The smooth-coated otter (Lutrogale perspicillata) is listed as Vulnerable on the IUCN Red List and as Endangered on Nepal’s National Red List of Mammals. Across its range, which stretches from the lowland rivers of the Indian subcontinent to Southeast Asia, the species has been squeezed by habitat loss, degradation of prey resources, direct persecution and illegal trade. In Nepal, the animal is recorded from the major river systems, including the Karnali, but remains sparsely distributed across the Terai lowlands and poorly documented outside a handful of surveyed stretches. Because otters sit at or near the top of the aquatic food web, changes in their distribution and diet integrate shifts across the entire riverine ecosystem, making them practical sentinels for tracking river health.

The research team, working with approval from Nepal’s Department of National Parks and Wildlife Conservation and Bardiya National Park, surveyed both banks of the lower western branch of the Karnali River below Chisapani Bridge. The stretch cuts through a Terai floodplain mosaic of braided channels, sand bars, riverine forests and grasslands that also support gharial and Gangetic river dolphins. Fieldwork ran from early January to late February 2024, deliberately timed before the monsoon so that floodwaters would not wash away the indirect signs the survey depended on. The river was divided into consecutive one-kilometre segments, and at the midpoint of each segment on both banks, the team established nested sampling plots measuring 100 metres by 10 metres.

The survey covered 70 transects in total. Latrine sites turned up at just 15 plots, roughly 21 percent of those examined, meaning that for every transect with otter evidence, about three had none. In all, the researchers documented 32 latrine sites, some inside the nested plots and others beyond them. The distances of these sites from the active river channel ranged from 13 to 1,021 metres, with a median of 200 metres. A striking pattern emerged when the team correlated spraint counts with distance from the water: the farther a latrine sat from the active channel, the more spraints it contained. The positive correlation, quantified with Spearman’s rank correlation coefficient of 0.531, suggests that otters favour marking sites where deposits are less likely to be erased by daily water-level fluctuations or shoreline wash.

Substrate mattered too. Sandy banks supported the highest and most variable spraint counts, averaging 4.75 per site, compared with means of just 2.00 at stone and mould sites. Statistical testing confirmed that spraint counts were significantly higher on sand than on stone. The finding echoes work from India’s Cauvery River system, where loose sand was a defining feature of otter sites used for grooming and territorial marking. Sand appears to offer a better grooming surface for these semi-aquatic carnivores and improves the persistence and detectability of their marks, a combination that makes sandy banks disproportionately important for otter communication along the Karnali.

To understand what drives latrine placement, the researchers measured a battery of environmental variables at each plot: bank height and slope, river velocity measured with a floating stick, river width recorded with a laser rangefinder, the presence of braided bars and retaining walls, vegetation cover, escape cover distance, proximity to settlements and graded levels of human disturbance. After screening out collinear predictors using variance inflation factors, ten variables entered a generalised linear model with a binomial error structure. Six predictors emerged as statistically significant, and all pointed in the same direction: latrine occurrence declined with increasing distance to escape cover, increasing distance from settlements, increasing river width, faster flow velocity, the presence of islands and the presence of retaining walls.

Model simplification sharpened the picture. From 176 candidate models restricted to a maximum of three predictors, two competitive models survived Akaike’s information criterion corrected for small sample size. Both contained distance to settlement and river width, each carrying the maximum summed Akaike weight of 1.00. The effect sizes were substantial. A one-standard-deviation increase in distance from settlements was associated with roughly 53 percent lower odds of latrine occurrence, while the same increase in river width corresponded to about 92 percent lower odds. In plain terms, otters mark most intensively near human settlements and along narrower, slower sections of the river, where stable marking surfaces and predictable access points between channel and bank are easiest to find.

The proximity-to-settlement result deserves careful reading. It should not be interpreted as a preference for disturbance, the authors caution, but as evidence that otter marking activity overlaps with river sections that experience fishing, foot traffic, livestock use and riverbank modification. That overlap sets the stage for conflict, and the dietary analysis supplied a dramatic confirmation of just how entangled the two species’ fortunes have become. When the researchers dissected 32 spraint samples under a binocular microscope, comparing scales and bones against reference slides prepared from fish caught in cast nets and mounted in permanent slides, fish remains appeared in nearly every sample, 31 of 32, or 96.88 percent. Crab remains appeared in 18.75 percent of samples and bird remains in a single sample, confirming the species’ predominantly piscivorous diet with opportunistic forays beyond fish.

Within the fish component, Labeo dero dominated, appearing in 65.62 percent of spraints, followed by Tor putitora at 31.25 percent. Both are locally important food fishes that communities along the Karnali harvest for subsistence, meaning otters and people are drawing on the same prey base. But the most alarming laboratory finding had nothing to do with prey at all: fishing net material was found wrapped within 15 of the 32 spraints examined. This is direct evidence that otters are regularly interacting with gill nets, most likely while removing or consuming entangled fish. Elsewhere in the species’ range, smooth-coated otters have been reported taking fish directly from nets and damaging gear, fuelling negative perceptions among fishers. Abandoned and lost nets compound the hazard, entangling and injuring wildlife long after they stop catching fish for anyone.

