Cats and seabirds: effects of feral Domestic Cat Felis silvestris catus eradication on the population of Sooty Terns Onychoprion fuscata on Ascension Island, South Atlantic

The population of Sooty Terns Onychoprion fuscata breeding on Ascension Island in the Atlantic Ocean was monitored over 17 years (1990–2007). This period spanned the programme of feral Domestic Cat Felis silvestris catus eradication from the island, which commenced in 2001 with the last Cat recorded in 2004. We report on the abundance of Sooty Terns and Black Rats Rattus rattus before and after Cat eradication. The Sooty Tern breeding population in the 1990s averaged 368 000 and Cats were killing Terns at an average rate of 33 adults per night. Following Cat eradication, adult Terns are no longer predated. However, egg predation by both Rats and Common Mynas Acridotheres tristis has continued with Mynas destroying more eggs than Rats. Unexpectedly, we observed a change in Rat predatory behaviour. Following Cat eradication, Rats have become a major predator of Sooty Tern chicks. Despite this change, the Tern population has shown a season-on-season increase since Cat eradication, 48.8% in 2005, 8.2% in 2006 and 6.1% in 2007, and the breeding population increased to 420 000 birds in 2007. Incubation success improved from 66.0 to 84.4% during Cat eradication, before dropping down again to 67.9% after Cats were eradicated and Rat control measures were introduced. Index traplines were set for Rats and Rat numbers fluctuated widely immediately after Cats were eradicated but there were no significant differences that could be attributed to changes in Cat numbers. Ascension Island Sooty Terns breed every 9.6 months and juveniles defer breeding for seven seasons. Hence 2008 is the first year in which an increase in the breeding Sooty Tern population directly attributable to Cat eradication is likely to be detected. We conclude that long-term monitoring is essential to guide conservation practice even in this relatively simple predator–prey system.     

Isolation and characterization of microsatellites in Rattus rattus

We isolated and characterized 10 microsatellite loci in the black rat Rattus rattus (Muridae, Rodentia), a widespread invasive species largely known to cause serious problems in agriculture and human health. Polymorphism was studied in two populations, one from Madagascar and one from Senegal. It ranged from three to 12 alleles in Madagascar, and from two to five alleles in Senegal. Together with the loci previously adapted from Rattus norvegicus, this set of markers should allow the conduct of thorough studies on the genetic structure of natural populations of R. rattus.     

Synchrony in small mammal populations of montane forest patches in southern India

1. Small mammal populations were studied in montane evergreen forests in the Nilgiris, southern India, using live-trapping from January 1994 to September 1996. Two sites were selected, one with a single large forest patch and adjoining plantations, and the other with several small forest patches separated by grassland.
2. Nine species were recorded, of which eight were trapped in the forest patches, two in the grasslands and five in plantations. Rattus rattus was the most abundant species (2–36 individuals ha⁻¹) followed by Suncus montanus (0–11 individuals ha⁻¹). Densities of seven other species recorded were very low.
3. Synchrony in various population variables – density, biomass, mean weight, density of adults and adult females, and proportion of adults, adult females and sub-adults – was examined for Rattus rattus populations in the forest patches and plantations. Density and biomass were studied in seven other species recorded at these sites. Spearman's rank order correlation was used as a measure of synchrony between the population variables.
4. Within-site synchrony was higher than between-site synchrony in population characters. Synchrony was also higher between plots within the unfragmented site than they were between plots in the fragmented site. Relatively high synchrony in proportions of adults, adult females and juveniles in the forest patches implied that breeding is probably influenced by climate and food availability, which are seasonal in this habitat.
5. Given the small patch sizes (≈1–10 ha) and low population sizes, asynchrony is likely to be an outcome of demographic and environmental stochasticity, and low dispersal rates may impede establishment of synchrony.     

