Habitat preferences for Long-eared Owls Asio otus and Little Owls Athene noctua in semi-arid environments at three spatial scales

Capsule There is a relationship between owl numbers and the availability of the agri-forest patchwork.

Aims To model habitat preferences at three different scales of two predators largely neglected within the framework of Environmental Impact Assessment (EIA) studies.

Methods We studied habitat preferences of Long-eared Owls and Little Owls by comparing habitat composition around 28 and 78 occupied territories respectively with 55 non-occupied territories in Alicante (eastern Spain). Generalized linear models were used to examine patterns of habitat preference at three different spatial scales: nest-site, home range and landscape.

Results At the nest-site scale, Long-eared Owls preferred wooded areas with few paved roads while Little Owls preferred arid plantations. Furthermore, the probability of finding an occupied territory increased with the proximity of another occupied territory in the surroundings. The home range scale models mirror the feeding requirements of the owls. Thus, Long-eared Owls occupied areas with high percentages of forest, arid plantations, edges between these two land uses, short distances between nests, with presence of conspecifics and little human disturbance. Little Owls occupied arid plantations with high availability of linear structures and the proximity of villages. At the landscape scale, Long-eared Owls eluded extensive forests, and Little Owls preferred arid plantations.

Conclusions We suggest a hierarchical process of habitat selection for both owls regarding fitting trophic resources at the broadest scales and adequate sites for breeding and roosting at the smallest scale. EIA studies must consider that protecting small areas around single nests may not be an efficient conservation option compared with preserving clusters of territories for both species.     

Determinants of avian species richness at different spatial scales

ABSTRACT. Studies of factors influencing avian biodiversity yield very different results depending on the spatial scale at which species richness is calculated. Ecological studies at small spatial scales (plot size 0.0025–0.4 km²) emphasize the importance of habitat diversity, whereas biogeographical studies at large spatial scales (quadrat size 400–50,000 km²) emphasize variables related to available energy such as temperature. In order to bridge the gap between those two approaches the bird atlas data set of Lake Constance was used to study factors determining avian species diversity at the intermediate spatial scales of landscapes (quadrat size 4–36 km²). At these spatial scales bird species richness was influenced by habitat diversity and not by variables related to available energy probably because, at the landscape scale, variation in available energy is small. Changing quadrat size between 4 and 36 km², but keeping the geographical extension of the study constant resulted in profound changes in the degree to which the amount of different habitat types was correlated with species richness. This suggests that high species diversity is achieved by different management regimes depending on the spatial scale at which species richness is calculated. However, generally, avian species diversity seems to be determined by spatial heterogeneity at the corresponding spatial scale. Thus, protecting the diversity of landscapes and ecosystems appears to ensure also high levels of species diversity.     

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.     

Ranges of males of the Great Hornbill Buceros bicornis, Brown Hornbill Ptilolaemus tickelli and Wreathed Hornbill Rhyticeros undulatus in Khao Yai National Park, Thailand

Ranges of individual males of three hornbill species were determined by radio telemetry during the breeding and non-breeding seasons in Khao Yai National Park, Thailand. Two Great Hornbills Buceros bicornis and two Brown Hornbills Ptilolaemus tickelli were studied in both 1988 and 1989, and two Wreathed Hornbills Rhyticeros undulatus were studied in 1989, 1990 and 1991.
In the breeding season, the home range of the Great Hornbill was 3.7 km², similar to that of the Brown Hornbill (4.3 km²), while the Wreathed Hornbill occupied the largest home range (10.0 km²). In the non-breeding season, the range size of the Wreathed Hornbill (28.0 km²) was greater than that of the Great Hornbill (14.7 km²). Differences in range sizes of different species may be related to differences in diet and breeding strategy. Ranges overlapped within and between the species, and this has implications for the estimation of the minimum area required for the conservation of hornbills within the Khao Yai National Park.     

