Earth’s majestic “apex predators” are some of the most prolific hunters in the world. But which ones kill the most?
Our new research showed solitary hunters such as bears, tigers and Eurasian lynx have higher individual kill rates than social predators such as wolves and lions. And smaller species, such as cheetahs and pumas, tend to kill relatively more prey because their kills are often stolen by more dominant carnivores.
Such information allows us to better understand how different predators affect their environment. It can also guide hunting quotas and help evaluate how humans affect carnivores.
Our research was a systematic, world-first literature review into the predatory behaviour of large land-based carnivores. In particular, we examined carnivore “kill rates” – the number of prey killed over time. We did this to better understand their foraging and impacts on prey populations and ecosystems.
We examined 196 papers that either quantified large mammal carnivore kill rates, or reported data we could use to calculate the rates ourselves.
We focused on the large land-based carnivores weighing 15?kg or more. We also searched for kill rate studies on four smaller species — coyote, wolverine, fossa (a cat-like predator found in Madagascar) and the Tasmanian Devil — as they’re all considered apex predators in certain regions and ecosystems.
We only found kill rate estimates for 17 (55%) of the 31 carnivore species included in our review. Studies came from 27 countries across five continents.
We found kill rates differ between carnivores with different social structures and hunting strategies.
Social predators, such as wolves and lions, tend to kill fewer animals per carnivore than solitary hunters such as bears, tigers and Eurasian lynx. For example, on average grey wolves made a kill every 27 days per wolf, compared with every four days per Eurasian lynx.
Larger wolf packs can bring down large animals such as bison more easily. Similarly, groups of cheetahs can tackle larger prey than solitary cheetahs. This could mean they don’t need to hunt as often.
Working as a team may also reduce losses to scavengers, as groups can better defend their kills through sheer numbers. Or they might be better at scavenging and stealing (“kleptoparasitism”) from others.
Canine predators such as wolves and African wild dogs often rely on high-energy pursuits over long distances. For example, grey wolves can pursue prey for more than 20km. In contrast, cats rely on stealth, using an ambush hunting strategy. This saves energy.
Solitary large carnivores such as tigers, leopards and Eurasian lynx, which mainly hunt hooved mammals, have similar kill rates regardless of body mass. This suggests large land-based carnivores are compelled to hunt prey closer to their own size or larger, to compensate for the energy used in the hunt.
Smaller carnivores such as cheetahs, pumas and African wild dogs often kill more prey than their larger counterparts, but only consume about half of what they kill.
If you’ve seen the Lion King movie, you’d be forgiven for thinking hyenas largely steal and scavenge their food. But that’s not the case. Lions often steal from hyenas, as well as from other carnivores such as cheetahs and African wild dogs.
Making a kill is the first challenge, avoiding having it stolen by more dominant predators is also difficult.
Bias in kill rate research
More than half (55%) of all kill rate studies have been conducted in North America. Africa follows with almost a quarter (24%), then Europe (12.5%).
Asia was a long way behind with 7% of all kill rate studies. That’s just 13 studies covering six species. This is despite being the largest continent, home to 17 (55%) of the 31 large carnivore species included in our review.
No reliable kill rate studies have been published from Australia.
A third (33%) of all kill rate studies focused on grey wolves, followed by pumas (20%), lions (12%) and Eurasian lynx (8%). This means we know little about the predatory behaviour and roles of other large carnivores.
Grey wolves are considered a threat to livestock and wildlife that humans value. This has prompted significant investment in research to understand their predatory behaviour and that of other large North American carnivores.
Such work has subsequently been used to inform appropriate management and conservation of these predators and their prey.
Kill rate studies provide more than just a tally of carnivore behaviour. They offer deeper insights into the relationships between predators and prey, and their effects on ecosystems.
Large carnivores shape ecosystems by scaring and killing prey, which can change their behaviour, distribution and abundance. They also supply food to other species, affecting the flow of nutrients and energy.
In many ways, large carnivores also help people. They can reduce the risk of vehicle collisions, by killing deer that might otherwise wander onto roads. They may limit the spread of disease by preying on sick animals, and control herbivores, aiding livestock producers.
Yet carnivores, including Australia’s dingo, are still widely persecuted. We need to do all we can to maintain their pride of place at the pinnacle of Earth’s ecosystems.
Of course, if you really want to know which species is the biggest killer, it’s humans. We are the dominant predator across Earth.
Euan Ritchie receives funding from the Australian Research Council and the Department of Energy, Environment, and Climate Action. Euan is a Councillor within the Biodiversity Council, a member of the Ecological Society of Australia and the Australian Mammal Society, and President of the Australian Mammal Society.
Luke Emerson 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.
It’s not easy finding food at sea. Seabirds often stay aloft, scanning the churning waters for elusive prey. Most seabirds take fish, squid, or other prey from the first few metres of seawater. Scavenging is common.
