Use of monitoring data and population viability analysis to inform reintroduction decisions: Peregrine falcons in the Midwestern United States

The peregrine falcon (Falco peregrinus anatum) has not yet recolonized natural cliff sites in Illinois and much of the lower Midwestern US, and remains restricted to urban areas. We constructed a landscape-linked population viability analysis using RAMAS/GIS software to compare possible reintroduction strategies for the species. Habitat-specific (i.e. cliff and urban) demographic parameters such as survival, fecundity, and dispersal rates were derived from the Midwest Peregrine Society Database for peregrines in the central Mississippi River region during 1982-2006. We simulated a base scenario of no reintroduction and 18 models of reintroduction with varying cohort sizes, supplementation schedules, and number of reintroduction sites, and used the Lake Superior population to test our model. Our analysis indicated that even without reintroductions in Illinois, the peregrine population in the lower Midwestern region is slowly increasing and is not likely to go extinct. Recolonization of cliff sites in southern Illinois likely will occur via dispersal from urban populations, however further research on dispersal rates between urban areas and cliffs is needed. Analysis indicated that the most cost-effective reintroduction strategy would be priced at approximately $280,000 and would result in only two additional breeding pairs compared to the no-action scenario. Thus, funds would be more effectively used in other management efforts such as habitat preservation. This study provides an example of how post-release monitoring can be used to inform future reintroduction plans.     

Conservation status of tigers in a primary rainforest of Peninsular Malaysia

This study provided the first reliable density estimate of tigers based on photographic capture data in Taman Negara National Park, Peninsular Malaysia's most important conservation area. Estimated densities () of adult tigers ranged from 1.10 ± 0.52 to 1.98 ± 0.54 tigers/100 km² (X²=1.56, df=2, P=0.46) with the overall mean of 1.66 ± 0.21 tigers/100 km². The tiger population in the 4343-km² park was estimated to be 68 (95% CI: 52-84) adult tigers. Prey biomass estimates ranged from 266 to 426 kg/km², and wild boar were the most important potential prey species in terms of abundance, biomass, and occupancy, followed by muntjac. Both tigers and leopards were more diurnal than nocturnal, which corresponded with the activity patterns of wild boar and muntjac. No evidence of poaching of large mammals was found in the 600-km² study sites and overall human impacts on the tiger-prey community appear to be minimal, but in the long run its viability needs to be evaluated in a greater landscape context.     

Estimating impacts of poison operations on non-target species using mark-recapture analysis and simulation modelling: an example with saddlebacks

Poison operations to control or eradicate exotic mammals are a key component of conservation management in the South Pacific. They also result in by-kill of native species. It is therefore important to develop reliable methods for estimating by-kill and assessing its impact. The North Island saddleback (Philesturnus carunculatus rufusater), a rare New Zealand forest bird, was reintroduced to Mokoia Island in 1992, and 4 years later there was an aerial drop of cereal pellets containing Brodifacoum aimed at eradicating mice. We used mark-recapture analysis on resighting data collected from 1992 to 1997 to estimate the by-kill of saddlebacks attributable to this poison drop. We nominated a set of candidate models to explain the data, and compared these using Akaike's Information Criterion. The analysis showed that saddleback survival was substantially lower than expected in the 6-week interval after the poison drop, taking age, density dependence, season and random variation into account. Taking expected survival rates into account, the probability of an adult being killed was estimated to be 0.45 (95% CI=0.34-0.56), and the probability of a juvenile being killed was estimated to be 0.35 (95% CI=−0.05-0.75). We then used a simulation model developed for the population to assess the longer-term impact of this mortality. While the mortality set back the expansion of the population by 1-2 years, we predicted that the population would have recovered fairly quickly and ultimately reach the same carrying capacity. Mark-recapture analysis permits precise estimates of background survival rates unconfounded by seasonal or random variation.     

Stock structure and seasonal distribution patterns of American lobster, Homarus americanus, inferred through movement analyses

Movement influences the annual distribution patterns of a species and is an important determinant of stock structure. In situations where monitoring programs have quantified movement or distribution patterns by sampling during particular times of the year, seasonal changes in abundance as well as the degree of connectivity among adjacent stocks can be underestimated. Here, a summer abundance trawl survey was combined with a 1-year mark-recapture tagging study to infer seasonal changes in distribution within and among American lobster (Homarus americanus) stocks. Within the study area, lobsters were concentrated in central Northumberland Strait (Canada) during August, yet their observed dispersal behaviour implied that density declined in the central portion and increased in the northern portion of Northumberland Strait during winter. Stock mixing among management zones was not observed and individual tendencies to move were predicted to decline precipitously in early December. These movement patterns are consistent with the hypothesis of seasonal limitation by hard-substrate habitat availability causing population redistribution. Such information can ultimately be useful when assessing changes in abundance or exploitation rates, and for guiding management efforts.     

