Author Archives: Euan Ritchie

About Euan Ritchie

I apply ecological theory with good doses of field work to seek solutions to the challenges of conserving biodiversity.

Feral cat cull: why the two million target is on scientifically shaky ground

The government’s target to kill 2 million feral cats sounds impressive, but lacks scientific rigour. Image credit Daniel Parks via Flickr

By Tim Doherty (Deakin University), Dale Nimmo (Charles Sturt University), Don Driscoll (Deakin University), Euan Ritchie (Deakin University), and Ricky Spencer (Western Sydney University).

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

The Australian government’s target of killing two million feral cats by 2020 attracted significant public interest and media attention when it was unveiled in 2015.

But in our new research, published today in Conservation Letters, we explain why it has a shaky scientific foundation.

The target was developed for the Threatened Species Strategy. At the time of its launch in 2015, there was no reliable estimate of the size of Australia’s feral cat population. Figures of between five million and 18 million were quoted, but their origin is murky: it’s possible they came from a single estimate of feral cat density in Victoria, extrapolated across the continent.

A recent review estimated a much smaller population size — probably varying from two million to six million, depending on environmental conditions. Using this estimate, the proportion of Australia’s cat population to be killed under the government’s target is now likely in the range 32–95%, rather than 11–40% based on the original population estimate.

Targets for the removal of pest animals should consider how they will affect an animal’s current and future population size. But because a scientific justification for the two million target was never provided, it is unclear whether or how the revised estimate would alter the target.

Hitting the target, missing the point

For cat control to have a lasting effect on feral populations, it needs to be intense, sustained, and carried out over large areas. This is because cats can rapidly reproduce and re-invade areas. To benefit threatened species, cat control also needs to be undertaken in areas that contain — or could potentially contain — native species that are threatened by cats.

Research commissioned by the government conservatively estimated that around 211,500 feral cats were killed in 12 months in 2015–16 (ranging between around 135,500 and 287,600). This estimate was used to report that the first-year target to kill 150,000 cats was met with room to spare.

The benefit to threatened species of achieving this target is unclear, because we don’t know if the control efforts had a measurable effect on cat populations; whether they took place in areas that would benefit threatened species; or how (or if) the target and related activities contributed to the estimated 211,500 cat deaths.

Around 75% of the killed cats were attributed to shooting by farmers and hunters. It is questionable whether such approaches could keep pace with high rates of population growth and re-invasion from surrounding areas.

These and other issues were known before the target was set, leading experts to recommend that an overall cat culling target should not be set.

Shifting focus

The focus on killing cats risks distracting attention from other threats to native wildlife. These threats include habitat loss, which has been largely overlooked in the Threatened Species Strategy.

Habitat loss is politically sensitive because its main driver is the clearing of land to make way for economic activities such as agriculture, urban development, and mining. The strategy mentions feral cats more than 70 times, but habitat loss is mentioned just twice and land clearing not at all. Australia has one of the world’s worst rates of land clearing, which has recently increased in some regions. For instance, clearing of native vegetation in New South Wales rose by 800% between 2013 and 2016.

A focus on feral cats is warranted, but not at the expense of tackling other conservation threats too. A comprehensive, integrated approach towards threatened species conservation is essential.

Any upside?

Despite its questionable scientific basis, it is possible that the ambitious nature of the two million target has raised the public profile of feral cats as a conservation issue. However, to our knowledge, there has been no attempt to measure the effectiveness of the target in raising awareness or changing attitudes, and so this remains a hypothetical proposition.

The Threatened Species Strategy has other targets that are more closely linked to conservation outcomes, such as the eradication of cats from five particular islands and the establishment of ten new fenced cat-free exclosures. Achieving these targets will make a small contribution to the culling target, but have a comparatively large benefit for some threatened species.

Australia’s target to kill two million feral cats is a highly visible symbol of a broader campaign, but the success of policies aimed at reducing the impacts of feral cats should focus squarely on the recovery of native species.

Conservation or politics? Australia’s target to kill two million cats

Authors: Tim S Doherty, Don A Driscoll, Dale G Nimmo, Euan G Ritchie and Ricky‐John Spencer

Published in: Conservation Letters

Abstract

The Australian Government’s five‐year Threatened Species Strategy contains four priority action areas and associated targets.

Here, we argue that the well‐publicised target to cull two million feral cats has a weak scientific basis because:

  1. reliable estimates of Australia’s cat population size did not exist when the target was set;
  2. it is extremely difficult to measure progress (numbers of cats killed) in an accurate, reliable way; and, most importantly,
  3. the cull target is not explicitly linked to direct conservation outcomes (e.g., measured increases in threatened species populations).

