources) and top-down influences (avoiding natural predators) on local densities. The research was published in the journal Population Ecology.
In the Tarangire Ecosystem, antelopes respond to changing climatic conditions and the fluctuating availability of resources by moving across space. Lead author Lukas Bierhoff, a graduate student in the Department of Evolutionary Biology and Environmental Studies at University of Zurich, said “these results demonstrate that antelopes depend upon water and forage availability, but are flexible in their responses to climatic variation when they have the option to move and seek out the necessary resources for the current conditions.”
Helping antelopes move across space to adapt to climate and habitat changes
As natural savanna habitats and climate are rapidly being altered by human activities, effective conservation strategies are needed to ensure the persistence of antelopes and all the services they provide to maintain healthy ecosystems. “This study provides further evidence that the protection of large, connected areas of different habitat types and permanent water sources are the best way to maintain high biodiversity and a functioning biosphere. Providing habitat options for the antelopes enables them to respond to a temporally changing world by moving across space,” Bierhoff said.
The research team also identified guilds of antelopes whose densities co-varied, and that might respond similarly to targeted and coordinated conservation strategies, thus increasing the efficiency of management actions.
“Effective conservation actions include protecting rivers and other water sources from diversion and pollution; reducing bushmeat poaching; keeping and restoring movement corridors; and maintaining the diversity of natural vegetation types” said Derek Lee, Wild Nature Institute principal scientist and senior author of the paper. “Antelopes are critically important to Tanzania’s economy as well as its ecology, so sustaining thriving populations of these animals is a win-win for people and wildlife.”
Citation: Bierhoff L, Bond, ML, Ozgul A, Lee DE. 2024. Anthropogenic and climatic drivers of population densities in an African savanna ungulate community. Population Ecology. https://doi.org/10.1002/1438-390X.12182
Giraffes in the East African savannas adapt well to warmer temperatures. However, they are threatened by increasingly heavy rainfall.
Climate change is expected to cause widespread declines in wildlife populations worldwide. Climate anomalies interacting with human pressures can place additional stress on already declining populations, but little is known about the interactions between climate and anthropogenic effects on large African herbivore species despite the growing importance of these pressures. Giraffes are endangered megaherbivores, but the combined climate and human effects on the survival rates not only of giraffes, but of any large African herbivore species, had not been studied. We concluded a decade-long study – the largest to date – of a giraffe population in the Tarangire region of Tanzania. The study area spanned more than a thousand square kilometers, including areas inside and outside protected areas. Contrary to expectations, higher temperatures were found to positively affect adult giraffe survival, while rainier wet seasons negatively impacted adult and calf survival. The results were published in the journal Biodiversity and Conservation.
First exploration into the effects of climate variation on giraffe survival
Our research team quantified the effects of local anomalies of temperature, rainfall, and vegetation greenness on the probability of survival of the giraffes. We also explored whether climate had a greater effect on giraffes that were also experiencing human impacts at the edges of the protected reserves.
Studying the effects of climate and human pressures on a long-lived and slow-breeding animal like a giraffe requires monitoring their populations over a lengthy time period and over a large area, enough to capture both climate variation and any immediate or delayed effects on survival. We obtained nearly two decades of data on local rainfall, vegetation greenness, and temperature during Tanzania’s short rains, long rains, and dry season, and then followed the fates of 2,385 individually recognized giraffes of all ages and sexes over the final 8 years of the two-decade period.
Masai giraffes in a heavy downpour, Tanzania. Photo credit: Derek Lee
Surprising effects of temperature on giraffe survival
We had predicted that higher temperatures would hurt adult giraffes because their very large body size might make them overheat, but higher temperatures positively affected adult giraffe survival. This is because the giraffe has several physical features that help it to keep cool, like long necks and legs for evaporative heat loss, specialized nasal cavities, an intricate network of arteries that supply blood to the brain, and they radiate heat through their spot patches. However, temperatures during our study period may not have exceeded the tolerable thermal range for giraffes, and an extreme heat wave in the future might reveal a threshold above which these massive animals might be harmed. So we will continue to monitor this population.