小良热带人工阔叶混交林中屋顶鼠施氏亚种的食性及其生态学意义

Rattus rattus slandeni的食性资料是在小良人工阔叶混交林中通过200个鼠箱观察残留食物的方法收集到的。屋顶鼠摄食植物39种,主要为果实、种子部分,并大量捕食金龟子、蝉和蝗虫等昆虫,偶尔捕食小脊椎动物。植物性和动物性两大类残食的总出现率相近,5-10月以动物性食物为主,11-4月以植物性食物为主。该鼠搬运和遗弃果实、种子的行为,有助于植物种类的传布,大量捕食害虫,有利于该系统的生态平衡,故对其益害问题应作客观评价。     

Community structure and demography of small-mammal populations in insular montane forests in southern India

bstract Small mammals were studied in insular montane forest patches in the Upper Nilgiris in southern India from February 1994 to September 1996. Nine patches were selected at two sites, one with a single large 600-ha patch, the other with several small patches ranging in size from 0.2 to 60 ha. The population characteristics and community structure of small mammals were studied in relation to patch size and habitat structure within the patches. The two most abundant species were Rattus rattus (2–36 individuals/ha) and Suncus montanus (0–11 individuals/ha), while the abundance of seven other species recorded were very low. The population characteristics of R. rattus examined were density, biomass, proportions of juveniles, sub-adults and adults, mean weight of all animals, mean weight of adults, sex ratio and persistence. The proportion of adults, sub-adults, mean weight of animals, and mean weight of adult males were correlated with patch size. Persistence of sub-adult females in the large patch was especially high. The density and biomass of other small-mammal species were also studied. Two indices of diversity, species richness and proportion of R.␣rattus were compared as measures of community structure. Seven habitat characteristics were measured; of these, canopy cover, canopy height and tree density were correlated with the size of the patch. Density and biomass of species other than R. rattus and proportion of R. rattus were correlated with canopy height. Density and biomass of species other than R. rattus were highest in smaller patches. While the population characteristics of R. rattus may be affected by patch size, the density of rare species may be influenced by factors related to lower canopy height. Migration between patches may be an important factor in maintaining populations in these patches. Received: 5 January 1998 / Accepted: 23 March 1998     

Do rats mind getting their feet dirty? Observing the behaviour of ship rats (Rattus rattus) towards footprint tracking tunnels

Monitoring rat populations by standard tracking tunnels assumes that rats do not avoid treading on the tracking ink. We observed the behaviour of 20 rats in four groups of five, spending 2 nights each (40 trials) in large observation pens. In only 10 of 40 trials did the rat run through a tunnel without hesitation on first encounter, while in four trials a rat approached the tunnel up to 35 times but refused to run though it all night. Most rats approached and turned away between two and 34 times before running through. Observations through transparent tunnels of rats pausing for a mean of 3.2 s before stepping on the ink suggest that they probably could detect it, but they usually chose to ignore it. Experience of encountering the ink pad inside a black tunnel did not deter rats from running across another one, and would not affect indices of rat abundance reaching levels high enough to trigger conservation concern, but variation in behavioural reactions to tracking tunnels could possibly affect the detection rate of rats at low density.     

Use of habitat by the black rat (Rattus rattus) at North Head,New South Wales: an observational and experimental study

This study investigated the habitats used by an introduced species of rodent, the black rat Rattus rattus (Linnaeus), at North Head in New South Wales, Australia. At a coarse scale, combined live‐trapping and radio‐tracking indicated that animals used forest proportionately more than open, heath or scrub macrohabitats that were available. To identify the components contributing to this pattern, microhabitat use was assessed by scoring vegetative and structural features around trap stations, and by using spool‐and‐line tracking. The results indicated that rats preferred microhabitats providing a deep cover of leaf litter and dense understorey with numerous vertical stems. As statistical analysis did not distinguish which of these components was more important in determining habitat use, we designed an experiment to test the importance of a single component: leaf litter. Cover of litter was enhanced experimentally at 75 trap stations and reduced at 75 others, and the response of rats monitored by live‐trapping on two occasions. Although no clear response was found in the first run of the experiment, due to low numbers, rats strongly selected trap stations with enhanced leaf litter in the second run. These results indicate that litter cover affects use of habitat by the black rat. Access to food resources and avoidance of predators may contribute to the observed local patterns of abundance.