STATUS AND ECOLOGY OF SOTALIA FLUVIATILIS IN THE CAYOS MISKITO RESERVE, NICARAGUA

In March through May of 1996–1998, we conducted research in the Cayos Miskito Reserve, Nicaragua, to assess the status, ecology, and distribution of Sotalia fluviatilis , a dolphin known from southern Brazil to Honduras. Aerial and boat surveys of lagoons, inlets, and coastal areas were conducted and observational information collected on Sotalia activity, behavior, and other factors relating to its ecology. During boat surveys 183 groups (536 individuals) were sighted (for areas with Sotalia , mean overall density = 0.604 individuals/km², coastal areas = 0.647/km², inlets = 0.578/km², and lagoons = 0.486/km²). Overall, based on all sightings, mean group size was 3.01 (SD = 1.79, range 1–15) and varied among years ( = 4.20 in 1996, 2.58 in 1997, and 3.39 in 1998), but not for different months. We estimate that 49 Sotalia inhabited the portions of the Reserve we studied. Sightings of Sotalia groups were non-random (nearest-neighbor analysis); clumping of sightings indicates that some areas were preferred. In both Pahara inlet and Wauhta lagoon, sightings were more frequent after 1200 than in the morning. In coastal areas Sotalia were sighted most often within 100 m of shore (54.0%), less often from 101 to 200 m (39.1%), and infrequently from 201 to 300 m (6.8%). Seldom were animals observed in more than 5 m of water, and usually it was considerably shallower ( i. e. , <2 m). Feeding was the predominant of five recorded activities ( i. e. , traveling, feeding, socializing, resting, and other), based on time of group sighting (70.3%) and during instantaneous sampling (56.3%). Resource distribution appears to be an important factor influencing Sotalia distribution in the Reserve.     

Carrying Capacity and Potential Production of Ungulates for Human Use in a Mexican Tropical Dry Forest

Data are provided on the carrying capacity and potential production for sustainable human use of white-tailed deer ( Odocoileus virginianus ) and collared peccary ( Pecari tajacu ) in a protected tropical dry forest at Chamela on the Pacific coast of Mexico. In this paper, the carrying capacity was defined as the equilibrium density plus the number of animals removed by predators. The equilibrium point was estimated from the density dependent relationship between the finite population growth rate and the current density according to a logistic model. Annual density was estimated using the line transect method. Carrying capacity estimates were 16.5 to 17.2 deer/km² and 9.3–9.5 peccaries/km², representing a combined biomass of 841–874 kg/km². A potential production for human use of 2.1 deer/km² and 4.4 peccaries/km² was estimated employing the model of Robinson and Redford (1991) . The data suggest that, in the protected tropical dry forest of Chamela, the density and biomass of wild ungulates can maintain a similar or greater density and biomass than other Neotropical forests. To obtain an accurate estimation of the maximum sustainable yield ( MSY ), it is necessary to consider predation. From a management point of view, it is important to consider that carrying capacity varies as a function of the rainfall pattern.     

Spatial organization and recruitment of lynx (Lynx lynx) in a re-introduced population in the Swiss Jura Mountains

We monitored seven resident (three males and four females) and six dispersing subadult Eurasian lynx from to in a population that was re-introduced to the Swiss Jura Mountains in the early 1970s. Home-range areas of the neighbouring adults were 71–281 km², and significant core areas 34–252 km². Males occupied significantly larger areas than females. Home-range overlap was 9% for neighbouring males and 3%) for females. Core areas of males did touch, but those of females were clearly separated. Each male's home range covered those of one or two females. Population density was 0.94 lynx/100 km² for resident animals. Pre-dispersal mortality was estimated to be 50%. Juveniles dispersed from their mothers' home area at the age of 10 months. Of six monitored subadults. only one survived the first year of independence. Human-caused mortality (traffic accidents. illegal killing) was high. This was also the case among resident adults. This might be a threat to the long-term survival of the reintroduced population.     

