Aegolius Funereus Research Articles

Trophic fate and biomagnification of organic micropollutants from staple food to a specialized predator

The environmental burden of organic micropollutants has been shown in aquatic ecosystems, while trophic fate of many compounds in terrestrial food chains remains highly elusive. We therefore studied concentrations of 108 organic micropollutants in a common European mammal, the bank vole (Clethrionomys glareolus), and 82 of the compounds in a specialized predator, Tengmalm's owl (Aegolius funereus) relying to >90 % on voles as its prey. We studied compounds in whole voles (n = 19), pools of 4–8 bank voles (npools = 4), owl blood (n = 10) and in owl eggs (n = 10) in two regions in Sweden. For comparison, we also included previously published data on 23 PFAS (per- and polyfluoroalkyl substances) in bank vole liver (npools = 4) from the same regions. In voles, concentrations of the organic micropollutants caffeine (maxIndividual 220 ng/g ww) and DEET (N,N-diethyl-m-toluamide) (maxPool 150 ng/g ww) were 2–200 times higher in voles relative to owl blood and eggs. Conversely, concentrations of nicotine, oxazepam, salicylic acid, and tributyl citrate acetate were 1.3–440 times higher in owls. Several PFAS showed biomagnification in owls as revealed by maximum biomagnification factors (BMFs); PFNA (perfluorononanoate) BMF = 5.6, PFTeDA (perfluorotetradecanoic acid) BMF = 5.9, and PFOS (perfluorooctane sulfonate) BMF = 6.1. Concentrations of organic micropollutants, alongside calculated BMFs, and Tengmalm's owl's heavy reliance on bank vole as staple food, suggest, despite small sample size and potential spatio-temporal mismatch, accumulation of PFAS (especially PFNA, PFTeDA, and PFOS) in owls and biomagnification along the food chain. Concentrations of PFAS in owl eggs (e.g., 21 ng/g ww PFOS) highlight the likely pivotal role of maternal transfer in contaminant exposure for avian embryos. These concentrations are also of concern considering that certain predators frequently consume owl eggs, potentially leading to additional biomagnification of PFAS with yet undetermined consequences for ecosystem health.

Leucocytozoon Infection Does Not Influence the Survival of Boreal Owl Aegolius funereus Nestlings.

Leucocytozoon infection has been observed to impact the reproductive ecology and physiology of avian hosts, but its influence on nestling survival remains unclear. We investigated the effect of Leucocytozoon infection intensity, determined through triplicate PCR sample analyses, on the survival of 256 boreal owl (Aegolius funereus) nestlings during an 8-yr study. Contrary to our expectations, the survival probability of boreal owl nestlings was not influenced by their Leucocytozoon infection intensity. Nestling age and Leucocytozoon infection intensity in male and female parents also did not impact nestling survival. Instead, food abundance and hatching order were the key factors influencing nestling survival. Additionally, we observed a significantly higher Leucocytozoon infection intensity in male parents compared to female parents and nestlings. We suggest a distinct division of parental roles may lead females and nestlings staying within the nest boxes (cavities) to experience lower exposure to potential vectors transmitting blood parasites than their male counterparts. Our study shows that Leucocytozoon disease may not be lethal for boreal owl chicks, exhibiting a below-average infection intensity compared to their male parents.

Pärlugglans Aegolius funereus häckningsekologi i en jämtländsk population 1976–1985

A long-term Boreal Owl Aegolius funereus nest box project ran 1976–1985 in central Sweden. Average occupancy among 200 nest boxes was 16% (range 0–54%) with average clutch size 6.0 eggs and number of fledged per successful breeding 4.6, while 41% of breeding attempts failed, primarily due to predation by pine marten Martes martes or desertion by the female. The highest observed breeding density was 0.9 breedings/km2. Five cases of bigamy were observed. Females weighed 50% more than males during egg laying and incubation, probably because of pre-emptive weight gain to compensate for the risk of subsequent changes to food availability. The male provisioned both the female and chicks for most of the breeding period, mainly with small rodents (87%). Population sizes of small rodents fluctuated in 3–4-year cycles. Reproduction was successful during phases of increasing rodent density (1977–1978, 1980–1981, and 1984–1985), while almost no breedings were initiated during nadir years (1976, 1979, and 1982–1983). Ringing recoveries suggested that juveniles recruited into the local population in years with abundant food resources, but dispersed if food availability was declining. Adult females were often nomadic, while most males were resident.

