Forest Owls Research Articles

Flammulated Owls Exhibit Diel Variation in Space Use

ABSTRACT A home range determines the resources animals can access, and the size of a home range often reflects resource availability and energetic requirements of individuals. The Flammulated Owl (Psiloscops flammeolus) is a cryptic small forest owl that breeds in mixed conifer forests in western North America. The home ranges of individuals generally comprise open forests with large trees, but we have yet to fully understand temporal variation in this species’ use of space and the habitat structures that drive space use at a fine scale. During the 2017 summer breeding season (May–July), we tracked the movement of six territorial males with GPS tags to estimate temporal variation in space use and examined resource selection for fine-scale habitat characteristics within home ranges. Results suggest that individual movement was more constrained around nests early at night, but the area of space used was consistent between the incubation and nestling stages. The owls’ activity centers near their nests had denser ground cover than available habitat, indicating that the forest understory may be valuable for this species’ breeding ecology. As forested landcover rapidly changes in western North America, understanding the spatial behavior and fine scale habitat associations of this species and others is increasingly important.

Habitat Selection in Forest Owls: The Roles of Vegetation Structure, Prey Density, and Competitors

Habitat Selection in Forest Owls: The Roles of Vegetation Structure, Prey Density, and Competitors

Habitat selection in forest owls: The roles of vegetation structure, prey density and competitors

Habitat selection in forest owls: The roles of vegetation structure, prey density and competitors

Detection dogs can help researchers with elusive forest owl conservation

AbstractElusive fauna are often studied indirectly, via traces they leave behind, or via other non‐invasive survey methods. Critically endangered Tasmanian masked owls are both rare and elusive, which hampers conservation efforts. Spotlighting and call playback often have low success rates in accurately determining the presence/absence of Tasmanian masked owls. Using indirect survey techniques for traces such as owl pellets can be more efficient and provide a more reliable source of detailed data regarding presence/absence, diet, health, population structure and environmental contaminants. However, pellets can be difficult for researchers to find in the field. We evaluate whether detection dogs are effective in finding owl pellets in two steps: an experimental trial comparing the performance of a dog team to that of an ecologist with significant field experience with masked owls; and in a pilot field study where the dog team searched potential owl habitat in Tasmanian forests. During the experimental trials, the dog team significantly outperformed the ecologist. The dog team was more sensitive, finding 89% versus 40% of pellets present for the ecologist, and took half as long to search an equivalent‐sized search area. The combined efficiency of the dog team was 4.5 times greater than that of an ecologist working alone. During the pilot study, in searching areas of potential masked owl habitat, no pellets were found. However, when sites were visited where owls were known to have been recently sighted, the dog team were able to find large numbers of owl pellets suitable for collection and potential data extraction. Our trials suggest that dogs can find owl pellets with considerably greater sensitivity and efficiency than ecologists working alone and that they would be best used in combination with targeted surveys, especially when the detection and subsequent collection of as many pellets as possible is desirable for DNA extraction or other analysis.

Thermal benefits of roost site selection in a small forest owl

Thermal benefits of roost site selection in a small forest owl

Climate Change Habitat Model Forecasts for Eight Owl Species in the Southwestern US.

The high-resolution forecasting of vegetation type shifts may prove essential in anticipating and mitigating the impacts of future climate change on bird populations. Here, we used the US Forest Service Ecological Response Unit (ERU) classification to develop and assess vegetation-based breeding habitat profiles for eight owl species occurring in the foothills and mountains of the Southwestern US. Shifts in mapped habitat were forecast using an ecosystem vulnerability model based on the pre-1990 climate envelopes of ERUs and the Intergovernmental Panel on Climate Change's (IPCC) A1B moderate-emission scenario for the future climate. For five of the eight owl species, the regional breeding habitat extent was projected to decline by at least 60% by 2090. Three species, the boreal owl (Aegolius funereus; at the trailing edge of its distribution), flammulated owl (Psiloscops flammeolus), and northern pygmy-owl (Glaucidium gnoma), were projected to experience the steepest habitat loss rates of 85%, 85%, and 76%, respectively. Projected vegetation shifts overlaid with well-documented flammulated owl breeding populations showed the complete or near complete loss of habitat by 2090 in areas of montane forest currently supporting dense aggregations of owl territories. Generalist or lower-elevation owl species were predicted to be less impacted, while, for the whiskered screech-owl (Megascops trichopsis), the contraction of the current habitat was nearly offset by a projected northward expansion. In general, the results of this study suggest high exposure to climate change impacts for the upper-elevation forest owls of semi-arid Southwestern North America. Long-distance migration and low natal philopatry may prove important to some montane owl populations in adapting to the regional loss of habitat.

