Common toads are explosive breeders: right after their winter rest they all head to the pond within a few weeks, and the males try to grab a female on the way or in the water. A male holds on to the female’s back, in a mating embrace called amplexus, often for several days until she lays her eggs. Single males keep trying to push paired males off.

The pond lies at 1,850 m below the Grosse Scheidegg pass, near Grindelwald. Every spring since 1982, toads there have been caught at night, weighed, measured, marked and noted as single or paired, and with whom: 2,122 males and 1,323 females in all. The number of males per female varied from 0.8 to 8 between years, which let us see how competition shapes who mates.

Size matters. A male of 70 mm (snout to vent) was 18 percentage points more likely to be paired than one of 60 mm, and 14 points less likely to be pushed off once he had a female. The more males there were per female, the lower each male’s chance: going from one to eight males per female lowered it by 56 percentage points. The number of toads at the pond, on its own, made no difference.

Age matters too, the other way round. Toads keep growing throughout life, so old males are big males, and they should do well. Yet a male that had been coming to the pond for ten years was 15 percentage points less likely to be paired than a first-timer of the same size. This decline in mating success with age, called reproductive senescence, is well known in birds and mammals but has rarely been shown in amphibians.

Does mating cost a male his life? Paired and unpaired males survived equally well from one year to the next (74% and 73%), and we found no sign that males skip breeding years. First-time breeders, however, survived less well (61%). One possible reason is inexperience: novice males may spend too much energy on fights they cannot win.

Long-term data like these are rare, and they exist only because so many people have kept the fieldwork going at this pond for four decades. The study was done with our co-authors from Info Fauna karch, the Federal Office for the Environment and independent researchers, together with Omar Lenzi and Benedikt Schmidt. For more on the same toads, see our earlier post on how they now breed a month earlier than 40 years ago, and our project on amphibian and reptile conservation.

Having spent his MSc with cold-blooded toads, Daniel has since moved on to warm-blooded animals: he is now doing his PhD in our group on the management of wild ungulates in Switzerland. We will let you know whether old stags fare any better than old toads.

In northern Bhutan, snow leopards share alpine meadows with yak herders, and the loss of livestock can turn people against them. In 2018, forest staff interviewed people from 1,046 randomly chosen households around six protected areas, using a questionnaire adapted from our earlier study of wolves in Switzerland.

Of the 835 people who answered every question, 79% were in favour of snow leopards and 12% against. Acceptance was higher among men, crop farmers, and people who knew about the fines for killing a snow leopard and the livestock insurance scheme, which only 27% knew of. It was lower at higher elevations, among yak herders and collectors of Cordyceps (a valuable mushroom), and among people who had lost livestock.

Laid over the habitat map, the acceptance map shows that suitable habitat where snow leopards are also accepted covers 5,696 km², 41% of the study area and 91% of all suitable habitat. Suitable habitat with low acceptance, where conflict could arise, covers 2,003 km² (15%).

No one in Bhutan has been reported killing a snow leopard in revenge for lost livestock. To keep it that way, we recommend better livestock protection, fair compensation, wider awareness of the insurance scheme and the law, outreach to women, who tend the livestock and were the least accepting, and working with monasteries. Our co-authors in the group are Dominik Behr, Stefan Sommer and Gabriele Cozzi, and the work is part of our project Snow leopards in Bhutan.

Every giraffe has its own coat pattern, which stays the same from birth to death and is partly inherited from its parents. Spots may help calves hide from predators, but they may also help giraffes control their body temperature: under each spot runs a network of blood vessels that can release heat. If that is the case, which spots are best should depend on the weather.

In our Masai giraffe project in the Tarangire Ecosystem of northern Tanzania, we photograph every giraffe we meet, three times a year, and recognise each one by its coat. For this study we measured the size and shape of the spots of 810 giraffes from photographs taken between 2012 and 2020, and compared them with how long the animals survived and with how unusually hot or cold each season was.

Spots mattered most for calves. Calves with smaller spots, and calves with more irregular, lobed spots, survived better. Temperature changed the picture: in unusually cold seasons, calves with large spots did best, perhaps because larger dark patches absorb more sunlight; in unusually hot seasons, they did worst. Calves with small spots survived about equally well whatever the weather.