But there are other tactics. Frigatebirds, skuas, and gulls rely on the success of other seabirds. These large, strong birds chase, harry, and attack their targets until they regurgitate or drop the prey they’ve just caught. They’re the pirates of the seabird world, stealing hard-earned meals from other species. This behaviour is known as kleptoparasitism, from the Ancient Greek word klépt?s, thief.
The strategy is brutal, effective, and a core behaviour for these important seabirds. But as our new research shows, it comes with major risks for the thieves. The new strain of avian flu is killing birds by their millions – and we found kleptoparasitism could spread the virus very easily.
Food thieves at sea
It’s not that frigatebirds, skuas, and gulls can’t hunt. They can and do catch their own food. But hunting fish and squid is hard work. It’s much easier to use extortion tactics to win the food from other seabirds.
These tactics have made these birds very successful as foragers. They hang around the breeding sites of birds such as gannets and terns waiting for a tired parent to return from the sea with a crop of food.
For the seabirds being targeted, these kleptoparasitic birds are just one more threat. The world’s 362 species of seabird can be found across every ocean and many islands. At sea, they prey on fish and squid. When they nest or rest on islands, their nutrient-rich guano shapes soil and plant communities, defining entire ecosystems.
But they are not doing well. Just under half of all seabird species (155) are now classified between “near threatened” and “critically endangered” on the world’s list of threatened species, the IUCN Red List. Of those with known trends, 56% have populations in decline.
The threats they face are daunting. Invasive predators such as mice and rats eat eggs or chicks on breeding islands. Many are caught by fishing boats as accidental bycatch, while overfishing depletes their prey. Then there’s climate change, habitat loss, and many other threats, including disease.
Seabirds are generally long-lived. They often raise only one chick every one or two years. Many species breed in only a few locations. They take many years to mature. Put together, these traits make recovery from population declines slow.
Three years ago, a more lethal strain of avian influenza virus emerged. This HPAI H5N1 2.3.4.4b strain has spread around the world, killing at least 280 million wild birds. The strain can also infect and kill marine mammals such as seals.
“HPAI” stands for Highly Pathogenic Avian Influenza, meaning the virus can more readily cause severe disease and death. The strain has become an animal pandemic (formally, a panzootic). It’s made it to Antarctica, but not yet to Australia or the rest of Oceania.
We know seabirds are particularly at risk. Our new research has shown kleptoparasites are at an even higher risk relative to other seabirds.
During the 2022 northern hemisphere summer, the virus killed roughly half of the world’s great skua (Stercorarius skua).
Food-stealing behaviour can enable the virus to spread. When a great skua harasses a gannet and makes it regurgitate food, the skua gets a fish meal – coated in saliva. If the gannet is infectious, its saliva will likely have a high viral load.
Once infected, these pirate birds can drive spread faster. Skuas, frigatebirds and gulls can cover great distances across polar regions and the tropics. They can transmit the disease to their mates, chicks, and other seabirds.
This means we could see outbreaks in new populations or places, hundreds or even thousands of kilometres apart. We have already seen signs of this in skua populations in the northern and southern hemispheres, with brown (Stercorarius antarcticus) and great skuas being some of the first detected H5N1 infections at new locations.
Skuas more often steal food from other seabirds when away from their breeding sites – including when they’re migrating back to these areas. If skuas get infected en route, they could bring the disease to their breeding sites and then beyond.
Frigatebirds are known for the red pouches on the necks of the males, which they inflate during breeding season. But they have other remarkable traits, such as travelling tens of thousands of kilometres across oceans outside breeding season. These travels are often broken up by “island-hopping”, where they will encounter and potentially infect other seabirds.
Frigatebirds are known for the large red pouches male birds have on their necks.buteo/Shutterstock
Frigatebirds and skuas have already suffered mass deaths from this strain of avian influenza.
While the virus is now almost everywhere, it hasn’t reached Australia, New Zealand, Oceania, and parts of Antarctica and the subantarctic. We can monitor skuas, frigatebirds and gulls for signs of illness to give us early warning that the virus has arrived.
By itself, avian influenza is a major threat to seabirds. But the outlook is even more dire when this is compounded with further human-caused threats. Identifying, managing, and reducing these threats is critical for their conservation, and the health of our islands and oceans.
Simon Gorta is a PhD student at the University of New South Wales and his PhD research is supported by the Australian Government Research Training Program scholarship.
Richard Kingsford is a Councillor on the Biodiversity Council
Rohan Clarke 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.
Cultural protection order has been framed as a push to curry favour with inner-city seats, ignoring grassroots campaigns from Indigenous and non-Indigenous locals
Among the concerns listed by the 2,000 farmers who converged on the lawns of Parliament House in Canberra last week was the protection of prime agricultural land from renewable energy developments.