The study arrives at a moment of real conservation opportunity. Rajapur and Tikapur municipalities have jointly declared Nepal’s first Fish Sanctuary, covering 3.9 square kilometres in the very stretch of river the researchers surveyed, a move intended to rebuild prey populations and regulate fishing pressure. The authors argue that practical action should include reducing destructive fishing practices and the safe disposal of damaged nets, implemented through local governments in collaboration with community-based organisations and the river-dependent Tharu and Sonaha communities. Their broader message is that otter conservation cannot be confined to remote, apparently undisturbed river sections, because the animals themselves mark, forage and raise their young in the human-dominated reaches where rivers are most at risk. In the spraints of the Karnali’s otters, scientists have found both a baseline for protecting a Vulnerable species and a blunt record of the pressures bearing down on one of Nepal’s great rivers.

Subject of Research: Latrine site selection and diet of the smooth-coated otter in the Karnali River, Nepal

Article Title: Determinants of Smooth‐coated Otter (Lutrogale perspicillata) Latrine Occurrence and Diet in the Karnali River, Nepal

Article References: Kathariya, R., Sapkota, R. P., Sada, R., Kapali, A., Kathariya, M., & Thapa, K. (2026). Determinants of Smooth‐coated Otter ( Lutrogale perspicillata ) Latrine Occurrence and Diet in the Karnali River, Nepal. Ecology and Evolution, 16(9), Article e74322. https://doi.org/10.1002/ece3.74322

Image Credits: AI Generated

DOI: 10.1002/ece3.74322

Keywords: smooth-coated otter, Lutrogale perspicillata, Karnali River, Nepal, latrine site selection, spraint analysis, diet composition, river conservation, human-wildlife conflict, fishing nets, habitat modelling, freshwater biodiversity

The Burrowing Parrot, Cyanoliseus patagonus, is no ordinary bird. It breeds in colonies dug into soft sandstone and limestone cliffs known as barrancas, and the colony near El Cóndor, beside the Río Negro estuary, is the largest known colony of any parrot species on Earth. Stretching 18.1 kilometers along the coast, it holds roughly 71 percent of the global breeding population, with long-term monitoring between 1998 and 2019 recording between 22,000 and 41,000 active nests. Understanding what these birds eat is therefore not a niche question of natural history; it is central to the survival of the majority of the species.

Historically, Burrowing Parrots were thought to feed mainly on the native vegetation of the Monte and Espinal ecoregions: seeds and fruits of chañar, caldén, algarrobo trees, berries of native shrubs such as Lycium, Discaria and Schinus, and grasses of the arid scrubland. Early naturalists, including W. H. Hudson in 1923 and Alexander Wetmore in 1926, described a diet rooted firmly in Patagonia’s native flora. The new study, published in The Science of Nature, tells a very different story. Of 202 valid plant molecular operational taxonomic units, or MOTUs, identified in the parrots’ droppings over the annual cycle, only 13 percent corresponded to native plants. Fully 40 percent were introduced species, with a further 4.5 percent presumed introduced, 12 percent ornamental garden plants, and 6.9 percent cultivated crops and pastures.

The methodology behind these numbers is a textbook example of modern molecular scatology. Between January and December 2021, the researchers collected 220 fresh fecal samples from the roosting flocks — 20 per month, except February, when the parrots mysteriously abandon the village roost. DNA was extracted from 178 samples using a stool kit optimized with bead-beating homogenization and extended incubation. Two primer sets were then amplified: one targeting the second internal transcribed spacer (ITS2) of plant nuclear ribosomal DNA, and a second targeting Bilateralia, the group that includes all animals with bilateral symmetry, to detect parasites and other animal DNA. The libraries were sequenced on an Illumina MiSeq with 250-base-pair paired-end reads.

The bioinformatic pipeline was equally rigorous. Reads were quality-trimmed with TRIMMOMATIC, merged with FLASH, de-replicated and screened for chimeras with USEARCH, and clustered into MOTUs. Each MOTU was then matched against the NCBI GenBank nucleotide database using BLASTn, with stringent thresholds: sequences had to be at least 190 base pairs long, with matches above 98 percent identity and an e-value below 0.00001. Species-level assignments required matches above 99.5 percent with consistent quality metrics across all retained hits. Negative extraction controls and PCR-grade water controls showed no contamination, and a dedicated gap analysis confirmed that the reference libraries were adequate: 69 percent of native plant species in the region have reference sequences in GenBank, rising to 97 percent at the genus level — sufficient given that 85 percent of the recovered MOTUs could be assigned to genus or better.

