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.
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.
The diversity of bird communities in the Swiss Alps is declining more and more, a joint study of the University of Zurich and the Swiss Ornithological Institute has found. An analysis of data from the past two decades has revealed a loss of functional and compositional diversity in Alpine bird communities. This trend is likely connected to rising temperatures and changes in land use.
Ecologists believe that global climate change has had a particularly strong impact on animals and plants living in alpine regions, with expected changes in the distribution, abundance and interaction of species. There is evidence that the habitats of some bird species in Switzerland – such as the tree pipit or the European pied flycatcher – have shifted to higher altitudes in the past two decades. However, the impact of these changes on the composition of bird communities was previously unknown.
Our new study, in collaboration with the Swiss Ornithological Institute (Vogelwarte) has shed new light on this issue. Our study, which is based on two decades’ worth of data collected by volunteer ornithologists, reveals a downward trend. We found that bird communities in the Swiss Alps are undergoing a process of biotic homogenisation; in other words, birds living in this region are becoming less and less diverse.
The crossbill is one of the most functionally distinctive species included in the study. (photo by Valentin Graf)
Functional diversity is important One of the most obvious and simplest ways to measure the diversity of bird communities is by the number of species living in them. However, beyond species richness, the functional diversity of a certain community also provides valuable information. “Different species use resources and interact with the environment in different ways,” says first author, Vicente García-Navas. “Not all species play the same role in an ecosystem. The loss of a given species can be more detrimental than that of several others.” Specialists such as some woodpecker species are particularly important. The holes that they make are used for nesting and as hiding places by other birds and small mammals.
To quantify this functional diversity of bird communities, we compiled information on 100 traits characterising, among other things, the body mass, diet and habitat of each species. This enabled us to examine how the functional diversity of communities changes along the altitudinal gradient and to determine the trend over the past two decades.
High-altitude specialists on the edge Our analyses suggest that the upper forest boundary represents a functional barrier between two distinct groups. One group comprises the lowlands dominated by agriculture landscape and high mountain forests, where species such as the yellowhammer, the common whitethroat and the blackcap live. The other is composed of alpine communities, whose species are adapted to life in the open habitats above the treeline. For example, these species eat fewer caterpillars and build their nests on the ground, such as the rock ptarmigan.
However, the data analyses revealed that functional diversity of Alpine bird communities has decreased over the past few years. “Our study shows that mountain specialists are under increasing risk of becoming misfits,” says co-author Arpat Ozgul. The combined effects of habitat shrinkage, impossibility to find optimal habitats at higher elevations, and upward invasion by generalists are critical factors for these species.
The rise of generalist species This increase in generalist species such as the robin or the European pied flycatcher might also be a reason for the downward trend in the level of variation, or beta diversity, among communities. Our study also found that Alpine bird communities are becoming more and more redundant, with less variation.
“Overall, the study’s results suggest that the joint effect of global warming and land-use changes are boosting an impoverishment of bird communities in the Alps,” says García-Navas. This promotes shrub encroachment and is pushing the treeline upwards, which requires urgent conservation and management actions.
Many animals have evolved life cycles and strategies (patterns of survival and reproduction) in line with predictable seasonal variation in environmental conditions. Short and mild summers produce bursts of vegetation and food, the perfect time to give birth to young. Long, harsh winters when food is scarce have shaped animals to largely depend on fat reserves for energy, and in extreme cases, to hibernate or migrate.
However, climate change is altering these seasonal conditions to which many species are adapted. Temperatures are increasing, winter snowfall is declining, snow is melting earlier, summers are extending, and the frequency of extreme events (e.g., droughts, floods) are on the rise.
Our study, published in the Proceedings of the National Academy of Sciences USA (July 6 2020), found that marmot survival is affected differently by climate change during summer and winter seasons.
In this research, we analysed 40 years of life-history data, collected at the Rocky Mountain Biological Laboratory in Colorado, to understand how yellow-bellied marmots (large burrowing ground squirrels) have responded to climate change during their active summer season and the long winter hibernation.