LONG-TERM TRENDS IN ABUNDANCE AND DISTRIBUTION OF MANATEES (TRICHECHUS MANATUS) IN THE NORTHERN BANANA RIVER, BREVARD COUNTY, FLORIDA

Four aerial survey projects were conducted between 1977 and 1986 to determine the abundance, density and distribution of West Indian manatees (Trichechus manatus), in the northern Banana River, Kennedy Space Center, Florida. Manatee density and distribution within selected portions of the 78.5 km² study area were determined. Peak numbers of manatees occurred in spring of each year. The maximum counts increased from 56 in 1978 to 297 in 1986. Manatee abundance was lowest in the winter of each year. Mean density per flight increased from 0.52 manatees/km2 in 1977–78 to 2.73/km² in 1984–86. This increase may reflect increases in the east coast population or shifts in the population distribution. Distributional changes were observed in the study area through time, with a lower percentage of manatees occurring in industrial areas and a correspondingly higher percentage of manatees in nonindustrial areas by 1985.     

Home range and habitat use by the serotine bat, Eptesicus serotinus, in England

Serotine nursery roosts with less than 20 bats were found to have home ranges of at least 24 to 77 km² and core areas of activity from 13 to 33 km². The size of the range may have increased further if more individuals had been tracked, as three of the four colonies studied had not reached their asymptotes. The total home-range area covered by four serotine colonies was 127.36 km². Excluding non-breeding bats, a density of one bat per 120 ha was estimated. However, actual density was likely to be higher if there were additional non-breeding females and immatures that were not in nursery roosts. Colonial home ranges and core areas overlapped, with individuals from different colonies feeding at the same sites. Individual home ranges ( n = 32) varied from 0.16 to 47.58 km², but these were not used exclusively by one individual. Around the colonial core area and breeding roosts, home ranges were used by all individuals from a single colony. It is only further from the core area that ranges appeared to be used by individuals. The distance from roost to feeding areas varied by up to 7.4 km, but the bat usually commuted along lines of trees and hedges and over pastures. This resulted in greater distances being travelled than if they had flown by a direct route. On average, individuals commuted distances of 8 km each night between feeding areas, with a maximum distance of over 41 km. They visited between 0 and 10 feeding sites each night (mean = 2.89).     

Movement Patterns and Home Range Of The Bongo (Tragelaphus Eurycerus) In The Rain Forest Of The Dzanga National Park, Central African Republic

Bongos ( Tragelaphus eurycerus Ogilby) were studied for 8 months in the Dzanga National Park, Central African Republic. Tracks were followed and mapped with a compass and a pedometer to study movement patterns and home range. Natural licks were shown to be central points in the home range of the bongos: they visited the licks recurrently to consume soil, but also to forage on grass and herb species, and for social reasons. Forest areas far from licks were used much less than forest areas close to licks. When a lick was visited, distances between two resting sites were longer than in the forest without lick visits, caused by a direct and straight movement from the denser forest areas toward a lick. The study area of about 150 km² was presumably occupied by two groups of bongos. One of them seemed to split temporarily into two subgroups. Groups were not larger than 10–20 individuals. Estimated home ranges were at least 49 km² and 19 km² for the two groups, respectively. Estimated density in the Dzanga National Park was 0.25 bongos per km^2. This study shows the importance of natural licks for the largest social forest antelope, the bongo, and provides information which is important for its future conservation.     

Residence and movement patterns of cownose rays Rhinoptera bonasus within a south-west Florida estuary

Between July 2003 and November 2004, 21 cownose rays Rhinoptera bonasus were tagged and tracked within Pine Island Sound estuary, Florida, using passive acoustic telemetry. Residence time of individuals ranged between 1 and 102 days. No relationship was detected between ray activity and tidal stage or time of day. Minimum convex polygons (MCP) and kernel utilization distributions (KUD) were calculated over several time frames to demonstrate the extent of an animal's home range and core areas of use. Total MCPs ranged between 0·81 and 71·78 km² (mean = 22·01 km²), with daily MCPs as large as 25·8 km². Total 95% KUDs ranged between 0·18 and 62·44 km² (mean = 22·63 km²), while total 50% KUDs were smaller, ranging from 0·09 to 9·68 km² (mean = 3·33 km²). Both MCP and KUD areas exhibited a positive relationship with residence time and R. bonasus size. As mobile, pelagic swimmers capable of traversing large distances, these data show that cownose rays travel extensively throughout this estuary, yet may remain within very small areas for extended periods.     

