Tassie devils’ decline has left a feast of carrion for feral cats



File 20181127 76737 frgu15.jpg?ixlib=rb 1.1
Healthy Tasmanian devil populations have cornered the market on carrion.
Menna Elizabeth Jones, Author provided

Calum Cunningham, University of Tasmania; Christopher Johnson, University of Tasmania; Menna Elizabeth Jones, University of Tasmania, and Tracey Hollings, University of Melbourne

The decline of Tasmanian devils is having an unusual knock-on effect: animal carcasses would once have been gobbled up in short order by devils are now taking many days longer to disappear.

We made the discovery, published today in the journal Proceedings of the Royal Society B, by placing carcasses in a range of locations and watching what happened. We found that reduced scavenging by devils results in extra food for less efficient scavengers, such as feral cats.

Tasmanian devils have struggled for two decades against a typically fatal transmissible cancer, called devil facial tumour disease. The disease has caused devil populations to plummet by about 80% on average, and by up to 95% in some areas.

DFTD has spread across most of Tasmania over a 20-year period. Dashed lines show the estimated disease front.
Calum Cunningham/Menna Jones

Scavengers are carnivores that feed on dead animals (carrion). Almost all carnivores scavenge to a greater or lesser degree, but the devil is Tasmania’s dominant scavenger. Since the extinction of the Tasmanian tiger, it is also the island’s top predator.

A scavenging experiment

In our study, we put out carcasses of the Tasmanian pademelon (a small wallaby weighing roughly 5kg) in a variety of places, ranging from disease-free areas with large devil populations, to long-diseased areas where devil numbers are very low. We then used motion-sensor cameras to record all scavenger species that fed on the carcasses.

The Carnivores of Tasmania: a Scavenging Experiment.

Unsurprisingly, much less carrion was consumed by devils in areas where devil populations have declined. This has increased the availability of carrion for other species, such as the invasive feral cat, spotted-tailed quoll, and forest raven. All of these species significantly increased their scavenging in places with fewer devils.

Consumption of experimentally placed carcasses.
Proceedings of the Royal Society B

The responses of native scavengers (quolls and ravens) were subtly different to those of feral cats. The amount of feeding by quolls and ravens depended simply on how much of each carcass had already been consumed by devils. Ravens and quolls are smaller and less efficient than devils at consuming carcasses, so they get the chance to feed only when devils have not already monopolised a carcass.




Read more:
Tasmanian devils reared in captivity show they can thrive in the wild


In contrast, feral cats tended to scavenge only at sites where devils were at very low abundance. This suggests that healthy devil populations create a “landscape of fear” that causes cats to avoid carcasses altogether in areas where they are likely to encounter a devil. It seems that the life of a feral cat is now less scary in the absence of devils.

Predator prevalence

By looking at 20 years of bird surveys from BirdLife Australia, we also found that the odds of encountering a raven in Tasmania have more than doubled from 1998 to 2017. However, we were unable to directly link this with devil declines. It is likely the raven population is growing in response to a range of factors that includes land-use change and agricultural intensification, as well as reduced competition with devils.

Other studies have shown that cats have also become more abundant in areas where devils have declined. This highlights the potential for devils to act as a natural biological control on cats. Cats are a major threat to small native animals and are implicated in most Australian mammal extinctions.

Carcass concerns

Although smaller scavengers consumed more carrion as devils declined, they were unable to consume them as rapidly as devils. This has resulted in the accumulation of carcasses that would previously have been quickly and completely eaten by devils.

In places with plenty of devils, carcasses were completely eaten within an average of five days, compared with 13 days in places where devil facial tumour disease is rife. That means carcasses last much longer where devils are rare.

DFTD has spread across most of Tasmania over a 20-year period. Dashed lines show the estimated disease front.
Calum Cunningham/Menna Jones

Around 2 million medium-sized animals are killed by vehicles or culled in Tasmania each year, and most are simply left to decompose where they fall. With devils consuming much less carrion, it is likely that carcasses are accumulating across Tasmania. It is unclear how much of a disease risk they pose to wildlife and livestock.

Conserving carnivores

Large carnivores are declining throughout the world, with knock-on effects such as increasing abundance of smaller predators. In recent years, some large carnivores have begun returning to their former ranges, bringing hope that their lost ecological roles may be restored.

Carnivores are declining for many reasons, but an underlying cause is that humans do not necessarily appreciate their pivotal role in the health of entire ecosystems. One way to change this is to recognise the beneficial services they provide.




Read more:
Tasmanian devils are evolving rapidly to fight their deadly cancer


Our research highlights one of these benefits. It supports arguments that we should help the devil population recover, not just for their own sake but for other species too, including those threatened by feral cats.

