Cats linked to small gardens

Gaston, K.J., Warren, P.H., Thompson, K. & Smith, R.M. 2005. Urban domestic gardens (IV): the extent of the resource and its associated features. Biodiv. Conserv. 14: 3327–3349.

Domestic (‘private’) gardens constitute a substantial proportion of ‘green space’ in urban areas and hence are of potential significance for the maintenance of biodiversity in such areas. However, the size and nature of this resource and its associated features are poorly known. In this study, we provide the first detailed audit, using domestic gardens in the city of Sheffield as a model study system. Domestic gardens, the mean area of which was 151 m², cover approximately 33 km² or 23% of the predominantly urban area of the city. The smaller gardens contribute disproportionately to this total because, although individually they add little, they are large in number. Conversely, the regions of the city with proportionately more garden area contribute most to the total garden area of the city, although such regions are limited in number. Based on the findings of a telephone based survey, 14.4% of dwellings with gardens were estimated to have ponds, 26% to have nest-boxes, 29% to have compost heaps, 48% to hold trees more than 3 m tall, and 14% of dwellings were estimated to be home to one or more cats. Whilst the absolute frequency of these features is low to moderate, by extrapolation they nonetheless yield estimates for domestic gardens in Sheffield of a total of 25,200 ponds, 45,500 nest boxes, 50,750 compost heaps, 360,000 trees, and a population of 52,000 domestic cats. These results are considered in the context of the role of gardens in urban areas as habitats for wildlife and the implications for housing policy.

Efficacy of an ultrasonic cat deterrent

Nelson, S. H., Evans, A. D., & Bradbury, R. B. (2006). The efficacy of an ultrasonic cat deterrent. Applied Animal Behaviour Science, 96(1), 83-91.

Ultrasound deterrents for a variety of mammals, including cats, are widely available in the commercial market, but few have been independently tested for efficacy. This study tested the efficacy of an ultrasonic cat deterrent ‘Catwatch©’, using 63 and 96 volunteer observers in two long-running (18 and 33 weeks) blind experiments. Results indicated that the device did have a moderate deterrent effect, reducing the probability of a cat intrusion into a garden by approximately 32% in the first experiment, but not in the second. The average duration of intrusions was reduced by approximately 38 and 22% in the two experiments, respectively. The magnitude of the deterrent effect appeared to increase with time, since the device was deployed. It is likely that the size of the deterrent effect could be increased by positioning the device(s) more carefully with regard to entry points to the garden that are regularly used by cats.

Predation of Birds at Feeders in Winter

Dunn, E. H., & Tessaglia, D. L. (1994). Predation of Birds at Feeders in Winter (Depredación de Aves en Comederos Durante el Invierno). Journal of Field Ornithology, 65 (1) 8-16.

A continentwide survey of homes with bird feeders produced 567 reports documenting 1138 incidents of predation. Of the 25 species of predators recorded, three (Sharp-shinned Hawk, Accipiter striatus; domestic cat; Cooper's Hawk, A cooperii) were responsible for 80% of the incidents in which the predator was known. Ten of the 62 species of prey identified accounted for 92% of all victims. The birds most vulnerable to predation were those that commonly occur at feeders throughout the continent (i.e., the most widespread species), but additionally, flocking species were more vulnerable to avian predators than more solitary ones. Prey size was correlated to size of avian predators, but cats concentrated on small birds. Hawks were attracted to feeders with particularly high levels of bird activity, but cats were not. The bird-feeding environment does not appear to expose birds to a higher risk of predation than is encountered in the absence of feeders.

Se hizo una encuesta, a nivel continental, en residencias en donde se les provee de comederos a aves, que produjo 567 informes en los cuales se documentan 1138 incidentes de depredación. De las 25 especies de depredadores informados tres de éstos, a saber Accipiter striatus, A. cooperii y el gato doméstico, fueron responsables del 80% de los incidentes en donde el depredador fue identificado. Diez de las 62 especies que sirvieron como presas, formaron el 92% de todas las víctimas. Las aves más vulnerables a la depredación fueron aquellas que más comúnmente utilizan comederos artificiales a nivel continental (ej. las especies más ampliamente distribuidas). No obstante las aves que se alimentan en grupos resultaron más vulnerables que las que lo hacen de forma solitaria. El tamaño de la presa se correlacionó al tamaño del depredador, aunque los gatos concentraron sus esfuerzos en aves pequeñas. Los halcones fueron atraídos a comederos, con altos niveles de actividad aviar, mientras que ocurrió lo opuesto con los gatos. Los ambientes en donde hay comederos artificiales no parecen exponer a las aves a un riesgo mayor de depredación, que en lugares en donde éstos no se encuentran.

"Cats kill an extraordinarily high number of birds in British gardens"

Cats killing huge numbers of British birds, Sir David Attenborough warns

The Guardian

Inside/outside cats' impact on a suburban nature reserve

Roland K, DeWan A (2004) Ecological impacts of inside/outside cats around a suburban nature preserve. Animal Conservation 7: 1–11.