Cost-effective abundance estimation of rare animals: Testing performance of small-boat surveys for killer whales in British Columbia

Top predators are often rare, subject to anthropogenic mortality, and possess life-history traits that make them inherently vulnerable to extinction. IUCN criteria recognise populations as Critically Endangered when abundance is <250 mature individuals, but estimating abundance of rare species can be more challenging than for common ones. Cost-effective methods are needed to provide robust abundance estimates. In marine environments, small boats are more widely accessible than large ships for researchers conducting sightings surveys with limited funds, but studies are needed into efficacy of small-boat surveys. This study compares line transect and mark-recapture estimates from small-boat surveys in summer 2004 and 2005 for ‘northern resident’ killer whales in British Columbia to true population size, known from censuses conducted by Fisheries and Oceans Canada. The line transect estimate of 195 animals (95% CI 27-559) used model averaging to incorporate uncertainty in the detection function, while the mark-recapture estimate of 239 animals (CI 154-370) used a simple two-sample Chapman estimator. Both methods produced estimates close to the true population size, which numbered 219 animals in 2004 and 235 in 2006, but both suffered from the small sample sizes and violations of some model assumptions that will vex most pilot studies of rare species. Initial abundance estimates from relatively low-cost surveys can be thought of as hypotheses to be tested as new data are collected. For species of conservation concern, any cost-effective attempt to estimate absolute abundance will assist status assessments, as long as estimates are presented with appropriate caveats.     

Population structure and movements of a threatened butterfly (Lopinga achine) in a fragmented landscape in Sweden

The red-listed butterfly Lopinga achine was studied by mark-recapture methods in southern Sweden for three seasons. We examined movement within and between populations and egg production in relation to age. The majority of the movements were small with mean movements between recaptures of 45-54 m for males and 94-116 m for females. There were few movements between sites, 20 of 996 recaptured males moved and 36 of 391 recaptured females, even though the distance to other sites was in many cases <100 m. The distance moved and the number of females moving between sites increased with increasing age. On average, a female that moves does so after laying two-thirds of its eggs in its natal site. It is therefore important to take account of the proportion of reproductive effort involved in dispersal when estimating colonisation ability. The males did not move more with increasing age. Female behaviour can be seen as a “spread-the-risk” strategy, an adaptation to the successional habitat of L. achine, whose natal site sooner or later will deteriorate. Butterflies like L. achine living in successional habitats may exhibit mobility that is intermediate between butterflies living in ephemeral habitats (very mobile) and in long-lived habitats (sedentary).     

Factors influencing survival and long-term population viability of New Zealand long-tailed bats (Chalinolobus tuberculatus): Implications for conservation

A population viability analysis is important for the management of endangered populations and requires the estimation of survival parameters. The long-tailed bat (Chalinolobus tuberculatus) is one of only two native terrestrial mammals currently found in New Zealand and is classed as vulnerable. Its viability in temperate beech (Nothofagus) forest, Eglinton Valley, Fiordland, New Zealand was estimated using mark-recapture data collected between 1993 and 2003 using the Program MARK. Survival was estimated based on a total of 5286 captures representing 1026 individuals. Overall annual survival varied between 0.34 and 0.83 but varied significantly among three sub-populations and with sex and age. Females generally had a higher survival rate compared to males; and adults had higher survival relative to juveniles. Survival of all bats was lower in years when the number of introduced mammalian predators was high and when the winter temperature was warmer than average. High numbers of introduced predators occurred during three of the 10 years in the study. Climate change may mean that the conditions that promote high predator numbers may occur more frequently. A preliminary population viability analysis using a projection matrix on the overall adult female population showed an average 5% decline per year (λ = 0.95). Increased predator control targeting a range of predators is required in years when their numbers are high in order to halt the decline of this population of long-tailed bats. Population estimates using minimum number alive estimates supported the population estimates derived from Program MARK and a population viability analysis using matrices.