Golden eagles deter foxes, facilitate forest grouse

Wetland ecology group_University of Helsinki_golden eagle

Top predators can have surprising effects on ecosystems. Golden eagle @Sari Holopainen

The effects of top and mesopredators on lower levels of food webs have been researched from many perspectives, but less focus has been given to the roles that avian top predators play on mid-sized mammalian predators. The cascade effects of raptors, which concurrently affect several trofic levels, have also gained little attention. However, researchers at the University of Turku have observed how the golden eagle (Aquila chysaetos) affects pine marten (Martes martes) and red fox (Vulpes vulpes) populations, along with the cascade affects induced on black grouse (Tetrao tetrix) and hazel grouse (Tetrastes bonasia) populations.

Golden eagles hunt black grouse, red foxes, and pine martens. When the opportunity arises they will also catch hazel grouse, but because of their smaller size and habitat preferences (thick forests), hazel grouse are better protected from golden eagles, which prefer open territory when hunting. The researchers initially hypothesized that the golden eagle would locally lessen the numbers of red foxes and pine martens, thereby causing a positive affect on the two grouse species.

However, the truth is not quite as simple. Pine marten and red fox densities actually increase in areas with large numbers of golden eagle. One possible reason behind this surprising result could be the large prey populations available for all three predators in these areas, along with the partially overlapping habitat preferences of pine marten and golden eagle. On the other hand, pine martens avoid open territory, possibly because of the non-lethal deterrent effect that golden eagles exert on pine marten.

Wetland_ecology_group_University_of Helsinki_hazel grouse

Top predators can have surprising effects on ecosystems. Golden eagle @Sari Holopainen

But the story doesn’t end here: high densities of golden eagles still does have an effect, as larger numbers of young hazer grouse and black grouse are present at these sites. The golden eagle may therefore facilitate the grouse by lessening the numbers of mesopredators in their territories through the deterrent effect. This would lead to less predation and egg eating by the pine marten and red fox. In other words, red fox and pine marten avoid golden eagles so effectively, that the two grouse species benefit from their weakened predation performance. A similar protective effect has also been observed with the goshawk (Accipiter gentilis).

Increasing golden eagle territory and offspring densities cause decreasing numbers of black grouse, but this does not occur with hazel grouse. The small size of the hazel grouse most likely protects it from golden eagle predation. The black grouse, on the other hand, favors open territory. Golden eagles therefore appear to have a protective effect on juvenile hazel and black grouse individuals, while threatening adult black grouse.

Wetland_ecology_group_University_of Helsinki_black grouse

Black grouse lekking @Stella Thompson

The cascade effects directed at these grouse species do not appear to change with fluctuating pine marten and red fox densities. The presence of other mesopredators, e.g. raccoon dogs (Nyctereutes procyonoides) and the American mink (Neovison vison), has been suggested as the reason for this. The effects of these other mesopredators were not assessed during the study.

The golden eagle affects mesopredator behavior without affecting their population densities. A similar deterrent effect has previously been observed from white-tailed sea eagles (Haliaeetus albicilla) on the American mink, and golden eagles most probably also deter minks and raccoon dogs. The eagles additionally deter the movements of other potential egg thieves such as corvids.

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Hunters and conservationists – with shared cause

Do hunters conserve nature? This seemingly controversial issue seems to be a source of never-ending debate. I recently found a text discussing this issue, published in the “Finnish Nature” (Suomen Luonto) magazine as early as 1944. While conservationists and hunters may sometimes be in direct conflict, some shared targets were recognized already in 1944.

Extensive red fox hunting makes it possible for the rare arctic fox to breed successfully in Sweden and Norway. Red fox in an arctic fox habitat in Varanger Peninsula, northern Norway. © Sari Holopainen

Extensive red fox hunting makes it possible for the rare arctic fox to breed successfully in Sweden and Norway. Red fox in an arctic fox habitat in Varanger Peninsula, northern Norway. © Sari Holopainen

O. Hytönen (1944) raised the very same observations that are still apparent. Although hunters kill animals, prey animal populations should not be eradicated by responsible hunting practices. Some hunting actions are straightly connected to nature conservation, such as feeding animals during harsh winters, habitat management and predator control. Currently discussed effect of trophy hunting as an important conservation tool in development countries is an example of an indirect connection: by paying for hunting permits hunters help to maintain local animal diversity. As noted in a recently published paper, banning of trophy hunting can lead to exacerbating biodiversity loss.