These limitations mean that the cull target fails to meet what would be considered best practice for pest management. The focus on killing cats runs the risk of distracting attention away from other threats to biodiversity, most prominent of which is widespread, ongoing habitat loss, which has been largely overlooked in the Threatened Species Strategy.

The culling target is a highly visible symbol of a broader campaign around feral cat research and management in Australia, rather than a direct indicator of conservation action and success. We are concerned that progress toward the 2 million target could be misinterpreted as progress toward conserving threatened species, when the link between the two is not clear.

Doherty TS, Driscoll DA, Nimmo DG, Ritchie EG, Spencer R (2019) Conservation or politics? Australia’s target to kill 2 million cats, Conservation Letters PDF DOI

Improving the assessment of food system sustainability

Authors: Michalis Hadjikakou, Euan G Ritchie, Kate E Watermeyer, and Brett A Bryan

Published in: The Lancet – Planetary Health

The global food system is causing unsustainable pressures on the environment, leading to widespread land use change, increased greenhouse gas emissions, disruption of the nitrogen and phosphorus cycles, biodiversity loss, and freshwater depletion and pollution. Environmental pressures are mounting as populations grow and diets change, escalating the need to make food production and consumption more sustainable. Yet, there are limitations in the current analysis of global food system sustainability. We believe there are four main areas that could be improved to make such analysis more comprehensive and insightful. These improvements could have important repercussions on the development of effective evidence-based policy that ultimately promotes production efficiencies and sustainable diets.

One set of opportunities for improvement in the analysis of food system sustainability relates to the robustness of the dietary scenarios that are modelled. First, these scenarios need to be made more plausible. Although assessment of radical shifts in human diets might be useful in highlighting the effects of animal-based versus plant-based foods, we question the benefit of emphasising the most extreme of scenarios (ie, a complete switch from omnivore to vegetarian or vegan diets), when the foreseeable global trend is heading strongly in the opposite direction. In addition, analyses of these extreme diet substitution scenarios tend to focus on greenhouse gas emissions, but in such scenarios, trade-offs between sustainability indicators are highly likely—aptly highlighted by the increased use of water in scenarios that model shifts from grass-fed livestock towards water-intensive crops. We argue that it is more insightful to model ambitious yet achievable, context-specific reductions in animal products, overconsumption (particularly of discretionary foods), and food waste, in line with those recently recommended by the EAT-Lancet Commission on sustainable food systems for overall planetary health.

Secondly, more granular and dynamic analyses are needed. Estimates of environmental effects underpinning global food system analyses are typically based on life cycle assessment, an environmental accounting framework that captures effects from farm-to-fork. While the rigour and comprehensiveness of available life cycle assessment data and associated meta-analyses are improving and encompassing important trade-offs between sustainability objectives,5 significant shortcomings remain, notably in terms of low commodity-level detail and the use of global averages to infer region-specific or nation-specific environmental intensities (defined in life cycle assessments as the impact per functional unit of production). In addition, most life cycle assessments are static, and therefore do not represent system feedbacks that incorporate changes in demand because of production efficiency enhancements, or marginal changes in environmental effects involved in large-scale dietary shifts—such as when animal-based products are completely eliminated. The quantification of these dynamics and their system-wide environmental impacts is an opportunity to greatly improve sustainability assessments of different food products and proposed substitutions.

Thirdly, protein sources beyond conventional livestock need greater consideration. In many parts of the world, alternative animal protein sources such as abundant native species that are better adapted to local conditions (eg, kangaroo in Australia and deer in the northern hemisphere) can contribute to human nutrition, with such sourcing having considerably lower environmental effects than farming of conventional livestock. Many countries are also host to introduced feral animal populations that could serve as alternative protein sources—for example, Australia has substantial feral deer, goat, rabbit, pig, horse, and camel populations. Partly replacing existing mainstream protein sources with wild harvests of these alternative sources could achieve co-benefits for the environment (eg, through reducing emissions, land degradation, and the effects on native biodiversity), and improve human health, since game meat is typically leaner than lamb and beef. Conventional analyses also fail to account for other transformative shifts in animal-sourced protein, such as those towards laboratory-grown meat, insect-derived protein, and feeding animals on ecological leftovers such as food waste or grass from pastures. Including potential shifts to novel low-impact protein sources would ensure more comprehensive modelling of the associated environmental effects.

