Skink Abundance Research Articles

Landscape scale control of selected mammalian predators fails to protect lizards

Invasive mammalian predators are a global biodiversity problem, particularly in archipelagos in which native fauna evolved in isolation from mammals. Landscape scale management of selected invasive mammalian predators is occurring across Aotearoa New Zealand to protect vulnerable forest birds and bats. In temperate southern beech forests, both predator irruptions and the timing of predator control is driven by mast seeding of beech trees. Relationships between predators targeted in this control, other invasive mammalian predators and other native taxa, particularly lizards and invertebrates, are poorly understood. We monitored southern grass skinks in the Eglinton Valley, Fiordland from 2009 to 2020 alongside monitoring of predators (stoats, rats and mice) in a system where predator control occurred in response to mast seeding. We evaluated relationships between skink abundance and abundance of rats (targeted in predator control operations) and mice (which also prey on small vertebrates like lizards, but are not controlled). Skink abundance declined over time and was negatively correlated with mouse abundance, but not correlated with rat abundance. Current landscape predator control to protect forest birds and bats is likely insufficient to protect ground-dwelling lizards, and may actually be detrimental to lizard populations if controlling the other predators contributes to a mesopredator release of mice. Mice are significant predators of a range of small vertebrates and large invertebrates, yet research into the sustainable suppression of mice to benefit vulnerable native populations is lacking. We strongly advocate for such research in order to deliver conservation management that benefits the full suite of biodiversity.

Estimating population parameters for the Critically Endangered Bermuda skink using robust design capture–mark–recapture modelling

AbstractReliably estimating population parameters for highly secretive or rare animals is challenging. We report on the status of the two largest remaining populations of the Critically Endangered Bermuda skink Plestiodon longirostris, using a robust design capture–mark–recapture analysis. Skinks were tagged with passive integrated transponders on two islands and captured on 15 sampling occasions per year over 3 years. The models provided precise estimates of abundance, capture and survival probabilities and temporary emigration. We estimated skink abundance to be 547 ± SE 63.5 on Southampton Island and 277 ± SE 28.4 on Castle Island. The populations do not appear to be stable and fluctuated at both sites over the 3-year period. Although the populations on these two islands appear viable, the Bermuda skink faces population fluctuations and remains threatened by increasing anthropogenic activities, invasive species and habitat loss. We recommend these two populations for continued monitoring and conservation efforts.

Predicting the occurrence of an endangered reptile based on habitat attributes

The endangered Blue Mountains water skink (Eulamprus leuraensis), a habitat specialist known from approximately 60 threatened highland peat swamps, is the sole endemic vertebrate of the Blue Mountains region, Australia. We quantified the species’ habitat associations by surveying 10 such swamps annually for three years. We scored habitat features and trapped skinks, comparing habitat attributes of trap sites where skinks were and were not captured. The distribution of E. leuraensis was non-random: skinks were found at sites with high values for some variables (soil moisture, live vegetation, surface water, understorey density and numbers of burrows) and low values for others (dead vegetation, logs, rocks, bare ground, canopy cover, sunlight penetration and numbers of invertebrates), and were mostly found in sites that were close to surface water and far from trees and logs. Eulamprus leuraensis is widely distributed within swamps, with weak associations between microhabitat variation and skink presence. Skink abundance and mean body size were highest within swamp centres, decreasing towards the margins; larger skinks were found closer to water, gravid female skinks were found at wetter sites and juveniles occupied marginal habitat. Skinks were rarely recaptured >10 m from their original site, with adult males travelling further than adult females and juveniles. We developed a quick field detection method for managers to assess the likely presence of E. leuraensis using two habitat attributes (soil moisture and burrow abundance). We mapped the species’ known and predicted habitat using GIS spatial layers, including locality records, associated vegetation communities and digital elevation models.

Vulnerability of Skinks to Predation by Introduced Mongoose in the Fiji Islands

Skinks are successful colonizers and are commonly found throughout the Pacific islands, but introduced predators such as mongoose are known to threaten their survival. The two most abundant skinks found within the Fiji Islands are Emoia cyanura and E. impar. Abundance of these species encountered during visual transect counts on 16 islands within four habitats formed the basis of this study. Half of these islands had mongoose present, and the other half were known to be mongoose free. Our results showed that skink abundance under mongoose-free conditions was approximately five times higher than when mongoose were present. We conclude that it is very likely that mongoose severely supress even commonly found skink species across all the habitat types on these small islands, and it is likely that they impact even more severely on rarer species. Conservation actions that could protect these native species include biosecurity mechanisms to prevent secondary invasion of introduced predators, habitat protection and management, and captive rearing programs. Failure to implement such actions is likely to result in even common species being at risk of extirpation.

