Dogs, catas and the fear of pest rodents

Themb’alilahlwa, A. M., Monadjem, A., McCleery, R., & Belmain, S. R. (2017). Domestic cats and dogs create a landscape of fear for pest rodents around rural homesteads. PloS one, 12(2), e0171593.

Using domestic predators such as cats to control rodent pest problems around farms and homesteads is common across the world. However, practical scientific evidence on the impact of such biological control in agricultural settings is often lacking. We tested whether the presence of domestic cats and/or dogs in rural homesteads would affect the foraging behaviour of pest rodents. We estimated giving up densities (GUDs) from established feeding patches and estimated relative rodent activity using tracking tiles at 40 homesteads across four agricultural communities. We found that the presence of cats and dogs at the same homestead significantly reduced activity and increased GUDs (i.e. increased perception of foraging cost) of pest rodent species. However, if only cats or dogs alone were present at the homestead there was no observed difference in rodent foraging activity in comparison to homesteads with no cats or dogs. Our results suggest that pest rodent activity can be discouraged through the presence of domestic predators. When different types of predator are present together they likely create a heightened landscape of fear for foraging rodents.

Feeding cats deplates native fauna

Hawkins, C.C., W.E. Grant & M.T. Longnecker. 1999. Effect of subsidized house cats on California birds and rodents. Transactions of the Western Section of The Wildlife Society, 35: 29-33

Cat advocates are establishing feeding stations in public parks, often claiming that well-fed cats pose little threat to wildlife. This claim was tested east of San Francisco, California, in a cat area and a no-cat area. In 1995, more harvest mice were trapped in the no-cat area. In 1996, more harvest mice (Reithrodontomys megalotis) and deer mice (Peromyscus sp.) were trapped in the no-cat area, and more house mice were trapped in the cat area. The numbers of trapped California meadow voles (Microtus californicus) were not different between the areas in either year. More native rodents were trapped in the no-cat area. Birds present during the breeding season were seen more often in the no-cat area. California quail (Callipepla californicus) and California thrashers (Toxostoma redivivum) were present in the no-cat area and absent in the cat area. Cats at artificially high densities, sustained by supplementary feeding, reduced the abundance or native rodent and bird populations, changed the rodent species composition, and may have facilitated the expansion of the house mouse into new areas. Thus we recommend that the feeding of cats in parks should be strictly prohibited. 

Bird and rat numbers on Little Barrier after cat eradication

Girardet, S. A. B., Veitch, C. R., & Craig, J. L. (2001). Bird and rat numbers on Little Barrier Island, New Zealand, over the period of cat eradication 1976–80. New Zealand Journal of Zoology, 28(1), 13-29.

Passerines were monitored on Little Barrier Island over 15 years (1975–89) spanning the period (1976–80) when feral cats were eradicated from the island. All birds seen and heard were recorded while walking three transects representing an altitudinal range from near sea level to approximately 550 m above sea level. Analysis of variance statistics were used to test for differences in bird numbers between transects and between years. Bird species were examined by transect to test for changes in numbers over time. Three species had increased on some transects, and two species had decreased on some transects, but it was difficult to attribute changes in bird numbers to the one cause which we were able to study: reduced cat numbers. Examination of numbers of individuals of 14 species recorded between transects showed significant differences for some individual species, but not for all species grouped together. Four species did not show any significant differences between transects. This study demonstrates different patterns in bird distributions on Little Barrier Island which cannot be understood from these data.

Index traplines were set for Pacific rats or kiore (Rattus exulans) between 1977 and 1984, before and after cat eradication. Rat numbers fluctuated widely, and there were no significant differences that could be attributed to the changes in cat numbers.

Related articles

Habitat structure mediates the non-lethal effects of mesopredation

Arthur, A. D., Pech, R. P., & Dickman, C. R. (2004). Habitat structure mediates the non‐lethal effects of predation on enclosed populations of house mice. Journal of Animal Ecology, 73(5), 867-877.