Finally, analyses should better quantify the diverse effects of food production on biodiversity and ecosystems. Food production contributes considerably to species extinction, which has detrimental effects on many ecosystems and plant and animal communities that are essential for supporting human life. Yet, there is an overreliance on proxy indicators such as land use when assessing terrestrial food systems. Previous research has highlighted how the extent of agricultural land area is not a good proxy for biodiversity impact, because of differences in production intensity and heterogeneity in biodiversity values. This limited analysis also extends to marine and freshwater food production. Stock depletion, bycatch, and habitat modification or loss, resulting from intensive aquaculture and fishing practices such as trawling, have substantial effects on the biodiversity of coastal and oceanic ecosystems. However, although some studies have considered the environmental intensities of aggregate categories such as farmed fish and crustaceans, the effect of fishing on wild stocks is typically not encompassed in life cycle assessments, despite appropriate data being available. Integration of a more diverse range of biodiversity indicators into the assessment of food system sustainability would allow for more meaningful analyses.

Taking advantage of the opportunities outlined here could facilitate a more complete understanding of the environmental effects of food production and consumption. Embracing these advances is a key prerequisite for developing effective policy recommendations. Our recommendations aim to foster a more comprehensive and nuanced debate on sustainable diets and the food system within the context of global environmental limits.

We declare no competing interests. We thank D Driscoll and BG Ridoutt for their insightful comments on the manuscript.

Hadjikakou M, Ritchie EG, Watermeyer KE, Bryan BA (2019) Improving the assessment of food system sustainability. The Lancet – Planetary Health PDF DOI

Feral horse impacts on threatened plants and animals in sub-alpine and montane environments in Victoria, Australia

Authors: Rebecca C Cherubin, Susanna E Venn, Don A Driscoll, Tim S Doherty, and Euan G Ritchie

Published in: Ecological Management & Restoration

Summary

Feral herbivores are a major driver of biodiversity loss globally and can alter the structure, composition and functioning of ecosystems. The direct impacts of feral herbivores on plant communities are well studied, but the direct and indirect effect they have on wildlife is not well understood.

In Victoria (south‐eastern Australia), a large feral Horse (Equus caballus) population coincides with highly sensitive and nationally endangered Alpine Sphagnum Bogs and Associated Fens communities, and several threatened animal species.

We assessed the impact of feral horses on this ecological community and the Alpine Water Skink (Eulamprus kosciuskoi) and the Broad‐toothed Rat (Mastacomys fuscus) at 20 sites with varying levels of horse disturbance. We used scat counts to determine an index of feral horse abundance and quantified impacts associated with their presence in the landscape. Active searches were used for Alpine Water Skink and scat and runway surveys for Broad‐toothed Rat. We also measured the vegetation structure and the abundance of different vegetation types (life forms).

Our results suggest that feral horses are associated with vegetation types and characteristics that negatively influence the presence or abundance of Alpine Water Skink and Broad‐toothed Rat. Sites with high horse activity had more low‐growing forbs, and the abundance of Alpine Water Skink was negatively related to this vegetation type. Grasses, sedges, rushes and shrubs were also less dense and lower in height in high horse activity sites, and Broad‐toothed Rat was less likely to be present in areas with these habitat attributes.

We recommend that feral horses are controlled to protect these threatened vertebrate species and their Sphagnum bog habitat.

Cherubin RC, Venn SE, Driscoll DA, Doherty TS, Ritchie EG (2019) Feral horse impacts on threatened plants and animals in sub-alpine and montane environments in Victoria, Australia. Ecological Management & Restoration PDF DOI

Impacts of feral horses in the Australian Alps and evidence-based solutions

Authors: Don A Driscoll, Graeme L Worboys, Hugh Allan, Sam C Banks, Nicholas J Beeton, Rebecca C Cherubin, Tim S Doherty, C Max Finlayson, Ken Green, Renée Hartley, Geoffrey Hope, Chris N Johnson, Mark Lintermans, Brendan Mackey, David J Paull, Jamie Pittock, Luciana L Porfirio, Euan G Ritchie, Chloe F Sato, Ben C Scheele, Deirdre A Slattery, Susanna Venn, David Watson, Maggie Watson, and Richard M Williams

Published in: Ecological Management & Restoration

Summary

New evidence of impacts by feral horses in Australia’s alpine parks systems confirms they endanger threatened species and extensively damage critically endangered bog communities that could take millennia to recover. These impacts are not confounded by effects of deer and accumulate over time, even when only a small number of feral horses (∼100) are present.