At home with the birds:Kalahari tree skinks associate with sociable weaver nests despiteAfrican pygmy falcon presence

AbstractThe way in which animals use habitat can affect their access to key resources or how they are buffered from environmental variables such as the extreme temperatures of deserts. One strategy of animals is to modify the environment or take advantage of structures constructed by other species. The sociable weaver bird (Philetairus socius) constructs enormous colonial nests in trees. These nests are frequented by Kalahari tree skinks (Trachylepis spilogaster) and the two species coexist over a large portion of theKalahariDesert inSouthAfrica. We tested whether skinks were more abundant in trees containing sociable weaver nests and asked whether the physical features of trees were important predictors of skink abundance. We then focused on potential costs of this association by examining the relationship between skink abundance and the presence of a potential predator, the pygmy falcon (Polihierax semitorquatus), which exclusively uses weaver nest colonies for roosting and nesting. Finally, we simulated a predatory threat to determine if skinks assess risk differently if a weaver nest is present. We found a significant positive association between the presence of weaver nests and skink abundance. In the absence of nests, the type of tree did not influence skink abundance. Skinks used weaver nests and were more likely to perch on the nest than the tree. When threatened with predation, skinks preferred to take refuge in nests. Surprisingly, the presence of nesting pygmy falcons in nests did not influence skink abundance, perhaps because of the abundance of nearby refuges within nests, tree crevices, or in debris at the tree base. We suggest that sociable weaver nests provide multiple benefits to skinks including lowered predation risk, thermal refuges and greater prey availability, although this requires experimental testing. In the current era of global climate change, sociable weaver nests may become a crucial resource for skinks seeking refuge as theKalahari climate warms.

Impacts of introduced European hedgehogs on endemic skinks and weta in tussock grassland

Context Control of introduced pest species is based on the premise that there is a relationship between pest abundance and impact, but this relationship is rarely defined. Aim We investigated the impacts of introduced European hedgehogs (Erinaceus europaeus) on two species of small endemic skink (Oligosoma spp.) and flightless, nocturnal endemic orthopteran ground weta (Hemiandrus spp.), using an enclosure-based experimental manipulation of hedgehog density in tussock grasslands in the South Island of New Zealand. Methods We used capture–mark–recapture methods to estimate the densities of skinks before and after exposure to a range of hedgehog densities over a 3-month period and also compared changes in indices of abundance of skink demographic groups and ground weta. Key results Faecal analysis confirmed that hedgehogs consumed skinks and invertebrates in the enclosures. The proportional change between capture sessions in numbers of captured juvenile McCann’s skinks (O. maccanni) declined with increasing hedgehog density. Similarly, the proportional change in the numbers of ground weta encountered in pitfall traps showed a highly significant negative relationship with increasing hedgehog density. Total species abundances and numbers in other demographic skink groups did not change significantly in relation to hedgehog density. For overall skink abundance estimates, there was an apparent trend suggesting that changes in abundance were more negative with increasing hedgehog density, but this did not reach statistical significance for either skink species. Conclusions Our results confirmed that hedgehogs are important predators of small native fauna, but suggested that highly abundant prey populations may be buffered against significant impacts. Implications Less abundant prey and some demographic groups within populations, however, may be at significant risk from hedgehog predation.

Bringing forward the benefits of coarse woody debris in ecosystem recovery under different levels of grazing and vegetation density

Restoration projects often do not effectively restore some key biological resources that take time, often centuries, to accumulate. Such resources are often characteristic of ‘natural’ ecosystems and are critical to successful ecosystem recovery. Deadwood or ‘coarse woody debris’ (CWD) is one such example. Coarse woody debris is depauperate in many of the world’s ecosystems due to stand structural simplification through vegetation clearing, logging and grazing. The lag time in the natural accumulation of CWD can be a major barrier to their effective ecological restoration in the short term. We examined the effect of experimentally adding CWD, in four different treatments, on reptile abundance in temperate woodlands in south-eastern Australia – one of the most highly degraded vegetation types on the continent. We then investigated the influence that varying grazing pressure and vegetation density had on those effects. We examined three key questions: (1) Does the addition of CWD change overall reptile abundance over a 4year period? (2) Does existing vegetation density or kangaroo grazing effect reptile response? (3) Is there evidence of high order interaction effects between CWD, kangaroo grazing and vegetation density on reptile response? Adding CWD increased reptile abundance significantly after only 4years. The spatial pattern of CWD distribution also significantly affected reptile abundance. The location where CWD was added also was important, with open and mid-dense vegetation gaining the highest number of small skinks compared to control sites. Reduction of grazing was the most effective way of increasing small skink abundance in high density vegetation. Open areas gained most from the addition of CWD where high kangaroo grazing occurred. We conclude that adding CWD can short-cut a 100–200year barrier to ecosystem restoration. By distributing CWD in particular patterns and places in the landscape, and in combination with different grazing levels, conservation managers can improve effectiveness of restoration programs.