Dr. Line Cordes, lead author from the School of Ocean Science at Bangor University: “Yellow-bellied marmots are a key indicator species for disentangling the seasonal impacts of climate change as they have a very distinct seasonal life history. They are found in western North America where climate change is more evident than anywhere else on the continent (with exception of the Arctic). Although they are a large rodent (reaching up to 6.5 kg), they are too small to remain active during winter and therefore hibernate for approximately 8 months. Marmots depend on energy stores acquired over the summer, and particular conditions to remain in deep torpor, which lowers energetic costs. Despite hibernation being an effective survival strategy in harsh environments, marmots can still lose up to 40% of their body weight.”
Over the course of four decades (1979-2018), marmot survival generally increased during summer but decreased during winter, and these effects were greatest among pups and one-year-olds.
Climate change at the study site has resulted in warmer winters with less snowfall, and warmer, drier summers which have become significantly longer in duration. Despite the similar seasonal survival trends across pups, one-year-olds and adults, the environmental factors driving these trends differed between the age-classes and seasons. For example, pup summer survival was higher following winters with reduced snowfall, possibly as mothers of these pups were in better condition during pregnancy and while caring for the pups as forage plants appeared sooner due to an earlier snow melt. Winter survival was lower following long, dry summers, most likely as pups were in poorer condition going into hibernation.
Dr. Arpat Ozgul, senior author of the study from the Department of Evolutionary Biology and Environmental Studies at the University of Zurich, said: “The effects of climate change on the fate of a population are determined by the complex interactions of individuals with their biological and physical environment. Our study shows that we need to characterize these complex interactions accurately in order to predict the ultimate effect of climate change on the fate of a population. Critically our findings highlight the care that should be taken in drawing conclusions from annual survival responses to climate change, as this may be a misinterpretation, simplification or even underestimation of the actual more complex responses that can differ dramatically across different times of the year.”
Until now climate change has affected marmot survival positively during the summer months while leaving marmots more vulnerable during winter hibernation. Overall, the net change in survival was negative for pups, positive for yearlings, while there was no change for adults. It is important to note that continued climate change may change the patterns we observed in summer survival, as the persistence of forage plants would ultimately be impacted by progressively warmer and drier summers. Indeed, no marmot population is found in persistently warm and dry habitats.
The fact that climate change may benefit certain species during one season while resulting in unfavorable conditions during another season has potentially wide-ranging consequences across other species occupying temperate to more extreme habitats, such as deserts, mountains and polar regions, where the most rapid changes in climate are being observed. For wildlife living near the poles or near mountain tops, like marmots, there is nowhere to go when environmental conditions become less suitable.
Dr. Line Cordes added: “Social, burrowing, herbivorous mammals, like marmots, play an important role in ecosystem function as they help shape important habitats, and serve as prey for many predators. The loss or decline of these species would likely have wider reaching implications for biodiversity of montane habitats.”
The research was carried out by scientists from Bangor University and the Universities of California Los Angeles, Kansas, Sheffield, Rhode Island, Ottawa, Florida, Zurich, and Chicago Botanic Garden. This research would not have been possible without Ken Armitage who initiated and led this project from the early 1960’s – one of the longest running mammalian studies. We would also like to thank all the “marmoteers” who contributed to long-term data collection. Nor would it have been possible without Billy Barr and the Rocky Mountain Biological Laboratory for the long-term collection of local environmental data. The study has been funded by the Swiss National Science Foundation, the National Geographic Society, UCLA, a Rocky Mountain Biological Laboratory fellowship, and NSF.
Accelerometers, Ground Truthing, and Supervised Learning
Accelerometers are sensitive to movement and the lack of it. Accelerometers are not sentient and must recognise animal behaviour based on a human observer’s cognition. Therefore, remote recognition of behaviour using accelerometers requires ground truth data which is based on human observation or knowledge. The need for validated behavioural information and for automating the analysis of the vast amounts of data collected today, have resulted in many studies opting for supervised machine learning approaches.
