Temporal genetic structure and relatedness in the Tufted Duck Aythya fuligula suggests limited kin association in winter

Conspecific aggregation of waterfowl in winter is a common example of animal flocking behaviour, yet patterns of relatedness and temporal substructure in such social groups remain poorly understood even in common species. A previous study based on mark‐recapture data showed that Tufted Ducks Aythya fuligula caught on the same day were re‐caught together in subsequent winters more often than expected by chance, suggesting stable assortments of ‘socially familiar’ individuals between wintering periods. The genetic relationships within these social groups were not clear. Based on 191 individuals genotyped at 10 microsatellite markers, we investigated the temporal genetic structure and patterns of relatedness among wintering Tufted Ducks at Lake Sempach, Switzerland, in two consecutive winters. We found no evidence of genetic differentiation between temporal groups within or between winters. The average levels of relatedness in temporal groups were low and not higher than expected in random assortments of individuals. However, Mantel tests performed for each sex separately revealed significant negative correlations between the pairwise relatedness coefficients and the number of days between the capture dates of pairs of wintering Tufted Duck in males and females. This pattern suggests the presence of a small number of co‐migrating same‐sex sibling pairs in wintering flocks of Tufted Ducks. Our findings provide one of the first genetic analyses of a common duck species outside the breeding season and contribute to the understanding of social interactions in long‐distance migratory birds.     

Effects of tail autotomy on survival,growth and territory occupation in free‐ranging juvenile geckos (Oedura lesueurii)

Abstract Many animals autotomize their tails to facilitate escape from predators. Although tail autotomy can increase the likelihood of surviving a predatory encounter, it may entail subsequent costs, including reduced growth, loss of energy stores, a reduction in reproductive output, loss of social status and a decreased probability of survival during subsequent encounters with predators. To date, few studies have investigated the potential fitness costs of tail autotomy in natural populations. I investigated whether tail loss influenced survival, growth and territory occupation of juvenile velvet geckos Oedura lesueurii in a population where predatory snakes were common. During the 3‐year mark–recapture study, 32% of juveniles voluntarily autotomized their tails when first captured. Analysis of survival using the program mark showed that voluntary tail autotomy did not influence the subsequent survival of juvenile geckos. Survival was age‐dependent and was higher in 1‐year‐old animals (0.98) than in hatchlings (0.76), whereas recapture probabilities were time‐dependent. Growth rates of tailed and tailless juveniles were very similar, but tailless geckos had slow rates of tail regeneration (0.14 mm day⁻¹). Tail autotomy did not influence rock usage by geckos, and both tailed and tailless juveniles used few rocks as diurnal retreat sites (means of 1.64 and 1.47 rocks, respectively) and spent long time periods (85 and 82 days) under the same rocks. Site fidelity may confer survival advantages to juveniles in populations sympatric with ambush foraging snakes. My results show that two potential fitness costs of tail autotomy – decreased growth rates and a lower probability of survival – did not occur in juveniles from this population. However, compared with juveniles, significantly fewer adult geckos (17%) voluntarily autotomized their tails during capture. Because adults possess large tails that are used for lipid storage, the energetic costs of tail autotomy are likely to be much higher in adult than in juvenile O. lesueurii.     

Trap‐shyness subsidence is a threshold function of mark–recapture interval in brown mudfish Neochanna apoda populations

The influence of capture interval on trap shyness, and temperature, rainfall and drought on capture probability (p) in 827 brown mudfish Neochanna apoda was quantified using mark–recapture models. In particular, it was hypothesized that the loss of trapping memory in marked N. apoda would lead to a capture‐interval threshold required to minimize trap shyness. Neochanna apoda trap shyness approximated a threshold response to capture interval, declining rapidly with increasing capture intervals up to 16·5 days, after which p remained constant. Tests for detecting trap‐dependent capture probability in Cormack–Jolly–Seber models failed to detect trap shyness in N. apoda capture histories with capture intervals averaging 16 days. This confirmed the applicability of the 16 day capture‐interval threshold for mark–recapture studies. Instead, N. apoda p was positively influenced by water temperature and rainfall during capture. These results imply that a threshold capture interval is required to minimize the trade‐off between the competing assumptions of population closure and p homogeneity between capture occasions in closed mark–recapture models. Moreover, environmental factors that influence behaviour could potentially confound abundance indices, and consequently abundance trends should be interpreted with caution in the face of long‐term climate change, such as with global warming.     

