On large inhabited islands where complete eradication of alien invasive rodents through the use of poison delivery is often not practical or acceptable, mechanical trapping may represent the only viable option to reduce their impact in areas of high biodiversity value. However, the feasibility of sustained rodent control by trapping remains uncertain under realistic operational constraints. This study aimed to assess the effectiveness of non-toxic rat control strategies through a combination of lethal and live-trapping experiments, and scenario modelling, using the example of a remote montane rainforest of New Caledonia. Rat densities, estimated with spatially-explicit capture-recapture models, fluctuated seasonally (9.5–33.6 ind.ha-1). Capture probability (.01–.25) and home range sizes (HR95, .23–.75 ha) varied greatly according to trapping session, age class, sex and species. Controlling rats through the use of lethal trapping allowed maintaining rat densities at ca. 8 ind.ha-1 over a seven-month period in a 5.5-ha montane forest. Simulation models based on field parameter estimates over a 200-ha pilot management area indicated that without any financial and social constraints, trapping grids with the finest mesh sizes achieved cumulative capture probabilities > .90 after 15 trapping days, but were difficult to implement and sustain with the local workforce. We evaluated the costs and effectiveness of alternative trapping strategies taking into account the prevailing set of local constraints, and identified those that were likely to be successful. Scenario modelling, informed by trapping experiments, is a flexible tool for informing the design of sustainable control programs of island-invasive rodent populations, under idiosyncratic local circumstances.

Invasive rats (Rattus rattus, R. norvegicus, R. exulans) are recognized as a major threat to native island ecosystems and biodiversity. On many islands, two or three invasive rat species co-occur, often sharing the same habitat; however few studies have focused on the effects of coexisting invasive rat species on native biodiversity. We investigated rat population ecology and diet in a New-Caledonian rainforest where black (Rattus rattus) and Pacific rats (R. exulans) coexist. Black rats dominated Pacific rats in relative abundance with a proportion varying between 80.9 and 88.9%. A total of 374 black rats and 87 Pacific rats were sampled for diet assessment through stomach and caecum analysis. Rat diet was mainly composed of plants, invertebrates and to a lesser extent Squamata, with black rats being more frugivorous and Pacific rats being more omnivorous. Ten of 15 endemic skink and gecko species were consumed, nine species by black rats and six species by Pacific rats. Thus, the presence of both rat species may strengthen the overall predation rate on each native prey species, and/or broaden the total number of native prey species impacted in the New-Caledonian rainforest. These results highlight the importance of preventing new rat species introduction on islands to avoid the strengthening and/or the broadening of negative effects on native biodiversity, and the importance of following the proportion of each rat species during rat control operations. Research to assess the threats generated by various assortments of rodent species on native biodiversity could improve priority setting in conservation actions.

Animals facing seasonal food shortage and habitat degradation may adjust their foraging behaviour to reduce intraspecific competition. In the harsh environment of the world's southernmost forests in the Magellanic sub-Antarctic ecoregion in Chile, we studied intersexual foraging differences in the largest South American woodpecker species, the Magellanic Woodpecker (Campephilus magellanicus). We assessed whether niche overlap between males and females decrease when food resources are less abundant or accessible, that is, during winter and in secondary forests, compared to summer and in old-growth forests, respectively. We analysed 421 foraging microhabitat observations from six males and six females during 2011 and 2012. As predicted, the amount of niche overlap between males and females decreased during winter, when provisioning is more difficult. During winter, males and females (i) used trees with different diameter at breast height (DBH); (ii) fed in trunk sections with different diameters; and (iii) fed at different heights on tree trunks or branches. Vertical niche partitioning between sexes was found in both old-growth and secondary forests. Such a niche partitioning during winter may be a seasonal strategy to avoid competition between sexes when prey resources are less abundant or accessible. Our results suggest that the conservation of this forest specialist, dimorphic and charismatic woodpecker species requires considering differences in habitat use between males and females.

Invasive rats are one of the world's most successful animal groups that cause native species extinctions and ecosystem change, particularly on islands. On large islands, rat eradication is often impossible and population control, defined as the local limitation of rat abundance, is now routinely performed on many of the world's islands as an alternative management tool. However, a synthesis of the motivations, techniques, costs, and outcomes of such rat‐control projects is lacking. We reviewed the literature, searched relevant websites, and conducted a survey via a questionnaire to synthesize the available information on rat‐control projects in island natural areas worldwide to improve rat management and native species conservation. Data were collected from 136 projects conducted over the last 40 years; most were located in Australasia (46%) and the tropical Pacific (25%) in forest ecosystems (65%) and coastal strands (22%). Most of the projects targeted Rattus rattus and most (82%) were aimed at protecting birds and endangered ecosystems. Poisoning (35%) and a combination of trapping and poisoning (42%) were the most common methods. Poisoning allows for treatment of larger areas, and poison projects generally last longer than trapping projects. Second‐generation anticoagulants (mainly brodifacoum and bromadiolone) were used most often. The median annual cost for rat‐control projects was US$17,262 or US$227/ha. Median project duration was 4 years. For 58% of the projects, rat population reduction was reported, and 51% of projects showed evidence of positive effects on biodiversity. Our data were from few countries, revealing the need to expand rat‐control distribution especially in some biodiversity hotspots. Improvement in control methods is needed as is regular monitoring to assess short‐ and long‐term effectiveness of rat‐control.