Adults differed by sex. In adult males, survival in unusually cold seasons was lowest for those with the smallest spots, and in hot seasons the pattern reversed, though more weakly. Adult females were less affected by their spots, but all females survived less well in unusually hot seasons. As far as we know, this is the first time that spot patterns have been shown to affect survival in adult mammals.

Why does this matter? Giraffes are long-lived and breed slowly, so the survival of adults drives whether populations grow or shrink. If different spot patterns do best under different weather, the variety of patterns within a population may help it cope with a changing climate. Keeping giraffe populations connected, so that animals and their genes can move between them, would help keep that variety.

The study was done with our long-time partners Derek Lee and James Madeli of the Wild Nature Institute and Douglas Cavener of Pennsylvania State University, together with Arpat Ozgul. For more on the same giraffes, see how rainfall, not rising temperatures, threatens their survival, and how baby giraffes hide in bushes from predators.

As always, we thank our donors and partners for supporting our giraffe research.

David Lack, who started the Wytham great tit study in 1947, argued that each female should raise the number of young that gives the most surviving offspring, because more chicks means less food for each. We used data from 1961 to 2018: 7,287 broods of 5,032 females and 53,753 chicks. A recently developed statistical model let the links between brood size, chick weight and later breeding change from year to year, with spring temperature and rainfall, the number of great tits, the beech seed crop, and how well breeding was timed to the peak of caterpillars, a key food for the chicks.

Mothers with larger broods had lighter chicks in all kinds of years: this trade-off was strong and barely affected by the environment. The benefit of heavy chicks, however, depended on the year. In harsh seasons, with a cold or dry spring or many great tits competing, heavier chicks were more likely to join the breeding population. In good seasons this advantage disappeared. Contrary to Lack’s expectation, brood size itself was not linked to how many young went on to breed, though this estimate was uncertain.

We did the study with the University of Oxford’s Edward Grey Institute, the University of Sheffield, Eawag and the Estación Biológica de Doñana. The approach could be applied to the many long-term bird studies that share their data through SPI-Birds.

The dewy pine (Drosophyllum lusitanicum) grows in the heathlands of southern Spain, Portugal and northern Morocco. It catches insects on sticky droplets on its leaves, and it depends on fire: after a fire clears the shrubs, its seeds germinate in large numbers. In many places, however, fire has been replaced by grazing or by clearing the vegetation by machine, and most dewy pines now grow in such disturbed sites.

Together with colleagues at the University of Cádiz and Maria Paniw, we followed 4,753 plants for seven years in three natural heathlands and five disturbed sites, and related their survival, growth and flowering to summer heat and rainfall. Hotter summers lowered survival everywhere. In the natural heathlands, rainy years made up for some of this, but in the disturbed sites they did not.

We then projected the populations 30 years into the future under climate change. The natural populations kept the same, fairly low, risk of dying out. The populations in disturbed sites, already declining today, were almost certain to disappear.

What does this mean for conservation? Natural heathlands need their fires, or other ways of opening up the vegetation now and then. In disturbed sites, further disturbance should be avoided, and some shrub cover could shade the dewy pines from extreme heat. More broadly, the study shows why we need long-term studies in landscapes used by people, not only in protected areas.

Together with our partners, we found that giraffe numbers in the centre of the Serengeti’s protected areas have been stable since the late 2000s, after major declines in earlier decades. But near the edges of the protected areas, giraffe numbers are still falling.

“We needed to understand whether protected areas in the Serengeti were effectively conserving giraffes,” says George Lohay, co-author and Head Scientist at the Grumeti Fund. “Our results clearly show where giraffes are doing well and where urgent action is needed.”

We put together several years of photos and identified 1,520 individual Masai giraffes in four subpopulations (groups living in different parts of the Serengeti). With statistical models, we estimated how many giraffes survived each year, how many calves were born, how many giraffes lived in each area, and how often they moved far. Adult survival differed a lot between subpopulations, and where fewer adults survived, numbers went down.

“Adult survival emerged as the strongest demographic driver of giraffe population trends,” says Dominik Behr, who led the study together with me. “This means that improving adult survival is key if we want to prevent further declines.”

We also found that giraffes hardly move between subpopulations: only one giraffe was seen crossing from one to another. So the subpopulations are quite isolated, and few genes flow between them. Over time this could lower their genetic diversity and raise the risk that a local population dies out.