Rangeland degradation is poised to cause Africa's first recorded avian extinction

Rangeland degradation by livestock threatens several restricted-range species, but is largely overlooked by conservation biologists. The Sidamo lark Heteromirafra sidamoensis , confined to the Liben Plain grassland in southern Ethiopia, is critically endangered by bush encroachment, permanent settlement and agricultural conversion. Its global range was previously estimated at 760 km², but in 2007–2008 available habitat covered<35 km². Density estimates from multi-model inference analysis of distance transect data provided a global population estimate of 90–256 adults (possibly with a serious sex-ratio bias towards males). Logistic regression models of habitat selection showed that males preferentially occurred in areas of grassland with greater cover of medium-length grass (5–15 cm), less cover of bare ground and fewer bushes. Habitat transects extending outward from its core range revealed massive and rapid bush encroachment, corroborating information from semi-structured interviews. The survival of both local Borana pastoralism and this species – mainland Africa's likeliest first avian extinction – depends on restoring seasonal patterns of grazing, resisting agricultural conversion of grasslands, reversing fire suppression policies and clearing bush.     

Brazilian Tapir Density in the Pantanal: A Comparison of Systematic Camera-Trapping and Line-Transect Surveys

The density of Brazilian tapirs ( Tapirus terrestris) was studied in the northeastern part of the Pantanal wetlands of Brazil using two simultaneous and independent methods: (1) systematic camera trapping combined with capture–recapture analysis, with camera traps spaced 1 km apart and distributed over 54 km²; and (2) line-transect sampling using an array of 12 linear transects, from 3.8 to 7.2 km long, covering the principal open and forest habitat types across the entire 1063 km² SESC Pantanal Reserve. The two methods yielded conservative density estimates of 0.58 ± 0.11 tapirs/km² (camera trapping) and 0.55 (95% CI 0.30–1.01) tapirs/km² (line transects). The study suggests that certain Pantanal habitats and sites can sustain relatively high population densities of tapirs when these animals are protected from hunting. Further testing of the camera-trapping methodology as applied to tapirs is required, particularly focusing on extending the survey period. As it represents a relatively rapid method for estimating population density, in comparison to line-transect surveys, and as it generates information simultaneously on multiple species that are conservation priorities, we recommend that camera-trapping surveys be applied more widely across a variety of Pantanal habitats and land-use categories in order to confirm the value of the vast 140,000 km² wilderness region for this vulnerable species.     

Wintering site fidelity and movement patterns of Western Sandpipers Calidris mauri in the San Francisco Bay estuary

Western Sandpipers Calidris mauri are the most numerous shorebird species in the San Francisco Bay estuary during winter. A sample of 106 Western Sandpipers was captured in mist nets and radio-marked with 1-g transmitters to examine their wintering site fidelity and movements. Differences in distances moved, home range extent and core area size were examined by age, sex, season, site, time of day and tide. All birds remained in the south San Francisco Bay region during winter and exhibited strong site fidelity, with a mean home range of 22.0 km² or only 8% of the study area. First-year birds had larger home ranges (26.6 ± 3.6 km²) than adults (17.2 ± 2.5 km²) in winter, but home range sizes of males and females were not significantly different in any period. Home range sizes were similar between seasons, but core areas were smaller in spring (6.3 ± 1.2 km²) than in early (9.6 ± 4.0 km²) or late (11.6 ± 1.6 km²) winter. Movements and home range size were similar for radio-marked birds located during day and night. The high degree of regional and local site fidelity demonstrated that the mixture of natural mud fiats and artificial salt ponds in southern San Francisco Bay provided sufficient resources for large wintering populations of Western Sandpipers.     