Landscape characteristics associated with the occurrence of the flying squirrel Pteromys volans in old-growth forests of northern Finland

We investigated whether the occurrence of the flying squirrel, a declined virgin forest species, was accounted for by the structure of the landscape in northeastern Finland We sampled 20 forest areas (1–77 km² in size) in 1995 for the occurrence of the species using a sampling plot method Landscape structure around occupied and unoccupied areas were compared using seven different radii ranging from 100 m lo 10 km Classified satellite images were analyzed with Geographic Information System (GIS) Ten areas could be determined to be occupied by the flying squirrel Results showed that occupied areas did not deviate from unoccupied ones in total area In unoccupied areas there were more mature pine-spruce forests, and less matrix habitat at the home range scale (100 m and 200 m radii) than in occupied areas Further more, in unoccupied forest areas open habitats (clear-cuts, open fens) were more common than in occupied ones at distances between 200 m and 2 km around sampling plots These differences resulted from both larger mean patch size of and smaller mean nearest neighbor distance between open habitat patches m unoccupied than in occupied forest areas According to a logistic regression analysis, information on the amount of open habitat within 1 km radius alone correctly classified 75% of the areas into occupied and unoccupied ones The probability of the presence of flying squirrel decreases with the increasing amount of open habitat within 1 km The results suggest that increasing the amount of open habitats (e g clear-cutting) at the local scale has a negative impact on the flying squirrel It is obvious that in the present situation where the population has severely declined and its optimal habitat is still diminishing, every patch suitable for the species - whether occupied or not -may be important for the population persistence     

Home range and habitat use of wolverines Gulo gulo in Yukon, Canada

Home ranges and habitat use are described for three adult female, one adult male, and one subadult male wolverines in the Kluane Game Sanctuary, Yukon. When long distance excursions are not included, home ranges of wolverines in the Kluane Game Sanctuary were between 76 and 269 km² for females and 209 and 269 km² for males. Habitat use of females was similar to habitat availability. Males used subalpine coniferous habitats more frequently than other habitat types during winter. Although individual variation in the use of forest cover types, aspects, slopes and elevations was apparent, seasonal use did not differ from availability for each sex. Within the 1590 km² study area, three adult males and six adult females were present, corresponding to a density of one resident wolverine 177 km^-2.     

Forest fragmentation due to agriculture affects the reproductive success of the ground-nesting black grouse Tetrao tetrix

We used data from the Finnish wildlife triangle censuses (1989-92) to test the prediction that the reproductive success of ground-nesting bird species is lowered in forest landscapes fragmented by the occurrence of agricultural land, presumably as a consequence of increased densities of generalist predators Our study was based on 201 wildlife triangles located in central Finland (total length 2412 km) As expected, the proportion of black grouse hens with a brood in August decreased relative to the increasing proportion of agricultural land in a landscape (100 km²) However, on a smaller spatial scale (10 8 km²), the probability of an observed hen being with a brood was higher in the vicinity of fields This finding may be explained by differences in habitat selection between hens with a brood and those without a brood We did not find any negative effect of landscape composition on brood size We conclude that increased predation pressure in forest landscapes fragmented by agriculture affects nesting success, but not the survival of black grouse chicks after hatching Our results also emphasize the importance of spatial scale in studies of landscape ecology     

Effects of topographic variability on the scaling of plant species richness in gradient dominated landscapes

