Sociospatial organization of a solitary carnivore, the Eurasian otter (Lutra lutra)

Low signs of territorial behavior in the Eurasian otter during low-water conditions in a Mediterranean river

The Eurasian otter Lutra lutra is a territorial semi-aquatic carnivore usually found at low densities in rivers, coastal areas, and wetlands. Its diet is based on prey associated with aquatic environments. Mediterranean rivers are highly seasonal, and suffer reduced flow during the summer, resulting in isolated river sections (pools) that sometimes can be left with a minimal amount of water, leading to concentrations of food for otters. To our knowledge, this process, which was known to field naturalists, has not been accurately described, nor have otter densities been estimated under these conditions. In this study, we describe the population size and movements of an aggregation of otters in an isolated pool in the Guadiana River in the Tablas de Daimiel National Park (central Spain), which progressively dried out during the spring-summer of 2022, in a context of low connectivity due to the absence of circulating water in the Guadiana and Gigüela rivers. Using non-invasive genetic sampling of 120 spraints collected along 79.4 km of sampling transects and spatial capture-recapture methods, we estimated the otter density at 1.71 individuals/km of river channel length (4.21 individuals/km2) in a progressively drying river pool, up to five times higher than previously described in the Iberian Peninsula. The movement patterns obtained with the spatial capture-recapture model are not quite different from those described in low density, which seems to indicate a wide home range overlap, with low signs of territoriality.

The Different Fate of the Pyrenean Desman (Galemys pyrenaicus) and the Eurasian Otter (Lutra lutra) under Climate and Land Use Changes

Climate and land use change can affect biodiversity in different ways, e.g., determining habitat loss, altering reproduction periods or disrupting biotic interactions. Here, we investigate the effects of climate and land use change on the spatial distribution of two semi-aquatic mammals, the Pyrenean desman (Galemys pyrenaicus) and the Eurasian otter (Lutra lutra). We first modeled the current potential distribution of the desman and the otter in the Iberian Peninsula, considering topographic, climatic and land use variables. Second, we predicted their potential distribution in 2050 under climate and land use change scenarios. We calculated the percentage of range gain/loss and shift predicted for the two species under such scenarios and quantified the present and future spatial overlap between the two species distribution. Irrespective of the scenario, desman models show loss of suitable habitat, whereas the otter will undergo an opposite trend. Aside from a preponderant habitat loss, the desman is predicted to increase its spatial overlap with otter range under the optimistic scenarios, potentially meaning it will face an exacerbated predation by otters. The potential increase of both habitat loss and otters' predation might represent a major threat for the desman, which may affect the long-term persistence of this endemic species in the Iberian Peninsula.

A Noninvasive Genetic Insight into the Spatial and Social Organization of an Endangered Population of the Eurasian Otter (Lutra lutra, Mustelidae, Carnivora)

The Eurasian otter is endangered in Italy, only surviving in southern river basins. The spatial and social structure of a population living at the border of the current range was explored through a noninvasive genetic study along 174 km of the Sangro river. Sampling was conducted in 2011 and 2012, collecting spraints and anal jellies at 62 marking sites. Samples were successfully genotyped at 13 nuclear microsatellites and the ZFX/ZFY locus for molecular sexing, resulting in 14 distinct genotypes (4 females, 2 possible females, 8 males), from 35 marking sites. Mean captures/recaptures rate was 3.8 captures/individual, with males being recaptured more frequently than females. Spatial overlap among individuals was analyzed through a linear regression model fitted against sibship categories and sex pairing. Nine out of the fourteen genotyped individuals belonged to three full-sib clusters, while five individuals had no full-sibs in the population. Full-sibs overlapped more than half-sibs, while male–male pairs showed significantly higher spatial overlap than both male–female and female–female pairs. Estimated mean density was 0.152 otters/km and 2.4 individuals/10 × 10 km grid cell. Accordingly, the 3440 grid cells of otter occurrence in Italy could likely host about 8000 otters, suggesting the current population has become larger than the minimum viable population size.

Evaluating otter reintroduction outcomes using genetic spatial capture-recapture modified for dendritic networks