In 1953 “Finnish Nature” (Suomen Luonto) published another text on the subject, this time written by G. Bergman. Bergman wrote that the relationships between hunters and conservationists has not always been smooth in Finland, or in other Nordic countries, while no benefits could be gained from these conflicts. Bergman noted that modern game management has several shared principles with nature conservation. He also pointed out that nature conservation and hunting have successfully been managed together in the US. As during Bergman’s times, Europe is still somehow on separate paths, and the situation has become particularly inflamed in some countries. Ironically, Bergman wrote that if we refuse to understand the interests of others, nature conservation aims may be disturbed.

The good old American way

What were the good manners already mentioned by Bergman in America? Maybe he meant the Federal Duck Stamp system established already in 1934. All US hunters must buy a Duck Stamp on a yearly basis, however, whoever can get one. With this small cost the buyers contribute to bird habitat conservation. The US Fish and Wildlife Service advertises that the stamp is “among the most successful conservation tools ever created to protect habitat for birds and other wildlife”. About 1 500 000 stamps are bought yearly, and 98% of the profits are given to the National Wildlife Refuge System for wetland conservation.

Coldwater River National Wildlife Refuge in Mississippi provides great circumstances for wintering ducks. The park is protected, but bird watching is aloud in some parts of the park. Duck hunting is possible outside the park in private lands. © Sari Holopainen

Coldwater River National Wildlife Refuge in Mississippi provides great circumstances for wintering ducks. The park is protected, but bird watching is aloud in some parts of the park. Duck hunting is possible outside the park in private lands. © Sari Holopainen

Another traditional American actor smoothly combining conservation and hunting is Ducks Unlimited (DU), founded by a group of hunters in 1937. DU targets habitat conservation, and is now claimed to be the world’s largest and most effective private waterfowl and wetlands conservation organization according to their website. Most DU members are still hunters.

The land of a thousand lakes

Wetlands have been destroyed for a long time due to differing human interests, also in Finland. Some areas have been lost altogether, while some have lost their value due to e.g. vegetation overgrowth. We still have many lakes left, but shallow eutrophic lakes – the waterbird lakes – are the ones that have been lost most often. Hunters are a group with an interest to construct and restore wetlands. According to a report by the Finnish Wildlife Agency, hunters have constructed or restored about 2 000 wetlands during the past decades. In addition to benefitting game animals, the entire ecosystem benefits. Wetlands also offer several other ecosystem services, including water purification and erosion control.

Many wetlands have been established in Finland to support game animals. Saarikko-wetland in southern Finland is a small, yet very productive duck habitat constructed by the REAH-project (active management of game animal habitats). © Sari Holopainen

Many wetlands have been established in Finland to support game animals. Saarikko-wetland in southern Finland is a small, yet very productive duck habitat constructed by the REAH-project (active management of game animal habitats). © Sari Holopainen

Methods matter

Sometimes hunting itself supports animal populations. For example, hunters can help to maintain animal communities through ecosystem engineering pushed by hunting and the co-evolution of animals and humans. In 2013 a scientific paper showed that in Australia Aboriginal hunting was one of the cornerstones supporting monitor lizard populations. Monitor lizards occur most densely in areas where they are hunted, because of the hunting method used; the burning method creates a patchy mosaic of regrowth in the landscape. In areas with no hunters, occasional lightning strikes burn land in a more homogenous way, and thus also lizards are scarcer. The same practice might also benefit several other desert species. However, in many cases Aboriginals have lost their traditional hunting possibilities, and the loss of these traditional practices sustaining habitats might have contributed to decreasing populations of several desert animal species.

While the debate between hunting and nature conservation has already lasted a long time, and is still on-going, common targets have been raised throughout the process by cooperative actors of both sides. There has always been, and currently still are, differing hunting methods for concerning conservational effects, but it is self-evident that all these practices are not against conservation targets.