Home range size of Tengmalm’s owl offspring during the post-fledging dependence period in Central and North Europe

A greater knowledge of the intrinsic and extrinsic factors of animal home range (HR) formation can help us to understand the fundamental biological issues underlying, for instance, movement patterns, habitat selection and survival. However, very little is known about the HRs of birds of prey fledglings, even though the post-fledging phase is recognised as crucial due to the high mortality of juvenile birds. We radio-tracked 138 Tengmalm’s owl (Aegolius funereus) fledglings from 43 broods to determine their HRs during the post-fledging dependence period and to investigate the factors affecting their sizes. The study was conducted during four breeding seasons in Czechia and two seasons in Finland. The mean fledglings’ HR size calculated according to the 95% IID Kernel Density Estimation method was 63.7 ± 43.9 ha (± SD; n = 71) during nocturnal activity and 52.0 ± 46.1 ha (n = 63) during diurnal roosting. The sizes of both nocturnal activity and diurnal roosting HRs increased with the longer individual duration of the post-fledging dependence period and also the higher rank of hatching within a brood. Diurnal roosting HRs were two times smaller in the Czech site, probably because of the very limited number of dense forest patches suitable for roosting as a legacy of the air pollution calamity in the 1970s, during which most coniferous stands died out. There was no difference in the size of nocturnal activity HR between the two study areas, although they differed markedly in terms of night length, altitude, weather, and forest age, structure and composition. This suggests that environmental factors are not decisive in determining the size of nocturnal activity HRs of Tengmalm’s owl fledglings. Since the diurnal HRs always occurred within the area of the nocturnal HRs, we suggest that conservation of the densest and preferably oldest forest stands within the areas of the study species occurrence may offer straightforward conservation tasks for protecting Tengmalm’s owl fledglings and also other species.

Rozšíření myšivky horské (Sicista betulina) v Pošumaví na základě rozboru potravy sov (Rodentia: Zapodidae)

Distribution of Sicista betulina in the Šumava Mts. (Bohemian Forest, SW Bohemia, Czech Republic) based on owl diet analysis (Rodentia: Zapodidae). The Šumava Mountains are one of the three areas of a relict occurrence of the northern birch mouse (Sicista betulina) in the Czech Republic. The present study summarises all records of this species obtained there by the analysis of diet of three species of owls, the Tengmalm’s owl (Aegolius funereus), to a lesser extent of the Ural owl (Strix uralensis) and tawny owl (Strix aluco). A total of 355 sample sets from 228 localities was processed, positive findings concern 57 localities where the northern birch mouse was found (322 individuals). The presence of the species was confirmed in an area of approximately 1,400 km2, which corresponds to 13 mapping fields of the KFME, four of which extend into the territories of Germany and Austria (field numbers 7047, 7148, 7249, 7350). More than a third of the localities (37.0%) and nearly two thirds of the individuals (62.4%) come from four mapping fields (7048, 7049, 7148, 7149) covering mainly a peaty alluvial plain of the upper stream of the Vltava river and its surroundings. Data obtained by observation or capturing of the northern birch mouse give a similar picture. Thus, this territory with the high proportion of relict vegetation can be considered as the core area of the current occurrence of the mouse in the Šumava Mts. The altitude range of the northern birch mouse records from owl pellets is 680–1160 m a. s. l. with a mean of 871.7 m a. s. l. Almost a third of the localities (32.0%) lie in the altitudinal range of 700–800 m a. s. l., and more than four fifths of the records (82.7%) fall within the range of 700–1000 m a. s. l. However, these are only indicative values that can be influenced by the size of the individual hunting territories of owls (especially in a landscape with a steep mountainous relief). Our results confirm the previously described zoogeographical profile of the northern birch mouse in the Šumava Mts., i.e., that its distribution is limited only to the south-eastern half of this mountain range and ends roughly in the Kvildské pláně region in the north-west. Records of the northern birch mouse on the Bavarian side of the mountain range are in full agreement with this. It can be assumed that the species occurrence in the whole Bohemian Forest is primarily shaped by its Holocene history. Furthermore, it has been confirmed that the analysis of the diet composition of the Tengmalm’s owl is an effective method of study of the geographical distribution of the northern birch mouse.

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.

Pine marten predation of common goldeneye nests: Effects of cavity age and habitat override any effect of microtine rodent abundance.