Heavy rains may increase parasites while reducing nutritional value of vegetation
Survival of giraffe adults and calves was reduced during rainier wet seasons, which we attributed to a possible increase in parasites and disease. A previous study in the Tarangire region showed giraffe gastrointestinal parasite intensity was higher during the rainy seasons than the dry season, and heavy flooding has caused severe outbreaks of diseases known to cause mortality in giraffes, such as Rift Valley Fever Virus and anthrax. The current study also found higher vegetation greenness reduced adult giraffe survival, potentially because faster leaf growth reduces nutrient quality in giraffe food.
Human pressure place additional stress on already declining populations
Climate effects were exacerbated by the giraffe’s proximity to the edge of protected reserves, but not during every season. Our findings indicate that giraffes living near the peripheries of the protected areas are most vulnerable during heavy short rains. These conditions likely heighten disease risks associated with livestock, and muddy terrain hampers anti-poaching patrols, leading to increased threats to giraffe survival.
Climate anomaly effects on seasonal survival of adult Masai giraffes in Tarangire Ecosystem, Tanzania 2012‒2019. MeanDistPA is mean distance from the edge of the protected area (km). M = male; F = female.Rainfall anomaly effects on Masai giraffe juvenile seasonal survival from the Tarangire Ecosystem, Tanzania 2012‒2019. PA distance is mean distance from the edge of the protected area (km). M = male; F = female, and U = unknown sex.
We concluded that projected climate changes in East Africa, including heavier rainfall during the short rains, will likely threaten persistence of giraffes in one of Earth’s most important landscapes for large mammals, indicating the need for effective land-use planning and anti-poaching to improve giraffes’ resilience to the coming changes.
To survive, animals must find nutritious food and drinking water—sometimes during long dry seasons or cold periods—and at the same time avoid being eaten. Plant-eating mammals with hooves for feet are an extraordinarily diverse group of animals and are critically important in East African savannas. Yet they must compete more and more with humans for space in a fast-changing world while also evading hungry lions, leopards, and other natural predators. A new study by scientists from the University of Zurich’s PopEcol group and Pennsylvania State University, published in the Journal of Mammalogy, investigated the habitat needs of a community of hooved-mammal species in the Tarangire Ecosystem of northern Tanzania, and how vegetation, water, presence of humans, and risks from predators influenced their use of these habitats.
This was the first study of its kind in the Tarangire Ecosystem, which supports the ecotourism hotspot of Tarangire National Park and is the heart of Maasailand where cattle herders and wildlife have thrived together for centuries. Tarangire differs from other areas where wild ungulates have been intensively studied—like Serengeti National Park or Kruger National Park—in that Tarangire’s wildlife, cattle-keeping people, and farmers all share the landscape, and animals can move unimpeded because the entire region is unfenced.
“Ungulates of different body sizes have different needs and threats,” said the study’s lead author Nicholas James, who conducted the research as a graduate student at University of Zurich. For instance, large ungulates like adult giraffes may have less to fear from natural predators but may face more danger from humans, and smaller animals may have more specialized food requirements. “We wanted to know what features draw each ungulate species to certain areas so we can pinpoint important habitat for each of those species,” James said. This information is important for land managers to maintain thriving populations of wild ungulates and keep the landscape healthy, which is the foundation of Tanzania’s important ecotourism economy.
James and his co-authors counted and mapped six hooved mammal species in dry and rainy seasons over seven years in and around Tarangire National Park and the adjacent Manyara Ranch Conservancy, including unprotected village lands. The ungulates studied included the iconic, massive giraffe down to the little dik-dik—both of which specialize on eating leaves of woody plants—as well as the large, water-loving, grass-eating waterbuck, and three medium-sized antelopes that eat both woody-plant leaves and grass, the impala, Thomson’s gazelle, and Grant’s gazelle. The scientists looked at how the different species used areas depending on the type and greenness of plant food, the thickness of the bushes (where lions often lurk), and how far the areas were from rivers (which provide vital drinking water but also hide predators) and cattle herder settlements (where human disturbance is higher but the humans also keep away predators). The study highlighted the importance of food (vegetation) for all species, as well as nearness to year-round rivers for most but not all. Some species appear to be tolerant of human presence and even congregated close to cattle herder settlements, presumably because of lower predator densities there. The researchers found that antelopes that ate both grass and woody-plant leaves allowed them to avoid areas with high human activity while meeting their dietary needs. Importantly, the presence and number of herbivores were sensitive to short and long-term variation in rainfall suggesting they are vulnerable to drought.
