Km Of Transects Research Articles

Thermal scanners versus spotlighting: New opportunities for monitoring threatened small endotherms

AbstractThreatened species monitoring is challenging for small, cryptic endotherms that are most effectively detected at night. Low detectability is a challenge for monitoring programmes, resulting in low statistical power and sparse or zero‐inflated datasets. To advance conservation management programmes, efforts to address this are required. In recent years thermal scanners have emerged as an effective tool for detecting small endotherms, but the diversity of available thermal tools, focal habitats and target species mean that their applicability in many key scenarios remain untested. We directly compared vehicle‐mounted thermal surveys with vehicle‐based spotlighting targeting small endotherms in Australian native grasslands. Our targets included both common species that occur at high densities, and species that are notoriously difficult to detect with spotlights, which may occur at very low densities. We completed paired surveys of roosting grassland birds, and nocturnally active small mammals at 22 sites, once using thermal scanners and once using spotlights. Ultimately, distance sampling was conducted across 136 km of transects. Thermal scanners facilitated greater detection distances and higher total detections for small endotherms when compared with spotlighting. Species of greatest conservation concern, the Plains‐wanderer (Pedionomus torquatus—Pedionomidae) and Fat‐tailed Dunnart (Sminthopsis crassicaudata—Dasyuridae) were only detected using thermal scanners. Detection distances generated for thermal scanners were reduced by higher vegetation density; however, thermal scanners continued to outperform spotlights under this scenario. Observers also detected more stationary animals and fewer birds were flushed upon detection using thermal scanners when compared with spotlighting. Thermal scanners have the potential to improve the quality of monitoring datasets by increasing detection probabilities for small endotherms. We recommend the adoption of thermal scanners as a best‐practice tool for monitoring small endotherms in open grassland habitats at night, offering new opportunities to monitor endotherms where monitoring has historically been challenging, inadequate or impossible.

Discrete seafloor features associated with juvenile haddock (Melanogrammus aeglefinus): A coarse-graining approach for identifying habitat scale

Ecological patterns and processes occur at a myriad of spatial and temporal scales. Determining the appropriate scale(s) to collect and analyze data depends on the phenomena being studied and no one scale is appropriate for all of these. Knowing relevant measurement scales avoids the risk of presenting results that are merely a function of measurement scale rather than those relevant to actual ecological processes. Attribution of patterns to ecological processes requires a means to measure and evaluate these patterns. We present a standardized method to determine relevant spatial scales of fish-habitat associations observed from linear transect data on juvenile haddock (Melanogrammus aeglefinus), collected from six sites on the Scotian Shelf, off Canada's eastern coast. The survey data came from a large spatial scale research project undertaken by Fisheries and Oceans Canada to investigate spatial distribution of demersal fish in relation to seabed habitat in 2002 and 2003. We examined the relationship between two elements of this extensive dataset – the “towcam” video survey of demersal fish, and the interpreted surficial geology maps derived from sidescan sonar. We used the data from these surveys (48 towcam survey transect lines; 6 study sites, 2 5-km transect lines per site, day and night surveys per line, in each of 2 years = 240 km of transects), superimposed on the interpreted surficial geology layer collected at the same time. The resolution of the observations (∼2.5 m) facilitated a detailed examination of the spatial scales of juvenile haddock association with seabed habitat. This was achieved using a “coarse-graining” approach, which we applied by summarizing fish abundance and seabed habitat proportions across bin sizes starting at 5 m and progressively doubling to 640 m. We tallied significant correlations by bin size to observe patterns in fish-habitat associations as a function of measurement scale, for each age group and diel period. We found that Juvenile haddock-seabed associations deteriorated at the grain limits marking the range of spatial scaling relevant for this phenomenon. We present a robust approach for quantifying appropriate scales of aggregations across linear transects which can serve as an important tool for basing observations to describe ecological patterns in space.