Food habits of Rufous-legged Owl in a protected area of south-central Chile affected by mixed wildfire

Abstract The diet of Rufous-legged Owl, Strix rufipes, a small raptor present in an Andean protected area, is described here. During the fall of 2017, 44 pellets were collected in the study area, being subsequently analyzed. The occurrence of small mammal prey items in pellets was compared with capture frequencies with live-trapping through Sherman traps. Regarding occurrence frequencies in the diet, arthropods were the most frequent (49.34%), followed by mammals (39.31%), birds (7.86%) and reptiles (3.37%). However, in terms of biomass, mammals had the highest biomass contribution. The observed frequency of consumed preys showed a random pattern, according to the captures of small mammals obtained with Sherman traps. The role of wildfire in the composition of prey in the observed trophic spectrum of these forest owls is also discussed.

Fragment size and isolation is associated with the presence of two forest owls in a fragmented environment in Central Argentina

In the semiarid Espinal ecoregion from central Argentina, deforestation has produced a large retraction of native forests and an accelerated process of fragmentation. Here we assess the effects of forest fragmentation within an agricultural matrix on the presence of two forest owls: the Ferruginous pygmy-owl (Glaucidium brasilianum) and the Tropical screech-owl (Megascops choliba). We searched for the species in fragments of different sizes and at different distances from large-continuous forest tracts. We detected one or both species at 43% of the 84 surveyed points. The Tropical Screech Owl was detected at 13 points, the Ferruginous Pygmy Owl was detected at 14 points, and both species were detected at 9 points. For the Ferruginous pygmy-owl, the area of the fragment where the point registration was made was the only variable associated with its presence. The model for Tropical Screech-Owl indicated that the variable that best explained its presence was the distance to the nearest forest fragment. For both species the association was negative. Our results suggest that despite being generalist and widely distributed species, both owls were negatively affected by the fragmentation process, highlighting the importance of the preservation of forest remnants and their connectivity.

Differential landscape use by forest owls two years after a mixed‐severity wildfire

AbstractOwls are important avian predators in forested systems, but little is known about landscape use by most forest‐adapted owl species in environments impacted by mixed‐severity wildfire. To better understand species‐specific patterns of post‐wildfire landscape use within an owl guild, we used passive acoustic monitoring using autonomous recording units. The technology is effective for multi‐species surveys, especially if some species are rare, nocturnal, or difficult to detect by traditional means. In 2017, we surveyed the interior and adjacent unburned areas of a 10,700‐ha mixed‐severity wildfire that burned in 2015 in southwest Oregon. We used occupancy modeling to identify patterns of landscape use by five species of forest owls: barred owls (Strix varia), great horned owls (Bubo virginianus), western screech‐owls (Megascops kennicottii), northern pygmy‐owls (Glaucidium gnoma), and northern saw‐whet owls (Aegolius acadicus). Our results showed a positive relationship between increasing fire severity and probability of use by western screech‐owls and a similar but somewhat weaker relationship for northern pygmy‐owls. Barred owls were rarely detected in severely burned areas and their use decreased with increased fire severity. We observed generally low landscape use for great horned owls, which decreased with increased fire severity and at higher elevations. Thus, four out of the five species appeared to use recently burned forests at different levels, with only northern saw‐whet owls showing near‐complete avoidance of the burned area. These findings increase our understanding of the basic ecology of each species and highlight the varied use of burned areas within this community. These previously undocumented patterns of landscape use in burned landscapes should provide insights to managers and policymakers in the Pacific Northwest as climate shifts, and fires may increase in size, frequency, and severity.