HARBOR PORPOISE (PHOCOENA PHOCOENA) ABUNDANCE IN ALASKA: BRISTOL BAY TO SOUTHEAST ALASKA, 1991-1993

Between 1991 and 1993, Alaska harbor porpoise ( Phocoena phocoena ) abundance was investigated during aerial surveys throughout much of the coastal and offshore waters from Bristol Bay in the eastern Bering Sea to Dixon Entrance in Southeast Alaska. Line-transect methodology was used, and only those observations made during optimal conditions were analyzed. Survey data indicated densities of 4.48 groups/100 km², or approximately 3,531 harbor porpoises (95% C. I. 2,206-5,651) in Bristol Bay and 0.54 groups/100 km², or 136 harbor porpoises (95% C. I. 11-1,645) for Cook Inlet. Efforts off Kodiak Island resulted in densities of 1.85 groups/100 km², or an abundance estimate of 740 (95% C. I. 259-2,115). Surveys off the south side of the Alaska Peninsula found densities of 2.03 groups/100 km² and an abundance estimate of 551 (95% C. I. 423-719). Surveys of offshore waters from Prince William Sound to Dixon Entrance yielded densities of 4.02 groups/100 km² and an abundance estimate of 3,982 (95% C. I. 2,567-6,177). Combining all years and areas yielded an uncorrected density estimate of 3.82 porpoises per 100 km², resulting in an abundance estimate of 8,940 porpoises (CV = 13.8%) with a 95% confidence interval of 6,746-11,848. Using correction factors from other studies to adjust for animals missed by observers, the total number of Alaska harbor porpoises is probably three times this number.     

Preliminary estimates of the population density of the Sokoke scops owl Otus ireneae Ripley in the East Usambara lowlands, Tanzania

Preliminary population density estimates are presented for a recently discovered population of the Sokoke scops owl Otus ireneae in the lowlands of the East Usambara mountains, Tanzania. Calling birds were mapped at two sites totalling 6·3 km². Approximate densities were 3–4 territories/km² in Kwamgumi Forest Reserve and <1·5 territories/km² in Manga Forest Reserve, a much more heavily logged site. Densities in prime habitat in Arabuko‐Sokoke forest, Kenya, the only other locality for the species, exceed seven territories/km². The total population in the East Usambaras cannot be calculated, but it is probably markedly smaller than in Arabuko‐Sokoke. Suggestions for more precise surveys are made.     

Behavioural ecology of the Sloth bear (Melursus ursinus)

The Sloth bear ( Melursus ursinus ), which is endemic to the Indian subcontinent and Sri Lanka, has declined in numbers in many areas in recent years probably as the result of over-killing and habitat alteration. In the 544 km² Royal Chitawan National Park in the Nepal terai, we estimated there were a minimum of 55 bears or a crude density of 0˙1/km². During peak concentrations in the lowlying riverine forest/tall grass habitat in March, the ecological density was 0˙5/km².
Cubs still with their mothers comprised 24 % of the 161 bears classified between December 1972 and November 1975. Females comprised 48% of the adults classified. Average size of 24 litters was 1˙6 (1–2). Seventy-two per cent of the observations were of lone individuals. Three (an adult female with two cubs), was the largest group of bears seen. The only extended social group observed was the female-young unit although newly independent siblings may remain together for a short time. Maternal relations, adult interactions, tree marking, ranging, feeding and anti-predatory behaviour are described.
Examination of 139 droppings showed that these bears fed on at least 17 different fruits (47% occurrence), flowers, grass, honey, and six different insects (52% occurrence). Fruits were an important food from March to June with individual species predominating throughout their fruiting season. Termites, including Odontotermes obesus , were in the diet for most of the year. The Sloth bear was not observed preying on mammals and according to other observers, only rarely feeds on carrion. The ecological basis for selected aspects of Sloth bear biology and behaviour is discussed.     