Native frugivores play an important role in native plant community dynamics by participating in seed dispersal. Today many island forests are invaded by introduced omnivores, such as rats, but their role in dispersing native plants is still little known. Here, we evaluated whether native seeds from New-Caledonian rainforests can germinate after passing through an invasive rat digestive tract and compared seed germinability and germination time between seeds ingested by invasive rats and native frugivores. We offered native fruits of Ficus racemigera and Freycinetia sulcata to the rats Rattus rattus and R. exulans, three flying foxes Pteropus spp. and the pigeon Ducula goliath. Our results showed that seeds can germinate after passing through an invasive rat digestive tract, and suggest that rats can disperse seeds of both plant species. However, invasive rats may be less efficient than native frugivores, as more seeds were destroyed when passing through rat digestive tracts than through native frugivores, and because germinability was lower and germination time was longer for seeds passing through invasive rats than through native frugivores. The reduced efficiency of rats may result from their generalized diet, the structure of their digestive tract, and/or their feeding behavior. In New-Caledonian rainforests, dispersal services on both plant species are likely well fulfilled by flying foxes and Ducula pigeons, but rats do not seem to be as efficient dispersers. Consequently, management measures to protect native frugivores should help to conserve seed dispersal services.

Invasive rats (Rattus spp.) are known to have pervasive impacts on island birds, particularly on their nesting success. To conserve or restore bird populations, numerous invasive rat control or eradication projects are undertaken on islands worldwide. However, such projects represent a huge investment and the decision-making process requires proper assessment of rat impacts. Here, we assessed the influence of two sympatric invasive rats (Rattus rattus and R. exulans) on native bird eggs in a New Caledonian rainforest, using artificial bird-nest monitoring. A total of 178 artificial nests containing two eggs of three different sizes were placed either on the ground or 1.5 m high and monitored at the start of the birds' breeding season. Overall, 12.4% of the nests were depredated during the first 7 days. At site 1, where nests were monitored during 16 days, 41.8% of the nests were depredated. The main predator was the native crow Corvus moneduloides, responsible for 62.9% of the overall predation events. Rats were responsible for only 22.9% of the events, and ate only small and medium eggs at both heights. Our experiment suggests that in New Caledonia, predation pressure by rats strengthens overall bird-nest predation, adding to that by native predators. Experimental rat control operations may allow reduced predation pressure on nests as well as the recording of biodiversity responses after rat population reduction.

Due to its unique biodiversity and extreme endemism rates, New Caledonia archipelago is listed as one of Earth's 35 biodiversity hotspots.New Caledonian biota is now threatened by invasive species, with introduced rats considered to be particularly damaging.At the initiative of local institutions and NGOs, an innovative scientific experiment has been launched to quantify the Response of Forest Ecosystems to Rodent and Cat Control (REFCOR) and to test the relevance of such control at a large spatial scale (200 ha) on a dense evergreen rainforest (Mont Panié Wilderness Nature Reserve).Rat control will begin mid-2014 with a short toxin knockdown, and will thereafter involve intensive trapping sessions over the next 6 years, together with biodiversity monitoring and experiments.Rat impact studies initiated in early 2013 also aim to identify possible biodiversity indicators that could be used for a rapid assessment of rat control efficiency and effects.One of the major impacts of invasive rats is the disruption caused to plant and bird reproduction processes, placing them at high risk.Pre-and post-control experiments include the assessment of palm fruit consumption rates and of predation risk to artificial bird nests.Initial surveys of both rat populations and palm fruits (2 species), as well as artificial bird nest predation experiments, were conducted in 2013.Rat abundance was high, fluctuating among study areas and seasons, with more individual reproducers in December than in May.Fruit predation was high for one of the two species, in line with the rat abundance pattern.Surprisingly, artificial bird nest predation by rats was far lower than expected.These first results corroborate the influence of rats on some taxa.Monitoring and experiments will be repeated after and throughout rat control.This "before-after-control-impact" project, conducted in close collaboration with local stakeholders (Dayu Biik NGO), offers a unique opportunity to evaluate 1) the feasibility of controlling rat populations in the New Caledonian rainforest by trapping as an alternative to long-term poisoning, and 2) the benefits of rat control for native biodiversity and rainforest ecosystem functioning.

The effect of the disturbances caused by the American beaver (Castor canadensis), introduced to the Cape Horn Biosphere Reserve, on species of birds that are forest habitat specialists is poorly understood. Using telemetry data, we determined which attributes of abandoned beaver meadows have a strong impact on habitat selection by the Magellanic woodpecker (Campephilus magellanicus). We detected a positive relationship between the woodpecker habitat use and the fraction of old-growth forest located near these meadows. These results suggest that favorable habitat conditions are generated around small meadows with old-growth forest, because they might increase availability of wood-boring larvae.

AimWe tested whether coarse-grained occurrence data can be used to detect climatic niche shifts between native and non-native ranges for a set of widely introduced freshwater fishes.LocationWorld-wide.MethodsWe used a global database of freshwater fish occurrences at the river basin scale to identify native and non-native ranges for 18 of the most widely introduced fish species. We also examined climatic conditions within each river basin using fine-grained climate data. We combined this information to test whether climatic niche shifts have occurred between native and non-native ranges. We defined climatic niche shifts as instances where the ranges of a climatic variable within native and non-native basins exhibit zero overlap.ResultsWe detected at least one climatic niche shift for each of the 18 studied species. However, we did not detect common patterns in the thermal preference or biogeographic origin of the non-native fish, hence suggesting a species-specific response.Main conclusionsCoarse-grained occurrence data can be used to detect climatic niche shifts. They also enable the identification of the species experiencing niche shifts, although the mechanisms responsible for these shifts (e.g. local adaptation, dispersal limitation or physiological constraints) have yet to be determined. Furthermore, the coarse-grained approach, which highlights regions where climatic niche shifts have occurred, can be used to select specific river basins for more detailed, fine-grained studies.