Monitoring the demographics and genetics of reintroduced populations is critical to evaluating reintroduction success, but species ecology and the landscapes that they inhabit often present challenges for accurate assessments. If suitable habitats are restricted to hierarchical dendritic networks, such as river systems, animal movements are typically constrained and may violate assumptions of methods commonly used to estimate demographic parameters. Using genetic detection data collected via fecal sampling at latrines, we demonstrate applicability of the spatial capture-recapture (SCR) network distance function for estimating the size and density of a recently reintroduced North American river otter (Lontra canadensis) population in the Upper Rio Grande River dendritic network in the southwestern United States, and we also evaluated the genetic outcomes of using a small founder group (n = 33 otters) for reintroduction. Estimated population density was 0.23-0.28 otter/km, or 1 otter/3.57-4.35 km, with weak evidence of density increasing with northerly latitude (β = 0.33). Estimated population size was 83-104 total otters in 359 km of riverine dendritic network, which corresponded to average annual exponential population growth of 1.12-1.15/year since reintroduction. Growth was ≥40% lower than most reintroduced river otter populations and strong evidence of a founder effect existed 8-10 years post-reintroduction, including 13-21% genetic diversity loss, 84%-87% genetic effective population size decline, and rapid divergence from the source population (F ST accumulation = 0.06/generation). Consequently, genetic restoration via translocation of additional otters from other populations may be necessary to mitigate deleterious genetic effects in this small, isolated population. Combined with non-invasive genetic sampling, the SCR network distance approach is likely widely applicable to demogenetic assessments of both reintroduced and established populations of multiple mustelid species that inhabit aquatic dendritic networks, many of which are regionally or globally imperiled and may warrant reintroduction or augmentation efforts.

Social organization of otters in relation to their ecology

Otter species are known to fluctuate intraspecifically from a solitary lifestyle to group-living arrangements. By examining what is known about habitat use and foraging style in otters of 13 different species, based on 93 studied sites, we assessed (1) the relationship between social habits and preferred habitats, (2) the relationship between species and prey preferences, and (3) the effect of predator avoidance on their social organization in order to assess the socio-ecological factors influencing otters. Females remain the core of their social stability. We show the major influence of habitats and feeding strategies (i.e. socio-ecology) of otters. The different species of solitary otters most often inhabit linear environments, such as freshwater ecosystems or wave-exposed marine coasts, and their habitat is often subject to disturbances that fragment their functional continuity. Social otters are more often found in extensive habitats with high plant cover, regular food resources and in areas with large predators compared to solitary species. The maintenance of regular resources and the fact that the main trophic resources are replenished rapidly might be determining factors driving sociality. Group-living and bachelor congregations among otters can also respond to pressure from large predators. This suggests that foraging, habitat use and the presence of large predators may be the drivers of sociality in otters. We conclude that most otters have a greater social potential than previously assumed, which is confirmed by their various vocalizations recently described.

Genetic relatedness and space use in two populations of striped hyenas (Hyaena hyaena)

Surprising social complexity and variability have recently been documented in several mammalian species once believed to be strictly solitary, and variation in resource abundance may drive this variation in sociality. Wagner et al. (Wagner, A. P., S. Creel, L. G. Frank, and S. T. Kalinowski. 2007. Patterns of relatedness and parentage in an asocial, polyandrous striped hyena population. Molecular Ecology 16:4356–4369) reported unusual space-use patterns among female striped hyenas (Hyaena hyaena) in central Kenya, where pairwise relatedness among females increased with the geographic distance separating them. The authors suggested that this pattern, very rare among mammals, might reflect attempts by females to avoid competition with close relatives for scarce resources in areas of range overlap. Here, we compare those data to new data, documenting genetic relatedness and space use in a previously unstudied wild population of striped hyenas in southern Kenya. We tested hypotheses suggesting that resource abundance and population density affect patterns of genetic relatedness and geographic distance in this species. Our results suggest that higher per capita prey density results in relaxed competition for food, and greater social tolerance among female striped hyenas. A hypothesis suggesting lower population density in the southern population was not supported. Relaxed resource competition also may lead to female–female cooperation in the southern population; we documented for the first time behavioral evidence of den sharing by adult female striped hyenas. Our data indicate that different populations of this little-studied species exhibit behavioral plasticity; in this case, markedly different space-use patterns and patterns of spatial relatedness under different ecological conditions.

Social organization of a solitary carnivore: spatial behaviour, interactions and relatedness in the slender mongoose

The majority of carnivore species are described as solitary, but little is known about their social organization and interactions with conspecifics. We investigated the spatial organization and social interactions as well as relatedness of slender mongooses (Galerella sanguinea) living in the southern Kalahari. This is a little studied small carnivore previously described as solitary with anecdotal evidence for male associations. In our study population, mongooses arranged in spatial groups consisting of one to three males and up to four females. Male ranges, based on sleeping sites, were large and overlapping, encompassing the smaller and more exclusive female ranges. Spatial groups could be distinguished by their behaviour, communal denning and home range. Within spatial groups animals communally denned in up to 33% of nights, mainly during winter months, presumably to gain thermoregulatory benefits. Associations of related males gained reproductive benefits likely through increased territorial and female defence. Our study supports slender mongooses to be better described as solitary foragers living in a complex system of spatial groups with amicable social interactions between specific individuals. We suggest that the recognition of underlying 'hidden' complexities in these apparently 'solitary' organizations needs to be accounted for when investigating group living and social behaviour.

