Impact of feral pets on island iguanas

Iverson, J. B. (1978). The impact of feral cats and dogs on populations of the West Indian rock iguana, Cyclura carinata. Biological Conservation,14(1), 63-73.

A population of rock iguanas, Cyclura carinata, inhabiting Pine Cay in the Caicos Islands was nearly extirpated during the three years following construction of a hotel and tourist facility. The decline, from an estimated adult lizard population of nearly 5500, was due primarily to predation by domestic dogs and cats introduced to the island simultaneously with hotel construction. Population declines on other nearby islands were also attributed to predation by these feral mammals.

Fearing the predator: Sublethal effects of cats

Bonnington, C., Gaston, K. J., Evans, K. L. (2013), Fearing the feline: domestic cats reduce avian fecundity through trait-mediated indirect effects that increase nest predation by other species. Journal of Applied Ecology, 50: 15–24.

Summary

Urban areas contain high densities of non-native species, which in the UK include the domestic cat Felis catus (Linnaeus 1758) and the grey squirrel Sciurus carolinensis (Gmelin 1788). The direct predation effects of domestic cats on prey populations attract intense debate, and such influences of the nest-predatory grey squirrel are receiving increasing attention. In contrast, theory predicts that sublethal and indirect effects are more important, but empirical evidence is currently lacking.

We conducted controlled model presentation experiments at active urban blackbird Turdus merula (Linnaeus 1758) nests to provide the first empirical evidence that quantifies the potential sublethal and indirect effects of predators (domestic cat and grey squirrel) on avian reproductive success.

Domestic cat models reduced subsequent parental provisioning rates, a strong indicator of sublethal effects, by one-third relative to a nonpredatory rabbit Oryctolagus cuniculus (Linnaeus 1758) control. There was no compensatory increase in food load size. Previous experiments demonstrate that this magnitude of reduced food delivery will reduce nestling growth rates by c. 40%. The grey squirrel model induced similar but weaker effects.

Following the brief presence of the domestic cat model, subsequent daily nest predation rates, chiefly by corvids, increased by an order of magnitude relative to the squirrel and rabbit models. The intensity of parental nest defence elicited in response to model presentations predicts the probability of such third-party predator predation events, and the domestic cat model generated significant increases in nest defence behaviour.

Synthesis and applications

The brief presence of a domestic cat at avian nest sites reduces subsequent provisioning rates and induces lethal trait-mediated indirect effects. We provide the first robust evidence for these latter effects in any avian predator–prey system, although they are likely to be common in many avian assemblages with high predator densities. It is imperative that future assessments of the impact of predatory species on avian prey species take lethal trait-mediated indirect effects into account, as so doing will prevent biased estimates of predator effects and facilitate the design of more effective control strategies. Full mitigation of the sublethal and indirect effects of domestic cats would problematically require permanent indoor housing.

See also this posts

Disturbance of dogs to Wildlife

Lenth, B., R.L. Knight & M.E. Brennan. 2008. The Effects of Dogs on Wildlife Communities. Natural Areas Journal, 28 (3): 218-227

Domestic dogs (Canis familiaris) are frequent visitors to protected areas, but little is known about how they affect wildlife communities. We studied the effects of dogs on wildlife communities by comparing the activity levels of wildlife in areas that prohibited dogs with areas that allowed dogs. We measured wildlife activity on trails and up to 200 m away from trails using five methods: (1) pellet plots, (2) track plates, (3) remote triggered cameras, (4) on-trail scat surveys, and (5) mapping prairie dog (Cynomys ludovicianus) burrow locations. The presence of dogs along recreational trails correlated with altered patterns of habitat utilization by several species. Mule deer (Odocoileus hemionus) activity was significantly lower within 100 m of trails in areas that allowed dogs than in areas that prohibited dogs. Small mammals, including squirrels (Sciurus spp.) and rabbits (Sylvilagus spp.), also exhibited reduced levels of activity within 50 m of trails in areas that allowed dogs when compared with areas without. The density of prairie dog burrows was lower within 25 m of trails in areas that allowed dogs. The presence of dogs also affected carnivore activity. Bobcat (Felis rufus) detections were lower in areas that allowed dogs, and red fox (Vulpes vulpes) detections were higher. These findings have implications for the management of natural areas, particularly those that allow dogs to be off-leash.