“We show that the focus of research and management should be directed towards the Tarangire Ecosystem’s free-flowing rivers and associated habitat along those rivers,” said Derek Lee, associate research professor at Pennsylvania State University and senior author of the study. “In dry landscapes like East African savannas, water resources are increasingly monopolized by humans, so protection of waterways in human-dominated landscapes, and ensuring sufficient access for wildlife is of primary conservation importance.” Another key finding of the study was that traditional cattle herders and some ungulate species can share the same space and thus appear to be compatible, so long as the human impacts remain relatively low.
Dispersal, the process where animals reaching sexual maturity move away from family, is important for maintaining genetic diversity and is key to the long-term persistence of natural populations. For most animals, this involves having to make risky journeys into the unknown in the hope of finding new communities in which to settle and reproduce. However, many animal societies—including those of humans—have structured social communities that overlap in space with one-another. These potentially provide opportunities for maturing individuals to disperse socially without having to make large physical displacements. New research published today in the Journal of Animal Ecologyshows that this strategy is employed by young dispersing giraffes.
The process of moving away from family is known as natal dispersal. Dispersal is a fundamental biological process that has been shown to reduce the chances of mating with a relative, ensuring that individuals have healthy offspring. However, dispersal is first and foremost a social process. Nevertheless, it has been mostly studied as a spatial process because in most animals, families defend physical areas excluding others, forcing young to have to leave this area to establish their own family. A research team, led by University of Zurich (UZH) postdoctoral research associate Dr. Monica Bond, tested whether animals that live in structured societies comprising social communities that overlap in space with one another could disperse simply by switching communities. Doing so would avoid the risks of moving through the unknown.
The researchers studied a large population of hundreds of giraffes in northern Tanzania. Using data on group composition collected over a huge 2200 km2 area, the team found that most male giraffes leave home once they reach reproductive maturity, and that a significant proportion of these achieve their dispersal by simply switching to new social communities, thereby avoiding the risks of moving far from home. On the other hand, most young female giraffes remained within the same community into which they were born. While sex differences in natal dispersal are well established in animals, this study is amongst the first to demonstrate how living in a structured society provides a unique opportunity for maturing individuals to find a new social community without having to move to new areas.
Complex Giraffe Societies
The team of scientists from UZH and Penn State University previously documented that the adult female giraffes form distinct social communities. The membership to these communities, comprising about 60 to 90 individual females, is very stable over time, despite social groups that are made up of these members merging and splitting throughout each day. They found that these social dynamics have two major consequences. The first is that females maintain enduring social bonds with other females in their community, with bonds likely to last over their entire lifetimes. The second is that these communities are completely structured socially, with different communities using the same physical space. Thus, while individuals from different communities might occasionally encounter one another, they rarely, if ever, form groups together.
“This led us to wonder whether maturing young giraffes might forge relationships with the members of nearby female communities that are different from their birth community, to avoid accidentally mating with their relatives, without having to travel long distances into unknown and possibly dangerous places,” says Dr. Damien Farine, co-author and UZH Eccellenza Professor.
What they found was that, like in most other mammals, dispersal was predominately done by males, with dispersers leaving at about 4 years of age. “The key question was then to ask what strategies young males used to find new communities in which they could search for unrelated mates or avoid conflict with relatives,” says UZH professor Dr. Barbara König, senior author of the study.
Females Stay in the Same Social Networks, Males Switch
The team used social network analyses to quantify the social communities of adult females, and then monitored which community 67 male and 70 female calves associated with as they matured over a 7-year period. The data revealed that while four out of five of young male dispersers switched to social communities different from their birth communities, about one in four of the male dispersers switched communities while staying relatively close their birth site. In other words, they were able to disperse without having to move far at all.
“This type of social dispersal, where males remained close to home but joined different female communities, would not be detected if only spatial movements were measured,” says Bond.