While subsidised populations of feral cats are known to impact their prey populations, little is known about the ecological impact of inside/outside hunting cats (IOHC). We studied IOHC around a suburban nature preserve. Mail surveys indicated an average of 0.275 IOHC/house, leading to a regional density estimate of 0.32 IOHC/ha. A geographical model of cat density was created based on local house density and distance from forest/neighbourhood edge. IOHC hunted mostly small mammals, averaging 1.67 prey brought home/cat/month and a kill rate of 13%. Predation rates based on kills brought home was lower than the estimate from observing hunting cats (5.54 kills/cat/month). IOHC spent most outside time in their or their immediate neighbours’ garden/yard, or in the nearby forest edge; 80% of observed hunts occurred in a garden/yard or in the first 10 m of forest. Radio-tracked IOHC averaged 0.24 ha in home range size (95% minimum convex polygon (MCP)) and rarely entered forest. Confirming this, scent stations detected cats more often near the edge and more cats were detected in smaller forest fragments. There was no relationship between the number of cats detected in an area and the local small mammal abundance or rodent seed predation rates. Cold weather and healthy cat predator populations are speculated to minimise the ecological impact of IOHC on this area.

Dogs in gardens could benefit some indigenous birds

Daniels, G.D. & J.B. Kirkpatrick. 2006. Does variation in garden characteristics influence the conservation of birds in suburbia? Biological Conservation, 133: 326-335.

Can enhancement of garden habitat for native birds have conservation benefits, or are garden bird assemblages determined by landscape and environmental characteristics? The relative roles of vegetation structure, floristics and other garden attributes, and environmental and landscape controls, on the abundance and richness of bird species in 214 back or front gardens in 10 suburbs of Hobart, Tasmania, Australia, are addressed to answer this question. Birds were counted in each garden and the resources they utilized noted. Vascular plant species and other attributes of the garden were noted, along with rainfall, altitude, distance from natural vegetation, distance from the city and garden size. Garden floristics and bird assemblages were ordinated, and garden groups characterized by particular assemblages of birds identified. General linear modelling was used to determine the combinations of independent variables that best predicted the richness of birds and the abundance of individual bird species and groups of species. The models for bird richness, bird species and groups of bird species were highly individualistic. Although native birds showed a preference for native plants, they also utilized many exotic plants. Exotic birds largely utilized exotic plants. Variation in garden characteristics does substantially affect the nature of garden bird assemblages in Hobart, with weaker environmental and landscape influences. The fact that gardens can be designed and managed to favour particular species and species assemblages gives gardeners a potentially substantial role in the conservation of urban native avifauna.

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One cat's diet over 17y in NZ

Flux, J. E. (2007). Seventeen years of predation by one suburban cat in New Zealand. New Zealand Journal of Zoology, 34(4), 289-296.

The 558 prey items brought home by one domestic cat, recorded over its 17‐year lifetime, included 221 mice, 63 rats, 35 rabbits, 4 hares and 2 weasels. The cat hunted up to 600 m from the house, and prey was caught both inside and outside the 0.5 ha garden. Of the 223 birds brought in, 54 were native, including 43 silvereyes (Zosterops lateralis), but those killed were quickly replaced, so there was always a resident population of 1–2 pairs. The other known native birds comprised five fantails (Rhipidura fuliginosa), four warblers (Gerygone igata), a kingfisher (Halcyon sancta), and a shining cuckoo (Chrysococcyx lucidus). Only nine skinks (Cyclodina aenea) and one frog (Litoria raniformis) were brought in. The abundance of birds and reptiles in the garden showed no apparent change over the 17 years compared with the previous 15‐year‐period without a cat. By contrast, the cat exterminated the rabbit population in the garden, and “farmed” surrounding burrows during its whole life; all other prey killed declined in frequency after the catwas 8–9 years old.

Do domestic cats impose an unsustainable harvest on urban bird populations?

van Heezik Y., A. Smyth, A. Adams & J. Gordon. 2010. Do domestic cats impose an unsustainable harvest on urban bird populations? Biological Conservation. 143(1): 121-130

We assessed the impact of domestic cats on population persistence of native and exotic urban bird populations using a model adjusted for habitat-specific catch rates, cat ownership and hunting activity data. GPS-derived home ranges of 32 cats and resource selection indices demonstrated the degree of penetration and preference for native vegetation fragments. Owners reported on prey brought back by 144 domestic cats in Dunedin, New Zealand, during 12 months. One third of cats never brought back prey, and 21% returned more than one item/month. Cats brought back a mean of 13.4 prey items/year (median = 4), with cats aged <1 year returning more prey than older cats. Birds were the most common prey, followed by rodents. Although cats penetrated adjacent vegetation fragments they did not catch more birds and preferred garden habitat, suggesting that predation pressure may be reduced in fragments. Cat home range size appears to be constrained by cat density while the number of birds caught depends on the density of available prey. Estimates of city-wide catch for six bird species were either more than total urban population size estimates or close to lower confidence intervals. Modelling of three species indicated low likelihood of population persistence with cat predation. The observed persistence of these prey species suggests a meta-population structure with urban populations acting as sinks with source populations located on the city fringe.