Demographic response of the Gambian Gerbil to seasonal changes in Savannah fallow fields

The Savannah gerbil, Gerbilliscus gambianus (Muridae: Gerbillinae) is important to the ecological relations of the dry grassland ecosystem of West Africa, as well as, being a zoonotic agent of human diseases and potential crop pest. We examined the impact of seasonal changes on the population dynamics of G. gambianus in northern Nigeria, by completing population estimates using capture–mark–recapture (CMR) and indirect population density indices (PDI) methods. The latter included fecal pellet counts and limited spotlightening. During 1990–1992 we collected both CMR and PDI data, and established their relationship by regression, thus calibrating the PDI values to CMR estimator. We also completed a separate, PDI only, study during 2015–2017, and estimated monthly densities indirectly by toning the PDI values to population sizes in the CMR estimator. The lowest declines (<20 gerbils ha−1) were in mid rains (July–August), and highest increases (>90 gerbils ha−1) were after the rains (October–January). Seasonal effects on densities were significant during 1990–1992 but not during 2015–2017. There were improved survival rates for both adults (0.95) and young (0.83), adult capture probability (0.56), and mean monthly recruitment of young (23) after the rains. There was no significant change in the overall population dynamic pattern of G. gambianus over a 25-year period. Because G. gambianus did not maintain colonies inside farmlands cultivated by rain or irrigation, and its tendency for large population drops in mid-rains, we are in doubt of its potential as crop pest in northern Nigeria.

Estimating macropod grazing density and defining activity patterns using camera-trap image analysis

Context When measuring grazing impacts of vertebrates, the density of animals and time spent foraging are important. Traditionally, dung pellet counts are used to index macropod grazing density, and a direct relationship between herbivore density and foraging impact is assumed. However, rarely are pellet deposition rates measured or compared with camera-trap indices. Aims The aims were to pilot an efficient and reliable camera-trapping method for monitoring macropod grazing density and activity patterns, and to contrast pellet counts with macropod counts from camera trapping, for estimating macropod grazing density. Methods Camera traps were deployed on stratified plots in a fenced enclosure containing a captive macropod population and the experiment was repeated in the same season in the following year after population reduction. Camera-based macropod counts were compared with pellet counts and pellet deposition rates were estimated using both datasets. Macropod frequency was estimated, activity patterns developed, and the variability between resting and grazing plots and the two estimates of macropod density was investigated. Key Results Camera-trap grazing density indices initially correlated well with pellet count indices (r2=0.86), but were less reliable between years. Site stratification enabled a significant relationship to be identified between camera-trap counts and pellet counts in grazing plots. Camera-trap indices were consistent for estimating grazing density in both surveys but were not useful for estimating absolute abundance in this study. Conclusions Camera trapping was efficient and reliable for estimating macropod activity patterns. Although significant, the relationship between pellet count indices and macropod grazing density based on camera-trapping indices was not strong; this was due to variability in macropod pellet deposition rates over different years. Time-lapse camera imagery has potential for simultaneously assessing herbivore foraging activity budgets with grazing densities and vegetation change. Further work is required to refine the use of camera-trapping indices for estimation of absolute abundance. Implications Time-lapse camera trapping and site-stratified sampling allow concurrent assessment of grazing density and grazing behaviour at plot and landscape scale.

Habitat-specific and season-specific faecal pellet decay rates for five mammalian herbivores in south-eastern Australia