Giraffes may not be unique in being able to disperse socially without having to move away from home. In many other species, including dolphins, elephants, and bats, researchers have reported merging and splitting of groups—called ‘fission-fusion’—within a larger, more stable social community. “It would be interesting to see if dispersing socially within the same physical space is a common strategy that is employed in species that live in societies with many overlapping social communities” Bond says. “Given the importance of maintaining healthy populations, the more we understand the natal dispersal process, the better we can help conserve wildlife.”
According to giraffe expert Dr. Fred Bercovitch, who was not part of the study: “This research has crucial implications for the conservation of giraffes because it demonstrates that the preservation of genetic diversity in giraffes requires saving large ecosystems that allow animals to disperse into different communities, and not the translocation of a handful of giraffes to a new area, where breeding opportunities are limited.”
Female Masai giraffes live in distinct social communities of up to 90 other friends, and although areas used by these ‘girl gangs’ often overlap, they have very different rates of reproduction and calf survival. This means the girl gang social units may be important to giraffe evolution. These findings were published this week in the Journal of Wildlife Management by a team of scientists from the Population Ecology group at University of Zurich and Penn State University, as part of one of the largest giraffe studies in the world. “We used social network analysis of hundreds of females and discovered this girl gang social organization from the giraffe’s own preference and avoidance behaviors,” said Derek Lee, associate research professor at Penn State and senior author of the study. “Gang membership was pretty tight, and even though members of different girl gangs often spent time in the same areas, members of different communities rarely interacted with each other.”
The scientists further found that calf survival and reproductive rates were different among these social communities, even when communities’ home ranges overlapped in space and therefore shared similar environmental conditions. “This shows that population structure can arise from social behavior rather than discrete space use,” noted Monica Bond, lead author and research associate at the University of Zurich. “These social subpopulations have different survival and reproductive rates, so some might have greater competitive abilities than others, like being able to dominate the better-quality food, or there might be cultural differences such as having better strategies for protecting their calves from predators.”
Each giraffe social community exhibited different social characteristics, like how strong the relationships were among the community members. There was also a gradient in environmental characteristics in which the giraffe communities lived: the Tarangire region of northern Tanzania where the study occurred includes two national parks, a livestock and ecotourism ranch, and unprotected lands inhabited by traditional cattle ranchers, as well as several densely populated towns surrounded by agricultural lands. The scientists wondered how the environmental or social conditions experienced by the giraffes might influence their survival and reproduction. “Survival and reproduction together determine whether a wildlife population (or subpopulation like a specific girl gang) increases or decreases and is therefore absolutely critical for conservation,” said Lee.
The team calculated the survival rates of more than 1,400 adult females and calves, and the annual number of calves per female, and examined if there were differences among the social communities. They then investigated if the differences were explained by social factors like the strength of relationships, or by features of the environment, such as how close to people the giraffes roamed, the fertility of the soils, or the kind of vegetation in their ranges.
Giraffe calf survival was higher in social communities that had less area of dense bushlands in their ranges, possibly because lions prefer to hunt in such thickets where they can stalk their prey unseen. “We also found that calf survival and reproductive rates were higher in the social communities that spent more time outside of the national parks,” said Bond, probably also because there are fewer natural predators like lions and hyenas near where people live. Some areas outside the parks also had more fertile volcanic soils and therefore possibly more nutritious food than on other soil types.
“The good news for conservation is that giraffes can survive and raise their offspring in areas close to people,” Lee pointed out. “We can help giraffes to thrive by giving them enough living space in the savanna—both inside and outside of national parks—and by taking care not to disturb them and disrupt their social relationships.”
Over the past few years, as part of a collaborative effort between the University of Zurich (Switzerland) and the Botswana Predator Conservation (BPC) and supported by the Botswana Department of Wildlife and National parks, we have equipped dispersing African wild dogs with GPS/Satellite radio collars. The aim of the project is (i) to follow dispersers after emigration from the natal group and to investigate the effect of landscape characteristics on dispersal distance, time and movements, and (ii) to gather crucial demographic parameters such as mortality rate, settlement success, and reproductive success after settlement in a new territory.