Environmental conditions and call-broadcast influence detection of eastern forest owls during standardized surveys

AbstractOwls play crucial roles in the environment and provide ecosystem services making them important to monitor and study. However, standardized methods for most species do not exist, and we lack understanding of the effects of many environmental variables and call-broadcast on detection of owls during surveys. We performed a multispecies occupancy analysis of owl monitoring data collected from 2004 to 2013 across the state of Maine to examine the effects of environmental variables, conspecific and heterospecific call-broadcast, and general survey protocols on detection of 3 forest owls: Northern Saw-whet Owl (Aegolius acadicus), Barred Owl (Strix varia), and Great Horned Owl (Bubo virginianus). We found that environmental variables such as cloud cover, precipitation, temperature, time of night, and wind had species-specific effects on detection probability, and ambient noise decreased detection probability for all species. Snow cover did not affect detection of any species. We also found that conspecific call-broadcast increased detection of each species, while heterospecific call-broadcast had variable effects. Specifically, we found that Long-eared and Barred owl broadcast increased the detection of Northern Saw-whet Owl, and our results suggest additional heterospecific effects may exist. Our study showed that, compared to the protocol of the Maine Owl Monitoring Program, surveys simultaneously examining all 3 of our focal species can increase efficiency and lower disturbance by only broadcasting Long-eared and Barred owl calls during a 10-min survey. We recommend that future owl surveys take into account species-specific effects of conspecific and heterospecific call-broadcast, and use our results when designing survey protocols that include one or more of our focal species.

Acoustic Monitoring Reveals a Diverse Forest Owl Community, Illustrating Its Potential for Basic and Applied Ecology

Bioacoustic surveys are an increasingly common tool for wildlife research due to increasing software performance and decreasing hardware costs. We conducted landscape-scale passive acoustic surveys across the northern Sierra Nevada to assess the distribution and density of barred owls (Strix varia) at the leading edge of their ongoing range expansion. From the resulting audio, we derived occupancy data on barred owls and spotted owls (S. occidentalis). We also documented seven other owl species; because the audio was passively recorded, it will be possible to extract systematic monitoring data on those nine species and others. Our findings reveal the tremendous latent potential of passively recorded acoustic survey data for studying otherwise cryptic species and biological communities. Photo credit: Connor M. Wood. Photo credit: Connor M. Wood. These photographs illustrate the article “Acoustic monitoring reveals a diverse forest owl community, illustrating its potential for basic and applied ecology” by Connor M. Wood, R.J. Gutiérrez, and M. Zachariah Peery published in Ecology. https://doi.org/10.1002/ecy.2764

Acoustic monitoring reveals a diverse forest owl community, illustrating its potential for basic and applied ecology

Acoustic monitoring reveals a diverse forest owl community, illustrating its potential for basic and applied ecology

Observations of Notable Parental Behaviours of Northern Spotted Owls (<i>Strix occidentalis caurina</i>)

Northern Spotted Owl (Strix occidentalis caurina) is a medium-sized forest owl of conservation concern in the Pacific Northwest of North America. We report two sightings of previously unreported parental behaviour: a Northern Spotted Owl feeding avian nestlings to its young and a Northern Spotted Owl defending a fledgling against a Black Bear (Ursus americanus). Further research may be warranted on the influence of brood size and habitat quality on dietary breadth. Although Black Bears have not been previously documented as Northern Spotted Owl predators, we suggest that they should be considered potential predators of nestling and fledgling owls.