Looking for a magic island in the sea of agriculture: factors affecting forest patch attractiveness for wild boar in human-dominated landscape

Landscape fragmentation carries the risk of habitat loss for many animal species. This may include wild boars, which are one of the main culprits of conflicts with humans, while isolated patches of forest (forest islands) scattered in the agricultural landscape may affect its ecology and the pressure on the crops. This study aimed to understand the importance of small forest islands located in a human-dominated agricultural landscape in the ecology of wild boar. It explores what features, both of the interior and exterior of the islands, influence their use. The study area covered approximately 220,000 ha of northern Poland, where wild boar use of 200 islands distributed across the agricultural landscape was investigated. For this purpose, the method of counting pellet groups was applied on transects of a total length of 51.6 km. In order to compare the use of islands with compact forest complexes, 84 km of transects were made in the latter, divided into developmental stages and forest type. Among the features of the interior of the islands, increasing cover conditions and the main species of trees (pine, spruce and alder) had a positive influence on the wild boar use. The utilization also depended on the presence of human settlements, other islands, and the type of agricultural crop around the island. When comparing island use to compact forest complexes, islands were used more often than forest regeneration sites and mature stands, but less often than pre-thickets. For the 25% most frequently used by wild boar, islands were more attractive than virtually all stand development stages in compact forest complexes. Due to the cover conditions provided, the occurrence of islands in the agricultural space enables wild boars to use areas more distant from compact forest complexes. This may cause the spread of damage caused by wild boars in the fields, but on the other hand it may reduce the pressure on agricultural areas in the immediate vicinity of compact forest complexes. Intensification of hunting pressure in the vicinity of islands with specific characteristics e.g. good cover conditions, considerable distance from human settlements) will increase the effectiveness of wild boar population control in the agricultural landscape and will have a limiting effect on the damage caused by this species in the fields.

Influence of Agricultural Expansion and Human Disturbance on the Encounter Rates of Nocturnal Mammals in Tropical Hill Forests in Bangladesh

Agricultural expansion has had a detrimental effect on tropical forests and the animal communities that depend on them. Agroforestry systems, however, with their more complex tree and plant communities, have been shown to be important habitats for a range of globally threatened species, including nocturnal animals. Here, we present novel data on the encounter rates of seven species of nocturnal mammals in relation to agroforestry systems within four national parks and associated plantations in Bangladesh to examine if encounter rates were influenced by the human population density, presence of plantations, and human access as represented by a Human Influence Index of anthropogenic disturbance. We walked 70.3 km of transects with only semi-natural forest, 26.9 km of transects with semi-natural forest and gardens, and 21.7 km of transects with semi-natural forest and monocultures over 55 nights from 2017–2019. Of the seven species of nocturnal mammals we detected, all were present in Satachari National Park, whereas six occurred in Lawachara National Park, Rajkandi Forest Range, and Rema-Kalenga Wildlife Sanctuary. Within these national parks, three species (Bengal slow loris, large Indian civet, particolored flying squirrel) were more frequently recorded in areas with human disturbance, especially agroforestry plantations. With declining forest cover in Bangladesh, we highlight here the potential of agroforestry systems as emerging important habitats for these species. We encourage long-term studies of these lesser-studied taxa to understand fully the capacity of agroforestry systems in order to support their long-term conservation.

Sunda Clouded Leopard Neofelis diardi (Cuvier, 1823) (Mammalia: Carnivora: Felidae) occupancy in Borneo: results of a pilot vehicle spotlight transect survey

The Sunda Clouded Leopard Neofelis diardi on Borneo is threatened principally by deforestation for oil palm plantations and the indiscriminate use of illegal trapping. Sunda Clouded Leopard populations are decreasing across their range, and the species has been categorised as Vulnerable on the IUCN Red List. Despite the persistence of threats and numerous surveys in recent years, information on its ecology is still limited. Most studies to date have relied on the use of camera traps as their primary sampling tool, as it is challenging otherwise to gather data on Sunda Clouded Leopards. This study aimed to test the feasibility of estimating the Sunda Clouded Leopard occupancy using a different approach. We conducted vehicle spotlight transect surveys in a mixed-use forest reserve and logging concession in Sabah. We drove a cumulative total of 8,433 km of transects at night and documented the occurrence of Sunda Clouded Leopards in eight out of 31 predetermined long-distance transects, yielding a relatively low naïve occupancy rate (nO = 0.26). When accounting for imperfect detection (ρ = 0.15), null occupancy of Sunda Clouded Leopards appeared much higher (ᴪ = 0.55), though our parameter estimates lacked relative precision. Despite this, our results suggest there may be potential to further refine and adapt a basic, cost-effective monitoring approach in a local mixed-use reserve with the help of concession managers and additional improvements to study design. We caution, however, that not all study sites may be suited for this type of approach and strongly advise the development of pilot studies to evaluate their overall feasibility.

