Occurrence Of Owls Research Articles

Tawny Owl Strix aluco Distribution in the Urban Landscape: The Effect of Habitat, Noise and Light Pollution

At present, the intensification of urban landcover is one of the most critical threats for biodiversity. Common side-effects of urban sprawl are anthropogenic noise and artificial light at night (ALAN). Although their negative effects have often been described, little research has concerned nocturnal wildlife, especially avian predators. Here, we investigated the effect of urban and tree cover, traffic noise and ALAN on the presence of the Tawny Owl Strix aluco, a common night-active predator in Europe. We conducted playback surveys along an urban gradient in Turin (Italy) to detect species presence. Traffic noise was measured in the field, the cover of built-up and (semi-)natural areas was estimated using GIS and multiple measures of ALAN were acquired from a light pollution map. We modelled species presence as a function of each environmental predictor and we found a significant negative relationship with light pollution, which was the foremost urban stressor affecting Tawny Owl occurrence. Our findings suggest that Tawny Owls are more likely to be found in less artificially illuminated areas and that their distribution in urban areas is not only influenced by noise pollution and the availability of suitable habitat, but also the intensity of ALAN. Therefore, light pollution could be a key driver of the spatial distribution of Tawny Owls and potentially other nocturnal species in urban ecosystems.

Community Reserves Serve as Refugia Sites for Cavity-Nesting Owls in Northeast India

ABSTRACT Community Reserves, which are Community Conserved Areas, form the majority of the Protected Area Network in northeast India. Because this biodiverse region is threatened by a variety of anthropogenic activities, Community Reserves likely serve as refugia sites for stenotopic, cavity-nesting species such as some owls. To test this hypothesis, we conducted nocturnal surveys in 11 Community Reserves comprised of primary or secondary forest and outside Community Reserves in Meghalaya state, northeast India. We then used nonparametric tests to assess differences in the occurrence of owls among these three categories. We found that on average, occurrence of owls was higher inside Community Reserves. Inside Community Reserves with secondary forests, we found significantly higher occurrence of the Asian Barred Owlet (Glaucidium cuculoides) and Collared Scops-Owl (Otus lettia), while in Community Reserves with primary forest, we found significantly higher occurrence of the Brown Wood-Owl (Strix leptogrammica), a declining old-growth forest specialist. Hence, Community Reserves are serving as sites of refugia for owls in northeast India. However, anthropogenic pressures such as logging, shifting cultivation, and developmental activities threaten the forests of the region. Old-growth forests are also scarce in Meghalaya and were present in only two of the Community Reserves. Therefore, we find it of prime importance to conserve these reserves, especially those containing primary forests, and to allocate more areas as Community Reserves in the region.

Habitat requirements of Boreal Owl (Aegolius funereus) and Pygmy Owl (Glaucidium passerinum) in rear edge montane populations on the Balkan Peninsula

Rear-edge populations of montane species are known to be vulnerable to environmental change, which could affect them by habitat reduction and isolation. Habitat requirements of two cold-adapted boreo-alpine owl species — Boreal Owl (Aegolius funereus) and Pygmy Owl (Glaucidium passerinum) — have been studied in refugial montane populations in the western Rhodopes, South Bulgaria. Data on owl presence and forest stand attributes recorded in situ have been used to identify significant predictors for owl occurrence. The results revealed Boreal Owl's preference for comparatively dense forests (high canopy closure values), big trees (diameter at breast height ≥50 ​cm) and large amount of fallen dead wood in penultimate stage of decay. For Pygmy Owl the only significant explanatory variable was the total amount of fallen dead wood. Results suggest preference of both owl species for forests with structural elements typical of old-growth forests (i.e., veteran trees, deadwood), the Pygmy Owl being less prone to inhabit managed forests. Being at the rear edge of their Palearctic breeding range in Europe both Boreal and Pygmy Owls are of high conservation value on the Balkan Peninsula. Hence, additional efforts are needed for their conservation in the light of climate change and resulting alteration of forest structural parameters. Current findings can be used for adjusting forest management practices in order to ensure both, sustainable profit from timber and continuous species survival.