According to the alternative prey hypothesis (APH), the temporal synchrony in population fluctuations of microtine rodents and other small herbivores in boreal areas is caused by generalist predators with numerical and functional response to microtines, leading to an increased predation of prey alternative to microtines in the low phase of the microtine population fluctuations. The tree-climbing pine marten (Martes martes) is a food generalist that includes bird eggs among its alternative prey, also eggs of the cavity-nesting common goldeneye (Bucephala clangula). We used long-term data to test whether pine marten predation of goldeneye eggs in nest boxes varied as predicted by the APH. As a measure of microtine abundance at the time of nesting, we applied two measures. First, for goldeneye nests located <40 km from our microtine trapping site, we applied the trapping index of microtine rodents. Second, to also use data from nests located >40 km from our microtine trapping site, and from nests in years when trapping was not conducted, we used two proxies for the microtine abundance: whether boreal owls (Aegolius funereus) nested in any of our boxes <40 km from each goldeneye nest and the average clutch size of these boreal owls. The probability of predation of a goldeneye nest was independent of the microtine trapping index and independent of the proxies for microtine abundance. However, it increased with cavity age, taken as the number of nesting seasons elapsed since the actual nest box was installed, and declined with distance from habitat with forest canopy. The effect of cavity age confirms that the long-term spatial memory of pine marten is an important factor in the pattern of its predation on nests in tree cavities.

Post-fledging survival of Tengmalm’s owl offspring in boreal forests: Interactive effects of varying dynamics of main prey and habitat composition

The knowledge about the mortality rate of offspring is crucial for estimating bird population dynamics and conserving species with declining populations. Parents of predatory birds provide food for their offspring during the post-fledging dependency period, which is frequently described as essential due to inexpert flying skills. Using radio telemetry, we studied fledglings’ probability of dying by starvation and predation in Tengmalms’ owls (Aegolius funereus). Nestlings (21 and 39) from 10 and 14 broods in 2019 and 2021, respectively, were equipped with leg-mounted tags and monitored throughout the post-fledging dependency period in west-central Finland. In total, 28 out of 60 fledglings did not survive the post-fledging dependency period (12 died due to starvation, and 16 were predated). The fledglings’ probability of dying by starvation and predation was 3.7 and 2.4 times higher, respectively, in the decreasing (2019) than during the increasing (2021) abundance of main foods (voles), showing that prey availability is essential for survival during the post-fledging dependency period. The probability of starvation increased with augmenting agricultural lands in the home range and increasing precipitation after fledging, which indicated that parent owls avoided hunting in open areas and during rainy nights. The predation rate during the post-fledging dependency period increased with augmenting cover of old-growth forests in the home range. This result suggested that coverage of old-growth forests is nowadays so small in the study area that they act as ecological traps for newly-fledged owlets. The reason is that the main avian enemies of Tengmalm’s owls’ (goshawks and Ural owls) also prefer old-growth forests for breeding and hunting.

Contributions and data regarding the Boreal Owl &lt;em&gt;Aegolius funereus&lt;/em&gt; phenology in Marche region

An analysis of the observations of Boreal Owl Aegolius funereus in the Marche region, also regarding a recent recovery of an adult of the species, which appears to be the southernmost movement in Italy.

Environmental Niche Modelling Predicts a Contraction in the Potential Distribution of Two Boreal Owl Species under Different Climate Scenarios.

Studying current and future geographic distribution is essential for conserving endangered species such as the Boreal Owl and Eurasian Pygmy Owl. The main aim of this study was to determine the potential distribution of both species in the Balkan Peninsula by using spatial distribution models (SDMs) in MaxEnt. We used data from field surveys, the scientific and grey literature, and an online database. We considered the current time and two future periods, 2041-2060 and 2061-2080. For future periods, we included different climate scenarios (SSP 126, 245, 370, and 585) in studying the potential geographic distribution of both species. We identified two types of potential future refugia for species: in situ and ex situ. Our study shows the highly suitable area for the Boreal Owl increased during the 2041-2060 period compared with the current area in all scenarios, except in SSP 585. However, during the 2061-2080 period, the highly suitable areas contracted. For the Eurasian Pygmy Owl, highly suitable areas decreased during 2041-2060, but during the 2061-2080 period, it was larger than the current area. Our study is of importance for conservation and preserving areas of potential distribution and refugia for Boreal and Eurasian Pygmy Owls in the face of climate change.