The seasonal patterns that emerged were striking. The parrots consumed 77 plant taxa during the breeding season, 172 during the post-breeding period, 72 in winter and 70 during pre-breeding — a statistically significant difference, with dietary diversity peaking just after the chicks fledge. This post-breeding explosion in dietary breadth coincides with the period when most plants in the region produce fruits and release seeds, and it is a critical window for juvenile survival, as young parrots must build up reserves before the harsh Patagonian winter. Non-metric multidimensional scaling and permutational multivariate analysis of variance revealed considerable overlap in diet across breeding, post-breeding and pre-breeding stages, but far less overlap with winter, when the birds turn to plants such as white spruce, velvet grass, perennial ryegrass and other introduced and ornamental species that are absent from the diet at other times of year.

Could the dominance of introduced plants be an artifact of sampling location? The researchers considered this carefully. Because samples were collected in the evening at the village roost, the diet might theoretically be biased toward items eaten near El Cóndor, where the landscape is most heavily modified. But several lines of evidence argue against it. Observations over five breeding seasons show the parrots flying over fields near the village without stopping to feed, and previous tracking studies show they forage between 58 kilometers northwest and 66 kilometers northeast of the colony. Moreover, digestive transit studies in parrots — corn-fed budgerigars empty their entire digestive tract within 26 hours — indicate that the DNA detected in evening droppings most likely reflects a full day of foraging, not just the last hours.

The most plausible explanation, the authors argue, is environmental degradation. Since the 1970s, a combination of increased rainfall and aggressive land clearing has transformed the region. In the Patagones department, natural vegetation that covered 65 percent of the land in 1975 has been reduced to an estimated 20 to 29 percent; in just three years, from 2015 to 2018, more than 216,000 hectares were cleared. In Adolfo Alsina department, home to El Cóndor, nearly 49,000 hectares were cleared between 1986 and 2006. Such landscape-scale disturbance disrupts native plant communities and opens the door to alien species. The parrots, it appears, are switching from a diet historically based on Monte and Espinal plants to one now dominated by introduced species — either a remarkable display of behavioral flexibility, or a warning sign of a suboptimal strategy that could undermine the persistence of the world’s largest parrot colony. A persistent La Niña event before and during the study may also have reduced the availability of native plants, though the authors caution that a single year of sampling cannot establish causation, and multi-year research is essential, especially as La Niña events are expected to become more frequent under climate change.

The study also delivered an unexpected bonus: a parasitological survey conducted entirely from droppings. Using the Bilateralia primer, the team identified 31 animal MOTUs, including four parasite families never before recorded in the digestive tracts of Burrowing Parrots: Gongylonematidae, which infects the oral cavity of birds and can cause starvation and death; Hymenolepididae and Onchobothriidae, both tapeworm groups previously unknown in parrots — Onchobothriidae had never been reported in any bird; and Capillariidae, thin nematodes known from captive parrots. The Gongylonematidae finding is particularly intriguing. During the 2020–2021 breeding season, at least 1,050 adult parrots died at El Cóndor — compared with the 20 to 30 typically found dead each year — and veterinary experts suspected infection rather than starvation as the primary cause. The authors stress that they can only speculate about a connection, but the possibility of a widespread Gongylonematidae infection driving that mortality event now demands investigation.

For decades, Burrowing Parrots were persecuted as agricultural pests, blamed for damage to maize, sunflowers, wheat and fruit orchards. The evidence tells a more nuanced story: systematic evaluations found that the birds affected only 0.1 to 0.4 percent of the sunflower harvest, leaving wheat and maize undamaged, and the species has been removed from Argentina’s pest-control lists. The new data reinforce this picture — cultivated plants made up just 6.9 percent of the diet, and official agricultural statistics suggest these mostly correspond to forage pastures of oats and barley rather than standing crops. As the clearance of the Monte continues and the El Cóndor colony concentrates the vast majority of the world’s Burrowing Parrots, the authors call for close monitoring of both population size and diet. The droppings collected under those Patagonian power lines have done more than reveal a menu; they have documented a dietary revolution in real time, flagged nine plant species newly introduced to the region, and possibly left a molecular clue to a mass mortality that still awaits explanation.

Subject of Research: Seasonal diet composition of Burrowing Parrots revealed by DNA metabarcoding of fecal samples

Article Title: Using next-generation sequencing to unravel the diet composition of Burrowing Parrots over the annual cycle

Article References: Masello, J. F., Failla, M., Leder, C. V., & Quillfeldt, P. (2026). Using next-generation sequencing to unravel the diet composition of Burrowing Parrots over the annual cycle. The Science of Nature, 113(5), Article 119. https://doi.org/10.1007/s00114-026-02159-3

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02159-3

Keywords: Burrowing Parrot, DNA metabarcoding, next-generation sequencing, diet composition, Patagonia, El Cóndor colony, molecular scatology, introduced plants, environmental degradation, parasites, Psittaciformes, La Niña