1 Prey behavioural changes in response to predation risk can result in significant effects on prey body growth rates and reduced reproductive output, with resultant impacts on prey population dynamics. This paper examines the influence of habitat structure on these non-lethal impacts of predation using a model, field-based experimental system, with house mice as prey.
2 Three treatments were employed in eight 50 × 50 m pens that contained mice, but allowed access to a suite of free-living vertebrate predators, which included feral foxes, feral cats and native raptors: a treatment where the natural grassland vegetation in the pens was maintained at a height < 10 cm; a treatment where small, felled cypress pine trees covered with wire netting were added to low grassland vegetation to create refuge areas covering 10–15% of the area in a pen; and a treatment where predators were excluded from a 25 × 25 m section of some pens with an underlying grassland structure. A 5 × 5 grid of felled trees was added to grassland and predator-exclusion pens to allow assessment of mouse behaviour.
3 Mice in grassland pens avoided open areas, had lower body growth rates, and began breeding later in spring than mice in both predator-exclusion areas, where they foraged more readily in the open, and in refuge pens, where mice avoided open areas but had safe access to supplementary food located within the refuge. These results occurred despite mouse population densities being much lower in grassland pens, and presumably competition for food being much less, compared with under the other treatments.
4 The results indicate predators can have significant non-lethal impacts on prey, and these effects can be mediated by habitat structure.

Controversy on cat's eradication on Macquarie Island: predator or pathogen's release?

Bergstrom D, Lucieer A, Kiefer K, Wasley J, Belbin L, Pedersen T & Chown S (2009). Indirect effects of invasive species removal devastate World Heritage Island. Journal of Applied Ecology, 46: 73-81

A feral cat roams among baby penguins on Macquarie Island.
Photo: Geoff Copson/ Tasmanian NPWS

1. Owing to the detrimental impacts of invasive alien species, their control is often a priority for conservation management. Whereas the potential for unforeseen consequences of management is recognized, their associated complexity and costs are less widely appreciated.

2. We demonstrate that theoretically plausible trophic cascades associated with invasive species removal not only take place in reality, but can also result in rapid and drastic landscape-wide changes to ecosystems.

3. Using a combination of population data from of an invasive herbivore, plot-scale vegetation analyses, and satellite imagery, we show how a management intervention to eradicate a mesopredator has inadvertently and rapidly precipitated landscape-wide change on sub-Antarctic Macquarie Island. This happened despite the eradication being positioned within an integrated pest management framework. Following eradication of cats Felis catus in 2001, rabbit Oryctolagus cuniculus numbers increased substantially although a control action was in place (Myxoma virus), resulting in island-wide ecosystem effects.

http://ingervandyke.com/conservation/

4. Synthesis and applications. Our results highlight an important lesson for conservation agencies working to eradicate invasive species globally; that is, risk assessment of management interventions must explicitly consider and plan for their indirect effects, or face substantial subsequent costs. On Macquarie Island, the cost of further conservation action will exceed AU$24 million.

Dowding, J. E., Murphy, E. C., Springer, K., Peacock, A. J., & Krebs, C. J. (2009). Cats, rabbits, Myxoma virus, and vegetation on Macquarie Island: a comment on Bergstrom et al.(2009). Journal of Applied Ecology, 46(5), 1129-1132.

1. Eradication of a single pest species from a multiply invaded island system may have unpredicted and detrimental impacts.Bergstrom et al. (2009) describe damage to vegetation following an increase in the number of rabbits on Macquarie Island. They propose that the increase in rabbit numbers was caused solely by eradication of cats.

2. However, their modelling is flawed and their conclusion that cats were controlling rabbit numbers is unsupported. We suggest the increase was because of some combination of four factors: reduced releases of Myxoma virus, abundant food after 20 years of vegetation recovery, release from cat predation and climate variability.

3. Recent high numbers of rabbits on Macquarie Island are not unprecedented; vegetation has been damaged in the past but has recovered. Rabbit numbers appear to be in decline again in the absence of both cats and Myxoma releases, suggesting that other factors can contribute to regulation of rabbit numbers in this system.

4. We do not agree with the implication that pest management could have been better integrated. Eradication techniques for rodents and rabbits on an island the size of Macquarie were unavailable when cat eradication was deemed necessary. The benefits to seabirds of cat eradication have been rapid. Our analysis further highlights the complexity of multiply invaded island ecosystems.

Bergstrom, D. M., Lucieer, A., Kiefer, K., Wasley, J., Belbin, L., Pedersen, T. K., & Chown, S. L. (2009). Management implications of the Macquarie Island trophic cascade revisited: a reply to Dowding et al.(2009). Journal of Applied Ecology, 46(5), 1133-1136.

1. The management of non-indigenous species is not without its complications. In Bergstrom et al.’s (2009) study, we demonstrated that feral cats Felis catus on sub-Antarctic Macquarie Island were exerting top-down control on the feral rabbit Oryctolagus cuniculus population, and that the eradication of the cats led to a substantial increase in rabbit numbers and an associated trophic cascade.