Density of red-brocket deer (Mazama americana trinitatis cetartiodactyla: cervidae) on the continental island of Trinidad, WI

ABSTRACT The Trinidadian red-brocket deer (Mazama americana trinitatis) is the only species of deer in Trinidad and is classified as a unique subspecies of red-brocket deer. Despite the importance of the species in Trinidad, to date there have been no published studies on their densities. We report on the densities of this species at four different sites in Trinidad over a 3-year period, with the first 2 years sampled during a hunting moratorium. Diurnal surveys were conducted, with density estimates calculated using King’s Estimator. Surveys were repeated in both the dry and rainy seasons. A total of 312 deer on 1131.4 km of transect were observed over the study. Density estimates varied between different sites (1–16 individuals/km2), and between one and eight individuals/km2 island-wide. Overall, the estimated density of red-brocket deer increased in two of four sites during the study period, indicating that the institution of the moratorium may have had a positive impact on populations of deer. The fact that density estimates varied considerably across the island suggests that harvest levels may need to be tailored for different sites.

Density, abundance and distribution of the guiana dolphin, (Sotalia guianensis van Benéden, 1864) in Sepetiba Bay, Southeast Brazil

Line transect surveys were conducted from August 2002 to July 2003 to examine the abundance and distribution of the guiana dolphin (Sotalia guianensis) in Sepetiba Bay-Southeast Brazil. A boat-based platform and 50 pre-determined line transects were used to assess the population on two main stratum-specific environments of the bay (entrance and interior). A total of 3,140km of transects were surveyed at 12-15km hr–1 and good sea conditions (Beaufort 0-2), resulting in 157 sightings of dolphin groups and 129 sightings after truncation of all sightings beyond 400m. From the 129 sightings the DISTANCE program generated a population density of 2.79 dolphins km–2 and calculated a population of 1,269 individuals (CI=739-2,196) for the bay. Sighting frequency (n=126 or 80.3%) was higher at the entrance of the bay compared with the interior (n=31 or 19.7%), although, the density and abundance were similar for the entrance (2.91 dolphins km–2 and 596 dolphins) and interior (2.69 dolphins km–2 and 672 dolphins). Results reveal an important population of guiana dolphin at Sepetiba Bay, the largest thus far studied off the South American coast, stressing the importance of the area for the conservation of this species. The study also indicated that line-transect sampling carried out from small boats in large bays can produce statistically robust estimates and therefore could be recommended for population monitoring in other areas of the Brazilian coast with similar characteristics.

Updated marine mammal distribution and abundance estimates in British Columbia

Information relating to the distribution and abundance of species is critical for effective conservation and management. For many species, including cetacean species of conservation concern, abundance estimates are lacking, out of date and/or highly uncertain. Systematic, line-transect marine mammal surveys were conducted in British Columbia’s (BC) coastal waters over multiple years and seasons (summer 2004, 2005, 2008, and spring/autumn 2007). In total, 10,057km of transects were surveyed in an 83,547km2 study area. Abundance estimates were calculated using two different methods: Conventional Distance Sampling (CDS) and Density Surface Modelling (DSM). CDS generates a single density estimate for each stratum, whereas DSM explicitly models spatial variation and offers potential for greater precision by incorporating environmental predictors. Although DSM yields a more relevant product for the purposes of marine spatial planning, CDS has proven to be useful in cases where there are fewer observations available for seasonal and inter-annual comparison, particularly for the scarcely observed elephant seal. The summer abundance estimates (with lower and upper 95% confidence intervals; all DSM method unless otherwise stated), assuming certain trackline detection (underestimates true population size) were: harbour porpoise (Phocoena phocoena) 8,091 (4,885–13,401); Dall’s porpoise (Phocoenoides dalli) 5,303 (4,638–6,064); Pacific white-sided dolphin (Lagenorhynchus obliquidens) 22,160 (16,522–29,721); humpback whale (Megaptera novaeangliae) 1,092 (993–1,200); fin whale (Balaenoptera physalus) 329 (274–395); killer whale (all ecotypes; Orcinus orca), 371 (222–621); common minke whale (B. acutorostrata) 522 (295–927); harbour seal (total; Phoca vitulina) 24,916 (19,666–31,569); Steller sea lion (total; Eumetopias jubatus) 4,037 (1,100–14,815); and northern elephant seal (CDS method; Mirounga angustirostris) 65 (35–121). Abundance estimates are provided on a stratum-specific basis with additional estimates provided for Steller sea lions and harbour seals that were ‘hauled out’ and ‘in water’. This analysis updates previous estimates by including additional years of effort, providing greater spatial precision with the DSM method over CDS, novel reporting for spring and autumn seasons (rather than summer alone), and providing new abundance estimates for Steller sea lion and northern elephant seal. In addition to providing a baseline of marine mammal abundance and distribution, against which future changes can be compared, this information offers the opportunity to assess the risks posed to marine mammals by existing and emerging threats, such as fisheries bycatch, ship strikes, and increased oil spill and ocean noise issues associated with increases of container ship and oil tanker traffic in British Columbia’s continental shelf waters.