Recently, an unusually large coalition of eight brothers born in 2018 has emigrated from their natal pack inhabiting the Third Bridge – Budumtau – Xini region of Moremi Game Reserve. Thanks to the GPS data regularly sent to a base station via the Iridium satellite system, we have been able to remotely follow their movements. After emigration, they covered over 175 km in only five days before hitting the permanent swamp that surrounds the Kwedi Concession in the northern side of the Okavango Delta. During the past month they have been stationary in an area of about 180 km2 stretching between Vumbura Plains Lodge and Mapula Lodge. But dots on a map represent only a small part of the story… Are the eight brothers still together or have they split? What have they been doing? Have they met unrelated females and formed a new pack?
Figure: Movement trajectory of a dispersing coalition of eight male African wild dogs
Despite the collar sends us regular information, keeping up with the dogs over such large areas is almost impossible, unless we can capitalize on “the many eyes out there”. Tourists, guides, camp managers, all can contribute with their sightings towards research. No sooner said than done. We informed people at the lodges about the presence of the dogs in their area and asked them to report of any sighting and to send as many pictures as possible. Just a few days later we received the first information: a group of 9 dogs, including a collared dog, had been seen a few kilometres north of Vumbura Plains by the lodge staff. The pictures allowed identifying five of the original eight males and four unknown females. As expected, the males had indeed split and three brothers had probably gone a separate way. Or had they died during dispersal? An answer to the question arrived just a week later when a second sighting of 12 dogs was reported to us near Bushman Plains camp. Again, thanks to the pictures sent to us, we were able to identify the three missing brothers, who had clearly not died, among the 12 dogs. Future sightings will tell if this newly formed pack composed of 12 dogs will remain together or if some individuals will spin off (process known as secondary dispersal) searching for new mates with whom to build the own pack. But why would some undergo the risks of a second dispersal? Well, because of the eight males and four females only one of each sex will become dominant and reproduce. The others who will remain will help raise future pups but won’t directly reproduce. Therefore, some dogs may decide to take on the extra risk and continue dispersing. Bets are open, and chances are that the three brothers will part again. Time, and your sightings (!), will tell.
We, researcher, can benefits from any report and sightings, as it has been the case here. In return will be able to centralize all information and put together all pieces of the puzzle to share our knowledge with policy makers, stakeholders, and the tourism industry.
Please, keep sharing your sightings with us, of both collared and non-collared individuals, to help us protecting these amazing animals.
A new study by an international team of scientists from the University of Zürich, Max Planck Institute of Animal Behavior and the University of Konstanz, Pennsylvania State University, and Wild Nature Institute showed that communities of giraffes living in proximity to human settlements have a tell-tale signature of disturbed social networks. While many of the most charismatic animal species are social, the effects of human-caused disturbances on the social relationships of wild animals has rarely been studied. The authors applied state-of-the-art social network analyses on 6 years of observations from more than 500 wild adult female giraffes to reveal that human proximity is correlated with weaker and more exclusive relationships with fewer individuals among giraffes. The study, published in the Journal of Animal Ecology, provides the first robust evidence that humans modify social structure in this iconic megaherbivore.
photo by Sonja Metzger
Effects of humans on social structure of wild animal populations has not been widely studied For social animals, including species such as elephants, lions, and giraffes, social behaviour is critical for survival and reproduction. Recent studies on laboratory populations of birds have suggested that disturbances to social groups can precipitate changes to the social structure of those groups, which then has consequences on how the groups can perform at tasks that are important for survival—such as feeding together. Scientists know little about the effects on wild animal social relationships from subtle or indirect disruptions caused by human presence and encroachment into natural habitats.