Read more:

Enrico Di Minin, Nigel Leader-Williams & Corey J.A. Bradshaw: Banning Trophy Hunting Will Exacerbate Biodiversity Loss. 2015. Trends in Ecology & Evolution. Online.

Connecting Aboriginal Land Use Management Strategies, Mammal Extinction Rates and Shifts in Fire Regimes in a Changing Climate: An Interdisciplinary Approach to Inform Conservation Strategies for Threatened Species in the Australian Western Desert

An interdisciplinary approach to understanding the role of anthropogenic fire in the desert grasslands of Australia

Battle of the foxes

Guest author: Samuli Karppinen

“It was the fifth red fox for the same day”. “Foxes are everywhere”, I thought numerous times during my summer job time in the region of Inari. I was amazed at the number of red foxes (Vulpes vulpes) present in the very northern part of Finland. Nearly every day and no matter where I went, I discovered foxes. I observed foxes close to settlements, and at the end of forest gravel roads. They were mainly lonely adults, but litters of the same year were common too. In addition, the number of red fox dens supported the idea that they succeed well in the northern part of Finland. The arctic fox (Vulpes lagopus) is adapted to life in arctic areas. In Finland, arctic foxes have bred in the regions of Inari and Utsjoki. Arctic fox populations are similar in size to those in Sweden and Norway. Population size at the end of the 1800s was estimated to be 15 000 individuals. At present, the size of the population is estimated to be only 120 individuals. Despite yearly sightings of arctic foxes in Finland, it is nearly 20 years since the last confirmed arctic fox litter. During the summer I began wondering how red foxes influence the declining arctic fox population?

The Arctic fox in Polar Park Norway. © Sari Holopainen

The Arctic fox in Polar Park Norway. © Sari Holopainen

Intensive hunting in the early 1900s was the ultimate reason for the collapse of the Fennoscandian arctic fox population. Even though arctic foxes were protected in 1940, the population did not return to its earlier size. There are several probable causes. Due to changes in reindeer husbandry, arctic foxes cannot exploit the same number of carrions. Global warming causes problems to arctic species and the arctic fox does not stretch the point. Climate change affects snow cover, which reflects on the amount of lemmings. Lemmings are a vital food source for arctic foxes. Arctic fox brood and litter sizes are bigger when the amount of voles and lemming are at their highest point. In addition, global warming is raising the tree line to higher altitudes on the fells. This improves the survival of red foxes in the areas inhabited by the arctic fox.

The red and arctic foxes cannot inhabit the same territory. Research has uncovered that red foxes colonize and annihilate arctic fox dens. The red fox is very adaptable to different habitats and competes for food with the arctic fox. The striking winning picture of the Wildlife Photographer of the Year 2015 –competition underlines the interactions between the two species. The arctic fox is smaller than the red fox and loses the competition for food and habitats. Exploring the number of litters in the last 20 years, it can be seen that while red fox litters have grown, arctic fox litters have declined. The first idea to prevent the spreading of red fox populations is extensive hunting. At the beginning of the millennium, red foxes were intensively hunted in the fell areas of Enontekiö and Utsjoki under the Naali Life – project. The catch quotas appointed by the Ministry of Agriculture and Forestrywere fulfilledvery well by hunters each year. Unfortunately, the hunting alone and the short hunting period in particular had hardly any significance for the arctic foxes.The hunting probably only improved the living conditions of the remaining red foxes and the population might even have strengthened.

Fox cub in Inari. © Samuli Karppinen

Fox cub in Inari. © Samuli Karppinen

Finnish hunters are active in culling semi-predators, like red foxes. It seems that Finnish hunters actively cull semi-predators up to the height of the Arctic Circle. Active culling does not occur in the regions of Inari and Utsjoki, at least in the same scales.Reasons for this are clear: hunters are less enthusiastic, distances are long, the road network is sparse, and snow coveris thick. Maybe hunters of northern Finland don’t feel that culling is as important as hunters in southern Finland do. Red fox culling has to be continuous and intensive year after year for it to have positive effects on the arctic fox population. In 2015, the Finnish wildlife agency, as a part of Management of invasive Raccoon Dogs (Nyctereutes procyonoides) in the north-European countries project, started a project to cull the raccoon dog population in Lapland. A similar project, focused on the red fox, could be a good motivator for local hunters to cull the red foxes.