Occupancy patterns of an apex avian predator across a forest landscape

AbstractApex predators are integral parts of every ecosystem, having top‐down roles in food web maintenance. Understanding the environmental and habitat characteristics associated with predator occurrence is paramount to conservation efforts. However, detecting top order predators can be difficult due to small population sizes and cryptic behaviour. The endangered Tasmanian masked owl (Tyto novaehollandiae castanops) is a nocturnal predator with a distribution understood to be associated with high mature forest cover at broad scales. With the aim to gather monitoring data to inform future conservation effort, we trialled an occupancy survey design to model masked owl occurrence across ~800 km2in the Tasmanian Southern Forests. We conducted 662 visits to assess masked owl occupancy at 160 sites during July–September 2018. Masked owl site occupancy was 12%, and estimated detectability was 0.26 (±0.06 SE). Cumulative detection probability of masked owls over four visits was 0.7. Occupancy modelling suggested owls were more likely to be detected when mean prey count was higher. However, low detection rates hindered the development of confident occupancy predictions. To inform effective conservation of the endangered Tasmanian masked owl, there is a need to develop novel survey techniques that better account for the ecology of this rare, wide‐ranging and cryptic predator. We discuss the potential to combine novel census approaches that exploit different aspects of masked owl ecology to obtain more robust and detailed data.

The use of socio-economy in species distribution modelling: Features of rural societies improve predictions of barn owl occurrence

Variation of habitats and resources important for farmland birds seems to be only partly captured by ordinary statistics on land-use and agricultural production. For instance, densities of rodents being prey for owls and raptors or structures of rural architecture providing nesting sites for many species are central for bird diversity but are not reported in any official statistics. Thus, modelling species distributions, population abundance and trends of farmland birds may miss important predictive habitat elements. Here, we involve local socio-economy factors as a source of additional information on rural habitat to test whether it improves predictions of barn owl occurrence in 2768 churches across Poland. Barn owls occurred in 778 churches and seemed to prefer old churches made of brick located in regions with a milder climate, higher share of arable land and pastures, low road density and low levels of light pollution. Including data on local unemployment, the proportion of elder citizens, commune income per citizen, the share of citizens with high education and share of farmers among working population improved the model substantially and some of these variables predicted barn owl occurrence better than several land-use and climate data. Barn owls were more likely to occur in areas with high unemployment, a higher proportion of older citizens in a local population and higher share of farmers among working population. Importantly, the socio-economy variables were correlated with the barn owl occurrence despite all climatic, infrastructure and land-use data were present in the model. We conclude that the socio-economy of local societies may add important but overlooked information that links to spatial variation in farmland biodiversity.

The use of plant stratification by Otus jolandae in the Natural Tourism Park of Kerandangan, Lombok

Otus jolandae is an endemic owl species of Lombok island. The previous study suggested exploring the ecology-related aspects more deeply since this species had been just identified in 2013 but their recent status is nearly threatened. This study was conducted in Natural Tourism Park (NTP) of Kerandangan forest from July to September 2016. The field observation was carried out during the night to observe the owl occurrence in different plant species and different vegetation structure (seedling, sapling, pole, and tree). The results reveal the most widely used plant species is Dalbergia latifolia and then followed by Tectona grandis, Tamarindus indica, Samanea saman, Mangifera indica, Delonix regia, and Swietenia mahagoni respectively. Moreover, about 71.6% Otus jolandae occurs dominantly in the tree structure, followed by 28.4% of the pole structure, while no occurrence found in seedling and sapling structure. This indicates the adult and subadult vegetation act as a critical part for being a territory for Otus jolandae. Hence, addressing the deforestation problem and at the same time protecting the forest in a good shape with more pole and tree vegetation structure will keep Otus jolandae population from the extinction.

Occurrence of the Eastern Barn Owl Tyto alba delicatula in the Centennial Parklands, Sydney

The occurrence of owls in the urban environment has been of interest, with recent records of the Eastern Barn Owl Tyto alba delicatula in highly urbanised locations in Sydney, New South Wales. During the long-term monitoring of bird assemblages in the Centennial Parklands, Barn Owls were consistently found roosting under the crowns of Canary Island Date Palms Phoenix canariensis in six major time periods between 2013 and 2018. Atlas records show two earlier records of this species in the Parklands. Since December 2013, there have been some site visits in which 2–3 Barn Owls have been found roosting in the Parklands.