Field research in Tanzania yields new insights into giraffe social relationships “Detecting signals of natural versus human-caused influences on social relationships among wild animals is challenging,” noted Monica Bond, member of the Population Ecology group at the University of Zürich and primary author of the study. “It requires large-scale studies of individually identified animals across numerous social groups living under different environmental conditions.” Individual giraffes can by identified by their unique and unchanging spot patterns. Over a period of 6 years, Bond and her research collaborators collected photographic identification data spanning 540 adult female Masai giraffes inhabiting a large, unfenced landscape in the Tarangire Ecosystem of Tanzania—an environment that features varying levels of anthropogenic (human-caused) disturbances. Bond’s team documented that the female giraffes in Tarangire live in a complex multilevel society, with individuals preferring to associate with some females while avoiding others. The result of these preferences are discrete social communities comprising 60-90 females with little mixing among the communities, even when these share the same general area. “This study reveals that social structuring is clearly an important feature of female giraffe populations,” noted Barbara König, professor at the University of Zürich and co-author of the study.
In Tanzania, giraffes are tolerated by humans because they do not create conflicts with farmers or livestock. “Despite the public tolerance and hunting restrictions, Masai giraffe populations have declined 50% in recent years,” stated co-author Derek Lee, associate research professor at Pennsylvania State University and leader of the long-term giraffe demography study. Several reasons have been suggested, including illegal poaching, habitat loss and fragmentation, lion predation on calves when migratory herds decline, and changes in food supply. Disruption to social systems also may be a contributing factor in population declines, but until now, anthropogenic effects on social structure of giraffes were unclear.
Using one of the largest-scale metapopulation networks ever studied in a wild mammal, the research team revealed that giraffes living closer to traditional compounds of indigenous Masai people exhibit weaker relationship strengths and more exclusive social associations. “This result signifies a disrupted social environment based upon previous experimental research,” noted Damien Farine of the Max Planck Institute of Animal Behavior and the Centre for the Advanced Study of Collective Behaviour at the University of Konstanz, and senior author of the study. “The patterns we characterise in wild giraffe’s response to proximity to humans reflect the predictions from experimentally disrupted social systems.”
Photo by Christian Kiffner
Near traditional human settlements called bomas, fuelwood cutting can reduce giraffe food resources, and groups of giraffes are more likely to encounter livestock and humans on foot, potentially causing groups of giraffes to split. However, human settlements might also provide protection from lions and hyenas which are fewer near bomas, and in other research the team found that groups of female giraffes with calves tended to occur closer to bomas, and giraffe communities closer to bomas produced more calves per female. “It seems that female giraffes face a trade-off between maintaining important social bonds and reducing risk to their calves near these traditional settlements,” stated Bond. She suggests that traditional pastoralist livelihoods do not necessarily pose a significant risk to giraffe population persistence as long as care is taken not to cause excessive disturbance.
The study’s results imply that human presence could potentially be playing an important role in determining the conservation future of this megaherbivore. Further, the study’s leading-edge methodology highlights the importance of using the social network approach to reveal otherwise hidden potential causes of population declines. “The effects of ever-increasing anthropogenic pressure on wildlife populations are determined by complex interactions of individuals with their social, biological, and physical environment,” said Arpat Ozgul, study co-author, professor at the University of Zürich, and head of the Population Ecology group. “Our study highlights the importance of characterising these complex interactions accurately for gaining much needed insight into population responses to environmental change [or anthropogenic pressure].”
Bond ML, König B, Lee DR, Ozgul A, Farine D (2020) Proximity to humans affects local social structure in a giraffe metapopulation. Journal of Animal Ecology➤
Big congratulations to Dechen. Her poster on the dietary habits of snow leopards in Bhutan got selected among the best posters at the Biology19 conference that was held in Zurich early this year.
The African wild dog is Africa’s most endangered large carnivore and is listed as endangered in the IUCN Red List. Less than 6’000 free-ranging individuals survive in the wild and the species has been given very high conservation priority.
The African wild dog, like few other territorial land species, is characterized by the need for vast semi-pristine and undisturbed areas. This peculiarity makes it particularly vulnerable to habitat loss, deterioration, and fragmentation. This highlights the importance of landscape connectivity between subpopulations in and around protected areas.
A deeper understanding of where and how resident packs and dispersing individuals move, and the demographic consequences of dispersal, is therefore important for the management and conservation of the species over larger landscapes such as the Kavango-Zambesi Transfrontier Conservation Area (KAZA/TFCA).