Giraffes have unique coat patterns, which we use to identify individuals from photographs. We combined all available giraffe images, taken during road surveys and by camera traps, to follow the fate of each individual and estimate population trends over time.

Earlier studies in the 1970s and 2000s had found dramatic declines, but land use and tourism have changed since then, so it was time for a new look. The central and southern subpopulations, in the middle of the protected areas, are now stable. The western and northeastern ones, along the borders of the protected areas, are still declining. Each subpopulation needs its own conservation plan.

“The best way to conserve giraffes and other large mammals is by protecting large areas of intact habitat,” says George Lohay. “Community conservation efforts have successfully raised adult survival in other parts of Tanzania. Scaling up these initiatives around the Serengeti could make a critical difference.”

“Our work shows how long-term demographic monitoring can guide conservation priorities in complex ecosystems,” says Arpat Ozgul, senior author of the study. “Targeted efforts that improve adult survival in key areas could determine the fate of these isolated subpopulations.”

We did this work with colleagues from the Wild Nature Institute, Pennsylvania State University, Estación Biológica de Doñana and the Grumeti Fund’s RISE program. It is part of our Masai giraffe project and our work on populations under environmental change.

We analysed 30 years (1984–2014) of data from the Serengeti Lion Project, led by Craig Packer: 1,347 individually known lions in 65 prides and 242 male coalitions (stable groups of males). For each season, we asked how survival, growing up, breeding and the raising of cubs changed with the number of females in a pride, the size of male coalitions, and the number of nomadic coalitions (males without a territory of their own) roaming through a pride’s area.

Larger coalitions helped resident males survive, especially in the dry season: from 89% a year for a coalition of two to 95% for three. In the dry season, larger nomadic coalitions were also more likely to take over a pride. The number of adult females in a pride lowered the survival of subadults (young lions not yet adult) in the wet season but raised it in the dry season.

Nomadic males did not change the survival of adult females, which depended only on age and habitat. But they mattered for reproduction: in the wet season, a pride whose home range held five nomadic coalitions raised 0.33 cubs per female to their first birthday, against 0.54 with two coalitions.

So density, the number of animals crowding an area, has to be measured with the animals’ social life in mind, and its effects can change with the seasons. The work is part of our project on populations under environmental change.

Conservationists are happy when there are many tadpoles in a pond. Yet at high density, tadpoles are stressed: they need longer to develop, are smaller when they turn into toads, and survive less well as young toads. To reduce this density stress, we need to build larger ponds.

A high number of tadpoles in a pond is pleasing, but crowding can cause stress. In our new paper in Basic and Applied Ecology, led by Tobias Weber, we raised tadpoles of the natterjack toad at different densities in outdoor tanks. We show that such density stress doubles the larval period, the time a tadpole needs before it turns into a toad. A longer larval period increases the risk that the pond dries up before the tadpoles are ready to leave. Also, at high densities the tadpoles are more than 50 percent smaller when they turn into toads, and on land small toads survive poorly.

For the highly endangered natterjack toad, these findings are particularly problematic. To reduce density stress for this species, it is important to build large ponds (ideally with an area larger than 100 m²). Also, these ponds should dry up, but not until autumn. This can be achieved by building ponds that can be drained.

Our findings are also important for counting amphibians. In a pond with high tadpole density, the tadpoles are present throughout the summer, providing evidence that toads have bred there. In a pond with low tadpole density, the tadpoles turn into toads after just 20 days. As a consequence, breeding may go unnoticed.

More about our work on amphibian and reptile conservation.

We decided to fill this gap by looking at how the timing of breeding has shifted over the past 40 years in a population of common toads (Bufo bufo) living at almost 2,000 metres in the Swiss Alps, just below the Grosse Scheidegg (Figure 1). We expected temperature and the amount of snow to play an important role. In fact, the toads can only come out of hibernation underground and breed once the snow melts and their breeding pond thaws.

Our results matched our expectations: warm temperatures and little snow in winter and spring went with earlier breeding. Interestingly, temperature and snow cover at our study site have not necessarily changed as expected over the past forty years. They vary a lot from year to year, and to this day we see both late breeding (mid to late June) and early breeding (late April). Despite this, the toads now breed on average about 30 days earlier than in the 1980s (Figure 2). Most of that shift happened before the mid-1990s; since then, the timing has stayed about the same.