Assessing patterns of barn owl Tyto alba occupancy from call broadcast surveys

Owing to habitat loss, changes in farming practices, urbanization, and high mortality through vehicle collisions, barn owls Tyto alba are a species of conservation concern in portions of their range. This species can be secretive and difficult to survey, particularly away from breeding sites, so factors related to barn owl occurrence often remain unknown. We conducted nighttime broadcast surveys for barn owls during the early‐ and post‐breeding seasons and used an occupancy modeling framework to understand how factors related to landcover, landscape features, and human development related to occupancy in southern Idaho, USA. We also assessed the effectiveness of using broadcasts of conspecific vocalizations to improve owl detection. Barn owls were detected during 52 of 666 point counts and at 37 of 222 locations in the early‐breeding season and 50 of 198 point counts and 31 of 66 locations in the post‐breeding season. The probability of detecting barn owls was 0.32 ± 0.06 (SE) and 0.45 ± 0.07 (SE) during the early‐ and post‐breeding seasons, respectively. Based on analysis within 1‐km buffers surrounding point‐count locations, occupancy in the early‐breeding season increased with percentage of crop coverage and presence of trees and decreased with background noise. Post‐breeding season occupancy increased with stream length and decreased with area of development and distance from the Snake River, a major geologic feature that likely provided roost sites in its canyon walls and riparian woodlands and a dispersal corridor for juveniles. Broadcast of barn owl vocalizations increased detection probability as much as nine times. Thus, incorporating call broadcast into future barn owl surveys should help investigators reduce false conclusions of absence. Ultimately, understanding factors influencing occupancy of barn owls will facilitate effective conservation, especially in light of population pressures related to factors such as roadway mortality and loss of nesting sites with increased urbanization.

Meta-replication reveals nonstationarity in multi-scale habitat selection of Mexican Spotted Owl

ABSTRACT Anthropogenic environmental changes are leading to habitat loss and degradation, driving many species to extinction. In this context, habitat models become increasingly important for effective species management and conservation. However, most habitat studies lack replicated study areas and do not properly address the role of nonstationarity and spatial scales in determining factors that limit species occurrence under different environmental settings. Here we provide an optimized multi-scale framework for analyzing habitat selection of the threatened Mexican Spotted Owl (Strix occidentalis lucida) between 2 meta-replicated study areas: the Sacramento Mountains, New Mexico, and the Mogollon Plateau, Arizona. The optimized scales of habitat variables strongly differed between the 2 study areas. Percent cover of mixed-conifer was more strongly associated with the relative likelihood of Mexican Spotted Owl occurrence in the Sacramento Mountains than in the Mogollon Plateau. Topographic covariates str...

Habitat Selection by Burrowing OwlsAthene cuniculariain the Pampas of Argentina: A Multiple-Scale Assessment

Fil: Baladron Felix, Alejandro Victor. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

Habitat selection by owls in a seasonal semi-deciduous forest in southern Brazil.

This paper tested the hypothesis that the structural components of vegetation have impact over the distribution of owl species in a fragment of a semi-deciduous seasonal forest. This paper also determined which vegetation variables contributed to the spatial distribution of owl species. It was developed in the Perobas Biological Reserve (PBR) between September and December 2011. To conduct the owl census, a playback technique was applied at hearing points distributed to cover different vegetation types in the study area. A total of 56 individual owls of six species were recorded: Tropical Screech-Owl (Megascops choliba), Black-capped Screech-Owl (Megascops atricapilla), Tawny-browed Owl (Pulsatrix koeniswaldiana), Ferruginous Pygmy-Owl (Glaucidium brasilianum), Mottled Owl (Strix virgata) and Stygian Owl (Asio stygius). The results suggest that the variables of vegetation structure have impact on the occurrence of owls. The canopy height, the presence of hollow trees, fallen trees and glades are the most important structural components influencing owl distribution in the sampled area.