New evaluation of cat's kill in US: probably tens of billions kills per year

Loss, S.R., T. Will & P.P. Marra. 2013. The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications 4, 1396 doi:10.1038/ncomms2380

Anthropogenic threats, such as collisions with man-made structures, vehicles, poisoning and predation by domestic pets, combine to kill billions of wildlife annually. Free-ranging domestic cats have been introduced globally and have contributed to multiple wildlife extinctions on islands. The magnitude of mortality they cause in mainland areas remains speculative, with large-scale estimates based on non-systematic analyses and little consideration of scientific data. Here we conduct a systematic review and quantitatively estimate mortality caused by cats in the United States. We estimate that free-ranging domestic cats kill 1.4–3.7 billion birds and 6.9–20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals. Scientifically sound conservation and policy intervention is needed to reduce this impact.

See also this entry.


Read more national surveys results on cat predation

Cats killing billions of animals in the US

By Rebecca Morelle
Science reporter, BBC World Service 29 January 2013 

Cats are one of the top threats to US wildlife, killing billions of animals each year, a study suggests. The authors estimate they are responsible for the deaths of between 1.4 and 3.7 billion birds and 6.9-20.7 billion mammals annually.

Writing in Nature Communications, the scientists said stray and feral cats were the worst offenders. However, they added that pet cats also played a role and that owners should do more to reduce their impact.

The authors concluded that more animals are dying at the claws of cats in the United States than in road accidents, collisions with buildings or poisonings. The domestic cat's killer instinct of has been well documented on many islands around the world. Felines accompanying their human companions have gone on to decimate local wildlife, and they have been blamed for the global extinction of 33 species. But their impact on mainland areas has been harder to chart.

To find out more, researchers from the Smithsonian Conservation Biology Institute (SCBI) and the US Fish and Wildlife Service carried out a review of studies that had previously looked at the predatory prowess of cats. Their analysis revealed that the cat killings were much higher than previous studies had suggested: they found that they had killed more than four times as many birds as has been previously estimated.

Birds native to the US, such as the American Robin, were most at risk, and mice, shrews, voles, squirrels and rabbits were the mammals most likely to be killed.

Dr Pete Marra from the SCBI said: "Our study suggests that they are the top threat to US wildlife."

The team said that "un-owned" cats, which they classified as strays, feral cats and farm cats, were killing about three times as many animals as pet cats, but that their owners could do more to limit the impact.

Dr Marra said: "We hope that the large amount of wildlife mortality indicated by our research convinces some cat owners to keep their cats indoors and that it alerts policymakers, wildlife managers and scientists to the large magnitude of wildlife mortality caused by cat predation."

A spokeswoman for the UK's animal welfare charity the RSPCA said that a properly fitted collar and bell could reduce a cat's success when hunting by at least a third.

http://www.bbc.co.uk/news/science-environment-21236690


Read a short review about belling effectiveness

Cats vs. birds in Japan

[PDF] de unh.edu

Takahashi, M. A. (2004). Cats v. Birds in Japan: How to Reconcile Wildlife Conservation and Animal Protection. Geo. Int'l Envtl. L. Rev., 17, 135.