So in the mountains, changes in timing can be hard to predict: the local weather does not always follow the global trend. You can find all the details in our paper “Four decades of phenology in an alpine amphibian: trends, stasis, and climatic drivers” (phenology is the timing of yearly events, such as breeding), which I led with Arpat Ozgul, Benedikt Schmidt and colleagues. It is published in the diamond open-access Peer Community Journal, free for both readers and authors. More about our work on amphibian and reptile conservation.

In East Africa’s savannas, antelopes are vital for a healthy ecosystem. They shape the vegetation, spread seeds, recycle nutrients, and provide food for other animals. A natural, ever-changing mosaic of plant types, water sources and weather forms a delicate balance with the antelopes, and people and a changing climate are disturbing it more and more. To protect these hotspots of biodiversity and keep the ecosystem working, we need healthy antelope populations.

Earlier studies have shown that the number of antelopes in an area changes with the place, the season and the year, but none had looked at all of these together. Doing so tells us which matters most.

In our new paper in Population Ecology, led by Lukas Bierhoff, a graduate student in our department, we used seven years of antelope counts from the Tarangire Ecosystem in Tanzania, in a collaboration between our group and the Wild Nature Institute. Of the five species we studied (impala, dik-dik, Grant’s gazelle, eland and waterbuck), numbers rose and fell together from year to year with the weather. Yet for four of them, numbers differed more from place to place than over time. What mattered was how close a place was to water and to people, and what plants grew there. This suggests both food (from the bottom up) and avoiding predators (from the top down) decide where antelopes live.

The five species we studied: Kirk’s dik-dik, eland, Grant’s gazelle, impala and waterbuck (photos: Wild Nature Institute)

In the Tarangire Ecosystem, antelopes cope with changing weather and with food and water that come and go by moving from place to place. Lukas 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

People are changing savanna habitats and the climate fast, so we need conservation that works, to keep antelopes and everything they do for healthy ecosystems. “Providing habitat options for the antelopes enables them to respond to a temporally changing world by moving across space,” Lukas said. In other words, the best way to keep nature rich and working is to protect large, connected areas with different kinds of habitat and water that never dries up.

We also found two groups of antelopes whose numbers rise and fall together (impala, dik-dik and waterbuck; eland and Grant’s gazelle). The species in each group might respond in the same way to the same conservation measures, which would make management more efficient.

What helps, according to senior author Derek Lee of the Wild Nature Institute: protecting rivers and other water sources from being diverted or polluted, reducing bushmeat poaching, keeping and restoring the routes animals use to move around, and keeping the variety of natural plant communities. Antelopes matter for Tanzania’s economy as well as its nature, so keeping their populations thriving is a win-win for people and wildlife.

Climate change is expected to cause wildlife declines around the world. Unusual weather, combined with pressure from people, can add stress to populations that are already declining. Giraffes are endangered, but nobody had studied how climate and people affect the survival of giraffes, or of any other large African herbivore. So we did: in a decade-long study, the largest to date, of a giraffe population in the Tarangire region of Tanzania. The study area covered more than a thousand square kilometres, inside and outside protected areas. Contrary to what we expected, higher temperatures helped adult giraffes survive, while rainier wet seasons lowered the survival of both adults and calves. Our paper, written with Arpat Ozgul and Derek Lee, is out in Biodiversity and Conservation.

A first look at how weather affects giraffe survival

We measured how unusual local temperature, rainfall and vegetation greenness were in each season (compared with the long-term average), and how this related to the chance that giraffes survived. We also asked whether the weather hit giraffes harder when they also lived near people, at the edges of the protected areas.

Studying a long-lived animal that breeds slowly, like a giraffe, means following the population for a long time and over a large area: long enough to capture both the ups and downs of the weather and any immediate or delayed effects on survival. We gathered nearly two decades of local rainfall, greenness and temperature data for Tanzania’s three seasons (the short rains, the long rains and the dry season), and followed the fates of 2,385 individually recognised giraffes of all ages and both sexes over the last eight years of that period.

Surprising effects of temperature on giraffe survival

We had predicted that higher temperatures would hurt adult giraffes, because such big bodies might overheat. Instead, adults survived better when it was warmer. Giraffes have several features that help them keep cool, like long necks and legs that lose heat, special nasal passages, an intricate network of arteries that supply blood to the brain, and spot patches that give off heat. But temperatures during our study may not have gone beyond what giraffes can tolerate, and an extreme heat wave in the future might reveal a limit above which these massive animals are harmed. So we will keep watching this population.

