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For whom the bell tolls: cats kill more than a million Australian birds every day

The Conversation

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On the prowl in the outback. Hugh McGregor/Arid Recovery, Author provided

John Woinarski, Charles Darwin University; Brett Murphy, Charles Darwin University; Leigh-Ann Woolley, Charles Darwin University; Sarah Legge, Australian National University; Stephen Garnett, Charles Darwin University, and Tim Doherty, Deakin University

Cats kill more than a million birds every day across Australia, according to our new estimate – the first robust attempt to quantify the problem on a nationwide scale.

By combining data on the cat population, hunting rates and spatial distribution, we calculate that they kill 377 million birds a year. Rates are highest in Australia’s dry interior, suggesting that feral cats pose a serious and largely unseen threat to native bird species.

Read more: Ferals, strays, pets: how to control the cats that are eating our wildlife

This has been a contentious issue for more than 100 years, since the spread of feral cats encompassed the entire Australian mainland. In 1906 the ornithologist A.J. Campbell noted that the arrival of feral cats in a location often immediately preceded the decline of many native bird species, and he campaigned vigorously for action:

Undoubtedly, if many of our highly interesting and beautiful birds, especially ground-loving species, are to be preserved from total extinction, we must as a bird-lovers’ union, at no distant date face squarely a wildcat destruction scheme.

His call produced little response, and there has been no successful and enduring reduction in cat numbers since. Nor, until now, has there been a concerted effort to find out exactly how many birds are being killed by cats.

Counting the cost

To provide a first national assessment of the toll taken by cats on Australian birds, we have compiled almost 100 studies detailing the diets of Australia’s feral cats. The results show that the average feral cat eats about two birds every five days.

We then combined these statistics with information about the population density of feral cats, to create a map of the estimated rates of birds killed by cats throughout Australia.

Number of birds eaten per square kilometre. Brett Murphy, Author provided

We conclude that, on average, feral cats in Australia’s largely natural landscapes kill 272 million birds per year. Bird-kill rates are highest in arid Australia (up to 330 birds per square km per year) and on islands, where rates can vary greatly depending on size.

We also estimate (albeit with fewer data) that feral cats in human-modified landscapes, such as the areas surrounding cities, kill a further 44 million birds each year. Pet cats, meanwhile, kill about 61 million birds per year.

Overall, this amounts to more than 377 million birds killed by cats per year in Australia – more than a million every day.

Which species are suffering?

In a related study, we also compiled records of the bird species being killed by cats in Australia. We found records of cats killing more than 330 native bird species – about half of all Australia’s resident bird species. In natural and remote landscapes, 99% of the cat-killed birds are native species. Our results also show that cats are known to kill 71 of Australia’s 117 threatened bird species.

Birds that feed or nest on the ground, live on islands, and are medium-sized (60-300g) are most likely to be killed by cats.

Galahs are among the many native species being killed by feral cats. Mark Marathon, Author provided

It is difficult to put a million-plus daily bird deaths in context without a reliable estimate of the total number of birds in Australia. But our coarse assessment from many published estimates of local bird density suggests that there are about 11 billion land birds in Australia, suggesting that cats kill about 3-4% of Australia’s birds each year.

However, particular species are hit much harder than others, and the population viability of some species (such as quail-thrushes, button-quails and ground-feeding pigeons and doves) is likely to be especially threatened.

Our tally of bird deaths is comparable to similar estimates for other countries. Our figure is lower than a recent estimate for the United States, and slightly higher than in Canada. Overall, bird killings by cats seem to greatly outnumber those caused by humans.

In Australia, cats are likely to significantly increase the extinction risk faced by some bird species. In many locations, birds face a range of interacting threats, with cat abundance and hunting success shown to increase in fragmented bushland, in areas with high stocking rates, and in places with poorly managed fire regimes, so cat impacts compound these other threats.

Belling the cat

What can be done to reduce the impact? The federal government’s Threatened Species Strategy recognises the threat posed by feral cats, albeit mainly on the basis of their role in mammal extinctions.

The threatened species strategy also prioritised efforts to control feral cats more intensively, eradicate them from islands with important biodiversity values, and to expand a national network of fenced areas that excludes feral cats and foxes.

But while fences can create important havens for many threatened mammals, they are much less effective for protecting birds. To save birds, cats will need to be controlled on a much broader scale.

Read more: The war on feral cats will need many different weapons

We should also remember that this is not just a remote bush problem. Roughly half of Australia’s cats are pets, and they also take a considerable toll on wildlife.