Burrowing Owl (Athene cunicularia) Habitat Associations in Agriculture Fields and along Canal Trails in Phoenix, Arizona

Burrowing Owls (Athene cunicularia) have experienced significant population declines over the last 100 years in parts of the United States and Canada. This decline may be associated with increasing urbanization and land-cover change; however, owls can occupy urbanized environments. To determine habitat selection in the southeast valley of Phoenix, Arizona, we conducted visual surveys for owls during summer 2011 and measured microhabitat and landscape characteristics in 23 agricultural fields (fields) and along 15 canal right-of-ways (trails). We estimated occupancy rate and detectability using Program MARK. We identified microhabitat selection to relate owl occurrence to landscape variables. Occupancy rate was 32% in both fields and trails and owls had greater detectability along trails. Burrowing Owl occurrence was similar in fields with varying agricultural stages (from undisturbed to harvested) and moisture conditions. Owl occupancy was positively associated with soil type and canal water presence, and occupancy decreased when developed landscape cover (e.g., roads and buildings) increased. These findings suggest that Burrowing Owls are able to live in urbanized environments below 40% developed land cover provided that water and suitable soils are available.

Predicting Occurrence of Mexican Spotted Owls in Arid Canyonlands of Southern Utah

Abstract The Mexican Spotted Owl (Strix occidentalis lucida) was listed as “threatened” by the U.S. Fish and Wildlife Service in 1993. Predicting the distribution of suitable habitat is an important step in the owl's recovery, and Geographic Information Systems (GIS) provide appropriate spatial and analytic tools. We developed and validated a GIS-based occurrence model for Mexican Spotted Owls in arid canyon environments in Utah. We generated a set of competing models with topographic and vegetation covariates, and ranked models using information theory. Our top-ranked models indicated slope and variation in elevation were important predictors for the occurrence of Mexican Spotted Owls in rocky habitats, and we averaged coefficients from the top models to estimate probability of owl occurrence. During a model validation survey, we detected Spotted Owls in 22 test plots, where mean estimated probability of occurrence, an index to habitat suitability, was 0.68 (SE = 0.03). In addition, we evaluated model ...

The impact of environmental factors on distribution of Scops Owl Otus scops in the wider area of Kras (SW Slovenia)

The impact of environmental factors on distribution of Scops Owl Otus scops in the wider area of Kras (SW Slovenia) The aim of the study was to determine the key environmental factors affecting Scops Owl Otus scops occurrence in the wider Kras plateau area (SW Slovenia, 665 km2). Scops Owl was systematically censused in 2006 (180 calling males) and in 2008 (167 calling males). Males were distributed either solitarily or clumped in groups, mostly situated in villages and its surroundings, indicating the species' synanthropic character. Crude densities were 0.3 males/km2 in 2006 and 2008, respectively, while ecological densities were 1.0 males/km2 in 2006 and 0.9 males/km2 in 2008. Population distribution remained roughly the same in both years, with the highest densities in the western and central parts of the Kras plateau, on Kraški rob and on Podgorski kras plateau. Habitat selection was analyzed at three spatial scales (regional, settlement and territory scales), based on spatial data layers (22 environmental variables), using Chi-square goodness-of-fit test and logistic regression. Results revealed that at the regional scale, Scops Owl preferably selected open habitats (extensively managed orchards, built-up areas, vineyards, permanent grasslands) and avoided dense forest and agricultural land with forest trees. As far as settlements were concerned, Scops Owl was more prone to select those that were more distant from the highway, with better preserved traditional agricultural landscape (with more hedgerows) and with higher average annual air temperature. In territory selection, Scops Owl occurrence was associated with longer distance from the highway, larger number of old buildings and higher landscape mosaics. The species seems to be threatened by traffic noise, habitat loss through abandonment and intensification of land and, potentially, by lack of breeding niches within settlements. Conservation measures should include the preservation of mosaic farmland, promotion of extensive agricultural practices, prevention of scrub and forest expansion, and maintenance of breeding niches (old trees, cavities in buildings).