Conservation status, threats and management options for the Open Bay Island skink (Oligosoma taumakae)

The Open Bay Islands are a Māori-owned Wildlife Refuge located in South Westland (South Island) and support two of the rarest lizard species in New Zealand: the Open Bay Island skink and the Open Bay Island gecko. Both species have been assigned a threat status of Nationally Critical – the highest priority for conservation action. The terrestrial and diurnal habits of the skink make it particularly vulnerable to predation by wēkā, a flightless rail native to New Zealand but introduced to the Open Bay Islands c. 100 years ago. Here, we present results from a 5-day survey of the two main islands (14.7-ha Taumaka and 2.2-ha Popotai) and consider options for reducing the negative impacts of wēkā on skinks and other terrestrial fauna (wēkā removal, exclosure fencing and refuge supplementation; all subject to iwi approval). In total, 19 skinks were caught over 125 trap-days. The majority (16 individuals) were caught on Popotai Island, from which skinks had not been previously recorded. We conclude that removing wēkā from both islands is the only option guaranteed to increase skink abundance, with collateral benefits to other terrestrial fauna on the Open Bay Islands.

Tropical reptiles in pine forests: Assemblage responses to plantations and plantation management by burning

Worldwide, the land area devoted to timber plantations is expanding rapidly, especially in the tropics, where reptile diversity is high. The impacts of plantation forestry and its management on native species are poorly known, but are important, because plantation management goals often include protecting biodiversity. We examined the impact of pine ( Pinus caribaea ) plantations, and their management by fire, on the abundance and richness of reptiles, a significant proportion of the native biodiversity in tropical northern Australia, by (i) comparing abundance and diversity of reptiles among pine plantations (on land cleared specifically for plantation establishment), and two adjacent native forest types, eucalypt and Melaleuca woodlands, and (ii) comparing reptile abundance and richness in pine forest burnt one year prior to the study to remove understorey vegetation with pine forest burnt two years prior to the study. We also examined the influence of fire on reptile assemblages in native vegetation, by comparing eucalypt woodland burnt two years prior to the study and unburnt for eight years. To quantify mechanisms driving differences in reptile richness and abundance among forest types and management regimes, we measured forest structure, the temperatures used by reptiles (operative temperature) and solar radiation, at replicate sites in all forest types and management regimes. Compared to native forests, pine forests had taller trees, lower shrub cover in the understorey, more and deeper exotic litter (other than pine), and were cooler and shadier. Reptile assemblages in pine forests were as rich as those in native forests, but pine assemblages were composed mainly of species that typically use closed-canopy rainforest and prefer cooler, shadier habitats. Burning did not appear to influence the assemblage structure of reptiles in native forest, but burning under pine was associated with increased skink abundance and species richness. Burned pine was not warmer or sunnier than unburned pine, a common driver of reptile abundance, so the shift in lizard use after burning may have been driven by structural differences in understorey vegetation, especially amounts of non-native litter, which were reduced by burning. Thus, burning for management under pine increased the abundance and richness of lizard assemblages using pine. Pine plantations do not support the snake diversity common to sclerophyllous native forests, but pine may have the potential to complement rainforest lizard diversity if appropriately managed.

Influence of woodland remnant edges on small skinks (Richmond, New South Wales)

Abstract Habitat fragmentation due to clearing often results in an increase in edge areas compared with overall remnant size, but there are limited data on the influence of increased edge areas on generalist species. Therefore, the abundance of small (<55 mm) generalist scinid lizards in small woodland remnants of the Cumberland Plain (western Sydney, Australia) was compared. Using pitfall trapping and points of transect survey techniques, three species were encountered: Lampropholis guichenoti, Lampropholis delicata and Cryptoblepharus virgatus. The abundance and diversity of these skinks differed significantly between edge and core areas; fewer individuals were encountered on the edge of the remnants than in core sites. Cryptoblepharus virgatus was only observed in edge sites where L. guichenoti made up the greatest skink abundance. In contrast, L. delicata abundance was greatest at core sites. There was also a significant difference between the edge and core with respect to the size structure of the L. guichenoti population. Larger numbers of subadults were observed in the edge sites, whereas there were significantly fewer adults and juveniles in these areas. Habitat characteristics did not account for the skink distribution observed.