The accuracy of population abundance estimates of mammalian herbivores from faecal pellet counts is potentially affected by pellet decay. We collected fresh pellet groups from hog deer (Axis porcinus), European rabbit (Oryctolagus cuniculus), eastern grey kangaroo (Macropus giganteus), swamp wallaby (Wallabia bicolor) and common wombat (Vombatus ursinus) (n = 300 per species) at Wilsons Promontory National Park, Victoria, Australia. We deposited five pellet groups per species per month within each of five vegetation types in the park, then monitored pellet group decay over 24 months. We demonstrate that age estimation of pellet groups was inaccurate and is unlikely to improve the efficiency of pellet counts. We present habitat- and species-specific estimates of pellet and pellet group decay using two measures: decay rate (the proportion of pellets surviving per unit of time); and mean time to decay. We explain how our data can be used to optimise faecal pellet count design, and to improve the accuracy of both indices and estimates of abundance from pellet counts. The variability observed in the decay of pellet groups among vegetation types, and for species among seasons, suggests that caution should be used if applying pellet decay rates over long time-frames or to locations with differing environmental conditions.

Habitat preference of the endangered Ethiopian walia ibex (Capra walie) in the Simien Mountains National Park, Ethiopia

Walia ibex (Capra walie) is an endangered and endemic species restricted to the Simien Mountains National Park, Ethiopia. Recent expansion of human populations and livestock grazing in the park has prompted concerns that the range and habitats used by walia ibex have changed. We performed observations of walia ibex, conducted pellet counts of walia ibex and livestock, and measured vegetation and classified habitat characteristics at sample points during wet and dry seasons from October 2009 to November 2011. We assessed the effect of habitat characteristics on the presence of pellets of walia ibex, and then used a spatial model to create a predictive map to determine areas of high potential to support walia ibex. Rocky and shrubby habitats were more preferred than herbaceous habitats. Pellet distribution indicated that livestock and walia ibex were not usually found at the same sample point (i.e. 70% of quadrats with walia pellets were without livestock droppings; 73% of quadrats with livestock droppings did not have walia pellets). The best model to describe probability of presence of walia pellets included effects of herb cover (β = 0.047), shrub cover (β = 0.030), distance to cliff (β = –0.001), distance to road (β = 0.001), and altitude (β = 0.004). Walia ibexes have shifted to the eastern, steeper areas of the park, appearing to coincide with the occurrence of more intense, human–related activities in lowlands. Our study shows the complexities of managing areas that support human populations while also serving as a critical habitat for species of conservation concern.

Factors affecting the distribution and abundance of the Endangered volcano rabbit Romerolagus diazi on the Iztaccihuatl volcano, Mexico

The volcano rabbit Romerolagus diazi is an Endangered species endemic to Mexico, with a range of < 400 km2. We investigated threats from destruction, fragmentation and degradation of habitat, hunting, and cattle grazing intensity in relation to the distribution and abundance of the volcano rabbit on the Iztaccihuatl volcano. Faecal pellet counts were taken as a proxy for rabbit abundance in 1,718 random 0.2 m2 quadrats at 859 sampling points along 25 transects, covering an area of c. 100 km2 at altitudes of 3,400–4,000 m. Presence of the species was significantly associated with absence of closed forest, absence of long grass types (not bunchgrass), shallow inclines, absence of cattle grazing, lower altitude, low hunting pressure (measured by proximity to ranger station), absence of bare ground and, contrary to previous findings, increased frequency of fire. The species was significantly more abundant in habitats with a greater percentage cover of zacaton (bunchgrass) and short grass types. It was significantly less abundant in areas with more hunting (measured by proximity to ranger station) and cattle grazing. Key conservation priorities are therefore the protection of the subalpine zacaton bunchgrass-dominated habitat type, strict enforcement of hunting laws and the removal of livestock from relevant national park boundary areas. However, the results suggest that frequent fires have a significant positive effect on the occurrence of the volcano rabbit as a result of habitat improvement and this is often a consequence of anthropogenic management of land for cattle grazing.