The dingo (Canis familiaris) as a secondary disperser of mycorrhizal fungal spores

Context Many mycorrhizal fungi are vital to nutrient acquisition in plant communities, and some taxa are reliant on animal-mediated dispersal. The majority of animals that disperse spores are relatively small and have short-distance movement patterns, but carnivores – and especially apex predators – eat many of these small mycophagists and then move greater distances. No studies to date have assessed the ecosystem services carnivores provide through long-distance spore dispersal. Aims In this study, we aimed to investigate whether Australia’s free-ranging dogs (Canis familiaris), including dingoes, act as long-distance spore dispersers by predating smaller mycophagous animals and then secondarily dispersing the fungi consumed by these prey species. Methods To answer this question, we collected dingo scats along 40 km of transects in eastern Australia and analysed the scats to determine the presence of fungal spores and prey animals. Using telemetry and passage rate data, we then developed a movement model to predict the spore dispersal potential of dingoes. Key results We found 16 species of mammalian prey to be eaten by dingoes, and those dingo scats contained spores of 14 genera of mycorrhizal fungi. These fungi were more likely to appear in the scats of dingoes if primary mycophagist prey mammals had been consumed. Our model predicted dingo median spore dispersal distance to be 2050 m and maximum dispersal potential to be 10 700 m. Conclusions Our study indicates that dingoes are providing a previously overlooked ecosystem service through the long-distance dispersal of mycorrhizal fungi. Many of the fungi found in this study form hypogeous (underground) fruiting bodies that are unable to independently spread spores via wind. Because dingoes move over larger areas than their prey, they are especially important to these ecosystem functions. Implications Our novel approach to studying an overlooked aspect of predator ecology is applicable in most terrestrial ecosystems. Similar modelling approaches could also be employed to understand the dispersal potential of both primary and secondary spore dispersers globally. Because this study highlights an unrecognised ecosystem service provided by dingoes, we hope that it will stimulate research to develop a more comprehensive understanding of other apex predators’ ecosystem functions.

Assessing the effects of survey-inherent disturbance on primate detectability: Recommendations for line transect distance sampling

Habitat destruction and over-hunting are increasingly threatening the arboreal primates of Central Africa. To establish effective conservation strategies, accurate assessments of primate density, abundance, and spatial distribution are required. To date, the method of choice for primate density estimation is line transect distance sampling. However, primates fleeing human observers violate methodological assumptions, biasing the accuracy of resulting estimates. In this study, we used line transect distance sampling to study five primate species along 378 km of transects in Salonga National Park, Democratic Republic of the Congo. We tested the effect of different levels of survey-inherent disturbance (i.e., cutting) on the number of observed (i) primate groups, and (ii) individuals within groups, by counting groups at three different time lags after disturbance of the transect, (i) a minimum of 3 h, (ii) 24 h, (iii) a minimum of 3 days. We found that survey-inherent disturbance led to underestimated densities, affecting both the number of encountered groups and of observed individuals. However, the response varied between species due to species-specific ecological and behavioral features. Piliocolobus tholloni and Colobus angolenis resumed an unaltered behavior only 24 h after disturbance, while Lophocebus aterrimus, Cercopithecus ascanius, and Cercopithecus wolfi required a minimum of 10 days. To minimize bias in density estimates, future surveys using line transect distance sampling should be designed considering survey-inherent disturbance. We recommend evaluating the factors driving primate response, including habitat type, niche occupation, and hunting pressure, peculiar to the survey-specific area and primate community under study.