IS THIS PHILOPATRY OR DISPERSAL IN FEMALE BOREAL OWLS?

Four cases of female Boreal Owls (Aegolius funereus) recaptured within varying distances of their natal or breeding sites are reported. We considered 3 recaptures within the natal or breeding neighborhood to be philopatry (site fidelity), and 1 case as dispersal. One banded female was recaptured as a 2y old, 3.4 km from her natal box. We considered this philopatry. She was later recaptured 15.8 km from her 2nd breeding site, and we considered this breeding dispersal. She lived at least 5 y, but we did not know her whereabouts in all years. A 2nd female banded as a nestling was recaptured 2.0 km from her natal box, breeding as a yearling (11 mo). We considered this natal philopatry. A 3rd female, previously banded as a breeding adult, was recaptured 2 y later breeding 2.5 km from her initial site of banding. We considered this philopatry. She was at least 4 y old. The 4th female was recaptured 3.6 km from her initial breeding box. We considered this philopatry. She was recaptured again the following year in the same nest box as her 2nd nest site. We considered the use of this same nest site philopatry. She was in her 5th calendar year. Our records are perhaps the 1st reports of natal philopatry and age of 1st breeding for female Boreal Owls in North America, and contribute additional records of female site fidelity and dispersal.

Haste makes waste: shorter time for nest-site assessment leads to higher nest predation in a cavity nester

A fundamental problem for any animal is how to weigh the benefits of making a rapid decision against the costs of making a poor decision, because time for detecting and evaluating all options is often restricted. For nest-site selection in birds, an important cost of a speedy decision would be nest predation, which is a major factor lowering reproductive success. I tested whether shorter time available for assessment of nest sites would lead to a decision with higher probability of nest predation. Where boreal owls (Aegolius funereus) had nested successfully in a box in the previous season, I manipulated nest box availability by offering a dyad of nest boxes. One box (kept or exchanged) was in the original nest tree and one box (new or taken from the original tree) was in a new tree for the season, each box containing either “post-nesting residue” from the successful nesting or new wood shavings. Hence, the owls could assess the risk of nest predation at a familiar site relative to that at a new site. The timing of nest box installation and relocation was such that time for assessment varied among localities, from the whole non-breeding season to just a few days prior to laying in spring. Owls that had had longer time in which to make their assessment and selection were less likely to have their nest predated by pine martens (Martes martes). Boreal owls are non-migratory and probably gained information on the relative safety of the two options by a Bayesian-like updating process in the days, weeks or months before the decision had to be made. A migratory cavity-nester exposed to the same landscape of nest predation would be more time-constrained and forced to rely on the win-stay loose-shift tactic, which underperforms relative to Bayesian-like updating.

Predation of boreal owl nests by pine martens in the boreal forest does not vary as predicted by the alternative prey hypothesis

The alternative prey hypothesis (APH) states that temporally synchronous population fluctuations of microtine rodents and other small herbivores are caused by generalist predators that show functional and numerical responses to the abundance of microtines. This would lead to an increased predation of alternative prey in the low phase of the microtine population fluctuations. One candidate for such a predator is the tree-climbing pine marten (Martes martes), which includes bird eggs in its diet, among them eggs of the cavity-nesting boreal owl (Aegolius funereus). I used long-term data to test whether pine marten predation of boreal owl eggs in nest boxes varied as predicted by the APH. The probability of predation of owl nests situated < 45 km from a site where microtines were trapped in spring during four decades increased with microtine trapping index, which is opposite to the prediction from the APH. As the data set was limited to one nest per box, I extended it spatially and temporally using the clutch size of each boreal owl nest as a proxy for the actual microtine abundance at the site. The probability of nest predation increased with clutch size. However, the effects of microtine index and owl clutch size became non-significant when I controlled for habitat, and in particular cavity age, which had an overriding effect. The increase in predation probability with cavity age suggests that the long-term spatial memory of pine marten is an important factor in the pattern of its nest predation in tree cavities.