The population density, growth rate and production of roach Rutilus mtilus (L.) in Tjeukemeer, The Netherlands

A method of estimating the population density of roach in Tjeukemeer (21.3 km²) using 20 529 introduced fin-clipped fish is described. Fyke nets proved to be an effective method of sampling the population for marked fish during the spawning season. A total of 20 277 roach were processed during the recapturing period. The population density of roach (⋝ 14 cm) was estimated to be 1 246 458. The growth rate of roach in the lake although relatively poor (von Bertalanffy's L ∞ for males and females, 22 and 26 cm respectively) for the species was similar to that recorded in three other Friesian lakes. The mortality rate of males was higher than that of females. Logarithmic length-weight regression analyses showed that the value of the coefficient varied both within and between the sexes, that of females being higher (range 3.03–3.375) than that of males (range 2.76–3.254). Seasonal changes in the size of the coefficient were due to a disproportionate loss of gonad weight in larger fish. The fecundity of the population was comparatively high for the species.
The total production of the population was estimated to be 95 hg ha⁻¹ of which 39 kg ha⁻¹ was contributed by fry. In older (⋝ IV) fish the production of females (12 kg ha⁻¹) exceeded that (2 kg ha⁻¹) of males, due to differences in their growth and mortality rates. The relatively poor performance of roach in Tjeukemeer, in terms of biomass and production was due to a scarcity of zoobenthos and competition from other species offish. There is no evidence either from this study or the literature that the productive potential of roach in lakes is high, even though macrophytes and detritus can be consumed in significant amounts.     

Population ecology of the white-nosed coati (Nasua narica) on Barro Colorado Island, Panama

The white-nosed coati, Nasua narica , is a common Neotropical carnivore with a social structure of band-living adult females and solitary adult males. A coati population on Barro Colorado Island, Panama, was studied over a four-year period by mark-recapture, radiotelemetry. and direct observation of habituated individuals. The population density was approximately 51.5 individuals/km² and the sex ratio was 1:1. Band size varied from six to 26 individuals (mean = 15.3) with extensive fluctuation within and between years. Mean foraging group size was smaller (7.2 individuals) than population group size, and fluctuated with food availability, synchronous parturition, and the emigration of mature males. Mean home-range size of six bands was 0.33 km², and ranges of adjacent bands overlapped from 0–66%. One band fissioned during the study; however, the resulting bands did not disperse from the original home range. Seven adult males had a mean home-range size of 0.37 km², each extensively overlapping the home ranges of several other males. Observations of 10 adult males whose natal bands were known indicate that when males disperse they do not simultaneously leave the band's home range. Rather, their home ranges remain within or broadly overlapping those of their natal bands. This dispersal pattern is unusual within the order Carnivora.     

Variable responses of waterfowl breeding populations to long-term removal of introduced American mink

It is suspected that feral American mink, an introduced predator in Europe, have seriously affected local densities of birds breeding in archipelagos and coastal areas. We studied the effects of mink removal on breeding densities of waterfowl in two manipulation and two control areas in the outer archipelago of SW Finland, Baltic Sea. The study was conducted in two phases: during 1992–2001 a total of 98 mink was removed from 60 islands and islets (total area 72 km²) whereas on 37 islands and islets (35 km²) mink was not removed. Additional mink removal and control areas were established during 1998–2001 to replicate the experiment. The breeding densities of the shelduck, tufted duck and the velvet scoter increased as a response to mink removal, while in the control areas their populations remained unchanged. The breeding densities of mallards increased during the first 7 yr of mink removal, but a steep decrease in the last study year resulted in a statistically non-significant overall increase. The species with low breeding densities (the gadwall, northern shoveler, pintail and the red-breasted merganser) increased as well. In contrast, the populations of large waterfowl species, the mute swan, greylag goose, common eider and the goosander, did not show obvious increases in breeding densities after mink removal. We conclude that feral mink may locally limit the breeding densities of some smaller waterfowl species and thus reduce the diversity of the waterfowl community in the outer archipelago.     

Serengeti real estate: density vs. fitness-based indicators of lion habitat quality

Habitat quality is typically inferred by assuming a direct relationship between consumer density and resource abundance, although it has been suggested that consumer fitness may be a more accurate measure of habitat quality. We examined density vs. fitness-based measures of habitat quality for lions in the Serengeti National Park, Tanzania. A 40-year average of female reproductive success (yearling cubs per female) was best explained by proximity to river confluences, whereas patterns of productivity (yearling cubs per km²) and adult female density (individuals per km²) were associated with more general measures of habitat quality and areas of shelter in poor habitat. This suggests that density may not accurately distinguish between high-quality 'source' areas and low-quality sites that merely provide refuges for effectively non-reproductive individuals. Our results indicate that density may be a misleading indicator of real estate value, particularly for populations that do not conform to an ideal free distribution.     