Ground-truthing. The acceleration data stream (recorded using the animal-borne data logger, bottom-left) is synchronised with simultaneously recorded video (near top right). Click on photo to view larger version. Photo credit: Kamiar Aminian.
In such approaches, the process of ground truthing involves time-synchronising acceleration signals with simultaneously recorded video, having an animal behaviour expert create an ethogram, and then annotate the video according to this ethogram. This links the recorded acceleration signal to the stream of observed animal behaviours that produced it. After this, acceleration signals are chopped up into finite sections of pre-set size (e.g. two seconds), called windows. From acceleration data within windows, quantities called ‘features’ are engineered with the aim of summarising characteristics of the acceleration signal. Typically, ~15-20 features are computed. Good features will have similar values for the same behaviour, and different values for different behaviours.
To automatically find robust rules to separate behaviours based on feature values, machine learning algorithms (e.g. Random Forest etc) are used. Here, candidate algorithms are trained (i.e. each algorithm is shown which datapoints correspond to which ground truthed behaviours). From here, algorithms are then tested by asking them to classify datapoints they haven’t seen yet into one of the behaviours. How well the algorithm does on testing data determines its ‘performance’. The model with the best performance wins and is selected for final use. Different ways of doing training and testing give rise to different forms of ‘cross-validation’.
Leveraging the Biomechanics Underlying Common Animal Behaviour
All animal behaviour is performed for a finite duration, following which the animal transitions to a different behaviour. The animal may be static for a while (e.g. resting), then begin foraging (involving movement), and then, perhaps perceiving threat, run (involving vigorous, periodic motion). Different behaviours may be performed in different postures (e.g. upright during vigilance, and horizontal while running).
We targeted an ethogram applicable to most animals: resting, foraging, and fast locomotion. This ethogram is a good match between covering most of an animal’s time budget and includes behaviours that an accelerometer is capable of ‘seeing’. For this however, features developed from the accelerometer signal must somehow be able to quantify posture, movement intensity, and movement periodicity. We reasoned that three well-engineered features – one each to quantify the posture, intensity, and periodicity – should be able to tell these three behaviours apart.
Feature engineering. Three biomechanically meaningful features were engineered from acceleration data – one each to characterise posture, movement intensity, and periodicity.
Using this approach, we predefined a hierarchical tree-like scheme that classifies broader behavioural categories into increasingly specific ones up to the desired level of behavioural resolution. Each node of this tree uses one or more features tailored to the classification at that node. Robust machine learning algorithms find optimised decision boundaries to separate classes at each node.
We demonstrate the application of this approach on data collected from free-living, wild meerkats (Suricata suricatta). The model accurately recognised common behaviours constituting >95% of the typical time budget: resting, vigilance, foraging, and running.
Model Performance: Leave-One-Individual-Out (LOIO) Cross-Validation
The ultimate goal of many behaviour recognition studies is to build models that will accurately classify data from a new individual previously unseen by the model. Leave-one-individual-out (LOIO) cross-validation is most appropriate to characterise the model’s ability to do this. Here, training is performed using data from all individuals but one, and the left-out individual’s data is used as the testing set. This process is carried out until each individual’s data has been the testing set exactly once.
Model validation. When it comes to evaluating model performance, a crucial aspect that sets leave-one-individual-out cross-validation (CV) apart is that it can test how well the model performs on data from an individual unseen by the trained model. Other approaches, such as train-test split (hold-out) mix data from different individuals, and hence cannot evaluate the model’s capability to generalise to new individuals. Note that for the sake of clarity, we’ve shown all individuals to have an equal number (M) of datapoints; in general, this might not be the case.