It is commonly assumed that variation in abiotic site conditions influences the number of niches, which in turn affects the potential species richness in an area. Based on theoretical considerations, abiotic variation is often used as an estimator of species richness at broad scales, while at finer landscape scales the diversity of habitat types is used. However, habitat estimators assume the landscape to be composed of discrete, homogeneous patches with sharp boundaries, and such a concept is hard to apply in gradient-dominated landscapes. The aim of this study was therefore to investigate the influence of topographic variability (TV) on species richness at the landscape level (gamma (γ) diversity) and on its components (alpha (α) and beta (β) diversity) at microsite and habitat group levels. Using floristic data from 12 "landscapes" of 1 km² we investigated the influence on diversity components of two simple and one complex measures of TV. While the standard deviation (SD) of altitude explained a high proportion of the variation in γ diversity (linear regression model, R²=0.63), the complex measure, SD of solar radiation explained it even better (R²=0.82). There were strong effects of TV on α and β diversity components at the microsite level, but only marginal increases of the diversity components at the habitat level. Further analyses revealed that the missing increase of the habitat level components was caused by differences between habitat groups and that only grassland diversity components increased significantly with TV. We conclude that TV at a landscape scale has strong effects on niche or microsite diversity and is an appropriate estimator of relative species richness in landscapes that are topographically heterogeneous and gradient dominated.     

Modelling breeding habitat preferences of Bonelli’s eagle (Hieraaetus fasciatus) in relation to topography, disturbance, climate and land use at different spatial scales

Predictive models on breeding habitat preferences of Bonelli’s eagle (Hieraaetus fasciatus; Aves: Accipitridae) have been performed at four different spatial scales in Castellón province, East of Iberian Peninsula. The scales considered were: (1) nest site scale (1×1 km² Universal Transverse Mercator (UTM) square containing the nest); (2) near nest environment (3×3 km² UTM square); (3) home range scale (5×5 km² UTM square); and (4) landscape level scale (9×9 km² UTM square containing the above mentioned ones). Topographic, disturbance, climatic and land use factors were measured on a geographic information system (GIS) at occupied and unoccupied UTM squares. Logistic regression was performed by means of a stepwise addition procedure. We tested whether inclusion of new subset of variables improved the models by increasing the area under the receiver operator characteristic plot. At nest site scale, only topographic factors were considered as the most parsimonious predictors. Probability of species occurrence increases with slope in craggy areas at lower altitudes. At the 3×3 km² scale, climate and disturbance variables were included. At home range and landscape level scales, models included climate, disturbance, topographic and land use factors. Higher temperatures in January, template ones in July, higher rainfall in June, lower altitudes and higher slope in the sample unit increase probability of occurrence of Bonelli’s eagle at broadest scales. The species seems to prefer disperse forests, scrubland and agricultural areas. From our results, we consider that there is a hierarchical framework on habitat selection procedure. We suggest that it is necessary to analyse what key factors are affecting Bonelli’s eagle nest-site selection at every study area to take steps to ensure appropriate conservation measures. The combination of regression modelling and GIS will become a powerful tool for biodiversity and conservation studies, taking into account that application depends on sampling design and the model assumptions of the statistical methods employed. Finally, predictive models obtained could be used for the efficient monitoring of this scarce species, to predict range expansions or identify suitable locations for reintroductions, and also to design protected areas and to help on wildlife management.     

Comparative demography of Burrowing Owls in agricultural and urban landscapes in southeastern Washington

ABSTRACT.   Anecdotal evidence suggests that Burrowing Owls have declined in the state of Washington. We examined the status of these owls in agricultural and urban habitats to better understand the underlying causes of these declines. Nest density was higher in the area dominated by agriculture (0.67 nests/km²) than in the urban area (0.28 nests/km²), and re-use of nest burrows was more common in the agricultural area. We found no difference in mean clutch size between the two areas, but nesting success was higher in the agricultural area. The mean number of fledglings per nesting attempt was higher in the agricultural area (2.02 vs. 1.47), but we found no difference between the two areas in the mean number of fledglings per successful nest (3.2 vs. 3.1). Both natal recruitment (4% vs. 8%) and annual return rate of adults (30% vs. 39%) were lower in the agricultural area than in the urban area, suggesting that the owl population in the agricultural area may not be stable and may be a "sink" population. Due to high burrow fidelity from year to year, and the tendency of some owls in Washington to overwinter, we recommend that legal protection of nest burrows be extended to the nonbreeding season.     