Long-term population dynamics in a Mediterranean aquatic snake

A review of several long-term studies has recently suggested that snakes might be declining in large parts of the world. Additional data from other long-term studies are therefore urgently needed in order to assess the generalities of such suggested declines. Based on a 20-year study, we analyzed demographic data on adult dice snakes (Natrix tessellata) studied in central Italy between 1985 and 2004. Both male and female dice snakes were relatively long-lived, with no significant differences in longevity between the sexes. Individual males and females were observed over a maximum of 10 and 14 years, respectively. However, the among-year recapture rates between the year the snakes were initially captured and the subsequent year (i.e., year 1 to year 2) was significantly lower (45%) than the among-year recapture rates during subsequent years (74%; i.e., year 2 to year 3), suggesting that a large proportion of the snakes at first capture were in fact not resident within our study area, and hence many snakes were migrating in and out of our 2-km stream study site, with no inter-sexual difference in dispersal rates. Sex ratio was virtually equal if we consider the study period as a whole. Significant annual fluctuations were, however, observed through the study. In 1985–1990, 1993–1995, 1998 and 1999 the sex ratio was male-biased, whereas in 2000–2004 female-biased. In terms of both survival and recapture probabilities, model selection showed that Akaike’s information criterion favored the model incorporating body size, with the model incorporating year having an intermediate likelihood, and the model with sex included being the most disfavored. Total population number estimates suggest an average 86 adult individuals along the 2 km of stream with only minor annual variations. However, a significant decrease in the number of males occurred during the last 6 years of our study. Thus, further monitoring of this population is warranted in light of the decline of snake populations reported recently.     

Growth and reproduction of the sea snake,Emydocephalus ijimae,in the central Ryukyus,Japan: a mark and recapture study

A mark and recapture study was carried out for three years on a population of the Ijima's sea snake, Emydocephalus ijimae, in the coastal shallow water of Zamamijima Island, central Ryukyus, Japan. The relatively high recapture (47% of 167 marked snakes) suggests that E. ijimae is a particularly philopatric, sedentary species among the sea snakes. The sex ratio (male: female), approximately 1.6:1, significantly skewed from 1:1. The growth rate in SVL declined with growth, with females thoroughly growing better than males. Males and females were estimated to begin reproductive activity in the second or third summer and the third spring after birth, respectively. Frequency of female reproduction is guessed to vary from annual to biennial, or even less frequent.     

Scale‐dependent Orientation in Movement Paths: A Case Study of an African Viper

Decisions relating to the orientation of movement by animals and how this translates into movement patterns can occur at multiple spatial scales simultaneously, but this interaction is poorly understood for many groups of animals. Using the tracks left by moving snakes in their sandy habitat, we studied the movement paths of the African snake Bitis schneideri (Namaqua dwarf adder) for evidence of broad‐scale directional persistence and short‐range avoidance of exposure. Although snakes clearly displayed directional persistence, they preferentially moved to nearby shrubs, thereby minimizing exposure to solar and thermal radiation and/or predation. Thus, snakes made decisions relating to orientation at a minimum of two scales, the interaction of which resulted in snakes moving ≈17% (mean straightness index = 0.85) further than the simple broad‐scale straight‐line distance. We assert that the actual path chosen by moving snakes represents a trade‐off of various costs and risks that include risk of predation, exposure to the elements, time and energy expenditure. Our study highlights the need for cognizance of the possibility of the scale dependence of orientation and movement in studies of snake movement, and adds to a growing literature demonstrating previously unrecognized behavioural complexity in snakes.     

