Imagine spotting a butterfly species in your garden you have never seen before. You might take a photo and upload it to a citizen science app, or tell a local nature group about your new encounter. It feels like a small moment of joy.
But if that butterfly has appeared in your backyard because its old home is becoming too hot, too dry or too damaged, the sighting is more worrying.
Around the world, ongoing environmental changes are prompting many butterfly species to relocate and search for new homes, a process referred to as species range shifts or species redistribution. As temperatures, rainfall and habitats change, butterflies can relocate over long distances, or even move vertically up and down mountain ranges.
Our new global study found one in ten known butterfly species has already shifted in range. So, where are they going – and why?
The gram blue (Euchrysops cnejus) expanded its range in Australia, Nepal and Oman.Shawan Chowdhury
How do we know butterflies are on the move?
The data used in our global study was comprehensive: more than 6,180 reports of butterfly range shift from 565 studies and 68 expert assessments, which covered 1,758 species across 105 countries.
These showed 80% of the documented butterfly species had expanded their ranges latitudinally, meaning east to west, or longitudinally, meaning north to south. We found 27% had reduced their range and 22% had shifted up or down slopes on hills or mountains. Many species showed a combination of these range changes.
The public narrative is often simplistic: as the world warms, species are shifting towards cooler temperatures at higher latitudes, or moving upwards in mountains. This is happening, but it is only one piece of the puzzle.
In fact, butterflies need more than to find new homes at the right temperature. Caterpillars often depend on specific host plants; adults need nectar, shelter and safe places to breed; and populations also require connected habitats so individuals can move easily through the landscape, meet, reproduce and breed.
Change can come quickly
Some species show how fast changes can happen. The tawny coster (Acraea terpsicore) native to the Indian subcontinent, has expanded through Southeast Asia and into Australia. In Brazil, (Godartiana byses) has expanded from Rio de Janeiro and Bahia into São Paulo, a shift linked to climate warming.
Other species show the opposite pattern. The small blue (Cupido minimus) has lost 40% of its habitat in the United Kingdom over the past 150 years. In Germany, the cranberry fritillary (Boloria aquilonaris) has lost much of its original habitat because of bog drainage. In Romania, an increase in farming has been linked to a severe range contraction of the danube clouded yellow (Colias myrmidone).
Even range shifts along mountain slopes are not always straightforward. In Mexico, the painted lady (Vanessa cardui) shifted upslope at a rate of about 83 metres per year between 1988 and 2011. Over the same period, the queen butterfly (Danaus gilippus) shifted downslope at a rate of about 32m per year.
Together, these examples show butterfly species range shifts are not simply a story of animals moving towards the poles.
The chocolate albatross (Appias lyncida) expanded and contracted its range in Sri Lanka, and moved down from higher elevations in Taiwan.Shawan Chowdhury
What’s causing this change?
In our study, climate change and extreme weather events were the most common reasons why butterflies shifted their range. But climate change is not the only factor. Agriculture, forestry, urban development and habitat destruction are also reshaping where butterflies can live and reproduce. These disturbances destroy host plants and breeding sites, and fragment large habitats into patches too small to sustain a healthy population.
Europe and North America have many long-term butterfly monitoring programs, run by expert volunteers and citizen scientists. We found that in some European countries, range shifts have been documented for more than half the national butterfly species. But in most countries, records exist for fewer than 10% of known butterfly species.
We know the least about butterflies in Central Africa, Southeast Asia, New Guinea and the Amazon Basin, some of the richest places on Earth for biodiversity. They are also places where many species may already live close to their upper thermal limits. Even small increases in temperature can make parts of their habitat unsuitable.
Supporting experts and volunteers to develop citizen science monitoring programs would better protect butterflies in these megadiverse countries.
The great orange tip (Hebomoia glaucippe) has expanded in India and contracted in Taiwan.Shawan Chowdhury
Why this matters
Why should people care? Butterflies are part of the living fabric around us. Adult butterflies contribute to pollination. Caterpillars feed birds, spiders and other insects. When butterflies disappear, it can signal the plants, grasslands or woodlands once visited by butterflies are also changing.
This matters for conservation. Many protected areas are based on maps of where species lived in the past. But if butterflies and other species are moving, those maps quickly become outdated.
The message is simple. Conservation cannot only protect habitats where species once lived – it must include the places where they will relocate, and the wildlife corridors they will use to get there. If not, we may keep protecting yesterday’s nature while tomorrow’s nature has nowhere left to go.
Aletta Bonn is member of the German Advisory Council on Global Change (WBGU).
Jonathan Lenoir and Shawan Chowdhury do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
Many people are blissfully unaware the world’s frogs and amphibians are fighting their own deadly pandemic. In fact, this fungal disease – chytridiomycosis, or chytrid for short – is the worst wildlife disease on record.