Reporting Metrics for Each Behaviour Reveals Fuller Picture of Model Performance
Overall accuracy (i.e. the sum of diagonal elements divided by the sum of elements in the confusion matrix), alone can be misleading and uninformative when it comes to characterising model performance in animal behaviour recognition applications. This is because of the issue of imbalanced classes, where durations of continuously filmed behaviours are naturally unequal. This makes the detection of rarer behaviours problematic.
Thus, overall accuracy alone cannot reliably guide model selection. A good model is one that has good sensitivity and precision for each behaviour of interest. This automatically guarantees good overall accuracy, whereas good overall accuracy does not guarantee good behaviour-wise performance.
Benefits of Biomechanically ‘Aware’ Learning
In our paper ‘A novel biomechanical approach for animal behaviour recognition using accelerometers’, we show that the proposed biomechanically driven classification scheme performs better than classical approaches based on black-box machine learning. Further, it is better able to handle the issue of imbalanced classes. Biomechanical considerations in the model can help provide valuable feedback on processes further upstream that are inaccessible to classical machine learning, such as defining the ethogram. The interpretability of the model sheds light on why some classes get consistently misclassified.
Grouping behaviours by biomechanical similarity in a hierarchical classification scheme can allow model sharing between studies on the same species. This eliminates the need to build entire models from scratch every time a new set of behaviours are to be recognised, as would have to be done with classical machine learning approaches.
Finally, we recently showed in this Movement Ecology methodological paper that our classification framework can be extended to magnetometer data as well. This helped to understand the similarity and complementarity of accelerometers versus magnetometers for behaviour recognition.
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➤
“…The scope of the workshop is to investigate several aspects of animal movement and spatial use and to relate them to newest challenges in wildlife management and conservation…”
10–15 January 2021
Faido, Ticino, Switzerland
Understanding how animals respond to human-induced degradation and fragmentation of suitable habitats is critical for developing appropriate management and conservation plans. New technologies have made it possible to collect animal location data and remotely sensed environmental data at finer spatial and temporal scales. This workshop will provide participants with a quantitative toolset to leverage these data sources so that they can address emerging questions in the field of animal movement ecology.
During day one, participants will learn how to source landscape information through freely available remote sensing imagery and to import, manipulate, and represent georeferenced environmental data in R. Environmental data may represent ecological (e.g. habitat types, topography) or human activities (e.g. landscape use, settlements distribution). The aim of day one is to give participants a toolset that enables them to obtain and prepare environmental information that can be used to understand and explain animal movement patterns and space use.
Day two will be dedicated to the decomposition of movement trajectories and characterization of movement modes and phases. Participants will be exposed to the concept of net-squared displacement, an analytical method used to classify movement trajectories into alternative modes such as sedentarism, nomadism, dispersal, and migration. These statistics can be fed into generalized linear mixed models to investigate the factors responsible for the emergence of such patterns.
During day three, participants will be exposed to methods commonly used to quantify animal home ranges; the pros and cons of these methods will also be discussed. Alternative methods such as minimal convex polygons, kernel density estimators, local convex hulls, and brownian bridges will be presented. Particular attention will be given to the temporal scale of the analysis and on the environmental and anthropogenic factors that influence home ranges.
During the next day, we will use presence/absence data to analyze habitat selection and create species distribution models. Participants will be exposed to the most common methods used to investigate habitat preferences such as resource-selection functions, step-selection functions and integrated step-selection functions. Assumptions and limitations of each method will be addressed.
Finally, during the last day, participants will discover how to apply what they learned during the first four days of the workshop to develop evidence-based recommendations for the management of their study subject. In particular, participants will learn how to create various connectivity maps. Connectivity between populations is one of the most important aspects in the management of wild population in human-dominated landscapes. Lastly, we will discuss new research avenues and research gaps that will need to be addressed in the future for the integration of the spatial dimension in the conservation and management of animal species.