Heavy rains may bring parasites and less nutritious food

Giraffe adults and calves survived less well in rainier wet seasons, which may be due to more parasites and disease. An earlier study in the Tarangire region showed that giraffes carry more gut parasites in the rainy seasons than in the dry season, and heavy flooding has caused severe outbreaks of diseases that kill giraffes, such as Rift Valley fever and anthrax. Adults also survived less well when the vegetation was greener, perhaps because fast-growing leaves are less nutritious.

Pressure from people adds to the stress

The effects of the weather were stronger for giraffes living near the edge of protected areas, but not in every season. Giraffes living near the edges were most vulnerable during heavy short rains. Then, diseases shared with livestock are probably more of a risk, and muddy ground makes it harder for anti-poaching patrols to get around.

East Africa is expected to get more rain, with heavier downpours during the short rains. This will likely threaten giraffes in one of Earth’s most important landscapes for large mammals. Good land-use planning and anti-poaching work will help giraffes cope with the coming changes. This work is part of our Masai giraffe project.

In the lemurs’ forest, the wet season has been bringing less and less rain, and the dry season has been getting hotter. These trends, we found, led to fewer lemurs surviving but more young joining the population each year. The two trends have balanced each other, so the population has not collapsed. But they have destabilised it by speeding up the lemurs’ life cycle even more, which was already one of the fastest among primates. Our projections for the next five decades suggest that if the recent temperature and rainfall continue, lemur numbers will swing up and down more and more, putting the population at a higher risk of dying out.

Short-lived mammals that breed a lot are expected to adapt quickly to a changing environment. Our results show that such species can still be threatened with extinction by climate change. The work is part of our project on populations under environmental change.

This was the first study of its kind in the Tarangire Ecosystem, which is home to Tarangire National Park, a favourite with tourists, and is the heart of Maasailand, where cattle herders and wildlife have thrived together for centuries. Tarangire is different from places where wild ungulates have been studied intensively, like Serengeti or Kruger National Park: here wildlife, cattle-keeping people and farmers all share the landscape, and animals can move freely because the entire region is unfenced.

“Ungulates of different body sizes have different needs and threats,” said Nicholas. For instance, adult giraffes may have less to fear from natural predators but may face more danger from humans, and smaller animals may be pickier about their food. “We wanted to know what features draw each ungulate species to certain areas so we can pinpoint important habitat for each of those species,” Nicholas said. Land managers need this to keep wild ungulate populations thriving and the landscape healthy, which is the foundation of Tanzania’s ecotourism economy.

Over seven years, in dry and rainy seasons, we counted and mapped six species in and around Tarangire National Park and the neighbouring Manyara Ranch Conservancy, including unprotected village lands. The species ranged from the massive giraffe down to the little dik-dik (both eat the leaves of trees and bushes), the large, water-loving waterbuck, which eats grass, and three medium-sized antelopes that eat both: impala, Thomson’s gazelle and Grant’s gazelle. We looked at how each species used an area depending on the type and greenness of the plants, how thick the bushes were (where lions often lurk), and how far it was from rivers (which provide vital drinking water but also hide predators) and from cattle herders’ settlements (more disturbance by people, but the people also keep predators away).

Food mattered for every species, and being near year-round rivers mattered for most, though not all. Some species seemed to tolerate people and even gathered close to herders’ settlements, probably because there are fewer predators there. Antelopes that eat both grass and leaves could avoid busy human areas and still find enough to eat. Importantly, where the animals were and how many of them there were changed with short- and long-term differences in rainfall, which suggests 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, the study’s senior author. In dry landscapes like East African savannas, people take more and more of the water, so protecting rivers where people live, and making sure wildlife can still reach them, comes first for conservation. Another key finding was that traditional cattle herders and some ungulate species can share the same space, as long as the human impact stays fairly low.

Leaving the family you were born into is called natal dispersal. It lowers the chances of mating with a relative, which helps animals have healthy offspring. Dispersal is first and foremost a social process. Yet it has mostly been studied as a matter of distance, because in most animals families defend an area and keep others out, so the young have to leave that area to start their own family. We tested whether animals living in societies with overlapping communities could disperse simply by switching communities, and so avoid the risks of moving through the unknown.