2. Dowding et al. (2009) claim our modelling was flawed for various reasons, but primarily that a reduction in the application of the rabbit control agent, Myxoma virus, coinciding with cat removal, was a major driver of rabbit population release.

3. We explore this proposition (as well as others) by examining rates of Myxoma viral release between 1991 and 2006 (with an attenuation factor for the years, 2003–2006) in association with presence/absence of cats against two estimates of rabbit population size. Myxoma viral release was a significant factor in the lower estimates of rabbit population, but the effect was small, and was not significant for higher rabbit population estimates. By contrast, the presence or absence of cats remained highly significant for both estimates.

4.Synthesis and applications. We re-affirm our position that top-down control of rabbit numbers by cats, prior to their eradication, was occurring on Macquarie Island. Nonetheless, we agree with Dowding et al. (2009) that systems with multiple invasive species represent complex situations that require careful scrutiny. Such scrutiny should occur in advance of, during, and following management interventions.

More on Macquarie island cats

Multiple predators on Corvo island

Hervías, S., A. Henriques, N. Oliveira, T. Pipa, H. Cowen, J. A. Ramos, M. Nogales, P. Geraldes, C. Silva, R. Ruiz de Ybáñez & S. Oppel. 2012. Studying the effects of multiple invasive mammals on Cory’s shearwater nest survival. Biological Invasions, DOI 10.1007/s10530-012-0274-1

The most common invasive mammals—mice, rats, and cats—have been introduced to islands around the world, where they continue to negatively affect native biodiversity. The eradication of those invasive mammals has had positive effects on many species of seabirds. However, the removal of one invasive mammal species may result in abundance changes of other species due to trophic and competitive interactions among species. Understanding the overall impact of several invasive species is a key challenge when evaluating the possible effects of eradication programmes. Here we assess the influence of the three most common invasive mammals on nest survival of Cory’s shearwater (Calonectris diomedea). We monitored six breeding colonies over 3 years and measured the activity of mice, rats and cats to examine the influence of invasive mammals on nest survival. We found that nest survival showed a similar temporal trend in all years, with lowest weekly survival probabilities shortly after chicks hatched.Cats were identified as major predators of chicks, but no measure of colony-specific cat activity was able to adequately explain variation in shearwater nest survival. Nest survival was on average 0.38 (95 % confidence interval 0.20–0.53) and varied among colonies as well as over time. We found a small positive influence of rats on nest survival, which may indicate that the presence of small rodents as alternative prey may reduce cat predation of chicks. Our findings suggest that the eradication of rodents alone may exacerbate the adverse effects of cats on shearwater nest survival.

Cats, rats and seabirds

Le Corre, M. 2008. Cats, rats and seabirds. Nature, 451: 134-135.
Cats kill birds, and therefore eradicating cats from an island would seem to be a good strategy for protecting the native population of seabirds. But that thinking does not take account of ecological complications.

Cats protecting birds, revisited

Meng Fan, Yang Kuang, Zhilan Feng, 2005. Cats protecting birds, revisited. Bulletin of Mathematical Biology, 67: 1081–1106


In this paper, we revisit the dynamical interaction among prey (bird), mesopredator (rat), and superpredator (cat) discussed in Courchamp, F., Langlais, M., Sugihara, G., 1999. Cats protecting birds: modelling the mesopredator release effect. Journal of Animal Ecology 68, 282–292. First, we develop a prey–mesopredator–superpredator (i.e., bird–rat–cat, briefly, BRC) model, where the predator’s functional responses are derived based on the classical Holling’s time budget arguments.
Our BRC model overcomes several model construction problems in Courchamp et al. (1999), and admits richer, reasonable and realistic dynamics. We explore the possible control strategies to save or restore the bird by controlling or eliminating the rat or the cat when the bird is endangered. We establish the existence of two types of mesopredator release phenomena: severe mesopredator release, where once superpredators are suppressed, a burst of mesopredators follows which leads their shared prey to extinction; and mild mesopredator release, where the mesopredator release could assert more negative impact on the endemic prey but does not lead the endemic prey to extinction. A sharp sufficient criterion is established for the occurrence of severe mesopredator release. We also show that, in a prey–mesopredator–superpredator trophic food web, eradication of introduced superpredators such as feral domestic cats in the BRC model, is not always the best solution to protect endemic insular prey. The presence of a superpredator may have a beneficial effect in such systems.