Research has indicated that lynx (Lynx lynx) regulate red fox populations. Foxes do not succeed in areas where lynx populations are abundant. One of the reasons for red fox success in the fell areas could be a lack of lynx. Unfortunately, it is not realistic to expect that lynx could be the arctic fox’s rescuer. The EU-Life project SEFALO+ (Save the Endangered Fennoscandian Alopex lagopus) has shown that a combination of actions, supplementary feeding, red fox culling, and protection of dens, could cease the decline of the arctic fox population and even enhance it. Nevertheless, I began wondering whether all these actions to save the arctic fox population in the Nordic countries will merely delay their extinction? Their population is small and genetic variation low. Diseases may heavily impact such a small population. Another possible threat to the arctic fox is the occurrence of escaped farm foxes on the mountain tundra. They can breed with wild arctic foxes, but hybrids do not survive in the wild. There are many problems and threats, which Fennoscandian arctic fox population have to face to avoid extinction.

The life of an orangutan on your plate

Do you eat instant noodles, margarine, chips or cereals? All these products may include palm oil. It can also be found in shampoos and lipsticks. One must be attentive when reading informative labels, because a vague marking of “vegetable oil” can also mean palm oil. Most palm oil production is for nutritional purposes, less is aimed at fuel. Palm oil is a product of oil palms, which are cultivated mainly in Malaysia and Indonesia. Plantations are established in rainforests, which destroys the habitats of orangutans (Pongo abelii and Pongo pygmeaus) and many other species. So far orangutans have lost about 80% of their original habitats.

Both proboscis monkeys (Nasalis larvatus) and orangutans are threatened by habitat loss. Proboscis monkeys only live in Borneo, orangutans also in Sumatra. © Sari Holopainen

Both proboscis monkeys (Nasalis larvatus) and orangutans are threatened by habitat loss. Proboscis monkeys only live in Borneo, orangutans also in Sumatra. © Sari Holopainen

Most oil palm plantations are established in rainforests. This means that the original rainforest nature is lost. After abandoning the plantation sites, secondary forest growing on the site does not correspond with the original forest. Plantations established on peatlands will make climate change worse due to the release of carbon dioxide.

Oil palm plantation established in the rainforest. The ground suffers from erosion, especially at the beginning of the cycle, when vegetation cover is particularly sparse. © Sari Holopainen

Oil palm plantation established in the rainforest. The ground suffers from erosion, especially at the beginning of the cycle, when vegetation cover is particularly sparse. © Sari Holopainen

Certification has been used to attempt to solve the environmental problems concerning palm oil production. For example WWF has contributed by planning the Roundtable of Sustainable Palm Oil (RSPO)-certificate that stamps for responsibly produced oil. The certificate requires production to be sustainable in both environmental and societal issues.

In addition to environmental issues, palm oil production causes serious societal problems. Unclear landownership relations have led to conflicts between palm oil farmers and indigenous people. Human rights organizations are also concerned of the working conditions of cheap imported labor and undocumented immigrants on the plantations.

Oil palm plantations are spreading in the rainforest. Monocultures formed by the palms pose a striking difference to the biodiversity of the rainforest.  © Sari Holopainen

Oil palm plantations are spreading in the rainforest. Monocultures formed by the palms pose a striking difference to the biodiversity of the rainforest. © Sari Holopainen

Voluntary agreements, such as RSPO try to respond to these gaps in national laws or the lack of following them. However, research published in 2014 found that RSPO has failed to conserve forest habitats, especially orangutan habitats in Indonesia.

The study found that the financial compensation is too small to encourage farmers to apply the certificate. The authors also suggest that there is too much room for interpretation in the guidance documents and that contradicting issues are not solved. In addition the authors saw that the integration of RSPO within the socio-politico-legal Indonesian context has failed and that there is not enough external control in the system. The authors suggest that the Indonesian palm oil sector needs to be reformed if we wish to conserve rainforest biodiversity. This would mean the implementation of a bottom-up approach that supports local development by socio-ecological regional planning.

Orangutans need large forest areas to survive. At the current rate orangutans are expected to become extinct from nature by 2020.