We studied hundreds of giraffes over a huge area of 2,200 km² in northern Tanzania. Most male giraffes leave home once they are old enough to breed, and many of them do so by simply joining a new social community, without moving far from home. Most young females, on the other hand, stayed in the community they were born into. Differences between the sexes in who leaves home are well known in animals, but this is one of the first studies to show how a structured society lets young animals find a new community without moving to a new area.

Complex giraffe societies

Together with Penn State University, we had shown earlier that adult female giraffes form distinct social communities of about 60 to 90 females. Membership is very stable over time, even though the groups these females form merge and split throughout each day. This has two big consequences. First, females keep lasting bonds with other females in their community, probably for life. Second, the communities are defined by who associates with whom, not by where they live: different communities use the same land. So while giraffes from different communities might meet now and then, 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 Damien Farine, co-author and UZH Eccellenza Professor.

As in most other mammals, it was mainly the males that left, at about four 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 Barbara König of the University of Zurich, senior author of the study.

Females stay in the same social networks, males switch

We first mapped the social communities of the adult females, and then followed which community 67 male and 70 female calves spent time with as they grew up over seven years. More than four out of five young males that left home switched to a different community from the one they were born into. And about one in four of these males stayed fairly close to where they were born. In other words, they left home without having to move far at all.

This type of social dispersal, where males stayed close to home but joined different female communities, would not be detected if only movements in space were measured.

Giraffes may not be the only animals that can leave home socially without moving away. In many other species, including dolphins, elephants and bats, groups merge and split (scientists call this ‘fission-fusion’) within a larger, more stable community. It would be interesting to see whether dispersing socially within the same physical space is a common strategy in species that live in societies with many overlapping social communities. Healthy populations depend on dispersal, so the more we understand it, the better we can help conserve wildlife.

According to giraffe expert 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.”

This work is part of our Masai giraffe project.

For African wild dogs, they mostly do. Between 2011 and 2019 we fitted GPS collars to 16 groups of young wild dogs as they left their family pack to find a new home (this is called dispersal). From their tracks we mapped how easy it is for a wild dog to move through each part of the landscape. Inside KAZA, moving was more than twice as easy as outside it, and the main travel corridors ran inside its borders. But some smaller routes are still unprotected, and how easy it was to move differed fivefold between the five countries. People’s activities, and rivers, swamps and open water, made the biggest difference.

Why does this matter? Setting aside land to link parks is costly, and money for conservation is limited. Wild dogs are among the most wide-ranging protected animals in the area, and their journeys let us test, with real data, whether the land set aside is in the right place. Our results also show where countries need to work together to keep, or restore, the links between their parks.

For a nice and easily accessible version, read the University of Zurich’s summary of this study, and you can download the full paper (PDF). More about this work on our African wild dog project page.

We also found that calf survival and the number of calves born differed between these communities, even when their home ranges overlapped and they lived in much the same conditions. This shows that population structure can arise from social behaviour rather than from separate use of space: a population can be divided by friendships, not only by where animals live. These social subpopulations have different survival and reproductive rates, so some might compete better than others, for example by dominating the better-quality food, or there might be cultural differences, such as better strategies for protecting their calves from predators.

Each gang had its own social character, for example in how strong the relationships among its members were. The gangs also lived in quite different surroundings. The Tarangire region of northern Tanzania, where we work, includes two national parks, a livestock and ecotourism ranch, and unprotected land used by traditional cattle herders, as well as several busy towns surrounded by farmland. So we wondered how these environmental and social conditions might affect 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,” says Lee.

We worked out the survival of more than 1,400 adult females and calves, and the number of calves per female each year, and compared the 10 social communities. Then we asked whether the differences were explained by social factors, such as how strong relationships were, or by the environment, such as how close to people the giraffes roamed, how fertile the soil was, or the kind of vegetation in their ranges. Adult females survived equally well in all communities; the differences were in the calves, and they were linked to the environment, not to how close the friendships were.

Calves survived better in communities with less thick bushland in their ranges, possibly because lions like 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 the national parks, probably because there are fewer lions and hyenas near where people live. Some areas outside the parks also have more fertile volcanic soils, and so possibly more nutritious food.

