No abstract

A number of cats in a captive population were fed 50 mg of Rhodamine B in non-toxic kangaroo meat baits. Samples of whiskers (mystacial vibrissae) taken 10 days later were examined for fluorescent marking. Examination of hairs for marking was carried out by means of a ‘single blind’ trial, with the investigator having no prior knowledge of which of 36 cats had received the dye. All of the cats that had ingested baits containing the dye were marked. Examining hair samples under ambient light or under a hand-held ultraviolet (UV) light without magnification was not as reliable as examining hair samples under a fluorescence microscope. These results indicate that Rhodamine B acts as a reliable systemic marker of bait consumption in feral cats and has potential application in field studies to assess bait uptake by feral cats.

Intensive destructive sampling of a population of red foxes (Vulpes vulpes) was undertaken over an area of 200 km2. A total of 204 foxes, estimated to be 94% of the total population on the site, was collected. Population density was 0.46–0.52 adult foxes km–2. Sampling was carried out in December, when young of the year were present and when data on female productivity could be obtained from counts of placental scars. Life-table analysis for vixens revealed that mortality was greatest for those aged 0–16 months and those older than 3 years. Average mortality of adult vixens was 39%. Adult vixens (n = 47) had an average (s.e.) of 3.7 0.3 placental scars; 8.5% of vixens failed to breed. The number of placental scars did not vary significantly with age. Various hypothetical scenarios were used to identify which social system(s) may have been operating in the area. Predictions of vixen productivity and cub mortality were compared with observed reproductive data and the actual number of cubs collected. The scenario that best matched the observations was a simple mated pair system. Pure dominance hierarchies were unlikely to have occurred. The implications of the findings are discussed in relation to the ability of foxes to overcome natural or artificially-imposed population reduction. It was estimated that under a fertility control regime, >45% of vixens would need to be sterilised before the fox population would begin to decline.