Daniel J. D. Natusch

Communally Nesting Migratory Birds Create Ecological Hot-Spots in Tropical Australia

Large numbers of metallic starlings (Aplonis metallica) migrate annually from New Guinea to the rainforests of tropical Australia, where they nest communally in single emergent trees (up to 1,000 birds). These aggregations create dense and species-rich faunal “hot-spots”, attracting a diverse assemblage of local consumers that utilise this seasonal resource. The starlings nested primarily in poison-dart trees (Antiaris toxicaria) near the rainforest-woodland boundary. Surveys underneath these colonies revealed that bird-derived nutrients massively increased densities of soil invertebrates and mammals (primarily wild pigs) beneath trees, year-round. Flying invertebrates, nocturnal birds, reptiles, and amphibians congregated beneath the trees when starlings were nesting (the wet-season). Diurnal birds (primarily cockatoos and bush turkeys) aggregated beneath the trees during the dry-season to utilise residual nutrients when the starlings were not nesting. The abundance of several taxa was considerably higher (to > 1000-fold) under colony trees than under nearby trees. The system strikingly resembles utilisation of bird nesting colonies by predators in other parts of the world but this spectacular system has never been described, emphasizing the continuing need for detailed natural-history studies in tropical Australia.

Jungle Giants: Assessing Sustainable Harvesting in a Difficult-to-Survey Species (Python reticulatus)

Sustainability of wildlife harvests is critical but difficult to assess. Evaluations of sustainability typically combine modelling with the measurement of underlying abundances. For many taxa harvested in developing countries, however, abundances are near-impossible to survey and a lack of detailed ecological information impedes the reliability of models. In such cases, repeated surveys of the attributes of harvested individuals may provide more robust information on sustainability. If the numbers, sizes and other demographic attributes of animals taken for the commercial trade do not change over biologically significant time intervals (decades), there is a prima facie case that the harvest is indeed sustainable. Here, we report the results of examinations of > 4,200 reticulated pythons (Python reticulatus) taken for the commercial leather industry in northern and southern Sumatra, Indonesia. The numbers, mean body sizes, clutch sizes, sizes at maturity and proportion of giant specimens have not decreased between our first surveys (1995) and repeat surveys (2015). Thus, despite assumptions to the contrary, the harvest appears to be sustainable. We use our data to inform the design of future monitoring programs for this species. Our study underpins the need for robust science to inform wildlife trade policy and decision-making, and urges wildlife managers to assess sustainability of difficult-to-survey terrestrial wildlife by drawing inferences directly from the harvest itself.

Geographic and Sexual Variations in Body Size, Morphology, and Diet among Five Populations of Green Pythons (Morelia viridis)

Abstract Body sizes and morphological traits of animals are often strongly influenced by their diet. Several studies have shown this to be true for snakes and have linked intraspecific differences in these attributes to geographic and sexual variations in prey sizes and diet. To help clarify anecdotal reports of morphological variation among populations of Green Pythons (Morelia viridis), we assessed geographic and sexual variations in the body size, morphology, and diet of 908 individuals from five sites in Australia and New Guinea. Body sizes and morphology differed among populations and, although some variation could be explained by sampling biases, we found no significant geographic dietary variation to help explain these differences. Juvenile Green Pythons preyed exclusively on small lizards and adults preyed on mammals, while birds comprised only 2.5% of all dietary records. Within all populations females grow to larger body sizes, although we observed little sexual dimorphism in other traits. Males and females selected the same prey types. However, large females, despite their larger overall size, consumed a greater proportion of small, diurnal prey (lizards and birds) than did males, suggesting a niche divergence. Although the two New Guinean mainland populations of Green Python are the most genetically divergent from one another, they are the most morphologically similar. Our data provide weak evidence to reject nonadaptive processes as creating geographic variations in the body sizes and morphology of Green Pythons and suggest that a better understanding of the relative importance of different prey may elucidate the mechanisms involved.

Cane toads beneath bird rookeries: utilization of a natural disturbance by an invasive species

Abstract Many invasive species exploit anthropogenically disturbed habitats, but most of those taxa evolved long before humans. Presumably, then, an ability to use natural (non-anthropogenic) disturbances pre-adapted invaders to a world later degraded by people. Studies on invasive species in naturally disturbed habitats thus can clarify the ancestral niche of invaders. In the Australian tropics, metallic starlings Aplonis metallica nest communally in emergent rainforest trees during the wet-season, and invasive cane toads Rhinella marina join other predators (mammals, birds, reptiles, and other anurans) to exploit the food resources beneath those trees. Compared to conspecifics found along nearby roads through the forest, cane toads beneath bird-nesting trees occur at higher densities, and are smaller in body size. The sex ratio is female-biased, and recapture records suggest that females may be philopatric at these sites (whereas recaptures were rare for both sexes found along the roads). Some toads were found under the same trees in successive wet-seasons. Spooling showed that distances moved per night were similar along the road versus under the trees, but toads under trees showed lower net displacements. Diets also differed (based upon scat analysis), with tree toads feeding more on beetles and less on ants. These nutrient-rich hotspots are exploited primarily by adult females and juvenile toads, whereas adult males congregate at breeding sites. By magnifying pre-existing intraspecific divergences in habitat use, bird rookeries may enhance population viability of cane toads by enabling critical age and sex classes to exploit food-rich patches that are rarely used by adult males.