Distribution and spatial genetic structure of wildcat in France

Say, L., S. Devillard, F. Léger, D. Pontier & S. Ruette. 2012. Distribution and spatial genetic structure of European wildcat in France. Animal Conservation , 15 (1): 18-27

Given the problem of hybridization with domestic cats, there is a growing need to identify populations of the European wildcat Felis silvestris silvestris in order to protect the genetic integrity of this subspecies. In this paper, we use known locations of observations of wildcats or recovered carcasses to reassess the distribution of the wildcat in France and, in cases where carcasses were collected, we use both phenotypic and molecular genetic analyses to distinguish wildcats from hybrids with domestic cats. Spatially explicit multivariate analysis of wildcat' genotypes was then performed to define genetic units. Our study confirms the presence of wildcats in a large area of c. 155 000 km² , suggestive of a range of expansion, and divided into two clearly distinct and unconnected areas – the Pyrenees and the north-eastern part of France. However, European wildcat populations may be decreasing in the French Pyrenees, whereas the north-eastern part represents the main area (MA) of wildcat presence. This extension does not appear to be primarily due to hybrids, as both wildcats and hybrids were located throughout the MA. In addition, we found that genetic diversity of wildcats in the MA is remarkably high, suggesting that French populations are not threatened by a lack of genetic diversity. Furthermore, wildcats of the MA are structured into two genetically distinct populations that are contiguous and probably extend into Germany to form the largest area of wildcat presence in Europe and an area of major interest for their conservation. Our study calls for localized examination of the feasibility and usefulness of wildlife corridors to enhance connectivity between the different populations, thereby allowing sufficient levels of immigration and gene flow within the regional meta-population to ensure the long-term viability of these populations.


See more on domestic cat introgression in wildcat

Behaviour changes in urban ecosystems

Ditchkoff, S. S., Saalfeld, S. T., & Gibson, C. J. (2006). Animal behavior in urban ecosystems: modifications due to human-induced stress. Urban Ecosystems, 9(1), 5-12.

Wildlife-human interactions are increasing in prevalence as urban sprawl continues to encroach into rural areas. Once considered to be unsuitable habitat for most wildlife species, urban/suburban areas now host an array of wildlife populations, many of which were previously restricted to rural or pristine habitats. The presence of some wildlife species in close proximity to dense human populations can create conflict, forcing resource managers to address issues relating to urban wildlife. However, evidence suggests that wildlife residing in urban areas may not exhibit the same life history traits as their rural counterparts because of adaptation to human-induced stresses. This creates difficulty for biologists or managers that must address problems associated with urban wildlife. Population control or mitigation efforts aimed at urban wildlife require detailed knowledge of the habits of wildlife populations in urban areas. This paper describes the history of wildlife in urban areas, provides examples of wildlife populations that have modified their behavior as an adaptation to urban stresses, and discusses the challenges that resource managers face when dealing with urban wildlife.

Colonias "controladas" de gatos

En un folleto de la American Bird Conservancy, producido dentro de la campaña Cats Indoors, se repasan los problemas asociados a las colonias de gatos "controlados". En ellas, los gatos callejeros se liberan tras su esterilización. En el folleto, firmado por una docena de organismos incluyendo varios colectivos de veterinarios y de activistas por los derechos de los animales, se comentan los problemas asociados a estas colonias. Entre ellos, la depredación que sigue existiendo sobre la vida silvestre, la posible transmisión de enfermedades a las personas y la falta de control sobre las condiciones de vida de los gatos, que siguen padeciendo crueldad o enfermedades. Además, las colonias atraen a gatos abandonados y sirven de "vertedero" de gatos no deseados.
Sin embargo, por ejemplo, el Ayuntamiento de Barcelona reproduce en su web, un documento técnico de trabajo sobre cómo crear y "controlar" una colonia de gatos vagabundos. En el artículo se recomienda contactar con los posibles colaboradores, y luego menciona los aspectos técnicos de la gestión de la colonia. No menciona ni por un momento la palabra "ave" o "depredación".
La información sobre las colonias controladas de gatos es enorme. Alley Cat Allies, por ejemplo, es una organización bien documentada y que tiende a argumentar su postura con criterios. Así, se oponen a los estudios sobre depredación realizada sobre aves y otra fauna silvestre apoyándose en que la extrapolación de los resultados no es realista y que las amenazas sobre las aves son otras. Así, por ejemplo, el artículo sobre el mímido gris que atribuye a los gatos la mayor parte de las bajas conocidas es criticado por extrapolar las causas conocidas de mortalidad al total. Sitios muy activos como Vox Felina, critican intensamente y de forma bastante documentada, los artículos publicados sobre el impacto de los gatos en la biodiversidad. En general, las críticas suelen caer en la ridiculización de los aspectos no tratados por un trabajo o en una caricaturización del método, así como en una demonización de la estadística como herramienta de fabricación de datos a medida. Si bien es cierto que las extrapolaciones son arriesgadas, las críticas simplemente intentan demostrar que la depredación es anecdótica, sin tener en cuenta la enorme cantidad de depredadores domésticos o errantes que constituyen, en su conjunto una presión considerable, si bien no la única, sobre los pequeños vertebrados silvestres. El debate tiene demasiados componentes emocionales (por ambas partes, todo hay que reconocerlo). 