On Christmas day 2018, we were able to observe the first high-resolution trans boundary dispersal from Botswana’s Okavango Delta to Zimbabwe’s Hwange National Park. This journey highlights the central role of Botswana in the KAZA/TFCA trans boundary conservation effort, as well as the role of the African wild dog as a flagship species.
On 16th December 2018, four sisters dispersed from their pack resident just outside Moremi Gamer Reserve in Botswana. The pack is part of a long term study and is regularly followed by our collaborators on site, the Botswana Predator Conservation Trust. This dispersing coalition is somehow unusual, as it is composed of females born to the same mother but in three different litters (in three consecutive years). The coalition dispersed in an almost straight line moving east and crossed the Zimbabwean border after covering an astonishing 280 km. They continued and covered additional 100 km within Hwange National Park, totalling 360 km in only nine days! Thanks to a collaboration with the Zimbabwean-based Painted Dog Conservation Program, we were able to confirm that all four females are still alive and in good conditions. As they seem to have slowed down a little, the daily covered distance much decreased in the past few days, we expect them to soon associate with unrelated males. The formation of a new pack and the settlement in a new territory is the ultimate goal of dispersal, as successful dispersal allow gene flow between subpopulations and for the recolonisation of empty areas.
We will be able to continue monitoring this dispersal event, thanks to the Satellite technology in the radio collar and to the support of the folks at Painted Dog Conservation in Zimbabwe. Stay tune for more updates on these girls and on future dispersers.
Trans boundary dispersal event from Botswana’s Okavango Delta to Zimbabwe’s Hwange National Park. The blue line represents the dispersal trajectory, the yellow line the international boundaries. The red square represents the last recorded location.
“Kuna twiga pale,” I say in Swahili to our driver Meshak. There are giraffes over there. My partner Dr. Derek Lee and I stand side-by-side in the back of our Land Cruiser, its top opened, and peer through our binoculars at a herd of Masai giraffes (Giraffa camelopardalis tippelskirchi) feeding on umbrella-shaped Acacia tortillis trees several hundred meters away. We are deep in the heart of Tarangire National Park in northern Tanzania, East Africa. “I see at least 12 giraffes,” Derek says. “Let’s head over there.” As our vehicle bumps across the savanna towards the herd, some individuals continue eating and milling around, while some lift their heads and watch our approach, serenely chewing their wads of cud. As long as we advance slowly and do not drive directly towards them, they are unconcerned.
A group of young male giraffes in Tarangire National Park
We carefully scan the ground for aardvark holes and logs hidden in the grass as we proceed forward. The closer we get to the giraffes, it strikes me how absurdly tall and oddly shaped, yet wonderfully elegant these majestic creatures are, the world’s tallest of animals. When we are about 70 meters from the closest giraffe, we swing the vehicle around to see her right side. Derek photographs her while I measure her exact distance away from the camera using a laser rangefinder, so later we can use photogrammetry to calculate her height. I record the photograph number, her distance from camera, and her sex and age class in our field notebook. Moving on to the other giraffes, we weave in and out of the trees and bushes, constantly adjusting our angle to get photos perpendicular to the animal. If we witness a nursing calf, we make a note connecting the cow-calf pair. We also record anything unusual such as signs of disease or injury. After everyone has been photographed, we mark a GPS location in the approximate center of the group, make a final count of all the giraffes, and follow our original tracks back to the road. As we drive off, the giraffes stare after us with their big, long-lashed eyes, chewing intermittently, but otherwise completely unfazed as we depart with more data points in our growing set of thousands of photographic giraffe ‘captures.’
A male giraffe in Tarangire National Park
Derek and I are implementing the world’s largest individual-based demographic study of giraffes in terms of sample size and area sampled. We conduct six surveys per year towards the end of each of Tanzania’s three precipitation seasons, with every survey lasting about 10 days. We are investigating births, deaths and movements of giraffes in the Tarangire ecosystem—a region undergoing rapid anthropogenic land-use changes—to understand where they are doing well and why, and using that information to conserve declining giraffe populations. For my PhD in the Program Ecology at the University of Zürich, I will be using our photographic capture-recapture data to study giraffe natal dispersal patterns and to quantify the fitness consequences of their social dynamics. I am part of both the ‘Population Ecology’ and the ‘Cooperation and Social Structuring in Mammals’ research groups.