Influence of woodland remnant edges on small skinks (Richmond, New South Wales)

Abstract Habitat fragmentation due to clearing often results in an increase in edge areas compared with overall remnant size, but there are limited data on the influence of increased edge areas on generalist species. Therefore, the abundance of small (&lt;55 mm) generalist scinid lizards in small woodland remnants of the Cumberland Plain (western Sydney, Australia) was compared. Using pitfall trapping and points of transect survey techniques, three species were encountered: Lampropholis guichenoti, Lampropholis delicata and Cryptoblepharus virgatus. The abundance and diversity of these skinks differed significantly between edge and core areas; fewer individuals were encountered on the edge of the remnants than in core sites. Cryptoblepharus virgatus was only observed in edge sites where L. guichenoti made up the greatest skink abundance. In contrast, L. delicata abundance was greatest at core sites. There was also a significant difference between the edge and core with respect to the size structure of the L. guichenoti population. Larger numbers of subadults were observed in the edge sites, whereas there were significantly fewer adults and juveniles in these areas. Habitat characteristics did not account for the skink distribution observed.

Shrinking forest shrinks skink: morphological change in response to rainforest fragmentation in the prickly forest skink ( Gnypetoscincus queenslandiae)

Large-scale fragmentation of rainforest occurred on the Atherton Tableland in the Australian Wet Tropics from 50 to 100 years ago, leaving numerous fragments of varying sizes. Eleven fragments (from <1 to 75 ha in area) and eight continuous-forest sites were studied to assess the effects of fragmentation on the morphology and demography of the rainforest-endemic prickly forest skink ( Gnypetoscincus queenslandiae). Skink abundance (number of individuals captured per hour of search effort) was significantly greater in continuous forest than in forest fragments. Moreover, both skink abundance and the availability of decaying logs, which provide key habitat for this species, increased with fragment area. Fragments contained a smaller proportion of adults, and individuals in fragments were smaller on average for all measured morphological features, than those in continuous forest. Thus, although prickly forest skinks appear to be maintaining populations in rainforest remnants, they are nonetheless being affected by fragmentation. These demographic and morphological changes may be caused by alterations in habitat and prey availability and/or by microclimatic changes associated with edge effects.

The Role of Guesswork in Conserving the Threatened Sand Skink

Because we possess little understanding of what constitutes optimal habitat for the threatened sand skink, any individual charged with choosing among habitat fragments to promote recovery of the species will need to employ some guesswork. We examined the relative values of employing two kinds of guesswork, “uneducated guesswork,” from literature descriptions of optimal habitat, and “educated guesswork,” from expert judgments of optimal habitat. The rank order of seven areas of scrub habitat in central Florida based on abundance of the sand skink (Neoseps reynoldsi) was compared with the rank order of the areas based on literature descriptions and on expert judgments. Ranks of areas based on expert judgments predicted ranks of areas based on sand skink abundance much better than did ranks of areas based on literature descriptions. Our results show, on the one hand, how uneducated guesswork could challenge recovery of the sand skink and, on the other hand, how educated guesswork could support its recovery.

Effects of human disturbance on five-lined skink, Eumeces fasciatus, abundance and distribution

We studied the effects of human disturbance on five-lined skinks at Point Pelee National Park, Canada. Surveys indicated low skink abundance and a lack of woody debris in areas heavily used by humans and a downward population trend concurrent with high disturbance levels. Skinks preferentially used large moderately decayed logs and boards for refuge sites. Human disturbance resulted in degradation and removal of debris. Degradation by fragmentation and accelerated decay resulted in decreased quality of available debris. To test the hypothesis that skink absence in human high-use areas was caused by a lack of suitable debris, we placed artificial microhabitats in areas which previously lacked woody debris and skinks. Experimental debris were colonized quickly and heavily used despite high disturbance rates. Skinks are resilient to minor disturbances such as displacements, but not to removal or degradation of debris. Essential microhabitat features must be actively preserved as well as suitable habitat to ensure the conservation of target species.

Habitat Use and Basking Site Selection in the Water Skink, Eulamprus quoyii

The water skink (Eulamprus quoyii) tends to be restricted to creekside habitats and moist areas. Factors correlated with the relative abundance of E. quoyii were demonstrated using multivariate techniques. Rocky, open creeks supported higher densities of E. quoyii than those in cool forests or thick vegetation, where basking sites were fewer. Rocks correlated well with presence or absence of skinks. Non-random utilization of basking sites occurred in sites where skinks were rare, in contrast to random utilization of basking sites where skinks were common. Basking sites and their associated environmental cues may influence skink abundance. Use of rocky basking sites was associated with substrate temperatures of ca. 29 C, similar to the preferred body temperature (PBT) of 28 C chosen in a thermal gradient. Lighting conditions had no effect on PBT, although a significant drop in PBT to 24 C occurred when skinks were deprived of water. Organisms are non-randomly distributed in space, and patchiness is often attributed to hab- itat selection. An optimal strategy for habitat selection should involve response to indicators of primary limiting variables (Heatwole, 1977;