‘Heaven’ for serpents? A mark–recapture study of tiger snakes (Notechis scutatus) on Carnac Island,Western Australia

Abstract Animals resident on small islands provide excellent opportunities to carry out detailed mark–recapture studies. Populations are closed and ecosystems are often simpler than those of mainland sites. These factors enable the study of cryptic species that have otherwise been neglected. Snakes are notable for their secretive nature and, as a result, few natural populations have been accurately described through long‐term mark–recapture monitoring. A population of tiger snakes (Notechis scutatus) was studied on Carnac Island, a small limestone island (16 ha) off the coast of Western Australia. Population estimates show that snake density is very high, with more than 20 adult snakes per ha. This equates to a biomass of more than 100 kg of a top predator concentrated in a very small area. Such a high predator density can be explained because adult snakes feed mainly on chicks of nesting birds that breed in large colonies on Carnac but forage elsewhere. Substantial annual growth rates in body size in most individuals suggest that food availability is high on Carnac. Growth rates decreased more sharply in adult females than in males, whereas annual changes in body mass were similar in both sexes, probably because of the high energetic costs of reproduction experienced by females. Surprisingly, the sex ratio was highly biased, with males largely outnumbering females.     

Ecological and methodological factors affecting detectability and population estimation in elusive species

Although mark-recapture methods are among the most powerful tools for monitoring wildlife populations, the secretive nature of some species requires a comprehensive understanding of the factors that affect capture probability to maximize accuracy and precision of population parameter estimates (e.g., population size and survivorship). Here, we used aquatic snakes as a case study in applying rigorous mark-recapture methods to estimate population parameters for secretive species. Specifically, we used intensive field sampling and robust design mark-recapture analyses in Program MARK to test specific hypotheses about ecological and methodological factors influencing detectability of two species of secretive aquatic snakes, the banded watersnake (Nerodia fasciata), and the black swamp snake (Seminatrix pygaea). We constructed a candidate set of a priori mark-recapture models incorporating various combinations of time- and sex-varying capture and recapture probabilities, behavioral responses to traps (i.e., trap-happiness or trap-shyness), and temporary emigration, and we ranked models for each species using Akaike's Information Criterion. For both banded watersnakes and black swamp snakes we found strong support for time-varying capture and recapture probabilities and strong trap-happy responses, factors that can bias population estimation if not accommodated in the models. We also found evidence of sex-dependent temporary emigration in black swamp snakes. Our study is among the first comprehensive assessments of factors affecting detectability in snakes and provides a framework for studies aimed at monitoring populations of other secretive species. © 2010 The Wildlife Society.     

Synchrony in population counts predicts butterfly movement frequencies

1. Measuring functional connectivity, the ability of species to move between resource patches, is essential for conservation in fragmented landscapes. However, current methods are highly time consuming and expensive. 2. Population synchrony‐ the correlation in time series of counts between two long‐term population monitoring sites, has been suggested as a possible proxy measure of functional connectivity. To date, population synchrony has been shown to correlate with proxies for movement frequency such as the coverage of suitable habitat types in intervening landscapes, and also least cost distances around hostile land cover types. 3. This provides tentative evidence that synchrony is directly driven by movements of the focal species, but an alternative explanation is that these land cover types affect the movement of interacting species (e.g. natural enemies of the focal species) which can also drive synchronous population dynamics. Therefore, what is needed is a test directly relating population synchrony to movement frequencies of a focal species. 4. Here we use data from a 21 year mark‐release‐recapture study and show that population synchrony does indeed predict movements of a focal butterfly species Boloria eunomia (Esper). 5. There is growing evidence that population synchrony can be a useful conservation tool to measure functional connectivity.     