Generating unbiased estimates of burrowing seabird populations

Maximising survey efficiency can help reduce the tradeoff between spending limited conservation resources on identifying population changes and responding to those changes through management. Burrow‐nesting seabirds are particularly challenging to survey because nests cannot be counted directly. We evaluated a stratified random survey design for generating unbiased population estimates simultaneously for four petrel species nesting on Macquarie Island, Australia, where the survey cue, burrow entrances, is similar for all species. We also compared the use of design‐based and model‐based analyses for minimising uncertainty in estimates. We recorded 2845 Antarctic prion burrows, 306 white‐headed petrel burrows and two blue petrel burrows while distance‐sampling along 154 km of transects. For blue petrels and grey petrels, we completed nocturnal searches along a further 71 km and searched 249 km of tracks during follow‐up ground searches. We failed to generate unbiased population estimates for two rare and localised species, blue and grey petrels, from our stratified random survey. Only for the most widespread and abundant species, Antarctic prion, did the estimate have reasonable power to detect a rapid population change. Model‐based analyses of the stratified random survey data did not improve upon traditional design‐based analyses in terms of uncertainty in population estimates, but they did provide useful spatial representation of current populations. Models that used the targeted survey data did not reflect current population sizes and distributions of the two rare and localised species. We found that when species ecologies, distributions and abundances vary, a multi‐method approach to surveys is needed. Species with low abundance that occur patchily across large islands are likely to be best estimated using targeted surveys, whereas widespread and abundant species can be accurately and precisely estimated from randomised surveys using informative model‐based analyses.

‘Animals under wheels’: Wildlife roadkill data collection by citizen scientists as a part of their nature recording activities

‘Animals under wheels’ is a citizen science driven project that has collected almost 90,000 roadkill records from Flanders, Belgium, mainly between 2008 and 2020. However, until now, the platform and results have never been presented comprehensively to the scientific community and we highlight strengths and challenges of this system. Data collection occurred using the subsite www.dierenonderdewielen.be (‘animals under wheels’) or the multi-purpose biodiversity platform observation.org and the apps, allowing the registration of roadkill and living organisms alike. We recorded 4,314 citizen scientists who contributed with at least a single roadkill record (207-1,314 active users per year). Non-roadkill records were registered by 85% of these users and the median time between registration of the first and last record was over 6 years, indicating a very high volunteer retention. Based on photographs presented with the roadkill records (n = 7,687), volunteer users correctly identified 98.2% of the species. Vertebrates represent 99% of all roadkill records. Over 145,000 km of transects were monitored, resulting in 1,726 mammal and 2,041 bird victims. Carcass encounter rates and composition of the top 10 detected species list was dependent on monitoring speed. Roadkill data collected during transects only represented 6% of all roadkill data available in the dataset. The remaining 60,478 bird and mammal roadkill records were opportunistically collected. The top species list, based on the opportunistically collected roadkill data, is clearly biased towards larger, enigmatic species. Although indirect evidence showed an increase in search effort for roadkill from 2010-2020, the number of roadkill records did not increase, indicating that roadkills are diminishing. Mitigation measures preventing roadkill could have had an effect on this, but decrease in population densities was likely to (partially) influence this result. As a case study, the mammal roadkill data were explored. We used linear regressions for the 17 most registered mammal species, determining per species if the relative proportion per year changed significantly between 2010 and 2020 (1 significant decrease, 7 significant increases). We investigated the seasonal patterns in roadkill for the 17 mammal species, and patterns per species were consistent over the years, although restrictions on human movement, due to COVID-19, influenced the seasonal pattern for some species in 2020. In conclusion, citizen scientists are a very valuable asset in investigating wildlife roadkill. While we present the results from Flanders, the platform and apps are freely available for projects anywhere in the world.