Orphan Tenten is learning orangutan habits in the Rasa Ria nature reserve.

Orphan Tenten is learning orangutan habits in the Rasa Ria nature reserve.

 

Read more: Ruysschaert, D. & Salles D. 2014. Towards global voluntary standards: Questioning the effectiveness in attaining conservation goals The case of the Roundtable on Sustainable Palm Oil (RSPO). Ecological Economics 107: 438–446.

Starving polar bears and disappearing male turtles

At the moment we are living in the sixth wave of mass extinctions. The last one 65 million years ago is well-known to have been caused by an asteroid collision (and possible some other factors), after which non-avian dinosaurs became extinct. Currently animal species are disappearing at a rate of 100-1000 times faster than in normal situations. Climate change, habitat loss, pollution and overexploitation are considered the main reasons for this loss, and all of these are human-driven phenomenon. Climate change is a controversial subject, but nevertheless, we are already seeing the effects of it in our co-animals.

Let’s make a short overview of the changes that current climate warming has caused to natural systems. Some changes are direct, but there are also some more complex traits. Climate change-driven impacts are found to work through population abundance, species distributions, morphology and behavior, and eventually impacting community structures.

It is possible that the polar bear, at least as we know the species, will disappear due to climate warming. In the future it might still be possible to see white polar bears in zoos, such as Ranua Zoo in Finland.

It is possible that the polar bear, at least as we know the species, will disappear due to climate warming. In the future it might still be possible to see white polar bears in zoos, such as Ranua Zoo in Finland.

Where will the habitats shift?

Habitat shifting is one of the most obvious effects of climate change. It does not just mean moving pole-wards, but also upwards. The Edith’s Checkerspot, a North American butterfly species, has shifted its range both northward (92 km) and upward (by 124 m). During this same time period the temperature isotherms shifted 105 km northwards and 105 m upwards, which corresponds well with the butterfly’s range shift.

The habitat of some animals is not shifting, but disappearing. The arctic ice cover is becoming thinner and ice time is becoming shorter. Icy landscapes are the habitat that polar bears are adapted to. When summers grow longer, polar bears need to spend longer times on land or swimming in the sea. The future of polar bears seems gloomy, and it is expected that the majority of the bears will be lost during coming decades.

In stark contrast to the polar bears, some animals are able to utilize the new areas formed due to the lost ice. In Europe, wintering duck numbers have increased in northern waterbodies, while concurrently decreasing in southern and western parts of Europe. Some areas that were previously avoided because of their hostile winter climate are now used, for example Steller’s eiders (Polysticta stelleri) can nowadays winter in the ice-free parts of the Russian White Sea instead of the Baltic Sea.

 

Temperature mixes biology

Puffin food catching is becoming difficult because of climate change.

Puffin food catching is becoming difficult because of climate change.

Some species are decreasing, because climate change can crucially affect their breeding success. Vulnerable sea ecosystems have already been shown to be responding to the warming climate. The breeding time of the Atlantic puffin (Fratercula arctica) is usually dependent on North Atlantic Oscillation, except that the effects disappear during certain years. It is expected that this connection is lost due to climate change, possibly via its effect on the availability of the puffins’ fish prey. Researchers suggest that there might be climate-induced changes in the availability of their prey species. Warm sea surface temperatures have also been found to crash the breeding success of tufted puffins (F. cirrhata). Even though they can adjust their breeding phenology according to water temperature, prolonged warm seasons affect the fledging production of this sensitive species and can make their southern breeding habitats unsuitable for them.

Several bird species are known to have changed their phenology during the last decades: since 1937 31% of bird species in Britain, and 53% since 1939, have been found to show long-term trends of breeding earlier. At the same time, only one species has delayed its breeding. The same breeding pattern has been found in Finnish duck species. Ducks have also delayed their autumn migration during the last three decades. In addition, some amphibian species are breeding earlier in Britain now than 30 years ago.

Many natural systems are adapted to working in certain temperatures. If they are disrupted, there will be consequences. For example, the sex of many reptiles is determined by temperature. All the offspring of turtles develop into females in a warm climate, and into males in a cooler climate. Changes in temperatures affect their sex ratio, and a warming of 2 degrees C could make their populations highly female-skewed.