Loss of wildlife to domestic cats

Paton, D. (1991). Loss of wildlife to domestic cats. In Potter, C. (ed), The Impact of Cats on Native Wildlife: Proceedings of a Workshop held on May 8-9 1991. ANPWS, Canberra

Questionnaires asked people how many animals they thought their cat(s) had killed in the previous 12 months. Of the 3000 questionnaires distributed, 709 were returned, covering 700 cats in Adelaide suburbs, in country towns and in rural areas. The majority of the questionnaires (88%) came from members of birders' associations.

• Cats in rural areas were reported to catch over twice as many prey as suburban cats. 
• The average number of prey reported caught per year was 30. 
• Suburban cats (the majority of cats) were reported to catch less, and rural cats (far fewer in number) caught more. 
• Bells were ineffective 
• Most preys were non native

Stable isotopes to know cat's diet on islands

MECKSTROTH, A. M., MILES, A. K. & CHANDRA, S. 2007. Diets of Introduced Predators Using Stable Isotopes and Stomach Contents. The Journal of Wildlife Management, 71: 2387–2392.

In a study of predation on ground-nesting birds at South San Francisco Bay (South Bay), California, USA, we analyzed stomach contents and stable isotopes of carbon and nitrogen to identify commonly consumed prey. We obtained the stomach contents from 206 nonnative red foxes (Vulpes vulpes regalis) collected in the South Bay area and Monterey County during 1995–2001 and from 68 feral cats (Felis silvestris) from the South Bay area during 2001–2002. We determined prey identity, biomass, and frequency, described seasonal diet trends, and derived an Index of Relative Importance. Avian species were the most frequent prey we found in the stomachs of red foxes from South Bay (61%), whereas small rodents were most frequent for red foxes from Monterey County (62%). Small rodents were the most frequent prey we found in feral cats (63%). Carbon and nitrogen isotopic signatures for foxes supported stomach content findings. However, isotope results indicated that cats received a majority of their energy from a source other than rodents and outside the natural system, which differed from the stomach content analysis. We demonstrated the utility of both stable isotope and stomach content analyses to establish a more complete understanding of predators' diets. This information aids natural resource managers in planning and evaluating future predator-removal programs and increases our understanding of the impacts of nonnative foxes and cats on native species.