The devil seems to be solving the disease problem itself, rapidly evolving resistance to facial tumours. Any management plan will need to help this process, and not hinder it. Potentially, returning devils to mainland Australia could provide similar benefit to wildlife threatened by feral predators.The Conversation

Calum Cunningham, PhD candidate, University of Tasmania, University of Tasmania; Christopher Johnson, Professor of Wildlife Conservation and ARC Australian Professorial Fellow, University of Tasmania; Menna Elizabeth Jones, Associate professor, University of Tasmania, and Tracey Hollings, Senior Scientist, Ecological Modelling at Arthur Rylah Institute for Environmental Research, and Honorary Research Fellow, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia: Large Fish Species in Serious Decline


The link below is to an article reporting on the serious decline in large fish species across Australia.

For more visit:
https://www.theguardian.com/environment/2018/jun/05/australias-large-fish-species-declined-30-in-past-decade-study-says

Citizen scientists count nearly 2 million birds and reveal a possible kookaburra decline


Kerryn Herman, Deakin University

The fourth Aussie Backyard Bird Count has just ended, with nearly 2 million birds from 635 species submitted to the BirdLife Australia app. The count, which is in its fourth year, has created a national database of birds found in our backyards.

We don’t know yet exactly how many people participated this year, but more than 60,000 people submitted checklists in 2016. Participants span the whole country, though participation is highest in our urban areas. By surveying our backyards (rather than “good” bird spots), these citizen scientists provide ecologists – like me – with information from urban areas we would not otherwise sample.

This includes data on a range of common bird species that are not frequently analysed because these species are believed to be secure. One of the most surprising results is a decline in the frequency of occurrence of the laughing kookaburra across southeast Australia.

Counting birds

Everyone has a bird story – and fortunately for ecologists, everyone is willing to share them. With 85% of Australia’s population living in cities and towns, birds are an important connection to our natural environment.


BirdLife Australia

But birds are also good environmental indices. They’re generally easy to measure, they respond quickly to environmental change and we know a reasonable amount about the ecology of most species.

Between 1998 and 2014, BirdLife Australia volunteers collected a significant amount of data. This was used to develop a terrestrial bird index in 2015 – a bird “Dow Jones” to track our biodiversity. It was here that the decline in kookaburras was first identified.

The data were drawn from BirdLife Australia’s ongoing atlas project, now called Birdata. However, there are biases in this data set, as people obviously like to go birdwatching where they will see more birds. This may inflate the frequency of encountering some species and decrease the chances of encountering others – particularly rare and cryptic species.

For the last four years, we’ve asked volunteers to add to this data by counting birds around their home for a week in October, when many birds are highly active and visible. These counts complement the data already available in Birdata by allowing access to backyards across Australia, which are generally poorly represented in the larger data set.

While there are still limitations in the Backyard Bird Count data, such as the risk of mis-identification, for common species like the laughing kookaburra we can generally be confident that the identification is correct. Even if the same bird is counted multiple times, our models report only a species’ presence or absence, so inflated numbers don’t affect the trend.

Are kookaburras really declining?

The below figures show modelled trends for the kookaburra across metropolitan Melbourne and Sydney. These figures are derived from the volunteer-collected Birdata, much of which comes from green spaces and remnant vegetation in these landscapes.

I wondered whether these declines are true changes in the populations, or reflect a change in the way kookaburras are using the landscape, possibly moving into the matrix of urban backyards that just don’t get surveyed. Looking solely at the backyard count data, I found similar trends in the reporting rates of kookaburras as those in the models, supporting that this decline is at the population level. What started out in 2014 as a way of engaging the broader community with their birds is now collecting useful ecological data.

Further exploration of the ABBC data across other capital cities found some interesting things. In both Perth and Hobart, where the kookaburra is considered an introduced species, the birds are recorded more frequently than in Melbourne and across the ACT. In Perth, increases in 2016 compared to previous years suggest an increase in the species there.

Modelled trends for Kookaburras from 1998-2014. The figure on the left is for Melbourne, and on the right is for Sydney. The reporting rate shows the percentage of surveys where kookaburras were recorded as present. The thick black line is the modelled trend (with confidence intervals in dashed line), the pink line shows the statistically significant linear trend, the thin black line shows the monthly calculated reporting rate, and the green spots show acceleration (or a favourable change) in the trend. Note that due to modelling method, the ends of figures tend to blow out as there is no data from which to predict trend.
Unpublished models/K. Herman/BirdLife Australia, Author provided

While three years does not make a trend, Aussie Backyard Bird Count data from heavily urbanised areas suggest we are seeing a decline in this iconic species in the eastern capitals. Likely reasons for this are the loss of nesting hollows and possibly reductions in the availability of prey as we increasingly modify our urban landscapes. We don’t really know as this is not an area that has been researched.

We need citizen scientists

Collecting enough data (especially from the backyards of towns and cities) to detect these kinds of changes can be an overwhelming task. This is where citizen science programs like the Aussie Backyard Bird Count can help.

As well as helping ecologists track large-scale biodiversity trends, it also gives people the chance to connect with their natural environment and gain a greater appreciation of our unique fauna.