 

Climate warming releases diseases

Climate change can also affect the sensitive disease balance. Amphibian populations all over the world have been in drastic decline during the last few decades. One of the causes seems to be a deadly fungus, chytridiomycosis. What is extremely worrying, is that the fungus needs a warm climate, and due to climate change, epidemics can occur in new areas. The fungus has so far caused an extinction of at least 93 amphibian species, and is threating amphibian species globally.

Amphibian species all over the world are threatened by a new fungus.

Amphibian species all over the world are threatened by a new fungus.

 

In the hope of evolution

The changes seen now are so rapid that it is unclear how well animal populations, at least long-living ones, can adapt to the new circumstances. But if possible, natural selection could make the polar bears return to their roots, and begin behaving like brown bears again. Or, after seeing a document on polar bears spending their summers swimming and hunting walruses, one could speculate that polar bears could evolve into a true marine species, if there were enough time. Could we also trust evolution to change the limiting temperatures of turtle sex determination? However, all this is speculation, and requires that climate change does not progress too rapidly for long-living species. Models suggest that populations with temperature-dependent sex determination may be unable to evolve rapidly enough. There is a threat that we will lose species such as the polar bears and turtles, unless we play some more time for them by slowing down climate warming.

 

Can the polar bear become the brown again? Salt, an albino brown bear in Polar park Norway.

Can the polar bear become the brown again? Salt, an albino brown bear in Polar park Norway.

 

Read more

REPORT Regime shifts in the breeding of an Atlantic puffin population

Climate change and temperature-dependent sex determination in reptiles

Tufted puffin reproduction reveals ocean climate variability

Climate Extremes: Observations, Modeling, and Impacts

 

An Awful Lot of Voles every five years or so…

Grey red-backed vole (Myodes rufocanus) ©Sari Holopainen

Grey red-backed vole (Myodes rufocanus) ©Sari Holopainen

A recent hiking trip to Lapland got me thinking of voles. The little critters were absolutely everywhere, happily (or with a vengeance) gnawing at our rucksacks during the night in hope of finding food. Several notes left in hiking huts along the way gave more proof of their high numbers: two people had had their rucksacks eaten through and one had lost a bag of nuts when a vole ate a hole through the tent.

Back home in southern Finland, not hair nor hide of a vole. Why not? What actually constitutes a vole cycle, how does it work, and why does it periodically crash? And how does it affect other animals?

Voles can reach sexual maturity as early as three or four weeks, depending on the species in question. This combined with large brood sizes and giving birth to several broods during the breeding season means that when conditions are right there will be an Awful Lot of Voles (called the peak of the cycle). This leads to increases in the numbers of predators (e.g. stoats Mustela erminea and least weasels Mustela nivalis), which marks the start of vole population declines and crashes as their mortality increases. The whole cycle appears to take around three to five years in northern Europe, but it is not synchronous everywhere. Hence a deluge of voles in Lapland, while populations in southern Finland crashed last winter and currently remain small.

Vole populations fluctuate on a yearly basis. Graph by Hannu Pietiäinen.

Vole populations fluctuate on a yearly basis. Graph by Hannu Pietiäinen.

Voles are of course, paramount to many predators. During our hike we saw a hawk owl (Surnia ulula) and several rough-legged buzzards (Buteo lagopus). Signs of martens and stoats were numerous. Unfortunately the elusive snowy owl (Bubo scandiacus) did not make an appearance. These are all species whose life cycles are influenced by voles. They produce larger numbers of offspring during vole-rich years, while breeding may plummet to zero when vole cycles are down. Many strict vole eating owl species are nomadic, wandering large distances to ensure being in the right place at the right time when it comes to food. However, several owl species are residential and will not travel in search of food, e.g. the tawny owl (Strix aluco). For these species in particular the vole cycle does not only determine breeding success or brood size, but actually influences the number of breeding pairs in the total population, the timing of nesting onset, even a young owl’s entire life expectancy and quality of life. For example, the phase of the vole cycle (aka the nutritional state of an owl) during the first year of an owl’s life correlates with the number of parasites it carries as an adult. The vole cycle also determines at what age residential owls are recruited into the population as breeders (e.g. whether at one or two years of age), as owls will not breed if the female is too weak.

