The foods of feral house cats in forest in the Orongorongo Valley, Wellington, were studied over 3 years and related to the availability of prey. Some cats were trapped, tagged, and released, and could be identified individually by coat colour and pattern. The number of cats, estimated from live-trapping and sightings, was stable during the study. Examination of 677 scats revealed that mammals (rat, rabbit, opossum, mouse, and stoat, in descending order of importance) formed the bulk of the diet by weight. Remains of birds occurred in 12% of scats, but birds were estimated to form only 4.5% by weight of the diet. Insect fragments were present in many scats; wetas (Orthoptera), cicadas (Hemiptera), and beetles (Coleoptera) were important seasonally. Although eaten in large numbers, they contributed very little by weight to the diet. Populations of rats, rabbits, and opossums were fairly stable during the study; mice were abundant for most of the first 18 months, but were scarce in the last year. The literature on the food habits of feral house cats is reviewed; it emphasises that cats are primarily predators of small mammals (rodents and lagomorphs). Predation by feral cats can be important in holding rat and rabbit populations at low densities and in reducing seasonal fluctuations in their numbers. Cats can also exert heavy predation pressure on low-density mouse populations. Although the cats now eat few birds, they may have been responsible for reducing the numbers of some forest birds in the past.

No abstract

In an investigation of the factors leading to geographic structuring among Adélie Penguin (Pygoscelis adeliae) populations, we studied the size and overlap of colony‐ specific foraging areas within an isolated cluster of colonies. The study area, in the southwestern Ross Sea, included one large and three smaller colonies, ranging in size from 3900 to 135 000 nesting pairs, clustered on Ross and Beaufort Islands. We used triangulation of radio signals from transmitters attached to breeding penguins to determine foraging locations and to define colony‐specific foraging areas during the chick‐provisioning period of four breeding seasons, 1997–2000. Colony populations (nesting pairs) were determined using aerial photography just after egg‐laying; reproductive success was estimated by comparing ground counts of chicks fledged to the number of breeding pairs apparent in aerial photos. Foraging‐trip duration, meal size, and adult body mass were estimated using RFID (radio frequency identification) tags and an automated reader and weighbridge. Chick growth was assessed by weekly weighing. We related the following variables to colony size: foraging distance, area, and duration; reproductive success; chick meal size and growth rate; and seasonal variation in adult body mass. We found that penguins foraged closest to their respective colonies, particularly at the smaller colonies. However, as the season progressed, foraging distance, duration, and area increased noticeably, especially at the largest colony. The foraging areas of the smaller colonies overlapped broadly, but very little foraging area overlap existed between the large colony and the smaller colonies, even though the foraging area of the large colony was well within range of the smaller colonies. Instead, the foraging areas of the smaller colonies shifted as that of the large colony grew. Colony size was not related to chick meal size, chick growth, or parental body mass. This differed from the year previous to the study, when foraging trips of the large colony were very long, parents lost mass, and chick meals were smaller. In light of existing data on prey abundance in neritic waters in Antarctica suggesting that krill are relatively evenly distributed and in high abundance in the Southern Ross Sea, we conclude that penguins depleted or changed the availability of their prey, that the degree of alteration was a function of colony size, and that the large colony affected the location (and perhaps ultimately the size) of foraging areas for the smaller colonies. It appears, therefore, that foraging dynamics play a role in the geographic structuring of colonies in this species.

Nothofagus produces heavy crops of seed infrequently, and then house mouse (Mus musculus) populations increase greatly. In the Orongorongo Valley, near Wellington, seedfall of hard beech (Nothofagus truncata) and the numbers of house mice were measured for 22 years. Four heavy seedings were recorded and the numbers of mice were significantly correlated with the beech seedfall. Most mouse stomachs contained remains of arthropods, especially caterpillars and spiders, as well as plant material. Moths emerging from the litter of the forest floor in summer were sampled for seven years; the numbers of Tingena epimylia (Oecophoridae), whose larvae are litter-feeders, were strongly correlated with beech seedfall. The correlation between the numbers of moths and mice was slightly stronger than that between the numbers of beech seed and mice. Because the numbers of T. epimylia varied so greatly, components of the litterfall were also measured for three years. In a seeding year spent male flowers were a substantial part of the litterfall and might be responsible for the higher numbers of moths. These results indicate that factors other than quantity of seed may be important in the beech seed -mouse relationship and need to be explored further.

No abstract