First telemetry data on wild individuals from the threatened, isolated Italian otter (Lutra lutra) population

The Eurasian otter (Lutra lutra) is among the most endangered mammals in Italy, its population being isolated and genetically distinct from other European populations. Yet, its ecology and behavior are largely unknown in Italy, preventing its much-needed effective conservation. We radio-tracked one male and one female otter daily in Southern Italy, for 1 year and 8 months, respectively. The male and female used nearly 30 and 20 km of river, respectively. The extension of the ranges varied among seasons. The male was more conservative in its spatial utilization, being mostly located around a trout farm. These first direct data on space use by wild Italian otters provided preliminary information potentially useful for a sound management of this endangered population.

Use of implanted acoustic tags to assess platypus movement behaviour across spatial and temporal scales

The platypus (Ornithorhynchus anatinus) is an evolutionarily distinct mammal, endemic to Australian freshwaters. Many aspects of its ecology and life-history, including detailed understanding of movements, are poorly known, hampered by its cryptic and mainly nocturnal habits and small numbers. We effectively trialled intraperitoneal implanted acoustic transmitters in nine platypuses in the Severn River (NSW), Australia, as a potential approach for studying movements in this challenging species. We tracked platypus movements over six months, at fine and broad spatial scales, using an array of acoustic sensors. Over six months (March-August 2016), four of five adult platypuses (two females\three males) maintained localized movements (average monthly maximums 0.37 km ± 0.03 sd), while one adult, one sub-adult, and one juvenile (males) moved further: average monthly maxima 1.2 km ± 2.0 sd, 0.9 km ± 0.6 sd, 4.5 km ± 5.9 sd, respectively. The longest recorded movement was by a male adult, covering 11.1 km in three days and travelling a maximum distance of about 13 km between records. Only one implanted animal was not detected immediately after release, indicative of transmission failure rather than an adverse event. High cumulative daily movements (daily 1.9 km ± 0.8 sd) indicated high metabolic requirements, with implications for previous estimates of platypus abundances and carrying capacities, essential for effective conservation. This novel approach offers new avenues to investigate relating to mating, nesting, and intraspecific competition behaviours and their temporal and spatial variation.

The effect of a major drainage divide on the gene flow of a semiaquatic carnivore, the Eurasian otter

Major drainage divides (separating the water flow draining to different seas) may significantly affect the dispersal, distribution, and genetic structure of semiaquatic animals. Assessing this effect is important for the proper management of both endangered and invasive riparian species. Here, I determined the fine-scale impact of the drainage divide between the Baltic Sea and the Black Sea drainage basins on the genetic structure and dispersal of the Eurasian otter (Lutra lutra) in the Bieszczady Mountains (Poland and Slovakia). I investigated the genetic structure of the otter population and assessed 3 alternative dispersal models using 6 landscape genetics methods. The analyses were based on 48 individual genotypes obtained from 622 fecal and gland secretion samples collected in 2008–2011. Results indicate that the major drainage divide is not a barrier to gene flow for this population. This was established by analyses of population genetic structure and confirmed by analysis of the spatial distribution of samples originating from closely related individuals. In line with these findings, the best-supported dispersal model assumed that otters migrate through mountain passes, away from streams, thus revealing that they are able to cross a drainage divide. The genetic structure of the population studied exhibits an isolation-by-distance pattern; however, the locations of several repeatedly recorded or closely related individuals revealed the occurrence of long-distance movements. Confirmation of the high mobility of otters and their ability to cross a major drainage divide ridge suggest that landscape obstacles and discontinuity of river network are unlikely to stop otter dispersal, gene flow, and recolonization of new areas.

The vocal repertoire of adult and neonate giant otters (Pteronura brasiliensis)

Animals use vocalizations to exchange information about external events, their own physical or motivational state, or about individuality and social affiliation. Infant babbling can enhance the development of the full adult vocal repertoire by providing ample opportunity for practice. Giant otters are very social and frequently vocalizing animals. They live in highly cohesive groups, generally including a reproductive pair and their offspring born in different years. This basic social structure may vary in the degree of relatedness of the group members. Individuals engage in shared group activities and different social roles and thus, the social organization of giant otters provides a basis for complex and long-term individual relationships. We recorded and analysed the vocalizations of adult and neonate giant otters from wild and captive groups. We classified the adult vocalizations according to their acoustic structure, and described their main behavioural context. Additionally, we present the first description of vocalizations uttered in babbling bouts of new born giant otters. We expected to find 1) a sophisticated vocal repertoire that would reflect the species’ complex social organisation, 2) that giant otter vocalizations have a clear relationship between signal structure and function, and 3) that the vocal repertoire of new born giant otters would comprise age-specific vocalizations as well as precursors of the adult repertoire. We found a vocal repertoire with 22 distinct vocalization types produced by adults and 11 vocalization types within the babbling bouts of the neonates. A comparison within the otter subfamily suggests a relation between vocal and social complexity, with the giant otters being the socially and vocally most complex species.