“The good news for conservation is that giraffes can survive and raise their offspring in areas close to people,” Lee points 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.”

This work is part of our Masai giraffe project.

With Arpat Ozgul from our group and Derek Lee, Damien Farine and Barbara König, we followed wild giraffes in Tanzania for five years. We compared three things that might affect whether adult females survive: their social life, their natural surroundings (food and vegetation), and people (how close they live to human settlements). Females living in larger groups had better chances of survival than more isolated ones.

Company leads to better survival

Giraffe groups are always changing: they come together and split up throughout the day. Yet adult females keep many of the same friends over the long term. Grouping with more females, called gregariousness, is linked to better survival of female giraffes, even though group membership changes often. This side of giraffe social life matters even more than their non-social surroundings, such as vegetation and how close they live to human settlements.

The benefits of many friends

Apart from poaching, adult female giraffes probably die mostly of disease, stress or poor nutrition, and these are all linked. “Social relationships can improve foraging efficiency, and help manage intraspecific competition, predation, disease risk and psychosocial stress,” says Barbara König of the University of Zurich, senior author of the study. In other words, friends can help with finding food, with competition from other giraffes, with predators, disease and stress. Female giraffes may seek out a good number of other females to share information about where the best food is. Larger groups may also lower stress by reducing harassment from males, let mothers share the care of young, or simply feel good because familiar females are around. We also found that females living closer to towns survived less well, possibly because of poaching.

Social habits similar to humans and primates

To map the giraffes’ social lives, we used network analysis: methods similar to those used by big social media platforms. It turns out that giraffes are surprisingly similar to humans and other primates, for whom more social connections bring more opportunities. Chimpanzees and gorillas, for example, live in communities where ties between many individuals make it easier to switch feeding strategies. It seems to be beneficial for female giraffes to connect with a greater number of others and belong to a larger community, without keeping to an exclusive subgroup.

This work is part of our Masai giraffe project.

Recently, an unusually large group of eight brothers born in 2018 left their pack in the Third Bridge – Budumtau – Xini area of Moremi Game Reserve. Their collar sends GPS positions to us by satellite, so we could follow them from afar. In only five days they covered over 175 km, until they reached the permanent swamp around the Kwedi Concession in the north of the Okavango Delta. For the past month they have stayed in an area of about 180 km² 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? What have they been doing? Have they met unrelated females and formed a new pack?

Although the collar sends us regular information, keeping up with the dogs over such large areas is almost impossible, unless we can capitalise on “the many eyes out there”. Tourists, guides, camp managers: all can contribute their sightings to research. No sooner said than done. We told the lodges that the dogs were in their area and asked them to report every sighting and send as many photos as possible.

Just a few days later, lodge staff saw a group of 9 dogs, including one with a collar, a few kilometres north of Vumbura Plains. From the photos we recognised five of the eight brothers and four unknown females. So the brothers had split up. But had the other three gone their own way, or had they died? A week later came the answer: a sighting of 12 dogs near Bushman Plains camp. In the photos we found the three missing brothers, alive and well.

Will this new pack of 12 stay together? Only one male and one female in a pack become dominant and breed; the others help raise the pups. So some dogs may take the extra risk and leave again to start their own pack (this is called secondary dispersal). Bets are open, and chances are that the three brothers will part again. Time, and your sightings (!), will tell.

We researchers can benefit from any reports and sightings, as has been the case here. In return, we bring all the pieces of the puzzle together and share what we learn with decision makers, local partners and the tourism industry.

Please keep sharing your sightings of wild dogs, with or without collars, to help us protect these amazing animals: how you can help (PDF).

Climate change is thought to hit animals and plants in the mountains especially hard, changing where species live, how common they are and how they interact. In Switzerland, some birds, such as the tree pipit and the European pied flycatcher, have moved to higher altitudes over the past two decades. But what this means for whole bird communities, the set of species living together in one place, was not known.

Our new study in Diversity and Distributions, which I led with Thomas Sattler and Hans Schmid of the Swiss Ornithological Institute (Vogelwarte), and Arpat Ozgul, looks into this. It is based on 20 years of data collected by volunteer ornithologists, and the trend points downwards: bird communities in the Swiss Alps are becoming more and more alike. Ecologists call this biotic homogenisation.