Petra Quillfeldt, P.,  I. Schenk, R.A. R. McGill, I. J. Strange, J.F. Masello, A. Gladbach, V. Roesch & R.W. Furness. 2008.Introduced mammals coexist with seabirds at New Island, Falkland Islands: abundance, habitat preferences, and stable isotope analysis of diet. Polar Biology 31:333–349 

The largest known colony of Thin-billed prions Pachyptila belcheri has been coexisting with introduced mammals for more than 100 years. Three of the introduced mammals are potential predators of adults, eggs and chicks, namely ship rats Rattus rattus, house mice Mus musculus and feral cats Felis catus. We here determine habitat preferences over three seasons and dietary patterns of the unique set of introduced predators at New Island, Falkland Islands, with emphasis on the ship rats. Our study highlights spatial
and temporal diVerences in the levels of interaction between predators and native seabirds. Rats and mice had a preference for areas providing cover in the form of the native tussac grass  Parodiochloa  xabellata or introduced gorse  Ulex europaeus. Their diet differed markedly between areas, over the season and between age groups in rats. During the incubation period of the prions in November–December, ship rats had mixed diets, composed mainly of plants and mammals, while only 3% of rats had ingested birds. The proportion of ingested birds, including scavenged, increased in the prion chick-rearing period, when 60% of the rats consumed prions. We used 13C and 15N to compare the importance of marine-derived food between mammal species and individuals, and found that rats in all but one area took diet of partly marine origin, prions being the most frequently encountered marine food. Most house mice at New Island mainly had terrestrial diet. The stable isotope analysis of tissues with different turnover times indicated that individual rats and mice were consistent in their diet over weeks, but opportunistic in the short term. Some individuals (12% of rats and 7% of mice) were highly specialized in marine-derived food. According to the isotope  ratios in a small sample of cat faeces, rodents and rabbits were the chief prey of cats at New Island. Although some individuals of all three predators supplement their terrestrial diet with marine-derived food, the current impact of predation by mammals on the large population of Thinbilled prions at New Island appears small due to a number of factors, including the small size of rodent populations and restriction mainly to small areas providing cover.

Diet of cats on islands

Bonnaud, E., F. M. Medina, E. Vidal, M. Nogales, B. Tershy, E. Zavaleta, C. J. Donlan,  B. Keitt, M. Le Corre & S. V. Horwath. 2011. The diet of feral cats on islands: a review and a call for more studies. Biological Invasions, 13: 581–603.

Cats are among the most successful and damaging invaders on islands and a significant driver of extinction and endangerment. Better understanding of their ecology can improve effective management actions such as eradication. We reviewed 72 studies of insular feral cat diet from 40 islands worldwide. Cats fed on a wide range of species from large birds and medium sized mammals to small insects with at least 248 species consumed (27 mammals, 113 birds, 34 reptiles, 3 amphibians, 2 fish and 69 invertebrates).
Three mammals, 29 birds and 3 reptiles recorded in the diet of cats are listed as threatened by the IUCN.
However, a few species of introduced mammals were the most frequent prey, and on almost all islands mammals and birds contributed most of the daily food intake. Latitude was positively correlated with the predation of rabbits and negatively with the predation of reptiles and invertebrates. Distance from landmass was positively correlated with predation on birds and negatively correlated with the predation of reptiles.
The broad range of taxa consumed by feral cats on islands suggests that they have the potential to impact almost any native species, even the smallest ones under several grams, that lack behavioral, morphological or life history adaptations to mammalian predators. Insular feral cat’s reliance on introduced mammals, which evolved with cat predation, suggests that on many islands, populations of native species have already been reduced.

Impact of cats on islands endangered vertebrates

Medina, F.M., E. Bonnaud, E. Vidal, B. Tershy, E.S. Zavaleta, C. J. Donlan, B.S . Keitt, M. Le Corre, S.V. Horwath & M. Nogales. 2011. A global review of the impacts of invasive cats on island endangered vertebrates.Global Change Biology, 17, 3503–3510


Cats are generalist predators that have been widely introduced to the world’s ~179 000 islands. Once introduced to islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators and can suffer severe population declines and even extinction. As islands house a disproportionate share of terrestrial biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threatened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on different native species in different types of island ecosystems can increase the efficiency of this conservation tool. We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported from at least 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds, and 27 mammals), many of which are listed by the International Union for the Conservation of Nature. A meta-analysis suggests that cat impacts were greatest on endemic species, particularly mammals and greater when non-native prey species were also introduced. Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles.