Ecological niche modeling for reintroduction and conservation of Aristolochia cathcartii Hook.f. & Thomson (Aristolochiaceae), a threatened endemic plant in Assam, India

Aristolochia cathcartii Hook.f. & Thomson is a medicinal plant species native to Assam (India). Karbi people have traditionally used the plant to treat a variety of ailments. The population stock of this species has been rapidly depleting in its natural habitats due to over-utilization, habitat fragmentation, and other anthropogenic activities. Extensive field surveys were carried out to investigate the population status of A. cathcartii in various forest areas of Assam’s Karbi Anglong district. In 20 km of transects, a total of 36 quadrats were observed. A. cathcartii density, frequency of occurrence, and abundance were recorded to be 0.65, 17.8, and 3.81, respectively. Ecological niche modelling was used to identify suitable habitat for the reintroduction and conservation of this plant in Assam in order to prevent its extinction in the future. The maximum entropy distribution modelling algorithm was used to identify suitable areas and habitat for the species’ reintroduction and conservation. Primary data on the occurrence of A. cathcartii was gathered from the natural habitat of Karbi Anglong district, Assam, for modelling. The model identified various forest areas in northeastern India that have suitable climatic conditions for plant reinforcement.

Probable extirpation of the hog deer from China: implications for conservation

AbstractThe hog deer Axis porcinus formerly occurred in south-west China but has not been recorded there since 1965. To investigate the current status of the species in China, we conducted interviews, and transect and camera-trap surveys during October 2018–June 2020 to search for signs of hog deer across its historical range in the country. We interviewed 50 local inhabitants and surveyed 14 line transects in four counties of Lincang City, Yunnan Province. The camera traps were deployed in Nangunhe Nature Reserve (39.4 km of transects, 82 camera stations, 15,120 camera days) and Daxueshan Nature Reserve (41.1 km of transects, 68 camera stations, 13,554 camera days). We found no hog deer tracks and no hog deer were trapped by cameras. The floodplain grasslands preferred by hog deer along Nanting River have been transformed into agriculture plantations and human settlements. Our findings suggest that hog deer may have been extirpated from China, most likely as a result of habitat loss and overhunting. The conservation priorities for this species in China are the establishment of a protected area in the Nanting River watershed, restoration of habitat and reintroduction of individuals from range countries.

Assessing year-round phenology and reproduction of the migratory painted lady butterfly, Vanessa cardui (Lepidoptera: Nymphalidae), in a Mediterranean area in southern Spain

The painted lady, Vanessa cardui (Linnaeus, 1758), migrates seasonally between Africa and Europe with a northward multigenerational migration from Africa to Europe in spring and a southward migration from Europe to Africa in autumn. However, little is known about the year-round phenology of this species in southern regions in the Mediterranean Basin. In this study the year-round phenology and reproduction of painted ladies was recorded during a seven-year period (2014-2020) at 7 lowland sites (< 80 m a.s.l) near the coast of CĂĄdiz (southern Spain). Overall, a total of 2341 painted lady butterflies (or 0.56 butterflies/km) were recorded along 4186 km of transects of the Butterfly Monitoring Scheme (BMS). Data pooled for all sites and years indicate a migration of painted ladies in autumn (mid and late October), another peak in abundance in winter (late February) and finally a migration in spring (late May). Abundance, however, varied greatly between sites and years. In July 2019, a spectacular migration of painted ladies was recorded across the study area that was also recorded in other European countries a few weeks later. Territorial behaviour of males, including hill-topping and courtship, oviposition and immature stages were recorded in autumn and winter. Reproductive behaviour was not recorded in spring or summer. Painted ladies were most abundant during the autumn migration, less abundant in spring and much less abundant in winter. This study confirms that the southern tip of Western Europe close to North Africa is an important stop-over region during the migration of painted ladies although numbers fluctuate enormously between years and sites. To my knowledge, this is the first time that the timing of year-round migration and the reproduction of painted ladies in the autumn-winter months have been described for a southern European population.