The other half of the coastal State Forest estate in New South Wales; the value of informal forest reserves for conservation

ABSTRACT There are 5.2 million hectares of public native forest within the coastal Integrated Forestry Operations Approval (IFOA) regions in New South Wales on and east of the Great Dividing Range. 4.3 million hectares or 83% of these forests are set aside in formal or informal conservation reserves. State Forests which comprise 1.55 million hectares or 30% of the public estate within the coastal IFOA regions in New South Wales are managed for a variety of reasons including timber production, recreation, and conservation. While commonly associated with timber harvesting, 43% (675,717 hectares) of the native State forest estate is set aside for conservation in informal reserves. State forest conservation areas include formal Flora Reserves, and a suite of informal reserves including riparian protections, ridge and headwater connection, old growth patches, rare and non– commercial forest types, rainforest, heath, rock outcrops, steep slopes, wildlife corridors, large forest owl protection areas and species ...

Owl survey of the Peel–Harvey Estuary in south-western Australia

Little is known of owls in south-western Australia compared with the owls of southern and eastern Australia. Surveys of forest owls in the south-west are almost completely lacking. This study sought to determine the abundance and detectability of owls immediately around the Peel–Harvey Estuary in south-western Australia. The southern boobook (Ninox boobook) and the masked owl (Tyto novaehollandiae) were the only owls detected (n = 23 and n = 1 respectively), although the nocturnal tawny frogmouth (Podargus strigoides) was detected from unelicited calls on three occasions. Southern boobooks were found to be common in this area though they are reported to be in decline in south-eastern and inland Australia. Their detectability was significantly greater in August (late winter) than at other times through unelicited calls; otherwise, there were no detections in winter. A variety of small mammals were detected during the surveys, including: a little red flying-fox (Pteropus scapulatus), a western ringtail possum (Pseudocheirus occidentalis), 19 southern brown bandicoots (Isoodon obesulus), 4 common brushtail possums (Trichosurus vulpecula), 21 rabbits (Oryctolagus cuniculus), a black rat (Rattus rattus), 2 red foxes (Vulpes vulpes) and 22 microbats.

Observations of mobbing and other agonistic responses to the Powerful Owl Ninox strenua

Mobbing is an anti-predator strategy in which prey animals, notably birds and mammals, aggravate a potential predator to either distract or drive them from the vicinity. The Powerful Owl Ninox strenua is a large forest owl endemic to eastern Australia that preys mainly on arboreal mammals and birds. We identified records of 30 species of birds and one mammal known to mob the Powerful Owl from scientific literature and unpublished studies. In our study in southern Sydney, Powerful Owls were most frequently mobbed by Noisy Miners Manorina melanocephala and Pied Currawongs Strepera graculina, followed by Grey Butcherbirds Cracticus torquatus and Australian Magpies Cracticus tibicen. We observed mobbing by three species of bird and one mammal that were not previously recorded as mobbing species, including agonistic responses by a Tawny Frogmouth Podargus strigoides and Common Brushtail Possum Trichosurus vulpecula during the time owls were active.

Determining the spacing of acoustic call count stations for monitoring a widespread forest owl

Nocturnal species are challenging to monitor, but with advances in bioacoustic technology, acoustic monitoring is becoming a more affordable, efficient technique for monitoring cryptic species. We tested the suitability of acoustic monitoring as a potential national monitoring method for morepork/rūrū (Ninox novaeseelandiae), in beech forest within the Eglinton Valley, Fiordland, during spring 2009–2010. We used radio telemetry and an acoustic call study to address two questions to help managers make evidence-based decisions on the spacing of acoustic call count stations: (1) What are the sex-specific and seasonal home-range sizes of rūrū? (2) How does acoustic detection decrease with increasing distance? Home ranges were the largest recorded to date for rūrū in New Zealand (mean 100% MCP = 307 ha, mean 75% kernel = 43.5 ha) with an average range spread of 270 m (75% kernel). Significant attenuation of recorded calls occurred after 150 m in southern beech (Nothofagaceae) forest and no calls could be detected by the recorders beyond 250 m. Acoustic monitoring is a promising technique to monitor rūrū nationally, but the spacing of stations needs to vary depending on home-range, habitat and the microphones used in the acoustic detectors.