As with all citizen science projects, there are limitations in the data being collected. However, the Backyard Bird app has been designed to make counting as simple and standardised as possible, providing confidence in the tally of common and “iconic” species, and filling in the gaps found in other data sets.

The good old kookaburra is neither rare or cryptic. If anything, if people are seeking out “good” bird habitat to survey we would expect that kookaburras would be one of those species subject to inflated reporting. But this is not what we encountered.

The ConversationIf we are starting to see declines in species that we have traditionally considered secure, what does this mean for those that are already at risk? Once all the data from the Aussie Backyard Bird Count have been collated and vetted we will continue to explore the developing trends in Australia’s urban birds. Increasing engagement and awareness in our communities can help ensure our backyard birds are still around to count next year.

Kerryn Herman, Research Ecologist, Deakin University

This article was originally published on The Conversation. Read the original article.

Environmental score card shows Australia is once again in decline


David Summers, Australian National University and Albert Van Dijk, Australian National University

After some unusually wet years, our landscape and ecosystems have once again returned to poorer conditions that were last experienced during the Millennium Drought.

That is the main conclusion of Australia’s Environment in 2015 – an environmental score card and accompanying data explorer that we have just released.

Australia’s natural environment is the bedrock of our economy, and our unique ecosystems and landscape are a fundamental part of our society and national identity. This latest report shows that for most of the country, our environmental fortunes are closely tied to the highs and lows of rainfall.

We combined and analysed huge amounts of satellite imagery, ground data and landscape modelling and compiled this data into 13 environmental indicators. With most data extending back to the year 2000, we can start to see how Australia’s environment is changing over time.

The big picture

National level environmental indicators show that soil moisture and river flows fell to near record lows in 2015, while tree cover continued its decline to reach the lowest level since 1972. Soil exposure, the lack of protection from vegetation or mulch cover, also returned to levels last seen during the drought.

Many of these changes are strongly driven by changes in rainfall. Other processes also play a role, however. For example, some of the estimated 530,000 hectares reduction in forest area in 2015 was due to clearing, particularly in southern Queensland, where around 300,000 ha were cleared in 2013-2014 (land clearing data for 2015 are not yet available).

Change in tree cover as percentage of country area

We can combine some of these indicators to get an overall score of the environment’s condition. Such a measure can only ever be an artificial and subjective index, similar to composite indices used for the economy, for example.

But because most environmental indicators are strongly linked to water availability, the overall pattern still remains similar if different calculations are made.

Change in national environmental condition score

The national environmental score declined from around average in 2014 (4.8) to well below average in 2015 (3.6). This is a cause for concern, particularly given the relatively short time since the plentiful rains that saw off the drought in 2010.

Winners and losers

While useful to understand general trends, the national indicators hide much regional variation. For example, scores increased to above average values in the Australian Capital Territory and New South Wales, which received good rains across most of the state in 2015.

On the other hand, in Queensland conditions were already relatively poor in 2014 and declined further in 2015, in some parts of the state to the worst conditions since at least 2000.

Environmental condition scores and changes from 2014

The different indicators also did not always change in the same way. For example tree cover declined in all states and territories except in Tasmania, where new plantations exceeded harvesting rates. (These numbers do not include the impact of large bushfires in early 2016).

Tree cover also increased in some other regions, whereas relatively strong losses occurred not only in Queensland, but also as a result of urban expansion in most metropolitan areas.

On the other hand, despite the general decline of agricultural land, the majority of our national parks remained in good shape in 2015. (You can see these regional patterns in our data explorer, which shows indicators by state, council area, catchment, national park, wetland, and so on.)

Tree cover change by region, showing largest decreases in red and increases in blue

Back to lean years

The Millennium Drought was arguably the worst drought on our historical record. Lasting around a decade, it had profound impacts on water resources, rivers and wetlands, ecosystems and agriculture.

The very wet years that followed brought some much needed relief to the desiccated ecosystems. Unfortunately, our report shows that the bounce was short lived, and that environmental indicators are once again in the red.

While this is a concern, we are still some way from experiencing the worst impacts of the Millennium Drought. We have only had three years with relatively low rainfall rather than ten, and some of the events that occurred towards the end of the Millennium Drought have not yet come to pass.

For example, many wetlands in eastern Australia have declined in extent, but not quite yet to the record lows observed before. The same is true for many of our water storage reservoirs, which have returned to the low levels seen during the first half of the last drought, but not yet the lows of later years.

Still, it is concerning that the lean years have come back so fast. Apparently, the rainfall abundance of 2010-2012 did not create a long lasting reserve, once more leaving our environment exposed to the next drought.

Indeed, we may already be in it.

The Conversation

David Summers, Research academic, Fenner School of Environment & Society , Australian National University and Albert Van Dijk, Professor of Water Science and Management, Fenner School of Environment & Society, Australian National University

This article was originally published on The Conversation. Read the original article.