For additional information and registration please contact Gabriele Cozzi at gabriele.cozzi@uzh.ch
This workshop is supported through funding by the UZH Graduate Campus
Please note: the date may be changed due to the current Corona virus situation
Masai giraffes are the world’s tallest herbivores and beloved by people around the globe, but were recently classified as an endangered species by the International Union for Conservation of Nature (IUCN). New research published in Oecologia showed how food, predators, and people all influence giraffe social behavior. In particular, the international team of researchers from University of Zürich and Penn State University pinpointed the special requirements needed by mother giraffes to keep their babies safe, which can help land managers to protect the places most important for giraffes.
Giraffes foraging in Tarangire National Park, Tanzania
“Like all herbivores, giraffes need to find quality food to survive, but also need to avoid lions, or at least see them coming,” noted Monica Bond, PhD candidate at the Department of Evolutionary Biology and Environmental Studies, University of Zürich, member of the Population Ecology research group, and lead author of the paper. “Giraffes in our huge, unfenced study area can choose from among many different places to spend their time – places with different kinds of trees and bushes, and places deep inside protected parks or closer to farming towns or ranchlands where people live. There are lots of options in this landscape, including fewer lions outside the parks versus inside. So we wondered, how do these options influence giraffe grouping behavior? These data help us know what places are most important for these magnificent animals.” The study found that groups composed of adult giraffes were food-focused, not affected by predation risk. Adults formed the largest groups, up to 66 individuals, in the rainy season when food is plentiful, but smaller groups during the dry season when food is harder to find. In contrast, predation risk was a very important factor influencing congregations with calves.
Lions are the major predators of giraffe calves
“Giraffe calves are vulnerable to being killed by lions and other carnivores, while adults are typically large enough to escape predation,” stated senior author Barbara König, professor at the University of Zürich. “We were testing hypotheses about mother and calf behavior to see if their strategy was for calves to hide in thick bushes to avoid predators, be in the open to see predators coming, or be in large groups for many eyes and lower individual risk.” The researchers documented that in areas with the most lions, groups with calves were found more often in dense bushes than open grasslands, and those groups were smaller in size. This suggests giraffe mothers and calves have a strategy of hiding in dense bushes, rather than staying in open areas to better see lions, or gathering in large groups to dilute the predation risk. These results mean that dense bushlands are important habitat for giraffe calves and should be protected. Some cattle ranchers promote shrub removal to encourage grass for their livestock, but they share the rangelands with giraffes and other browsers that use shrubs.
The study also explored the influence of humans on giraffe grouping behaviors. “Outside the parks the human population has been rapidly expanding in recent years,” said Derek Lee, associate research professor of biology at Penn State University and co-author of the study. “Therefore, we felt it was important to understand how human presence affected grouping behavior, as natural giraffe habitat is ever-more dominated by people.” Interestingly, adult females with calves were more likely to be found closer to traditional pastoralist compounds called bomas, made by livestock-keeping, non-farming people. “We suspect this is because the pastoralists may disrupt predator behaviors to protect their livestock—and this benefits the giraffe calves,” noted Lee. Conversely, calf groups avoided areas close to farming peoples’ towns, suggesting a difference between traditional bomas versus more densely populated human settlements for giraffe mothers seeking food and safety for themselves and their calves.
Giraffes congregating on the shore of Lake Manyara National Park, Tanzania
“We were happy to find that traditional human settlements by ranchers appear to be compatible with the persistence of giraffe populations,” stated Bond. “But on the other hand, disturbances around towns likely represent a threat and should be limited in areas favored by giraffes.” The study was part of the world’s largest giraffe research project and used data from six years of systematic seasonal surveys across a 2,000 square kilometer area. The University of Zürich’s Population Ecology research group and its collaborators are at the forefront of giraffe conservation science. Learn more about giraffe research and conservation at http://www.wildnatureinstitute.org/giraffe.html
At present only in Swiss German, the English version will follow soon. For now, if you do not understand Swiss German, just lay back and enjoy some beautiful footage, of an amazing species 🙂
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.