Wildlife response to dogs

Miller, S.G., Knight, R.L. & Miller, C.K. 2001. Wildlife responses to pedestrians and dogs. Wildlife Society Bulletin, 29 (1): 124-132.

You can download here the homonimous report from 1996 

As participation in outdoor recreational activities escalates, land managers struggle to develop management policies that ensure coexistence of wildlife and recreation. However, this requires an understanding of how wildlife responds to various forms of recreational activities and the spatial context in which the activities occur. Therefore, we measured responses of 2 species of grassland songbirds, one species of forest songbird, and mule deer (Odocoileus hemionus) exposed to a pedestrian, a pedestrian accompanied by a dog on leash, and a dog alone (only for grassland birds), on and away from recreational trails. We assessed the "area of influence" for each treatment by determining the probability that an animal would flush or become alert (for mule deer only) given its perpendicular distance to a trail or a line of movement in areas without trails. When animals were disturbed, we measured flush distance (the distance between the disturbance and the animal when flushed), distance moved, and, for mule deer, alert distance (the distance between the disturbance and the deer when it became alert). For all species, area of influence, flush distance, distance moved, and alert distance (for mule deer) was greater when activities occurred off-trail versus on-trail. Generally, among on-trail and off-trail treatments in grasslands for vesper sparrows (Pooecetes gramineus) and western meadowlarks (Sturnella neglecta), the smallest area of influence and shortest flush distance and distance moved resulted from the dog-alone treatment, and these responses were greater for the pedestrian-alone and dog-on-leash treatments. In forests, for American robins (Turdus migratorius), the area of influence, flush distance, and distance moved did not generally differ between the pedestrian-alone and dog-on-leash treatments. For mule deer, presence of a dog resulted in a greater area of influence, alert and flush distance, and distance moved than when a pedestrian was alone. Natural lands managers can implement spatial and behavioral restrictions in visitor management to reduce disturbance by recreational activities on wildlife. Restrictions on types of activities allowed in some areas such as prohibiting dogs or restricting use to trails will aid in minimizing disturbance. Additionally, managers can restrict the number and spatial arrangement of trails so that sensitive areas or habitats are avoided.

Predation on NZ shorebirds

Dowding, J. E., & Murphy, E. C. (2001). The impact of predation by introduced mammals on endemic shorebirds in New Zealand: a conservation perspective.Biological Conservation, 99(1), 47-64.

The avifauna of New Zealand has been severely depleted since human colonisation and currently contains a disproportionately high number of threatened species. Of the 23 threatened shorebird species worldwide, six are endemic to New Zealand. We review the status of New Zealand's endemic shorebirds and examine the impact on them of various threats, particularly predation by introduced mammals. The conservation status of the 10 extant species (three oystercatchers, one stilt, four plovers and two snipe) is outlined and the factors that predisposed them to predation by introduced mammals are summarised. Individual species accounts are presented, including data on population trends, known or suspected impacts of predation, identification of important predator species, other threats, and conservation measures currently in place or required. One species and two subspecies are extinct, three species are confined to predator-free islands and another is found only on the Chatham Islands group. Six survive on the mainland but three have declined to varying degrees and are assigned threatened status by Collar et al. (1994). Only one plover and two oystercatchers are still relatively numerous and/or widespread. Rats, cats and mustelids have had the greatest overall impacts. Conservation measures in place to mitigate the effects of introduced predators include the formulation of recovery plans, predator control around breeding areas, captive breeding and rearing programmes and the founding of new populations by translocation. There are often substantial differences in susceptibility to predation of closely related or ecologically similar taxa, and we stress the importance of basing conservation management decisions on relevant and detailed demographic and ecological studies. The main threat to threatened shorebirds elsewhere in the world is loss or degradation of habitat; the disproportionate impact of mammalian predators on New Zealand shorebirds is unusual but not unique.