Forest structure determines nest box use by Central European boreal owls

Nest boxes represent a popular tool to support secondary cavity-nesting species. Surprisingly, the benefits and limitations of nest boxes for target species in different environments are poorly understood. We performed a 3-years experimental study in two different Central European forests to evaluate nest box use and breeding performance of boreal owl (Aegolius funereus) — a species well known for its readiness to occupy nest boxes. Based on territorial vocalisation, two boreal owl populations 200 km apart were similarly abundant in their environments. However, only the boreal owl population in young restored Norway (Picea abies) and blue (Picea pungens) spruce-dominated forests on mountain plateaus readily occupied nest boxes with the occupancy reaching 8–15%. Nest boxes lost their supporting function for the boreal owl in mature Scots pine (Pinus sylvestris)-dominated forests in the lowland, where the nest box occupancy reached 0–1%. As a result, the population of boreal owls that used nest boxes in the young restored forests produced 10 times more fledglings than the population inhabiting mature Scots pine forests. We explain the differences by the contrasting availability of natural tree cavities between the two study areas being much higher in mature Scots pine forests. For the first time, this study documents differences in nest box use despite similar food availability and population size of the target species. The study provides the findings-related recommendations for deploying nest boxes for boreal owls and points out a general lack of practical guides.

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.

Molecular Identification of Sarcocystis sp. (Apicomplexa, Sarcocystidae) in Offspring of Tengmalm's Owls, Aegolius funereus (Aves, Strigidae).

Background: Birds act as intermediate or definitive hosts of cyst-forming coccidia parasites of the genus Sarcocystis Lankester, 1882. However, the spectrum of species of Sarcocystis in birds and the role of the latter in the transmission of coccidia are still incomplete for many avian species, including the Tengmalm's owl Aegolius funereus (Linnaeus, 1758). During the research on Tengmalm's owls in Finland, some fledglings were found dead and subsequently parasitologically examined. Therefore, this study is focused on the morphological and molecular description of a Sarcocystis species found in the intestine of the Tengmalm's owl and its possible role as a definitive host.Methods: Eleven fledgling owls in the Kauhava region of west-central Finland were found dead and subsequently were submitted for necropsy and parasitologically examined through the flotation–centrifugation coprological technique for the presence of oocysts/sporocysts of the genus Sarcocystis by light microscopy. Wet mounts were used for the examination of muscle samples (breast, legs, and heart). Polymerase chain reaction (PCR) and nested-PCR were carried out using primers for 18S rRNA, 28S rRNA, ITS1 region, and CO1 genes.Results: All 11 examined owls were parasitized by numerous sporocysts and oocysts in the intestinal mucosa scrapings (prevalence, 100%). Sporulated oocysts and sporocysts measured 16.34–16.96 × 11.47–12.09 μm and 11.85–13.52 × 7.77–9.25 μm, respectively. The skeletal and heart muscles were negative for sarcocysts. Sarcocystis sp. ex Aegolius funereus (hereafter Sarcocystis sp. Af) is closely related to Sarcocystis strixi in the barred owl (Strix varia Barton, 1799) from the USA and Sarcocystis sp. isolate 5 in the European shrew (Sorex araneus Linnaeus, 1758) from the Czech Republic. Phylogenetic analysis allowed determining the relationship of the herein reported Sarcocystis sp. with its congeners.Conclusions: This work provided the first and most comprehensive record on Sarcocystis from owls obtained in Finland, thus highlighting the importance of molecular data in species identification.

Differential responses of coexisting owls to annual small mammal population fluctuations in temperate mixed forest

Montane temperate forests in central and southern Europe host diverse small mammal assemblages, but the fluctuations in these assemblages in correlation with owl predators are still poorly explored. The key questions of our study were how coexisting owls responded to different prey fluctuations and whether any particular small mammal species governed predator–prey co‐dynamics. We conducted a long‐term study (2004–2020) in low‐elevation (300–1100 m above sea level) mixed Beech and Silver Fir forest in the northern Dinaric Alps (central Slovenia). Monitoring data on the main small mammal groups – mice Muridae, voles Cricetidae, dormice Gliridae and shrews Soricidae – and three owl species – the Ural Owl Strix uralensis, Tawny Owl Strix aluco and Boreal Owl Aegolius funereus – were collected annually. To find relationships between prey and predator populations, we used two types of supervised machine learning approaches and addressed three predictive modelling tasks of multi‐target regression. The dominant species in the small mammal assemblage, the Yellow‐necked Mouse Apodemus flavicollis, had a key role in determining predator populations and their breeding performance. We noted higher sensitivity to small mammal fluctuations in boreal zone owl species (Boreal Owl and Ural Owl), which reach their southern distribution limit in the Dinaric Alps, whereas the temperate zone species (Tawny Owl) seemed to be less affected. In years of prey shortage, the Boreal Owl was found to presumably abandon its territories, the Ural Owl suppressed breeding and the Tawny Owl sustained breeding activity by shifting prey selection. Low‐elevation forests appeared to be suboptimal habitat for the competitive subordinate Boreal Owl, which may exploit occasional outbreaks of small mammal populations in these habitats even in the presence of larger competitors. Whether low‐elevation forests can play a role in maintaining threatened and cold‐adapted Boreal Owl populations in central and southern Europe in the face of recent ecosystem changes due to climate and environmental changes remains an open scientific question.

