Although wild rabbits have an important beneficial role in European ecosystems, we should not assume the same for natural ecosystems in Australia. Despite biological control, rabbits continue to reduce biodiversity and prevent the maintenance of natural ecosystems across southern Australia. The failure to recognise the severity of this problem and a mistaken preoccupation that rabbits have become widely integrated within Australian ecosystems that now hinders conservation rather than our lack of capacity to control rabbits. Photograph by Brian Cooke.
Volume 39 Number 4 2012
WR11150Genetically defining populations is of limited use for evaluating and managing human impacts on gene flow
Populations are frequently described using genetic data, the rationale being that they are important units for conservation management. However, use of the term ‘population’ is inconsistent and the methods require cautious interpretation. Poorly defined study units are problematic when formulating management-focussed questions. Genetic structure, gene flow and individual dispersal can be described without reference to populations, and defining land areas as the management units will benefit communication between geneticists, policy makers and conservation managers.
Artificial refuges are important tools in conservation management. Optimum design of such refuges for a species can significantly increase success of conservation programs. The endangered pygmy bluetongue lizard accepts simple artificial burrows, but our experiments show a previously unreported risk for lizards. We suggest a requirement for more careful design before adopting artificial burrows in future conservation management programs. Photograph by Mehregan Ebrahimi.
Roads can have far-reaching consequences on wildlife including mortality, disturbance and habitat degradation. Because these consequences are of special concern to threatened species such as the Florida scrub-jay (Aphelocoma coerulescens), we assessed physiological measures and found that roads and roadside habitat have neutral or potentially beneficial effects on the scrub-jay. While vehicle-induced mortality rates cannot be disregarded, these findings provide further evidence that roads might provide beneficial conditions to generalist and opportunistic foragers. Photograph by Gina Morgan.
Heterogeneous detection probability can hinder our ability to accurately estimate population density or trends from count data. The most common methods to estimate detection probability during avian surveys involve recording a distance between the survey point and individual birds detected during the survey period. We tested the assumption that surveyors can accurately estimate a distance to wetland-dependent birds aurally during a survey. Our results suggest that distance-estimation error is prevalent, but surveyor training may be the easiest way to reduce distance-estimation error. We encourage the use of field trials (such as those presented here) to evaluate distance-estimation error so that investigators can (1) report the extent of the error, and (2) employ recently developed models to incorporate distance-estimation error into analyses. Photograph by Courtney Conway.
Snow depth is a key factor affecting population dynamics in northern climates; however, snow-depth data are limited across space and time. We describe a method for using widely available snow water equivalent (SWE) data in place of snow depth in an existing climate index. The SWE model can be used for other species’ climate indices requiring snow-depth data. Photograph by Sarah Anderson.
WR11035Effects of egg oiling on ground-nesting double-crested cormorants at a colony in Lake Ontario: an examination of nest-attendance behaviour
In the past two decades, tens of thousands of eggs laid by double-crested cormorants have been oiled as part of extensive population control measures, yet our understanding of how cormorants respond to such activities was limited. While cormorants with oiled eggs did not attend their nest as long throughout the season compared with birds with unoiled eggs, in other comparisons they behaved similarly. Egg oiling, administered judiciously, may be an appropriate technique for ground-nesting cormorants, although population targets must be clearly articulated prior to management actions. Photograph by Gail Fraser.
Estimates of hunter harvest are used primarily to determine the efficacy of hunting regulations, but they also help wildlife managers assess the status of game animal populations. National surveys are conducted annually to estimate waterfowl harvest in the USA, and we found that they apparently overestimate duck and goose harvest by substantial margins. This does not reduce the value of the estimates for evaluating relative differences resulting from regulatory changes, but population status assessments and models that use them should account for the bias.
WR11127Behavioural responses of brushtail possums to live trapping and implications for trap-catch correction
Trap catch indices are used routinely in New Zealand to estimate relative abundance of possums, and indices are usually corrected for sprung traps to avoid biases, using the assumption that animals are trapped, on average, halfway through a trap-night. Timing devices attached to traps showed that possums were caught after only 11% of the trap-night, and traps were sprung by other causes after only 22% of the trap-night. These data indicate a need to alter the commonly used correction factor for population indices for possums, and suggest a need to re-examine the validity of the correction for other species whose populations are indexed using trap catch rates. Photograph © Landcare Research NZ Ltd.
Determining the sex ratio of a population can form an important step in understanding the dynamics of a population. We used closed-population mark–recapture methods to determine the population size of each sex for a frog and compared these values to raw counts of each sex. A perceived bias in sex ratio from count data was eliminated with mark–recapture methods without the assumption of equal catchability between sexes. Photograph by Evan Pickett.
The impact of traffic noise on less-vocal mammals is poorly understood but the potential for negative effects could be great. In contrast to studies on vocal species, we found that traffic noise caused no increase in avoidance and was not a barrier to movements when the noise was isolated from any other disturbances associated with roads. However, two of the species studied showed possible habituation to the traffic noise, which could result in increased vulnerability to road mortality.
WR11171Effect of small-scale woodland clearing and thinning on vertebrate fauna in a largely intact tropical savanna mosaic
Habitat modification is a key threat to global biodiversity yet in largely uncleared environments the threat is thought to be benign. We examined the changes in bird, mammal and reptile communities due to small scale clearing and thinning in extensive tropical savannas and found birds and reptiles were most affected, and largely declined. As agricultural intensification occurs in northern Australia there will be increasing negative consequences on native fauna and pre-emptive conservation planning is needed. Photograph by Eric Vanderduys.