Scientists have responded with ingenious and novel ways to help frogs survive, such as frog saunas – where amphibians can warm up and bake off their infections – and captive breeding programs.
But our new research suggests some of these may come at a cost to a core aspect of frog survival: their ability to reproduce.
Frogs are more robust than we often give them credit for, having survived several previous mass extinctions. But some scientists argue amphibians are now on the front line of a sixth mass extinction.
Under the combined pressures of disease, habitat destruction and rising temperatures, we are now seeing an alarming decline in frog species. If we want frog populations to recover in the long term, we need to ensure not only their survival, but their reproductive health.
Australia is home to roughly 250 frog species, many of which are found nowhere else on Earth. They are also among the worst affected globally by chytrid, which is thought to have caused seven frog extinctions. A further 36 species are under threat.
The chytrid fungus and many frogs flourish in cool, moist habitats. So scientists have experimented with making the environment inhospitable to chytrid without harming frogs.
Deliberately exposing frogs to chytrid and following this with heat therapy in “frog saunas” offers a protective effect in some frogs. This approach was tested on green and golden bell frogs and found to act like a vaccination, making it more likely they would survive reinfection. These interventions are vital for helping amphibians survive, and should continue to be developed and used.
But survival is not the same as recovery. Our new research found both being infected with the fungus and the use of heat therapy may reduce frog sperm quality. And this could affect their reproductive ability long after they recover. Our findings suggest we need to carefully study what happens after interventions are used.
Successful treatment but unexpected side-effects
The green and golden bell frog, Ranoidea aurea, is one of the species hit hardest by chytrid. It has disappeared from more than 90% of its former range in southeastern Australia.
We examined the effects of chytrid infection and heat treatment on sperm quality in male green and golden bell frogs. We found frogs with moderate infections produced higher concentrations of sperm than uninfected frogs, which may reflect a phenomenon known as “terminal investment”.
This occurs when animals facing a threat to their survival respond by increasing their reproductive effort, in an attempt to pass on their genes before it’s too late. Similar responses have been observed in other amphibian species affected by chytrid, but responses to chytrid can vary.
Some frogs may increase sperm numbers, calling effort (to attract mates) or breeding displays, while in others there has been no observed effect to these traits. Research in this area is still ongoing, and trends can be hard to identify because we don’t know how one reproductive trait may correlate with another – for example, an increase in calling effort may not mean there are increased sperm numbers.
Interestingly, in our study, frogs with the worst infections did not have higher sperm counts. Instead, they had poorer sperm quality, particularly reduced sperm movement, which is essential for fertilisation. Frogs with only moderate infections had higher sperm counts, but lower sperm movement. We believe these findings indicate more energy being directed to mounting an immune response as infection progresses.
Frogs that underwent heat treatment to clear the fungal infection also showed substantial declines in sperm concentration, which persisted for months. While this sperm movement recovered over time, sperm numbers remained unusually low six months later.
So while heat treatment successfully eliminated the disease, the treatment itself appeared to impose a reproductive cost. This hidden cost could be missed if we consider survival from disease as the only indicator of success.
A Peron’s tree frog that died from chytrid fungus disease.Ken Griffiths
Does this mean no more frog saunas?
We are definitely not saying conservationists should abandon heat treatments or other disease management strategies. The evidence overwhelmingly shows these tools are valuable and can help save frogs from a disease that has devastated amphibian populations worldwide.
Instead, our findings suggest conservation programs should broaden what success looks like. If a frog survives infection but its reproductive capacity is reduced, conservation managers may need to account for this when they plan breeding programs, translocations and population recovery efforts.
Monitoring the reproductive health of frogs alongside their disease status could help identify any hidden long-term consequences before they affect population growth. Encouragingly, researchers overseas and in Australia are already exploring a diverse range of approaches. These include assisted reproductive technologies, captive breeding and genetic biobanking.
Our study highlights how solutions can sometimes have unexpected trade-offs. Understanding this is critical if we want conservation efforts to keep frogs alive today, and ensure thriving populations for generations to come.
The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
Australia is now confronting an outbreak of a deadly bird flu strain.
As of Monday, the highly pathogenic H5N1 virus had been detected in 78 wild birds across mainland Australia. Until now, there had been no evidence of a large-scale outbreak.
But authorities have confirmed the first instance of mass death caused by H5N1 among dozens of greater crested terns off South Australia’s south-east coast. They are also conducting further testing on a cluster of sick and dead terns in south-west Victoria.
As H5N1 spreads across the country, researchers, wildlife managers and the broader public are increasingly concerned about the risks it may pose beyond birds.