Combining capture–recapture data and known ages allows estimation of age‐dependent survival rates

In many animal populations, demographic parameters such as survival and recruitment vary markedly with age, as do parameters related to sampling, such as capture probability. Failing to account for such variation can result in biased estimates of population‐level rates. However, estimating age‐dependent survival rates can be challenging because ages of individuals are rarely known unless tagging is done at birth. For many species, it is possible to infer age based on size. In capture–recapture studies of such species, it is possible to use a growth model to infer the age at first capture of individuals. We show how to build estimates of age‐dependent survival into a capture–mark–recapture model based on data obtained in a capture–recapture study. We first show how estimates of age based on length increments closely match those based on definitive aging methods. In simulated analyses, we show that both individual ages and age‐dependent survival rates estimated from simulated data closely match true values. With our approach, we are able to estimate the age‐specific apparent survival rates of Murray and trout cod in the Murray River, Australia. Our model structure provides a flexible framework within which to investigate various aspects of how survival varies with age and will have extensions within a wide range of ecological studies of animals where age can be estimated based on size.     

Are we overestimating recovery of sturgeon populations using mark/recapture surveys?

Mark‐recaptures studies are often conducted to monitor trends in sturgeon populations. However, many of these studies experience low recapture rates, minimal movement between marking‐recapture phases suggesting that sturgeon as a group are not conducive to mark‐recapture techniques. In this study, two mark‐recapture studies that were conducted differently were reviewed. A study was conducted on the Mattagami River using random nets set throughout the study area in both the mark and recapture phases. The other study was conducted on Lake of the Woods and marked sturgeon in tributaries during the spawning period and the recapture phase within the lake and river during the summer foraging period using random nets sets. Sturgeon's conduciveness to mark‐recapture studies was assessed on the Mattagami River mark‐recapture study by determining detection probability (p) using a hierarchical Bayesian model with data augmentation among three effects: individual effect, temporal effects, and behavioural response effects. Detection probability was constant over individuals and temporally suggesting model M₀ (Otis, Burnham, White, & Anderson, 1978 ) was suitable for lake sturgeon in the Mattagami River; only the M₀ would converge for the Lake of the Woods study. For this study, the assumption that “all individuals have the same probability of being captured during the marking phase” was believed to have been violated given approximately 16%–20% of adult Lake Sturgeon from a population spawn within a year. A population estimate accounting for p provided estimates 56% lower than calculated by a Chapman modification of the Peterson estimate for a closed population. Bias was believed to have been introduced as the Lake of the Woods population did not account for the non‐spawning adults that were encountered during the recapture phase and not vulnerable during the initial marking phase. This was not unique to the Lake of the Woods study as other sturgeon studies, especially multi‐year, assumes a closed population which potentially biased estimates and overestimated their recovery.     

REPLICATED ORIGIN OF FEMALE‐BIASED ADULT SEX RATIO IN INTRODUCED POPULATIONS OF THE TRINIDADIAN GUPPY (POECILIA RETICULATA)

There are many theoretical and empirical studies explaining variation in offspring sex ratio but relatively few that explain variation in adult sex ratio. Adult sex ratios are important because biased sex ratios can be a driver of sexual selection and will reduce effective population size, affecting population persistence and shapes how populations respond to natural selection. Previous work on guppies (Poecilia reticulata) gives mixed results, usually showing a female‐biased adult sex ratio. However, a detailed analysis showed that this bias varied dramatically throughout a year and with no consistent sex bias. We used a mark‐recapture approach to examine the origin and consistency of female‐biased sex ratio in four replicated introductions. We show that female‐biased sex ratio arises predictably and is a consequence of higher male mortality and longer female life spans with little effect of offspring sex ratio. Inconsistencies with previous studies are likely due to sampling methods and sampling design, which should be less of an issue with mark‐recapture techniques. Together with other long‐term mark‐recapture studies, our study suggests that bias in offspring sex ratio rarely contributes to adult sex ratio in vertebrates. Rather, sex differences in adult survival rates and longevity determine vertebrate adult sex ratio.     