Monica Bond holds a giraffe skullDr. Derek Lee photographs a giraffe for identification in Tarangire National Park
Despite being an African icon and one of the planet’s last mega-herbivore species, giraffes remain understudied in the wild. In part, this is because giraffes were not intensively hunted until recently in some areas: they don’t produce tusks or horns that are coveted as trophies or medicine and they are not an aggressive species. Sadly, however, giraffes are becoming increasingly endangered throughout their range in sub-Saharan Africa due to conversion of savanna woodland habitat to agriculture, deforestation for charcoal, and bushmeat poaching.
A giraffe browses on Acacia
Giraffe numbers have plummeted across Africa by an estimated 40 percent in the last few decades, to the point where they now number far fewer than African elephants. The IUCN recently upgraded the species Giraffa camelopardis to “vulnerable” on the Red List (while scientists are debating the number of species, all giraffes are currently still considered to be one species). Most giraffe populations are now largely restricted to lands in and around national parks. Predation by lions and hyenas also can negatively affect giraffe survival—a natural phenomenon that becomes a problem as wildlife are squeezed into small protected areas.
Lions prey upon giraffe calves and sometimes adults
After decades of little research on the wild giraffes, scientists are showing renewed interest in these gentle giants because of their declining numbers. Derek and I began photographing individual giraffes in 2011 to build a database of demographic information on giraffes across the Tarangire ecosystem. This region, which contains two national parks and a large private ranch embedded within a matrix of village lands, is known for its extraordinary diversity and abundance of large mammals including giraffes, elephants, zebras, antelopes, lions, and leopards, but these magnificent animals exist in a landscape undergoing rapid changes.
Drinking can be awkward for a giraffe
The Tarangire ecosystem is second in giraffe density only to the nearby world-famous Serengeti ecosystem, but unlike the Serengeti, land in Tarangire is largely unprotected. Since the 1940s, human population and agricultural expansion in Tarangire have increased fivefold, causing substantial habitat loss and fragmentation. Bushmeat poaching is also a serious problem—recent research suggests that each year poachers kill about 90 giraffes in just one small part of the Tarangire ecosystem. Giraffes are hunted at night, dazed by spotlights or confused by loud horns and killed with machetes or spears; giraffes are also targeted with wire neck snares set high in the tree canopy.
Monica Bond speaks with local Masai tribal members
We study wild giraffes using two technologies, digital photography and pattern-recognition software, to identify and track individuals by their coat patterns. Every giraffe has unique and unchanging spot patterns, much like the human fingerprint. These patterns enable us to identify and monitor individual giraffes with the aid of a computer algorithm that matches the thousands of photographs we collect during our surveys. We can determine where and when we last saw the animal, whether a female was pregnant or nursing, and who else was in the herd. Demographic studies of uniquely patterned species using the non-invasive photographic method have grown in popularity as digital cameras and pattern-recognition software have improved. These technologies allow us to compile demographic data on thousands of giraffes—sample sizes unheard of in the days before computers. The method is also much less expensive than physical captures for marking of large mammals, and is entirely non-invasive and non-traumatic. Other recent demographic studies using pattern-recognition software with digital photographs have been conducted on wild dogs, wildebeests, and even toads (my UZH colleagues Sam Cruickshanck and Benedict Schmidt just published a study on yellow-bellied toads in Switzerland using the same pattern-recognition software that we use).
Wild ID pattern-matching computer software
To date we have identified and are monitoring over 3,100 individual giraffes. We aim to understand factors affecting survival and reproduction in landscapes subjected to different human uses, including parks and village lands, and also to identify important calving grounds and critical movement pathways. My PhD research will help ascertain how human and natural factors influence sociality and fitness, and how these mega-herbivores move around the ecosystem, which will provide insights into what may be the most effective conservation measures. The ultimate goal is to enable healthy populations of giraffes to continue roaming across this ecosystem as they have for eons, fulfilling their important ecological functions and delighting humans for generations to come. The Masai Giraffe Conservation Demography Project is being conducted by the Wild Nature Institute. Visit their website to learn more.