While recognising the many benefits of pet ownership, we should also work to reduce the detrimental impacts. Fortunately, there is increasing public awareness of the benefits of not letting pet cats roam freely. With such measures, cat owners can help to look after the birds in their own backyards, and hence contribute to conserving Australia’s unique wildlife.

The ConversationWe acknowledge the contribution of Russell Palmer (WA Department of Biodiversity Conservation and Attractions), Chris Dickman (University of Sydney), David Paton (University of Adelaide), Alex Nankivell (Nature Foundation SA Inc.), Mike Lawes (University of KwaZulu-Natal), and Glenn Edwards (Department of Environment and Natural Resources) to this article.

John Woinarski, Professor (conservation biology), Charles Darwin University; Brett Murphy, Senior Research Fellow, Charles Darwin University; Leigh-Ann Woolley, Research Associate, Charles Darwin University; Sarah Legge, Associate Professor, Australian National University; Stephen Garnett, Professor of Conservation and Sustainable Livelihoods, Charles Darwin University, and Tim Doherty, Research Fellow, Deakin University

This article was originally published on The Conversation. (Reblogged by permission). Read the original article.

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Bird tree of life shows ‘explosive evolution’: studies

The Conversation

By Bryonie Scott, The Conversation and Tessa Evans, The Conversation

Today’s land birds, from ducks to eagles, shared a common ancestor after dinosaurs went extinct – just one finding from bird gene studies published in journals, including Science and GigaScience, today.

Genetic data of 48 bird species were sequenced in a massive international collaboration to create a new and detailed version of the avian tree of life.

“Birds have always been very good for this kind of work because we have a greater understanding about the world’s birds than we do about any of the other vertebrate groups,” Simon Griffith, Associate Professor of Avian Behavioural Ecology at Macquarie University, said.

“We are familiar with almost all the birds in the world – around 10,000 species – and we know how they differ, in important characteristics such as how long they live, how many offspring they have each year, how old they are when they breed.”

About 66 million years ago, a mass extinction event wiped out around 80% of Earth’s plant and animal population, but opened the door for the rapid expansion of birds.

Giant terror birds are similar to a common ancestor of all land birds. Marcelo Braga/Flickr, CC BY

Only a few bird lineages survived the mass extinction, and most modern land birds such as songbirds, owls and woodpeckers share a common apex predator ancestor.

This top-of-the-food-chain brute was similar to the giant terror birds which stalked the Americas between 27 million and 15,000 years ago.

“The main problem in resolving the relationships among birds is that they diversified very quickly,” Research Director and the Curator of the Australian National Wildlife Collection, CSIRO, Leo Joseph said.

Extreme adaptations

Birds are among the most widespread land animals and have experienced evolutionary adaptations to extreme environments. Penguins live in some of the harshest conditions on Earth, and DNA analysis, published in GigaScience, confirmed fossil evidence that penguins first appeared in Antarctica around 60 million years ago.

“If you have a complete genome, you can compare the variations between the chromosomes and get a picture of the population history” Sankar Subramanian, a research fellow at Griffith University and who worked on the project, said.

“By comparing the complete genome of penguins living today we can track when evolutionary changes occurred, up to 200,000 years ago.”

This aspect of the research, Emperor penguins were found to have a stable population, but Adélie penguins present a very different story, showing fluctuations in population matching extreme climactic periods.

In a warmer period 150,000 years ago there was a large population explosion, but in a more recent glacial period the population declined dramatically.

Adélie penguins struggle in glacial periods as they require ice-free land for nesting. Dominique Génin/Flickr, CC BY-NC-ND

Rather than being evolutionary in origin, Dr Subramanian explained the fluctuations depended on “how much ice-free land is available for nesting and breeding”.

Compared to other bird species, penguins had more genes for lipid metabolism, which is essential for forming layers of blubber to withstand the cold.

This subgroup of the project hopes to look at penguins which live in tropical and temperate waters such as the Galápagos Islands and New Zealand to see how more recent evolutionary adaptations have affected genes of modern penguins.

Now that these hallmark studies have been completed, and the bird tree of life established with some degree of authority, it provides a scaffold for further research.

“This new study helps tease apart the rapid diversification of birds, which has been a long-standing problem,” Dr Joseph said.

“We can now address really interesting questions,” Associate Professor Griffith said. “When did song learning evolve? When did birds evolve different patterns of parental care?”

These insights provide sought-after answers about how species can diversify so quickly to fill the ecological niches.

This articled was edited on Friday December 12, 2014, to clarify some quotes by Dr Leo Joseph.

The ConversationThis article was originally published on The Conversation. (Republished with permission). Read the original article.

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