Once bitten twice shy: long‐term behavioural changes caused by trapping experience in willow warblers Phylloscopus trochilus

In dangerous situations, animals learn from experience to anticipate risks during similar subsequent occasions. Mist netting may represent just such a dangerous occasion and may serve as a tool to get insight into whether and how memorizing and recognition of the circumstances that form the prelude to a recapture can alter the animal's behaviour after capture, as well as it may affect the subsequent recapture rates. We used a playback lure to study the capture latency in willow warblers Phylloscopus trochilus, both without any and with a previous capture experience (either in the same year or in a previous one). We found increased response latencies to the playback lure for experienced males, compared to naive males. Naive males responded faster in the presence of a mist net than without a mist net; while experienced males tended to increase their response latencies. Individuals with between‐year capture experience showed exactly the same response pattern as individuals with a capture experience within the same year. These findings suggest that the birds may recall the capture event even a year later. It is very likely that the playback lure, with or without the net's presence, contributed significantly to the apparent risk of detection. We believe our study reveals that long‐lasting modifications of behaviour induced by capture and handling deserve further attention, as they might have a serious impact on the value of behavioural and ecological data, which is either based upon observing captured individuals and/or upon the recapture rates.     

Does rock disturbance by superb lyrebirds (Menura novaehollandiae) influence habitat selection by juvenile snakes?

Abstract: Vertebrates that destroy or disturb habitats used by other animals may influence habitat selection by sympatric taxa. In south‐east Australian forests, superb lyrebirds (Menura novaehollandiae) displace soil, leaf litter and rocks during their daily foraging activities. We investigated whether superb lyrebirds disturb small sandstone rocks that endangered broad‐headed snakes Hoplocephalus bungaroides and common small‐eyed snakes Cryptophis nigrescens use as diurnal thermoregulatory sites. To estimate the frequency of lyrebird rock disturbance, and to assess whether lyrebirds also attack small snakes, we placed 900 plasticine snake replicas under stones on rock and soil substrates along transects on three sandstone plateaux. Because juvenile snakes must select retreat sites that simultaneously allow them to thermoregulate and minimize predation risk, we quantified the thermal environments underneath stones on rock and soil substrates. During the 6‐week experiment, animals disturbed rocks on soil substrates twice as often (16.9%) as rocks lying on rock substrates (8.2%). Disturbed rocks were significantly smaller and lighter than undisturbed rocks on both substrates. Lyrebirds were the major agents of disturbance, and attacked 40% of snake models under disturbed rocks. Rocks on soil substrates conferred the greatest thermal benefits to snakes, but both species of snake avoided these microhabitats in the field. Instead, juvenile snakes selected rocks on rock substrates, and sheltered under stones that were too heavy for superb lyrebirds to disturb. By disturbing rocks over millennia, superb lyrebirds not only have shaped the physical landscape, but also may have exerted strong selection on habitat selection by sympatric snakes.     

Phenotypic divergence between seasnake (Emydocephalus annulatus) populations from adjacent bays of the New Caledonian Lagoon

Populations of widespread species often differ in phenotypic traits, although rarely in such a dramatic fashion as revealed by research on turtle‐headed seasnakes (Emydocephalus annulatus). These snakes are highly philopatric, with mark–recapture studies showing that the interchange of individuals rarely occurs even between two adjacent bays (separated by < 1.2 km) in Noumea, New Caledonia. Data on > 500 field‐captured snakes from these two bays reveal significant differences between these two locations in snake morphology (mean body length, relative tail length, head shape), colour, ecology (body condition, growth rate, incidence of algal fouling), behaviour (antipredator tactics), and locomotor performance. For some traits, the disparity was very marked (e.g. mean swimming speeds differed by > 30%). The causal bases for these phenotypic divergences may involve founder effects, local adaptation, and phenotypic plasticity. The spatial divergence in phenotypic traits offers a cautionary tale both for researchers (sampling of only a few populations may fail to provide a valid overview of the morphology, performance, and behaviour of a species) and managers (loss of local populations may eliminate distinctive genetic variation). © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ??, ??–??.     

