giraffe – PopEcol

Rising Rainfall, not Temperatures, Threaten Giraffe Survival

July 3, 2023July 3, 2023 by Monica Bond

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.

The paper is available for download at https://doi.org/10.1007/s10531-023-02645-4

Leaving by Staying: Dispersal Decisions of Young Giraffes

September 20, 2021 by Monica Bond

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 Ecology shows 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.”

Giraffe Social Communities are Important to Giraffe Populations

April 8, 2021 by Monica Bond

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.”

Friends Matter: Giraffes that Group with Others Live Longer

February 10, 2021 by Monica Bond

Adult female giraffes who spend time in larger groups with other females live longer than less sociable individuals. The effects of sociability on survival outweigh other factors such as environment or human presence, a study of giraffes in Tanzania led by the University of Zurich has shown.

The research team, including UZH PopEcol members Monica Bond and Arpat Ozgul, studied giraffes in Tanzania for five years. The biologists examined the relative effects of sociability, the natural environment, and human factors on survival of the mega-herbivore. They have now shown that adult female giraffes living in larger groups have higher survival chances than more socially isolated individuals. The study was published today in the Proceedings of the Royal Society B.

Gregariousness leads to better survival

Giraffe group formations are dynamic and change throughout the day, but adult females maintain many specific friendships over the long term. “Grouping with more females, called gregariousness, is correlated with better survival of female giraffes, even as group membership is frequently changing,” says Bond. “This aspect of giraffe sociability is even more important than attributes of their non-social environment such as vegetation and nearness to human settlements.”

The benefits of many friends

Aside from poaching, the main causes of adult female giraffe mortality are likely to be disease, stress or malnutrition, all of which are interconnected stressors. “Social relationships can improve foraging efficiency, and help manage intraspecific competition, predation, disease risk and psychosocial stress,” says UZH professor Barbara König, senior author of the study. Female giraffes may seek out and join together with an optimal number of other females in order to share and obtain information about the highest-quality food sources. Other benefits to living in larger groups might be lowering stress levels by reducing harassment from males, cooperating in caring for young, or simply experiencing physiological benefits by being around familiar females. The study also finds that females living closer to towns had lower survival rates, possibly due to poaching.

Social habits similar to humans and primates

The team documented the social behaviors of the wild free-ranging giraffes using network analysis algorithms similar to those used by big-data social media platforms. According to the results, the giraffes are surprisingly similar in their social habits to humans and other primates, for whom greater social connectedness offers more opportunities. Chimpanzees and gorillas, for example, live in communities where ties between many individuals facilitate the flexibility of feeding strategies. “It seems to be beneficial for female giraffes to connect with a greater number of others and develop a sense of larger community, but without a strong sense of exclusive subgroup affiliation,” adds Monica Bond.

Human presence weakens social relationships of wild giraffes

June 10, 2020 by Monica Bond

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.

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.”

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 ➤

On the Trail of Giants: Population Ecology of Giraffes in Tanzania

November 23, 2017November 22, 2017 by Monica Bond

“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.

Dr. 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.

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.

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.