Asian snake farms: conservation curse or sustainable enterprise?

Snake farming in Asia has increased over the past decade, and conservationists have expressed concerns that farms may foster overexploitation of wild populations and create legal conduits for illegally harvested wild individuals. We conducted face-to-face interviews with snake farmers in Viet Nam and China, with the aim of describing the basic models under which snakes are farmed for meat. We synthesized this information to assess the feasibility of farming snakes for human consumption, drawing conclusions about the impact of this industry on the conservation of wild snake populations. The most commonly farmed snakes include the monocled cobra Naja kaouthia , the Chinese cobra Naja atra , the oriental rat snake Ptyas mucosus and the king cobra Ophiophagus hannah . These species have life histories that are compatible with the demands of intensive livestock production, including early maturity, rapid growth rates, high reproductive output, efficient food assimilation rates and undemanding space requirements. Snake farmers appear to be capitalizing on the unique energy-efficiency of snakes to produce meat for human consumption. We conclude that the ease and profitability of farming snakes in China and Viet Nam make farming a viable substitute for harvesting wild snakes, with apparently minimal threat to wild populations. Snake farming offers a range of novel agricultural opportunities and has the potential to play a pivotal role in sustainable development.

Determining the source and geographic origin of traded python skins using isotopic and elemental markers

Commercial production systems for wildlife increasingly involve closed-cycle captive breeding, in which effective regulation requires methods for verifying the provenance of stock. We compared the isotopic and elementalcompositions of skin from wild and captive-bred pythons raised under different diet regimes in Indonesia and Viet Nam to examine the efficacy of using these techniques as a means of determining the source and origin ofskins entering international trade. We found significant differences in both isotopic and elemental markers between wild and captive-bred snakes, as well as those from different geographic origins. Combinations of both techniques were able to discriminate between diet treatments and geographic origins with up to 100 persen accuracy. Moreover, our experimental manipulation of python diets confirmed that the application of specific diet regimes (or the addition of known elemental markers) for captive-bred snakes can create signatures specific to those animals, vastly improving the efficacy of these methods. Our study strongly suggests that the analysis of isotoperatios and elemental markers offers a powerful tool for verifying the provenance of reptile skins entering trade – but these methodologies will be most applicable (and cost-effective) for species with small populations of genuine conservation concern, rather than for large volume trade in species for which there is little conservation risk. Biological Conservation 209 (2017) 406–414

Examination of Sarcocystis spp. of giant snakes from Australia and Southeast Asia confirms presence of a known pathogen – Sarcocystis nesbitti

We examined Sarcocystis spp. in giant snakes from the Indo-Australian Archipelago and Australia using a combination of morphological (size of sporocyst) and molecular analyses. We amplified by PCR nuclear 18S rDNA from single sporocysts in order to detect mixed infections and unequivocally assign the retrieved sequences to the corresponding parasite stage. Sarcocystis infection was generally high across the study area, with 78 (68%) of 115 examined pythons being infected by one or more Sarcocystis spp. Among 18 randomly chosen, sporocyst-positive samples (11 from Southeast Asia, 7 from Northern Australia) the only Sarcocystis species detected in Southeast Asian snakes was S. singaporensis (in reticulated pythons), which was absent from all Australian samples. We distinguished three different Sarcocystis spp. in the Australian sample set; two were excreted by scrub pythons and one by the spotted python. The sequence of the latter is an undescribed species phylogenetically related to S. lacertae. Of the two Sarcocystis species found in scrub pythons, one showed an 18S rRNA gene sequence similar to S. zamani, which is described from Australia for the first time. The second sequence was identical/similar to that of S. nesbitti, a known human pathogen that was held responsible for outbreaks of disease among tourists in Malaysia. The potential presence of S. nesbitti in Australia challenges the current hypothesis of a snake-primate life cycle, and would have implications for human health in the region. Further molecular and biological characterizations are required to confirm species identity and determine whether or not the Australian isolate has the same zoonotic potential as its Malaysian counterpart. Finally, the absence of S. nesbitti in samples from reticulated pythons (which were reported to be definitive hosts), coupled with our phylogenetic analyses, suggest that alternative snake hosts may be responsible for transmitting this parasite in Malaysia.