With protected areas representing only a small proportion of the area of the Australian states of New South Wales (9.3%) and Victoria (17%), allowing feral horses to degrade reserves is not a reasonable management compromise, is contrary to the purpose of the protected area system and conflicts with international obligations.

Modelling and decades of management experience indicate that trapping alone does not control feral horse numbers. Trapping and fertility control can work in small populations, but not when there are several thousand horses in remote areas. Aerial culling is needed to cost‐effectively and humanely control feral horse populations.

The relatively small amount of suffering feral horses experience during a cull is outweighed by

  1. avoiding suffering and death of horses from starvation and thirst,
  2. avoiding the suffering of native animals displaced by horses, and
  3. avoiding the ethical concerns of driving threatened species towards extinction.

Objections to aerial culling on welfare and cultural grounds are contradicted by evidence.

Improving knowledge in the general community about what is at stake is long overdue because without this knowledge, small groups with vested interests and unfounded claims have been able to dominate debate and dictate management actions.

As a result of ineffective management, horse populations are now expanding and causing well‐documented damage to Australia’s alpine parks, placing at risk almost $10M spent on restoration after livestock grazing ended. The costs of horse control and restoration escalate the longer large horse populations remain in the alpine parks.

It is crucial that feral horse numbers are rapidly reduced to levels where ecosystems begin to recover. Aerial culling is needed as part of the toolbox to achieve that reduction.

Driscoll DA, Worboys GL, Allan H, Banks SC, Beeton NJ, Cherubin RC, Doherty TS, Finlayson CM, Green K, Hartley R, Hope G, Johnson CN, Lintermans M, Mackey B, Paull DJ, Pittock J, Porfirio LL, Ritchie EG, Sato CF, Scheele BC, Slattery DA, Venn S, Watson D, Watson M, Williams RM (2019) Impacts of feral horses in the Australian Alps and evidence-based solutions. Ecological Management & Restoration PDF DOI 

Animal movements in fire-prone landscapes

Authors: Dale G Nimmo, Sarah Avitabile, Sam C Banks, Rebecca Bliege Bird, Kate Callister, Michael F Clarke, Chris R Dickman, Tim S Doherty, Don A Driscoll, Aaron C Greenville, Angie Haslem, Luke T Kelly, Sally A Kenny, José J Lahoz‐Monfort, Connie Lee, Steven Leonard, Harry Moore, Thomas M Newsome, Catherine L Parr, Euan G Ritchie, Kathryn Schneider, James M Turner, Simon Watson, Martin Westbrooke, Mike Wouters, Matthew White, and Andrew F Bennett.

Published in: Biological Reviews

Abstract

Movement is a trait of fundamental importance in ecosystems subject to frequent disturbances, such as fire‐prone ecosystems. Despite this, the role of movement in facilitating responses to fire has received little attention.

Herein, we consider how animal movement interacts with fire history to shape species distributions. We consider how fire affects movement between habitat patches of differing fire histories that occur across a range of spatial and temporal scales, from daily foraging bouts to infrequent dispersal events, and annual migrations.

We review animal movements in response to the immediate and abrupt impacts of fire, and the longer‐term successional changes that fires set in train.

We discuss how the novel threats of altered fire regimes, landscape fragmentation, and invasive species result in suboptimal movements that drive populations downwards.

We then outline the types of data needed to study animal movements in relation to fire and novel threats, to hasten the integration of movement ecology and fire ecology.

We conclude by outlining a research agenda for the integration of movement ecology and fire ecology by identifying key research questions that emerge from our synthesis of animal movements in fire‐prone ecosystems.

Nimmo DG, Avitabile S, Banks SC, Bliege Bird R, Callister K, Clarke MF, Dickman CR, Doherty TS, Driscoll DA, Greenville AC, Haslem A, Kelly LT, Kenny SA, Lahoz-Monfort JJ, Lee C, Leonard S, Moore H, Newsome TM, Parr CL, Ritchie EG, Schneider K, Turner JM, Watson S, Westbrooke M, Wouters M, White M, Bennett AF (2018) Animal movements in fire-prone landscapes. Biological Reviews PDF DOI

ABC Science: If extinct animals could be brought back from the dead, should we do it?

We’re living in the middle of an extinction crisis, on par with what wiped out the dinosaurs 65 million years ago. But an asteroid isn’t responsible this time; we are.

Imagine walking into the most beautiful museum, taking all the artworks off the shelves and burning them or throwing them in the bin. That’s what we’re doing. We’re losing species every day all over the world.

De-extinction science can never replicate the wonder of evolution, nor how long it takes for species to evolve…

Read the full article on the ABC website