Counting species is the simplest way to measure diversity, but species also differ in what they do: what they eat, where they nest, how they use their surroundings. This is called functional diversity. “Not all species play the same role in an ecosystem,” says Vicente. “The loss of a given species can be more detrimental than that of several others.” Specialists such as some woodpeckers are especially important: the holes they make are used by other birds and small mammals for nesting and hiding. To measure functional diversity, we gathered 100 traits for each species, such as body mass, diet and habitat. This let us see how functional diversity changes from the valleys up to the high mountains, and how it has changed over 20 years.

High-mountain specialists on the edge

The tree line acts as a boundary between two quite different groups of birds. Below it live the birds of the farmland in the lowlands up to the high mountain forests, such as the yellowhammer, the common whitethroat and the blackcap. Above it live species adapted to open habitats above the trees. They eat fewer caterpillars, for example, and some, like the rock ptarmigan, nest on the ground. It is these alpine communities whose functional diversity has dropped. “Our study shows that mountain specialists are under increasing risk of becoming misfits,” says Arpat. Their habitat is shrinking, they cannot find good habitat higher up, and generalist species are moving up into it.

The rise of the generalists

Generalists, such as the robin or the European pied flycatcher, can live in many places, and they have become more common. This is probably one reason why bird communities in different places are becoming more similar to each other. The communities are also becoming more redundant: more of their species play much the same role.

When bird communities become more alike, the Alps lose some of their variety, and the mountain specialists come under pressure. Warming and changes in land use, such as shrubs spreading on abandoned pastures and the tree line moving upwards, are likely behind this trend. Protecting these mountain specialists will need urgent conservation and management action.

Climate change is now altering these seasons. Temperatures are rising, there is less snow in winter, snow melts earlier, summers are getting longer, and extreme events such as droughts and floods are becoming more common.

In our new paper in PNAS, led by Line Cordes, we found that climate change affects marmot survival differently in summer and in winter. We analysed 40 years of records collected at the Rocky Mountain Biological Laboratory in Colorado, USA, to see how yellow-bellied marmots (large burrowing ground squirrels) have fared during their active summer and during their long winter hibernation.

Yellow-bellied marmots are a good species for telling apart what climate change does in each season, because their year is so clearly split in two. They live in western North America, where climate change is more evident than anywhere else on the continent except the Arctic. Although they are large for a rodent (up to 6.5 kg), they are too small to stay active in winter, so they hibernate for about eight months. They depend on the fat they put on over the summer, and even in deep hibernation they can lose up to 40% of their body weight.

Over four decades (1979–2018), marmots generally survived the summer better but the winter worse, and these changes were largest for pups and one-year-olds. At the study site, winters have become warmer with less snow, and summers warmer, drier and much longer. What drove survival differed between ages and seasons. For example, pups survived the summer better after winters with little snow, perhaps because their mothers were in better shape during pregnancy and while caring for them, as plants appeared sooner after an early snowmelt. Winter survival was lower after long, dry summers, most likely because pups went into hibernation in poorer condition.

As Arpat put it: “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.” Looking only at survival over whole years can be misleading, or underestimate what is really happening, because the responses can differ so much between times of the year.

So far, climate change has helped marmots in summer and left them more vulnerable in winter. Overall, survival went down for pups, up for one-year-olds, and did not change for adults. But the summer benefit may not last: as summers get ever warmer and drier, the plants marmots eat will suffer too. Indeed, no marmot population lives in places that are always warm and dry.

Climate change may help a species in one season and harm it in another. This could matter for many other animals living with strong seasons, in deserts, mountains and polar regions, where the climate is changing fastest. For wildlife near the poles or on mountain tops, like marmots, there is nowhere to go when conditions get worse.

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 study was carried out by scientists from Bangor University, the University of California Los Angeles, the Universities of Kansas, Sheffield, Rhode Island, Ottawa, Florida and Zurich, and the Chicago Botanic Garden, as part of our project on populations under environmental change. It would not have been possible without Ken Armitage, who started and led this project from the early 1960s, making it one of the longest-running studies of any mammal, and all the “marmoteers” who helped collect the data over the years. Nor would it have been possible without Billy Barr and the Rocky Mountain Biological Laboratory, who have recorded the local weather for decades. The study was funded by the Swiss National Science Foundation, the National Geographic Society, UCLA, a Rocky Mountain Biological Laboratory fellowship and the US National Science Foundation.