Isotopic signatures, foraging habitats and trophic relationships between fish and seasnakes on the coral reefs of New Caledonia

A predator’s species, sex and body size can influence the types of prey that it consumes, but why? Do such dietary divergences result from differences in foraging habitats, or reflect differential ability to locate, capture or ingest different types of prey? That question is difficult to answer if foraging occurs in places that preclude direct observation. In New Caledonia, amphibious sea kraits (Laticauda laticaudata and L. saintgironsi) mostly eat eels—but the species consumed differ between snake species and vary with snake body size and sex. Because the snakes capture eels within crevices on the sea floor, it is not possible to observe snake foraging on any quantitative basis. We used stable isotopes to investigate habitat-divergence and ontogenetic shifts in feeding habits of sympatric species of sea kraits. Similarities in δ15 N (~10.5‰) values suggest that the two snake species occupy similar trophic levels in the coral-reef foodweb. However, δ13C values differed among the eight eel species consumed by snakes, as well as between the two snake species, and were linked to habitat types. Specifically, δ13C differed between soft- vs. hard-substrate eel species, and consistently differed between the soft-bottom forager L. laticaudata (~ −14.7‰) and the hard-bottom forager L. saintgironsi (~ −12.5‰). Differences in isotopic signatures within and between the two sea krait species and their prey were consistent with the hypothesis of habitat-based dietary divergence. Isotopic composition varied with body size within each of the snake species and varied with body size within some eel species, reflecting ontogenetic shifts in feeding habits of both the sea kraits and their prey. Our results support the findings of previous studies based on snake stomach contents, indicating that further studies could usefully expand these isotopic analyses to a broader range of trophic levels, fish species and spatial scales.     

Experimental Validation of Sex Differences in Spatial Behavior Patterns of Free‐Ranging Snakes: Implications for Social Interactions

Social interactions often play a significant role in determining patterns of spatial use. Although snakes are generally thought of as asocial, recent spatial dispersion studies suggest that the spatial ecology of snakes may be more strongly influenced by social interactions than previously thought. We investigated the spatial behavior patterns of a western cottonmouth (Agkistrodon piscivorus) population in east Texas by uniquely combining radio‐telemetry studies on free‐ranging snakes with experimental arena trials with captive individuals from the same population. Observations from the radio‐telemetry study on free‐ranging A. piscivorus indicated that females were more gregarious than males. In the follow‐up study, spatial dispersion data from captive snakes maintained in experimental field arenas yielded similar results to spatial behavior patterns of free‐ranging individuals. When compared to random experimental controls, these data suggest that observed spatial behavior patterns are related to mechanisms associated with both active avoidance among males and conspecific attraction among females. In addition to uniquely combining both free‐ranging and captive observations, this is the first snake study to demonstrate sex differences with both of these divergent (attraction and avoidance) spatial patterns within a single population. Thus, similar to other vertebrate groups, a growing body of literature suggests that social interactions in snakes should be strongly considered in interpretations of spatial ecology and behavior.     

Validation of back‐calculated body lengths and timing of growth mark deposition in Hawaiian green sea turtles

Somatic growth rate data for wild sea turtles can provide insight into life‐stage durations, time to maturation, and total lifespan. When appropriately validated, the technique of skeletochronology allows prior growth rates of sea turtles to be calculated with considerably less time and labor than required by mark‐–recapture studies. We applied skeletochronology to 10 dead, stranded green turtles Chelonia mydas that had previously been measured, tagged, and injected with OTC (oxytetracycline) during mark–recapture studies in Hawaii for validating skeletochronological analysis. We tested the validity of back‐calculating carapace lengths (CLs) from diameters of LAGs (lines of arrested growth), which mark the outer boundaries of individual skeletal growth increments. This validation was achieved by comparing CLs estimated from measurements of the LAG proposed to have been deposited closest to the time of tagging to actual CLs measured at the time of tagging. Measureable OTC‐mark diameters in five turtles also allowed us to investigate the time of year when LAGs are deposited. We found no significant difference between CLs measured at tagging and those estimated through skeletochronology, which supports calculation of somatic growth rates by taking the difference between CLs estimated from successive LAG diameters in humerus bones for this species. Back‐calculated CLs associated with the OTC mark and growth mark deposited closest to tagging indicated that annual LAGs are deposited in the spring. The results of this validation study increase confidence in utilization of skeletochronology to rapidly obtain accurate age and growth data for green turtles.     