Detecting supraglacial debris thickness with GPR under suboptimal conditions

The thickness of a supraglacial layer is critical to the magnitude and time frame of glacier melt. Field-based, short pulse, ground-penetrating radar (GPR) has successfully measured debris thickness during a glacier's melt season, when there is a strong return from the ice–debris interface, but profiling with GPR in the absence of a highly reflective ice interface has not been explored. We investigated the performance of 960 MHz signals over 2 km of transects on Changri Nup Glacier, Nepal, during the post-monsoon. We also performed laboratory experiments to interpret the field data and investigate electromagnetic wave propagation into dry rocky debris. Laboratory tests confirmed wave penetration into the glacier ice and suggest that the ice–debris interface return was missing in field data because of a weak dielectric contrast between solid ice and porous dry debris. We developed a new method to estimate debris thicknesses by applying a statistical approach to volumetric backscatter, and our backscatter-based calculated thickness retrievals gave reasonable agreement with debris depths measured manually in the field (10–40 cm). We conclude that, when melt season profiling is not an option, a remote system near 1 GHz could allow dry debris thickness to be estimated based on volumetric backscatter.

A Sea Turtle Population Assessment for Florida's Big Bend, Northeastern Gulf of Mexico

Coastal waters of Florida’s Big Bend, Gulf of Mexico (GOM) once supported one of the largest sea turtle fisheries in the United States. To fill an information gap in this region on abundance and distribution of sea turtles, we used vessel—based distance sampling and active capture methods to characterize current foraging aggregations near the St. Martins Marsh Aquatic Preserve. Over 10 sampling periods between 2012—2018, we completed 513 km of transects and recorded 819 turtles among 4 species—green turtle (Chelonia mydas, n = 624), Kemp’s ridley (Lepidochelys kempii, n = 147), loggerhead (Caretta caretta, n = 47), and a single hawksbill (Eretmochelys imbricata). Turtle densities in 4 study plots within the 200 km2 study site ranged from 57—221 immature green turtles/km2, 16—56 immature Kemp’s ridleys/km2, and 1—14 juvenile—to—adult loggerheads/km2. Of 200 green turtles captured, 67.5% showed skin tumors consistent with fibropapillomatosis, a frequency similar to that from urbanized estuaries of Florida’s east coast. The largest green turtles (> 60 cm straight standard carapace length), abundant in the southern portion of our study area, are of note because this size class is uncommonly recorded within US territorial waters. Analyses of green turtle mtDNA haplotypes found contributions from rookeries in the western GOM, Mexican Caribbean, and Costa Rica. Although Big Bend protected areas were principally designed to conserve marine and coastal habitats, these regulatory zones have also effectively encompassed a hotspot for foraging sea turtles.

La mastofauna nativa como indicador de efectividad en el corredor biológico río Carcarañá, Sur de Santa Fe, Argentina / The native mastofauna as an indicator of effectiveness in the biological corridor Carcarañá river, south of Santa Fe, Argentina

In the south of the province of Santa Fe, the region presents a degree of subdivision and use of the ground that modified its original aspect, becoming a plain where the grain and oilseed crops predominate. The communities of wild mammals are increasingly threatened by this development, which is leading to the limit of fragmentation and loss of habitat. The objective of this work is to show the influence of the Carcarañá River on native mammals and its importance as a biological corridor. For this purpose, the area of study was the Carcarañá River basin in Santa Fe province. Within this area, five sampling zones were established (distant from each other by 50 km), both on the margin of the Carcarañá River and its tributaries. From this, three transects of 3 km in length were established in each study zone, taking into account that the first one is located on the margin of the river/tributary, while the remaining ones are parallel to it with a distance of 5 and 10 km respectively in order to generate a gradient. The field work was carried out during two consecutive years (2018-2019), in a seasonal manner. The methodology used was the collection of indirect evidence (footprints and faults) and the collection of information from direct evidence (sightings). The transect tours were carried out on foot, during the daytime hours and at an average speed of one km/h. To obtain complete parameters of the diversity of species in each transect, the number of species and their representativeness were quantified. For this purpose, it was established the specific richness (S) which refers to the number of species registered for each transect and its equity. The latter was calculated from the Shannon-Wiener function. With a sampling effort of 80 days of field work and 360 km of transects, it was possible to obtain a specific richness (S) of 12 species for the total of the transects located on the banks of the Carcarañá River ( Lutreolina crassicaudata, Didelphis albiventris, Chaetophractus villosus, Pseudalopex gymnocercus, Puma concolor, Puma yaguaroundi, Leopardus geoffroyi, Leopardus colocolo, Conepatus chinga, Galictis cuja, Hidrochoerus hydrochaeris and Myocastor coypus ) with a diversity index of H' = 2. 79. For the sum of the species registered in the transects located 5km from the river, the specific richness was 5 species ( D. albiventris, C. villosus, P. gymnocercus, C. chinga and G. cuja ) with a diversity index (H')= 0.94. Finally, the sum of species registered for the transects located 10km from the river was also 5 species with a somewhat lower diversity (H'= 0.63). Although incipient as a process and premature to test conclusive results, the evidence that biological corridors in areas widely disturbed by anthropogenic activity are a tool that contributes to the recovery of favorable environmental conditions for native mammals, is consolidated as the information generated ratifies the initial hypothesis about the value of biological corridors as a tool for biodiversity conservation.

