Paper title: Dietary niche overlap of free-roaming dingoes and domestic dogs: the role of human-provided food
Abstract: As both companion animals and opportunistic predators, dogs (Canis lupus spp.) have had a long and complex relationship with humans. In Australia, the dingo (C. l. dingo) was introduced 4,000 years ago and, other than humans, is now the continent’s top mammalian predator. Domestic dogs (C. l. familiaris) were introduced by Europeans more recently and they interbreed with dingoes. This hybridization has caused growing concern about the roles that domestic dogs and dingoes play in shaping ecosystem processes. There is also considerable debate about whether anthropogenic environmental changes can alter the ecological roles of dingoes. We used scat analysis to test whether the dingo, as the longer-established predator, occupies a different dietary niche from that of free-roaming domestic dogs, irrespective of human influence. Our results demonstrate considerable dietary overlap between dingoes and domestic dogs in areas where humans provide supplementary food, providing evidence against our hypothesis. However, the consumption by dingoes of a greater diversity of prey, in association with historical differences in the interactions between dingoes and humans, suggests a partial separation of their dietary niche from that of domestic dogs. We conclude that anthropogenic changes in resource availability could prevent dingoes from fulfilling their trophic regulatory or pre-European roles. Effective management of human-provided food is therefore required urgently to minimize the potential for subsidized populations of dingoes and domestic dogs to negatively affect co-occurring prey.
Just Out – Opinion Piece on Dingoes in The Conversation:
Paper title: Experiments in no-impact control of dingoes: comment on Allen et al. 2013
Abstract: There has been much recent debate in Australia over whether lethal control of dingoes incurs environmental costs, particularly by allowing increase of populations of mesopredators such as red foxes and feral cats. Allen et al. FIZ 10:39, 2013 claim to show in their recent study that suppression of dingo activity by poison baiting does not lead to mesopredator release, because mesopredators are also suppressed by poisoning. We show that this claim is not supported by the data and analysis reported in Allen et al.’s paper.
In December last year I spent two weeks out on the Washington Wolf-Deer project. The biggest eye opener was the diversity of large predators in the system. On top of wolves, there are bears, cougars, coyotes and bobcats.
For an Australian who is used to studying the interactions between three small-medium sized predators (the dingo, red fox and feral cat) the idea of having all these large predators within a study site is a new challenge.
For example, there is debate in Australia about the ecological role of dingoes. Indeed, we struggle to unravel the complex relationships between dingoes, red foxes and feral cats. So attempting to understand how wolves, bears, cougars, coyotes and bobcats interact with each other is a whole new ball game.
Because wolves have recently recolonised Washington State it is possible to study interactions between predators in two different scenarios being with and without wolves.
As mentioned in a previous post (http://thomasnewsome.com/2013/11/26/from-desert-dingoes-to-alpine-wolves/), the research group from the University of Washington are putting camera and GPS collars on two deer species to look at behavioural changes in response to recolonising wolves.
During my first two weeks on the Washington Wolf-Deer project we set out traps to catch the deer each night. Unfortunately the lack of snow made it difficult to lure deer into the traps using alfalfa, old apples and molasses (deer are much easier to catch when there is snow because the grass is covered and inaccessible to eat).
In early January I made the trip back to the field site hoping that with more snow there would be a higher chance of catching deer. Fortunately, success!
The additional impetus for heading back out in the field was the company of a fellow Australian researcher, Prof. Chris Dickman, who had a few days to spare after we attended the Gordon Research Conference on Predator-Prey interactions in California.
Chris has spent his career working in the arid deserts of Australia. Fortunately, I found enough warm clothes to see him through a North American winter field experience.
Working in a complex multi-predator system raises a plethora of ecological questions for consideration.
For example, with wolves in the system, is the “top-dog” canine or feline?
Cougars and wolves will both be competing for resources (deer) so there is the question of whether or not wolves will out-compete cougars. Wolves are also known to suppress coyotes so there is the question of whether or not coyote density will decline in areas where wolves are present.