Common species affects the utility of non‐invasive genetic monitoring of a cryptic endangered mammal: The bridled nailtail wallaby

Non‐invasive methods of monitoring wild populations (such as genotyping faeces or hair) are now widely used and advocated. The potential advantages of such methods over traditional direct monitoring (such as live capture) are that accuracy improves because sampling of non‐trappable individuals may be possible, species in difficult and remote terrain can be surveyed more efficiently, and disturbance to animals is minimal. Few studies have assessed the effects of interactions between species on remote sampling success. We test the use of non‐invasive monitoring for the cryptic, forest‐dwelling, solitary and endangered bridled nailtail wallaby (Onychogalea fraenata) that is sympatric with the ecologically similar and more common black‐striped wallaby (Macropus dorsalis). Six types of hair traps were tested for 3668 trap days, and hairs were caught with about a 10% success rate. Camera traps showed that baited hair traps targeted both wallaby species. We microscopically identified hair as bridled nailtail wallaby or black‐striped wallaby. We compared these hairs and their genotypes (using seven microsatellite loci) with known bridled nailtail wallaby hairs and genotypes derived from animal trapping. Trapped bridled nailtail wallaby hairs had characteristics that could be mistaken for black‐stripe wallaby hairs; characteristics were not diagnostic. Genetic assignment tests consistently differentiated the known bridled nailtail wallaby samples from identified black‐striped wallaby samples, however genetic overlap between most of the microsatellite markers means that they are not suitable for species identification of single samples, with the possible exception of the microsatellite locus B151. With similar trapping effort and within the same area, live‐capture mark‐recapture techniques estimated 40–60 individuals and non‐invasive methods only detected 14 genotypes. A species‐specific genetic marker would allow more efficient targeting of bridled nailtail wallaby samples and increase capture rates.     

Population ecology of the velvet gecko,Oedura lesueurii in south eastern Australia: Implications for the persistence of an endangered snake

Abstract Ecological specialization, such as major dependence upon a single‐prey species, can render a predator taxon vulnerable to extinction. In such cases, understanding the population dynamics of that prey type is important for conserving the predator that relies upon it. In eastern Australia, the endangered broad‐headed snake Hoplocephalus bungaroides feeds largely on velvet geckos (Oedura lesueurii). We studied growth, longevity and reproduction in a population of velvet geckos in Morton National Park in south‐eastern Australia. We marked 458 individual geckos over a 3‐year period (1992–1995) and made yearly visits to field sites from 1995–2006 to recapture marked individuals. Female geckos grew larger than males, and produced their first clutch at age 4 years. Males can mature at 2 years, but male–male combat for females probably forces males to delay reproduction until age 3 years. Females lay a single clutch of two eggs in communal nests in November, and up to 22 females deposited eggs in a single nest. Egg hatching success was high (100%), and juveniles had high survival (76%) during their first 6 months of life. Velvet geckos are long‐lived, and the mean age of marked animals recaptured after 1995 was 6.1 years (males) and 8.4 years (females). Older females (7.5–9.5 years) were all gravid when last recaptured. Like other temperate‐climate gekkonids, O. lesueurii has a ‘slow’ life history, and population viability could be threatened by any factors that increase egg or adult mortality. Two such factors – the removal of ‘bush rocks’ for urban gardens, and the overgrowth of rock outcrops by vegetation – could render small gecko populations vulnerable to extinction. In turn, the reliance of predatory broad‐headed snakes on this slow‐growing lizard species may increase its vulnerability to extinction.