Genetics of a dockyard cat population

Dards, J. L., & Robinson, R. (1983). Gene frequencies in a population of feral cats in Portsmouth naval Dockyard. Theoretical and Applied Genetics, 64(3), 197-204.

The free-living or feral cats of Portsmouth Dockyard were examined for the frequency of six mutant colour and coat genes. With the exception of one mutant, they were found to differ from the values to be expected for Southern England cat populations. The differences observed may have resulted from selection in the isolated environment (to produce a unique gene profile in terms of frequencies) or from a founder effect. If the latter, the observed frequencies could represent a relict population reflecting the frequencies of the town of Portsmouth before the dockyard was totally enclosed by a high wall. Some evidence of selection related to coat colour was found.

The behaviour of dockyard cats

Dards, J. L. (1983). The behaviour of dockyard cats: Interactions of adult males.Applied Animal Ethology, 10(1), 133-153.

A study was conducted on the feral cats living in Portsmouth Naval dockyard, an enclosed site with an area of less than 100 ha, supporting a population of about 200 adult cats. Data were collected by direct observation, and individuals were recognized primarily by coat pattern. The behaviour of mature tom-cats was observed with respect to females and to other mature males. Most toms visited several groups of females, but the frequency with which a particular group was visited varied between toms. Some toms spent most of their time with one group, adopting a role similar to that of a “pride lion”. The courtship and mating behaviour observed in the dockyard conformed with that recorded for laboratory cats. However, females in oestrus were not heard to call, but toms which were apparently seeking oestrus females emitted a characteristic cry. Up to 6 toms were observed in attendance on unreceptive oestrus females. Sexual behaviour was observed in most months, with peaks in the spring and autumn. Most of the aggressive interactions observed between toms and females were initiated by unreceptive females during courtship. Male aggression towards females was rare. Amicable behaviour was shown, and was more frequently initiated by females than by toms. Females appeared to interact amicably more frequently with toms with which they were familiar. No amicable behaviour between mature toms was observed. Interactions were characterised by aggression, tolerance or avoidance. Agonistic encounters were mainly ritualised, and few fights were observed. It is possible that a dominance hierarchy existed between toms, formed by fights when young toms first became sexually mature.

Feral dogs in Galápagos

Barnett, B. D., & Rudd, R. L. (1983). Feral dogs of the Galápagos Islands: Impact and control. International Journal for the study of Animal Problems, 4:44-58.

Organisms introduced onto insular ecosystems, after they have become established, frequently increase to destructive numbers. Several species of mammals introduced onto the Galápagos Islands illustrate this ecological axiom. For example, domestic or pariah, and feral. Problems derived from their presence are most apparent on the islands of Santa Cruz and Isabela. Feral and pariah dogs are both scavengers and predators. While other introduced mammals (chiefly feral cattle and pigs) have served as prey, in recent years severe depredations on the unique endemic Galapagan fauna have been caused by the dogs. The chief targets have included land and marine iguanas, tortoises, and colonially nesting marine birds. To counter this problem, a coordinated and an eradication program on Isla Isabela, begun in 1981, continues with marked success. Control rests primarily on carefully placed flesh baits poisoned with Compound 1080 (sodium monofluoroacetate). Field studies on distribution, demography, behavior, and disease transmission also began on Isla Isabela in 1981. Particularly notable is the high incidence of filarial heartworm in several species of mammals, including the local human residents. Dogs are important reservoirs of this parasite. Descriptions of the problems created by the dogs and speculations on the nature of selective return to the wild state are presented.

Photo Galapagos Conservation Society

Socorro island's endemics and cats

Arnaud, G., A. Rodriguez, A. Ortega-Rubio, S. Alvarez-Cardenas. 1993. Predation by Cats on the Unique Endemic Lizard of Socorro Island (Urosaurus auriculatus), Revillagigedo, Mexico. Ohio Journal of Science, 93 (4): 101-103

During 1990 the distributions of the endemic lizard (Urosaurus auriculatus) and the feral cat (Felis catus) of Socorro Island were observed and scats of the last species were collected. A total of 46 cat scats were analyzed, showing that lizards were an important prey item, varying in frequency from 33.33% in February to 66.66% in November. Because of the impact of sheep (Ovis aries) on the natural vegetation and because of the impact of cat predation, we recommend that a plan be developed for the removal of exotic species and the restoration of natural vegetation to Socorro Island.

Jehl, J.R.& K.C. Parks. 1983. 'Replacements' of landbird species on Socorro Island, Mexico. Auk 100: 551-559.
The endemic dove Zenaida graysoni of Socorro Island, an oceanic island in the Pacific south of Baja California, became extirpated between 1958 and 1978 and the endemic mockingbird Mimodes graysoni diminished during the same years and was approaching extinction by 1981. The mainland mourning dove Z. macroura became established on Socorro between (probably) 1971 and 1978 and the mainland northern mockingbird Mimus polyglottos between 1978 and 1981. Superficially an instance of replacement of island endemics by mainland relatives through competitive exclusion, the case is actually more complicated. It is argued that extermination of the endemics was probably caused by predation by feral cats introduced in 1957 or later. There is no evidence of any actual competition between the pairs of species and their preferred habitats overlap only slightly. The nearly concurrent establishment of the 2 invading species, known to have occurred frequently as casual visitors to Socorro and other islands is attributed largely to the provision of fresh water made available as a result of human settlement. Simple comparison of island species lists compiled at intervals is an inadequate base for theories of island species turnover.

More info about Socorro's threatened birds:
BirdLife International (2013) Species factsheet: Zenaida graysoni. Downloaded from http://www.birdlife.org on 12/04/2013.
BirdLife International (2013) Species factsheet: Mimus graysoni. Downloaded from http://www.birdlife.org on 12/04/2013. 

BirdLife International (2013) Species factsheet: Aratinga brevipes. Downloaded from http://www.birdlife.orgon 12/04/2013.
BirdLife International (2013) Species factsheet: Troglodytes sissonii. Downloaded from http://www.birdlife.orgon 12/04/2013.
BirdLife International (2013) Species factsheet: Puffinus auricularis. Downloaded from http://www.birdlife.orgon 12/04/2013.