Current and future effectiveness of Natura 2000 network in the central Alps for the conservation of mountain forest owl species in a warming climate

Climate change is causing range shifts in many species, and impacts are predicted to be highest in mountain regions. The effectiveness of protected areas in preserving suitable habitats for target species in the face of climate change is particularly concerning, as many protected sites may lose suitable conditions for those species. We investigate the potential effect of temperature increase on the regional distribution of pygmy and boreal owl, mountain forest specialists in the Italian Alps, and the relative effectiveness of the Natura 2000 network at the regional level. We modelled current and future distributions by MaxEnt, relating occurrence to climate and land cover, considering current and future climates (changes predicted for 2050 considering representative concentration pathways of +4.5 and +8.5 W/m2). The distribution of both species is affected by climate variables and by the availability of coniferous forests, and of a few other habitat types (such as grassland, bare soil, broadleaved forest, mixed forest). The potential regional distribution of the two species will undergo a significant reduction, more marked for boreal owl (52–54 %) than for pygmy owl (23–34 %). Although Natura 2000 covers (and will cover also in the future) more than 30 % of suitable sites of both species, 64 % of the sites suitable for both species now and in the two alternative future scenarios are not included in any Site of Community Importance or Special Protection Areas (SPAs). Those sites are ideal candidate for new SPAs. Network enlargement or adequate forest management also outside protected areas is required for the conservation of those and other forest-specialist species in a warmer future.

Occurrence patterns and niche relationships of sympatric owls in South American temperate forests: A multi-scale approach

Habitat-specialists have narrower niches, but achieve higher or similar peak performance (e.g. occurrence probability, ψ) than habitat-generalists along resource gradients that may be selected from the stand- to landscape-levels. Understanding the relationship between niche width and ψ of forest owls will facilitate the development of appropriate management recommendations for their conservation. We assessed ψ of the threatened habitat-specialist rufous-legged owls (Strix rufipes) and habitat-generalist austral pygmy-owls (Glaucidium nana) across three spatial scales, and tested whether they differed in resource utilization and peak ψ in temperate forests of southern Chile. We conducted 1145 broadcast surveys at 101 sites and used multi-season occupancy models, accounting for imperfect detection, to estimate ψ. For S. rufipes, ψ ranged between 0.05 and 1 across sites, and was positively associated with the variability (standard deviation, SD) in diameter at breast height (DBH) of trees and bamboo understory density. For G. nana, ψ ranged between 0.67 and 0.98, and was positively associated with forest-patch shape index (irregularity and edge effects) and forest cover at 180ha, although the parameter estimates were imprecise. Relative to G. nana, S. rufipes had lower total resource utilization due to lower ψ over gradients of all covariates, but achieved similar peak ψ for resources related with stand-level forest complexity and forest stability at the landscape scale. Occurrence of habitat-specialist owls will be promoted if multi-aged stands with a variety of tree sizes (SD of DBH=19.9±9cm), including large old-growth trees, with relatively high bamboo cover (34.2±26.6%), are retained. Landscapes with forest cover >63.5% would also favor occurrence by habitat-specialist owls.

Large Forest Owls in the River Red Gum State Forests of south-western New South Wales - an account of their 2008 status

This survey aimed to determine whether Barking Owls McGregor.Ninox connivens are still declining in south-west NSW; and if there are resident pairs of Powerful Owls Ninox strenua present in south-west NSW State Forests. Surveys for Barking Owls were conducted in and around eight locations they had been detected in 2004. During August 2008, call playback for Barking Owls was conducted in 175 sites at and surrounding these locations for a single night each. Powerful Owl calls were played at 12 of these sites. From the eight locations where Barking Owls were detected in 2004, only one was detected in 2008. A Powerful Owl was detected at one site during surveys and a pair seen there the following year, suggesting residency. In regards to the initial aims, Barking Owls appear to be declining, and Powerful Owls are present in south-west NSW State Forests. This needs to be incorporated into conservation strategies for both species.