Latitudinal trends, population size and habitat preferences of the Damara Tern Sterna balaenarum on Namibia's desert coast

The Damara Tern Sterna balaenarum is a rare, near-endemic breeder along the southwestern coast of Africa. Found predominantly in Namibia, its world population was once believed to be 4000 birds. Population surveys in the northern Namib Desert have recently estimated that 12,000 adults exist. The aims of this study were to (1) determine the population status along the southern coast, thereby completing Namibian surveys, (2) assess latitudinal trends (over 10̀) in relation to ocean upwellings for the entire coast and (3) determine breeding habitat preferences. This was completed in 1994 and 1996 using random sampling techniques. Survey squares of 1 km², randomly plotted on 1:50,000 maps, were located in the desert with a Global Positioning System (GPS) unit and searched for breeding terns. A total of 1780 km² was sampled in the southern desert and extrapolations indicated that about 1450 adult terns occur in this region. This gives a global population estimate of 13,500 adult Damara Terns. Significant habitat preferences were apparent with terns nesting most often on gravel plains in the north but switching to salt pans in the south. Lower salt pan temperatures in the south may account for these trends. The peak density was in central areas (23|dGS) with a decreasing density north and south along Namibia's 1470 km-coast. This is parallel to recent findings for linear shorebird densities and macro-invertebrate density. This suggests that primary productivity of the Benguela is highest in the central regions and not where the upwellings occur 400 km south. We propose a delayed blooming effect to account for these trends and conclude that this diminutive tern is influenced in many aspects of its life history by Namibia's cold offshore upwellings.     

An attempt to estimate the predatory pressure exerted by the lesser weever, Trachinus vipera Cuvier, in the southern North Sea

In order to evaluate the impact of the lesser weever on the ecosystem of the southern North Sea, geographical distribution, density, growth, production and food requirements have been estimated. High densities were found on and around the Brown Ridge, an area with high tidal current velocities, medium grain-size of the sediment and a poor benthic fauna. Growth is restricted to the months of June October. During the winter cessation of growth a considerable loss of weight (about 20%) takes place. Mortality has been estimated by using the average size frequency distribution of all catches made from 1972 to 1984. The resulting convex type of survival curve indicates a high survival rate of the II to IV-group fishes. The production (estimated with Allen's graphical method) of a population of 100 individuals including all age groups (0-VI) amounts to 123.7 g AFDW-year'. In areas with highest densities, consequently, production amounts to 0.018–0.078 g AFDW-m² -year^-1. With an assumed transfer efficiency of 10% through the year, food requirements amounts to 0.18–0.78 g AFDW-m ² -year ^-1. Since the lesser weever feeds mainly on fish (85.6%), almost exclusively on gobies (Pomatoschistus sp.), and with an assumed transfer efficiency of approximately 10%, the indirect predatory pressure exerted by it may amount to 1.6 6.7g AFDW-m ².year ^-1. A possible feeding by gobies on pelagic organisms (calanoids, mysids) is discussed.     

Spatial organization of leopards Panthera pardus in Taï National Park, Ivory Coast: is rainforest habitat a 'tropical haven'?

Between June 1992 and July 1994, two female leopards and one male were radio-tracked. Regular locations of the leopards, the use of a phototrap, and spoor data, provided the first detailed ecological data about this elusive felid in tropical rainforest habitat. The home range of the male was 86 km², those of the two females were 29 km² and 22 km², respectively. One female's home range was fully included within that of the male. Home ranges of neighbouring residents were not exclusive. Population density is estimated at one leopard per 9-14 km². Intraspecific interactions were rare and predominantly involved mating. The large size of the home ranges and a relatively high population density imply large overlap between adjacent resident leopards' ranges. Differences in the leopard's land tenure system between the rainforest and the savanna are discussed. Doubt is cast on the validity of the often-quoted estimate of one leopard per 1 km² in tropical rainforest habitat.