Spatial ecology of cheetahs on north-central Namibian farmlands

Knowledge of a species' ranging behaviour is both fundamental to understanding its behavioural ecology and a prerequisite to planning its management. Few data exist on the spatial ecology of cheetahs Acinonyx jubatus outside protected areas, but such areas are particularly important to their conservation. Cheetahs on Namibian farmlands occupied exceptionally large home ranges, averaging 1651 km² (±1594 km²), with no detectable effect of sex, social grouping or seasonality. Despite such large ranges, cheetahs tended to utilize intensively only a small fraction of that area: 50% of the fixes were located within an average of 13.9±5.3% of the home range. Ranges were not exclusive, overlapping on average by 15.8±17.0%, with male cheetahs showing more intra-sexual range overlap than did females. Coalitions of males appeared to select for a dense, prey-rich habitat, but this preference was not apparent for other social groupings. Conflict with humans is an important contributor to the species' decline, and these large, overlapping cheetah home ranges result in the movements of each individual cheetah encompassing many farms (21 based on the average home-range size). Consequently, many cheetahs may be exposed to a minority of farmers attempting to kill them, and also that many farmers may see the same cheetahs, thereby gaining an exaggerated impression of their abundance. Conservation priorities for cheetahs outside protected areas are the development of techniques for conflict resolution, as well as the maintenance and restoration of suitable habitat and promotion of land-management practices compatible with the continued existence of large carnivores.     

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.     

Factors affecting breeding habitat selection in a cliff-nesting peregrine Falco peregrinus population

We studied factors affecting breeding habitat selection in a population of cliff-nesting peregrines Falco peregrinus across multiple spatial levels (cliff site, cliff context and land-use of the surrounding landscape), over a 2,100 km² study area in the Alps (Italy and Switzerland). We detected 30 breeding pairs (density: 1.43 territorial pairs/100 km²), whose territories were uniformly distributed over the study area. We compared 15 habitat features characterising occupied cliffs and 30 randomly selected unoccupied cliffs by means of stepwise forward logistic regression and hierarchical partitioning. The logistic regression analysis showed that occupied cliffs were longer (horizontal length), steeper, and had a greater extension of urban areas in the surrounding landscape compared to non-occupied cliffs. The model had a discrimination ability of 0.95. Hierarchical partitioning indicated that the logistic regression model was appropriate. Neither the distance of cliffs to the nearest site occupied by a potential competitor and predator, the eagle owl Bubo bubo, which occurred at a low density (0.67 pairs/100 km²), nor the distance to the nearest site occupied by peregrines had any effect on the cliff suitability model. Therefore, habitat selection in cliff-nesting peregrines was mainly influenced by cliff site features and surrounding landscape characteristics, whereas the proximity to conspecifics and to an intraguild predator had no apparent effects on peregrine settlement in our study population.     

Spatial organization in the Ethiopian wolf Canis simensis: large packs and small stable home ranges

The spatial organization of the rare Ethiopian wolf ( Canis simensis ) was studied in the Afroalpine heathlands of Bale Mountains National Park, southern Ethiopia, between 1988 and 1992. Nineteen animals were radio-tracked, 48 ear-tagged and 64 others recognized by coat patterns and observed directly. Dry season (October—March) home ranges of resident wolves covered between 2 and 15 km². The ranges of adult males were slightly larger than those of females, and subadults' home ranges were slightly smaller than those of adults. The population density of the wolves was correlated with prey biomass. In optimal habitat, wolves lived in packs of 3—13 adults (mean 5.9 wolves > 1year old) containing several close-kin males; adult sex ratio favoured males 1.88: 1 and combined pack home ranges averaged 6.0km². In an area of lower prey productivity, wolves lived in pairs or small groups (mean 2.7), adult sex ratio was 1:1 and home ranges averaged 13.4 km².
Home ranges overlapped extensively (mean 85%) between members of the same pack. Four to seven percent of the population was additionally composed of non-resident females, inhabiting larger ranges (mean 11.1 km²). Home ranges of neighbouring packs were largely discrete, forming a tessellating mosaic of packs occupying all available habitat. Pack home ranges were stable in time, drifting only during major pack readjustment after the disappearance of a pack or significant demographic changes. Ethiopian wolf home ranges were smaller than would be expected for a carnivore of its size and sociality, presumably as a result of the high rodent productivity of the Afroalpine ecosystem.     