Distributional shifts among seabird communities of the Northern Bering and Chukchi seas in response to ocean warming during 2017–2019

In the northern Bering Sea and eastern Chukchi Sea, 2017–2019 were record-breaking years for warm ocean temperatures and lack of sea ice. The region supports millions of seabirds that could be affected by shifts in prey distribution and availability caused by changing environmental drivers. However, seabirds are highly mobile and often flexible in diet, and might alter their foraging distributions accordingly. To determine if there was evidence of long-term changes in abundance of seabirds, or if seabirds used the offshore habitat differently during recent warm years, we compared species richness, community composition, and distribution and abundance of selected species and Total seabirds (all species combined) between two periods, 2007–2016 and 2017–2019. We also evaluated annual changes in abundance during 2007–2019. We used 79,426 km of transects from vessel-based surveys conducted July through September. Total seabird density for the entire study area increased by ~20% during 2017–2019, but changes were not consistent across the study area, nor among species, and species richness declined except for a slight increase in the northern Chukchi Sea. Total seabird density declined most in the northern Bering Sea (−27%), although it increased in the Chirikov Basin by 73%. During 2017–2019, abundance of piscivorous murres (Uria spp.) decreased everywhere, whereas planktivorous Aethia auklet density increased by 70% in Chirikov Basin; auklets apparently abandoned their post-breeding migration to the Chukchi Sea. Short-tailed shearwaters (Ardenna tenuirostris) expanded farther into the northern Chukchi Sea, with nearly twice the density of the previous decade. We identified five seabird community types, three of which (all dominated by an alcid species) contracted spatially in the later period, and shifted south or near colonies. In contrast, a short-tailed shearwater dominated community expanded northward, and a community defined by low seabird density expanded throughout the eastern portion of both the northern Bering and Chukchi seas, suggesting higher-density communities had shifted westward. The variable responses among species correspond to documented changes in the environment as well as their natural history.

An abundance estimate of free-roaming horses on the Navajo Nation

Free-roaming horses (Equus ferus caballus) occur throughout arid and semiarid regions of the western United States, where they can decrease plant biomass and diversity, impair water quality, and reduce forage available to native wildlife and domestic livestock. Management of free-roaming horses on Bureau of Land Management (BLM) and US Forest Service lands is determined by protections and population targets established by law, but these do not apply to other federal or Tribal Lands, where relatively little is known about the abundance and distribution of free-roaming horses. To address this information gap, we conducted the first comprehensive survey of free-roaming horses within the Navajo Nation, which is the largest Tribal Land holding in the contiguous United States and covers portions of the states of Arizona, New Mexico, and Utah. We used stratified random sampling and double-observer distance methods to produce estimates of horse abundance corrected for detection bias. During the summer of 2016, we used fixed-wing aircraft to survey 4 975 km of transects across our 67 089-km2 study area. We observed 4 290 horses distributed among 527 groups and estimated 38 223 horses lived within the study area during the survey period (standard of error [SE]: 6 052, 90% confidence interval: 29 365–47 080), with 29 394 horses in open areas (SE: 5 511, 90% confidence interval [CI]: 21 328–37 460) and 8 829 horses in forested areas (SE: 2 331, 90% CI: 5 417–12 240). Overall density of 0.570 horses/km2 (SE: 0.090, 90% CI: 0.438–0.702) was 23% higher than density of horses and burros (Equus asinus) in all BLM herd management areas (HMAs) in 2016 and exceeded by 17% the density in Nevada, the only state with an HMA of comparable size to the Navajo Nation. Our results will inform management of a free-roaming horse population that this study has revealed to be the among the largest in the United States.