Phase of vole cycle affects nesting and owling survival. Modified from picture by Hannu Pietiäinen.

Phase of vole cycle affects nesting and owling survival. Modified from picture by Hannu Pietiäinen.

A worrying phenomenon has possibly begun to unfold during the last few decades concerning vole cycles. Twice the cycle has been disrupted, and an anticipated peak has not occurred. If disturbances in the cycle become more frequent, this will play havoc for countless northern species. The reasons behind this disturbance are unclear, but a warming climate with thin snow cover has been suggested.

Rough-legged buzzards use voles as their primary food source. ©Sari Holopainen

Rough-legged buzzards use voles as their primary food source. ©Sari Holopainen

Not so cute and cuddly – it’s time for the cat wars

Feral cats (Felis catus) have spread globally thanks to their reputation as cuddly house pets. Their habitat use is very diverse, ranging from urban areas to e.g. agricultural, woodland, and grassland landscapes. Feral cats also rapidly become semi-wild if given the chance to move freely in the great outdoors. Combining their ability to spread fast and wide with their ability to eat very varying diets (small mammals, birds, reptiles, amphibians, everything goes) is apt to spell major trouble for native wildlife. And though they are fairly small-sized mammals, they do not only go for small animals, but have been recorded to kill animals weighing up to four kg (nearly 9 lbs).

Feral cats have also been dubbed “compulsive killers”. That means that not only do semi-wild feral cats hunt food for their survival, but house cats momentarily let loose in back yards etc. will go after anything moving, despite having a meal waiting back home. They effectively conquer the niches of several native small or medium-sixed predators around the world, thus disrupting food webs and ecosystems. And to top it all of, feral cats can also spread toxoplasmosis, a parasitic disease that threatens humans and livestock (e.g. sheep in Australia).

Native and endemic island populations have been particularly hard struck by the spreading of feral cats, but the numbers behind this feline invasion are massive everywhere: an estimated 18 million native animals are eaten by feral cats every year in Australia alone, and a single cat is believed to kill five to 30 animals a day. This is no small-scale problem; the US alone has an estimated 100 million pet cats, each of which kills around 5 to 15 birds per year. That’s 1,500 000 000 birds. Feral cat-caused mortality rates of birds in Great Britain are estimated at 50 million a year.

The Australian government has reacted to feral cats with the strongest measures. They are not hard-pressed to find reason, as 100 native Australian species are in direct extinction threat caused by feral cats. Australia has issued a national threat abatement plan for predation by feral cats, aiming to eradicate them from three islands, with plans to evict the species from two more in the near future. New Zealand also has a zealous plan for lessening the damage caused by small mammals (including feral cats), with the aim of eradicating the species completely (except as an indoor pet) from the country.

Urban and rural feral cats can devastate native wildlife populations. ©Stella Thompson

Urban and rural feral cats can devastate native wildlife populations. ©Stella Thompson

Cat wars are being waged across the world with one common denominator: high-tech technology. Eradication measures include using thermal imaging, motion and remote sensing cameras, and GPS tracking collars along with more traditional baiting, trapping, and using tracking dogs. Several countries have also issued desexing programs and cat-free zones around particularly important areas (e.g. nesting sites). Fines can also be issued in some countries (including Finland) to cat owners whose cats have killed native animals. These fines can reach thousands of euros/dollars, depending on the species in question.

It seems unlikely that pet cats are going anywhere in the near future (and why should they); however, maybe what remains a question is whether their freedom in the great outdoors should be restricted or whether laws should be passed mandating cat owners to fasten little bells or colorful cat collars around their pets’ necks. Both have been shown to significantly lessen the numbers of birds, reptiles, and amphibians falling prey to this miniscule feline predator. It is important to remember that what people think is cute play when witnessed at home is actually stalking that will result in native species mortality when the cat is let loose. Attitudes must also change; all too often people believe it is okay to abandon their pet cats after caring for them for a while. Such cats can form populations of tens or hundreds of semi-wild individuals, living in abandoned buildings around the countryside and cities. Many may believe this to be a random occurrence, but e.g. 20 000 pet cats are abandoned yearly in Finland.