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.     

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.     

Detecting decline in a formerly widespread species: how common is the common blue butterfly Polyommatus icarus?

Grid square distribution maps have been used widely to measure rates of decline and target conservation resources. However, common species that may have many populations per grid square can decline substantially from within squares without being lost from entire squares. In order to quantify this process, fine scale population and habitat data have been collected for the common blue butterfly Polyommatus icarus in a 35 km² area of fragmented landscape in north Wales. Present day habitat associations, determined from over 2000 transect walks, combined with data on historical and present day habitat distributions reveal that the species has declined by about 74% since 1901. Similar data concerning the species major host plant Lotus corniculatus indicate a decline of 46%. Based on 1 km² grid maps, neither species have been assessed as declining at all. These results suggest that apparently 'common' species may have declined just as much as many of Britain's rare species: using present methods of assessment these declines are undetected.     

Ranging behaviour and foraging habitats of breeding Sparrowhawks Accipiter nisus in a continuous forested area in Norway

The ranging behaviour and foraging habitats of Sparrowhawks Accipiter nisus were studied in a continuous forest area in southern Norway by use of radiotelemetry in 1995 and 1996. The mean size of the home ranges was 9.2 km² for males (sd ± 3.7, n = 6) and 12.3 km² for females (sd ± 6.4, n = 6), but the difference was not significant. Females ranged farther away from nests (mean 1824 m) than did males (mean 1240 m). None of the Sparrowhawks were located outside forest habitats. For the three pairs where both mates were radiotracked in 1996, habitat use did not differ between the sexes. Habitat composition in the home ranges differed from that of the study area. The most important difference was a higher proportion of medium-aged forest and a lower proportion of old forest in home ranges than in the study area. The selection for medium-aged forests was probably a response to high food supply and good hunting opportunities. Mixed regeneration and old forests were used more than clear-fell areas, which were seldom used. Mixed regeneration was also used more than coniferous replanting. The large home ranges in this study compared with those in studies in Great Britain is probably due to lower land productivity and associated lower densities of prey species in the present study. The study indicates that the Sparrowhawk benefits from modern forestry, which has created an increased proportion of medium-aged stands in the forest landscape.     

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.     

Local habitat patch pattern of the Siberian flying squirrel in a managed boreal forest landscape

We examined how the structure of a boreal forest landscape is related to the occurrence of the Siberian flying squirrel Pteromys volans in northern Finland. The flying squirrel inhabits mature spruce-dominated ( Picea abies ) mixed forests and is categorised as vulnerable species due to habitat loss and change. We classified a landscape of 374.5 km² into potential habitat patches, potential dispersal areas, and areas incapable of being inhabited using national forest inventory data, and surveyed all 136 potential habitat patches for the presence of the species. Different landscape variables were defined, and also connections by the shortest distances to neighbouring habitat patches along both straight lines and least-cost distances based on specific movement costs were measured. Occupied patches were larger in size, contained more deciduous trees for food and nesting cavities, and were in closer proximity to the nearest occupied patches. Occupied patches were mainly located below 300 m a.s.l. The occurrence of flying squirrels was correctly predicted for 88% of the habitat patches using landscape variables. This modelling result proved to be rather general. In addition, the configuration of occupied patches was mainly clustered across the landscape, and distant occupied patches seemed to be linked to other patches via forested connections. We suggest that maintaining a clustered arrangement of good quality habitat patches and regenerating new potential habitat as well as dispersal areas between the habitat patches seem to be appropriate goals for long-term forest management planning to sustain populations of the flying squirrel in the landscape.