Some of these questions were addressed after wolves were reintroduced into Yellowstone National Park in 1995-1996. However, in Washington State, wolves have recolonised managed lands where there are hunting seasons, logging and cattle ranching. Therefore, the future persistence of wolves in managed lands depends on minimising negative interactions between people and wildlife.
It also depends on the ecological role of wolves in managed lands i.e. how they interact with other predators and prey.
The results from the Washington Wolf-Deer project therefore have important implications for understanding how people, wolves and other wildlife might be able to coexist in managed lands.
When results from the project become available I will be sure to share them here.
Paper title: Human-resource subsidies alter the dietary preferences of a mammalian top predator
Abstract: Resource subsidies to opportunistic predators may alter natural predator–prey relationships and, in turn, have implications for how these predators affect co-occurring prey. To explore this idea, we compared the prey available to and eaten by a top canid predator, the Australian dingo (Canis lupus dingo), in areas with and without human-provided food. Overall, small mammals formed the majority of dingo prey, followed by reptiles and then invertebrates. Where human-provided food resources were available, dingoes ate them; 17 % of their diet comprised kitchen waste from a refuse facility. There was evidence of dietary preference for small mammals in areas where human-provided food was available. In more distant areas, by contrast, reptiles were the primary prey. The level of seasonal switching between small mammals and reptiles was also more pronounced in areas away from human-provided food. This reaffirmed concepts of prey switching but within a short, seasonal time frame. It also confirmed that the diet of dingoes is altered where human-provided food is available. We suggest that the availability of anthropogenic food to this species and other apex predators therefore has the potential to alter trophic cascades.
Next week I will be heading out on my first official field trip.
I am well equipped to working in the arid deserts of Australia, but working with wolves and deer in the snow is a whole new ball game.
I will be working with students from the Predator Ecology Lab at the University of Washington (http://faculty.washington.edu/wirsinga/) who are investigating the impact of recolonising gray wolves on deer species in Washington state. The study site is located in the Okanogan and Ferry counties where there are sites with and without wolves:
Map courtesy of Justin Dellinger (http://students.washington.edu/jad17/Wolf-Deer%20Project%20Report%201.pdf)
The research group are putting camera collars on the deer to look at short term behavioural changes in response to recolonising wolves. They are also using GPS collars to collect long-term movement data. The bulk of the field work will involve catching deer in traps like those shown below:
Photos courtesy of Justin Dellinger (http://students.washington.edu/jad17/Wolf-Deer%20Project%20Report%201.pdf)
Why is the research important?
Wolves were never re-introduced into Washington state, like they were in Montana, Wyoming and Idaho. However, since the mid 1990’s wolf populations in North America have begun to recover and they have expanded into other areas. In fact, by March 2013 the Washington Department of Fish and Wildlife confirmed that there were at least 10 wolf packs in Washington state – the packs have all been given names and can be followed on this link: http://wdfw.wa.gov/conservation/gray_wolf/packs/.
With the newly established presence of a top-predator in Washington state it provides an ideal opportunity to assess how ecological communities, who have lived for almost 70 years without wolves, will respond. The research will also help to develop management plans and shared use of deer by (i) hunters, which bring in substantial revenue from buying tags and (ii) wolves, which are afforded protection and can also attract tourist dollars.
I am very much looking forward to learning more and reporting back to you all about my time on the Washington Wolf-Deer Project: https://nwsportsmanmag.com/editors-blog/to-cry-or-not-to-cry-wolf-or-something-in-between/
In Australia, there has been more talk recently regarding proposals to reintroduce Tasmanian Devils to the mainland (https://theconversation.com/should-we-move-tasmanian-devils-back-to-the-mainland-16388).
So it seemed timely to consider a couple of more established examples of “rewilding” that I encountered on a recent journey through Texas, New Mexico and Arizona. I’m talking about black bears in Big Bend, Texas, and the Californian condor in the Grand Canyon.