It has become a common refrain. The National party leader, David Littleproud, warned at the party’s annual federal council on Friday of the risk to prime agricultural land from energy transition projects. The mining magnate Gina Rinehart took to the stage at a business event last year to warn that one-third of Australia’s prime agricultural land could be “taken over” by renewable energy projects. In almost every campaign against a proposed development in the bush, the potential impact on prime agricultural land is raised as a key concern.
It wasn’t supposed to be like this. Back in the heady new government days of July 2022, Tanya Plibersek told the National Press Club that change was coming for environmental protection in Australia after a decade of disaster and neglect.
Releasing the five-yearly state of the environment report, which the previous Coalition government had received months earlier but put in a drawer until it was turfed from office, the new environment minister said it told a “story of crisis and decline in Australia’s environment”.
The destruction of nature is a global crisis. Establishing protected areas of forest is a common policy governments use to tackle the problem.
Indeed most countries, including Australia, have signed a global agreement to protect 30% of land by 2030. But to what extent do protected areas, such as national parks and nature reserves, actually preserve forests?
My new research examined this question. The findings are the first global-scale estimate of where protected areas are succeeding and failing.
Alarmingly, I found protected areas fail to prevent forest loss in many parts of the world. Clearly, we must make these areas more effective to conserve the remaining diversity of Earth’s plants and animals.
Establishing protected areas such as national parks is a key tool to preventing biodiversity loss.Shutterstock
Probing protected areas
Forests are often destroyed through human activity such as logging with chainsaws or the deliberate use of fire. The aim is usually to extract timber, or to clear land for agriculture, roads, housing or other human purposes.
Natural bushfires can also damage forests. In some cases, ecosystems are so badly burnt they cannot recover. There’s a link to human activity here too, because human-caused climate change is leading to more severe, frequent, and wider-ranging bushfires in places such as Australia.
I wanted to know how well protected areas prevent forests from being lost.
To work this out, I first took a map that covers the precise boundaries of about 300,000 of the world’s protected areas. I overlaid it with high-resolution satellite data from between 2001 and 2022 showing forest loss just inside and just outside these boundaries.
This method assumed if forest loss was much higher just outside the boundary of a protected area than inside, the protection was working.
Conversely, if forest loss was relatively similar inside and outside the boundary, that shows the protection did not have a strong effect.
This idea can apply even if forest loss on both sides of the boundary is low – because it suggests the area is remote or otherwise not sought-after for human activity. In these cases, we have no evidence that protection is effective, because the forest probably would have been retained even if the protection wasn’t in place.
What I found
I found protected areas prevent an average 30% of forest loss that would have occurred if the policy was not in place. Forest loss occurred in protected areas in all countries – including Australia – but less frequently than in unprotected forest.
The 30% figure is discouragingly low. But it does indicate protected areas are effective to some degree. And effectiveness varies significantly across countries, as the below graphic shows.
World map showing effectiveness of protected areas around the world. Red is least effective, dark blue is most effective. White indicates data was insufficient.Author provided
The policy is almost completely ineffective in many countries, including Indonesia, the Democratic Republic of the Congo, Bolivia, Venezuela, Madagascar, Russia and Gabon. Several of these countries house vast amounts of the planet’s remaining biodiversity. Most, but not all, are developing economies.
In the case of forest loss due to fire, protected areas in advanced economies were also ineffective in some cases.
Australia is a good example. Protected areas here were fairly effective from 2001 to 2018. But the horrific 2019–20 Black Summer fires burned indiscriminately through large swathes of protected forest.
In better news, protected areas were highly effective in some areas, such as New Zealand, Canada, Scandinavia and the Baltic states (Estonia, Latvia and Lithuania).
Protected areas in Canada are reasonably effective.Shutterstock
What this all means
My research illustrates the large improvements needed in many protected areas across the globe to genuinely conserve forests. More research is also needed to understand the best policies to achieve this, before it’s too late.
Developing countries clearly need help to protect their forests. Corruption, political instability, and a lack of resources can make it difficult for governments in these nations to enforce forest conservation laws. Government indifference can also play a role.
How do we turn this around? Schemes such as REDD+, which pays local communities to conserve forest that may otherwise be cleared, could be scaled up.
Foreign aid for forest conservation, from countries such as Australia, can also help. And non-government organisations such as African Parks can put rangers on the ground to help patrol and enforce the integrity of protected areas.
Technology such as real-time deforestation alerts from satellite data can also help.
My findings also highlight the threat climate change poses to forest ecosystems in Australia and elsewhere. Obviously, fire does not respect the boundaries of a national park or other protected area.
So yes, it’s great to see governments around the world signing up to protect 30% of their land. But my work shows attention is needed to make sure those protected areas are working.
Timothy Neal 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.