A rapid survey method for estimating population density of European rabbits living in native vegetation

European rabbits are severe environmental pests in Australia but reporting of density-damage relationships has been hindered by a lack of simple methods to estimate the density of rabbit populations in native vegetation. A methodology for quantifying rabbit densities suitable for use in sparse populations of rabbits in conjunction with surveys of the condition of native vegetation is proposed. Dung pellets were counted in 11 629 regularly-spaced quadrats of 0.1 m2 in semiarid, coastal and cool-temperate areas of southern Australia. Mean pellet counts in latrines and the relationship between dung counts outside of latrines and the proportion of quadrats falling on latrines were quantified. This allowed density of dung pellets to be estimated by using a correction factor for latrines instead of attempting to count all pellets within quadrats that included parts of latrines. Rabbit density was calculated from pellet density based on mean pellet size, pellet breakdown rate and estimates of rabbits’ dry matter intake and digestive efficiency. Results were validated against estimates of rabbit density from long-term studies using a combination of spotlight transect counts and burrow entrance counts. The proposed methodology allows estimates of rabbit density in native vegetation to be obtained from just a few hours work and can be used in conjunction with surveys of the condition of native vegetation to quantify rabbit impacts. This methodology is seen as particularly useful in providing a tool to allow rabbit densities to be estimated and then compared with the thresholds, determined separately, at which damage occurs for given ecosystems.

Population increase at a calving ground of the Endangered Tibetan antelope Pantholops hodgsonii in Xinjiang, China

Females in most populations of chiru or Tibetan antelope Pantholops hodgsonii migrate up to 350 km each year to summer calving grounds. These migrations characterize the Tibet–Qinghai Plateau. The Ullughusu calving grounds adjacent to the Arjinshan Nature Reserve in Xinjiang, China, are used by multiple chiru populations and this calving ground recovered from major poaching events in 1998 and 1999, with a population increase from 2001 to 2006. We used direct methods (vehicle/walking transects and radial point sampling) and an indirect method (faecal pellet counts) from 30 June to 4 July 2011 to assess the chiru population at this calving ground. We saw substantially more chiru with all methods in 2011 compared to 2006, demonstrating that the population has increased and suggesting that conservation efforts have been effective.

Effects of large-scale high-severity fire on occupancy and abundances of an invasive large mammal in south-eastern Australia

Context Despite large mammals being an important component of many ecosystems, there is little information on the impacts of fire on large mammal populations. Aims We evaluated the effects of the large-scale high-severity ‘Black Saturday’ fires of 7 February 2009 on occupancy and abundances of an invasive large mammal, the sambar deer (Cervus unicolor), in south-eastern Australia. Methods The effects of the Black Saturday fires on the abundance of sambar deer were assessed using repeated annual counts of faecal pellets during 2007–11 in Kinglake National Park, which was burnt, and in Mount Buffalo National Park, which was not burnt. Pre-fire occupancy was modelled from data collected at 80 4-km2 cells using three survey methods. The same survey methods were used at 15 burnt (n = 9 sampled pre-fire) and 15 unburnt (n = 5 sampled pre-fire) cells 16–24 months after Black Saturday. Because multiple surveys were performed in each cell, we used a Bayesian state–space site-occupancy model to partition changes in the probability of occupancy from changes in the probability of detection. Key results Counts of sambar deer pellets increased linearly during 2007–11 in the unburnt Mount Buffalo National Park. Pellet counts also increased linearly in Kinglake National Park from 2007 to 2008, and then decreased (to zero) following Black Saturday; pellet counts increased again in 2010 and 2011. Sambar deer occupancy was weakly reduced (from 0.99 to 0.88) in burnt cells 16–24 months after Black Saturday, but was little changed in unburnt cells (from 0.99 to 0.98). Conclusions We conclude that the abundance of sambar deer was substantially reduced by the large-scale high-severity Black Saturday fires, but that most burnt habitat was reoccupied 16–24 months later. Implications There is concern about the negative impacts of invasive sambar deer on native biodiversity, particularly immediately post-fire. Our study suggests that it takes at least 8 months before sambar deer recolonise areas burnt by a large-scale high-severity fire; however, a risk-averse approach would be to act (e.g. by erecting fences or culling) sooner than that.