The Big Bend Story
Apart from scattered sightings, bears were virtually absent in Big Bend when the National Park was established in 1944. This was primarily because bears were shot and trapped by ranchers, federal pest control agents and recreational hunters. Widespread loss of habitat played its part too.
However, in the late 1980’s sightings of bears began to increase. A remarkable turn of events given the rarity of large animals naturally returning after extirpation. In this case, it apparently began with a black bear making the journey from the Sierra del Carmen Mountains in Northern Mexico, which is near the south-eastern border of the park. By the late 1990’s there were 343 annual sightings of black bears in Big Bend.
The story in the park today is one of managing interactions between people and wildlife. Like the main campgrounds I saw in Yosemite, the Big Bend campsite is an excellent example of the use of very strict regulations on food storage, waste disposal and water use to prevent negative interactions.
There are, however, some obvious differences between the parks as to the approach to managing the interactions. In Yosemite there is an active policy of chasing bears away to restore bears’ fear of humans. Throughout the main campgrounds one sees radio antennas fixed to the pines and which are used to track bears and alert the park rangers when a bear is approaching the campsites.
In Big Bend the situation is slightly different. According to the Camp Host at the Big Bend campsite, there are currently a few female bears bringing the cubs near or through the camp on most days. I was also told that the female bears and cubs actively forage during the day because rival male bears often kill the cubs at night. On a walk one morning this provided for a chance close encounter:
The Plight of the Condor
Californian condors once ranged from Canada to Mexico. About 10,000-15,000 years ago condors underwent a dramatic range reduction, coinciding with the extinction of many other large mammals in the Pleistocene (~2.6 million to 11.7 thousand years ago). When Europeans arrived in western North America condors were restricted to the Pacific coast from British Columbia to Baja California. Like the bears in Big Bend, condors were subjected to widespread anthropogenic control. They were also unintentionally poisoned by cyanide traps set for coyotes and after ingesting fragments of bullets in carcasses (left by humans) they were poisoned by the lead. From the talks I listened to at the Grand Canyon, lead poisoning still remains the greatest threat to the Californian condor today.
As a result of the persecution of condors by humans, by the late 1930’s there were apparently no condors outside of California. By 1982 the population was down to just 22 birds.
The dramatic decline of the condors sparked one of the worlds largest wildlife recovery efforts. This included captive breeding and staged releases. Puppets were used to feed the chicks while in captivity so that these remarkable birds would one day be able to survive again in the wild. There are now around 400 condors in the wild.
One thing that struck me of the story of the condor was the significance of volunteer effort and publicity to the rewilding project. Even today a team of volunteers in the canyon monitors condor chick activity every hour of daylight, every day of the year. As to publicity, integral to the long-term success of the reintroduction of the condor is the effort to reduce the risks of lead poisoning. That involves a widespread publicity campaign aimed at convincing hunters and land managers to replace lead bullets (which fragment on impact, splintering into hundreds of pieces) with copper ones that remain substantially intact on impact. For more details on lead and copper bullets see the video in the link below:
Though still rare and revered, condors are frequently seen in the Grand Canyon. At the time of my visit there was a chick in a cave that could be watched via telescope. The location of the cave in the canyon is shown below:
So what do these examples of rewilding add to the debate?
First, they represent the possibility for large predators, such as bears, to return to the landscape after a period of extirpation as long as the original threats are removed.
Second, that although called “rewilding”, the on-going threat to the viability of the projects remain not the dangers of the “wild”, but the ability of the project to manage successfully human and wildlife interactions. That is more about rethinking the “human” dimension as opposed to the “wild” one.
Third, with a little help from science, and a large bucket of funding, an iconic bird such as the condor can be assisted to recovery. If we take on the lessons about the amount of funding required, and also the enormous and invaluable contribution that can be made by harnessing the potential of volunteer assistance and wide-spread publicity, perhaps there is hope for the Tasmanian Devil after all?
Ps I also saw this elk quietly grazing in someone’s front yard!