Recent outbreaks have threatened aquatic mammals, including southern otters, dolphins and porpoises. H5N1 has also decimated pinniped populations around the globe, including in South America. Pinnipeds are marine mammals that live in the sea and form colonies but spend extended periods on land, such as sea lions, fur seals and elephant seals.
As the risk of a broader outbreak rises, Australia must protect its wildlife by drawing on lessons from other continents already battling bird flu.
Looking to South America
H5N1 poses an urgent threat to wildlife worldwide. Since 2021, this fatal strain of bird flu has spread to every continent and infected poultry flocks, dairy cattle, wild birds and a growing range of wild mammals. In June, it finally reached Australia, first detected in a sick brown skua.
This strain has been particularly devastating in South America. In late 2022, H5N1 spread rapidly from infected seabirds into pinniped colonies. At least 30,000 South American sea lions died in Peru, Chile, Argentina, Uruguay and Brazil during the subsequent outbreak. In some areas, major breeding colonies lost up to one third of their population within a single breeding season.
Two sea lions from a South American sea lion breeding colony.Martín Brogger
Current evidence suggests H5N1 also caused mass deaths in southern elephant seals – the same species as Neil the seal – with more than 17,000 pups dying at Península Valdés in Argentina. Scientists still don’t know how many adults died.
Our team of researchers – from the Universidad Nacional del Comahue in Argentina and Deakin University in Australia – documented a dramatic decline in the number of seals in northern Patagonia following the 2022-23 outbreak.
Subsequent studies across South America show infected pinnipeds developed severe neurological and respiratory disease. Symptoms include lethargy, tremors, impaired coordination and laboured breathing, among others. Affected animals showed severe respiratory disease and neurological signs, and post-mortem examinations revealed marked lung lesions. Many animals died within a short period after clinical signs appeared.
Though confronting, the South American outbreak gives us crucial insight into how H5N1 spreads, which species may be most vulnerable and what strategies could reduce its impacts.
Each time H5N1 infects and replicates in a mammal, the virus becomes better at adapting to mammalian hosts.
Monitoring how efficiently it spreads between mammals is therefore essential for protecting wildlife. It also allows us to assess the risk of human infection — which currently remains low — and the potential for a broader pandemic.
Two Australian sea lions (Neophoca cinerea) resting on a beach.Henrik Karlsson/Getty
For now, H5N1 has not yet reached Australia’s pinniped colonies, which are already under pressure from fishery nets and hooks, pollution, habitat destruction and climate change.
So we still have time to protect them from H5N1. Authorities should start with Kangaroo Island, where infected seabirds have been found near the breeding habitat of the endangered Australian sea lion.
Other threatened marine mammals may also be vulnerable. This includes the rare Burrunan dolphin, of which there are less than 200 individual animals swimming around Victoria’s Port Phillip Bay and Gippsland regions.
There are fewer than 200 Burrunan dolphins left in the wild.tracielouise/Getty
So, how can we protect them?
As Australia’s number of confirmed H5N1 cases rises, urgent action is needed to protect our vulnerable marine mammals.
Australian authorities can learn from the South American outbreak by:
frequently conducting population censuses, to detect unusual deaths and sudden changes in the size of seal and sea lion colonies
closely monitoring live animals and taking samples of any dead animals, to track how the virus is circulating before any mass deaths happen
removing all carcasses, particularly near tourist areas, to stop scavenging birds, dogs and animals from being exposed to infected animals
ensuring researchers, wildlife managers and tourism operators stick to strict biosecurity protocols, such as wearing appropriate personal protective equipment when handling sick or dead wildlife and disinfecting boots and equipment between sites
tightening biosecurity measures around food production, particularly intensive poultry farms where commercial poultry may be exposed to infected wild birds.
The public can also help protect our vulnerable pinnipeds by:
not approaching any sick wildlife
keeping pets away from wildlife
reporting any sightings of sick or dead birds, seals, sea lions or other animals to the 24-hour Emergency Animal Disease Hotline by ringing 1800 675 888, noting details about the date, location, type and number of animals.
As the number of infected seabirds rises, so does the threat of a H5N1 outbreak among Australia’s marine mammal colonies. South America reveals how devastating this virus can be for entire ecosystems. Australia should heed that warning while there is still time to protect our precious pinnipeds.
Correction: This article originally stated post-mortem examinations of infected pinnipeds revealed the virus directly affected animals’ brains and lungs, and could lead to death within a short period. This has been corrected to say post-mortem examinations of infected pinnipeds revealed marked lung lesions, and many of them died within a short period after clinical signs appeared. Full necropsies were not carried out on the Argentinian seals due to biosecurity concerns, meaning the cause of death cannot be definitively attributed to the virus.
Saia Nahir Bartes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