The effect of environmental variables on owl distribution in Central Europe: A case study from the Czech Republic

Species distributional data from atlas projects collected by volunteers and professionals play an essential role in ecology and biodiversity conservation. Atlas data primarily allow evaluating longitudinal and latitudinal gradients in species distribution. However, the effects of additional factors such as elevation and associated climatic conditions and landscape structure are rarely assessed. We used the original data from the Atlas of birds breeding in the Czech Republic in terms of the presence and absence (0/1) of breeding occurrence of seven owl species in 604 mapping quadrates (each quadrate 12.0 × 11.1 km in size) to assess the effect of elevation (reaching from 100 to 1100 m a.s.l.) and temperature on the distributional patterns of the owls. Using a multivariate spatial analysis with latitude and longitude as space predictors and landscape structure as covariates, we found that elevation and temperature significantly affected owl distribution; the model explained 94.8% of the variability (p = 0.002). Only the boreal owl (Aegolius funereus) showed a clear preference for the highest elevation, and simultaneously, boreal and pygmy (Glaucidium passerinum) owls preferred the coldest environments. Eagle owl (Bubo bubo) and tawny owl (Strix aluco) most often occupied low and middle elevation of moderate temperatures. Barn owl (Tyto alba) and long-eared owl (Asio otus) inhabited the warmest areas in low elevations. Finally, little owl (Athene noctua) most often occurred in the lowest elevations of intermediate temperatures. We have documented that the elevation and associated climate conditions can work as an effective predictor to assess distributional preferences of owl species based on atlas data. The findings can be helpful when the management of owls' habitats is considered and implemented. For example, the results of our case study suggest that the boreal owl can be susceptible to global warming and intensive logging at high elevations.

Win \u2013 and stay, but not too long: cavity selection by Boreal Owls to minimize nest predation by Pine Marten

Site fidelity after successful nesting and site shift after nest predation (win–stay, lose–shift) is a well-documented adaptation to spatially heterogeneous and temporally auto-correlated predation risk. However, site shift even after a successful nesting (win–shift) may become a better tactic than site fidelity (win–stay), if a successful nest site becomes more risky until the next nesting opportunity, and if new low-risk nest sites regularly appear. Correspondingly, selecting a new non-used nest site may become a better tactic than selecting one previously used successfully by a conspecific. I studied this dynamic by focusing on nest cavities that may be available for many years, and using nest boxes to allow an experimental design. At localities where Boreal Owls (Aegolius funereus) had nested successfully, a dyad of nest boxes was made available each year, one box in the original nest tree and one in a new tree for the season, each containing either old nest material from the successful nesting or new wood shavings. Boreal owls were more likely to select the box in the new tree when more years had elapsed since the successful nesting and since a box was installed in the original nest tree, independent of box content. The pattern of selection differed between young and old individuals for males, but not females. Young males based their selection of nest tree mainly on box content, while old males based it on time elapsed since the successful nesting in the original nest tree and how long a box had been present there. The probability of depredation of Boreal Owl nests by Pine Marten (Martes martes) has previously been found to increase with cavity age and number of nesting seasons elapsed since the previous successful nesting. This pattern of nest predation thus predicted the pattern of nest site selection found.

Distribution of the parasitic mite Bubophilus aegolius sp. n. (Acariformes: Syringophilidae) on the Boreal Owl Aegolius funereus (L) (Strigiformes: Strigidae) and the low effectiveness of infestation

The mite family Syringophilidae (Acariformes: Prostigmata) includes permanent parasites of birds exclusively, occupying their quill feathers where they reproduce and feed on living tissue fluids, piercing the quill-wall with their long and stiletiform chelicerae. The Boreal Owl, Aegolius funereus (L.) (Strigiformes: Strigidae) is parasitised by the Bubophilus aegolius, which is a new species of syringophilid mite described herein. In our study a total of 55 Boreal Owls were examined, including birds from Poland, Austria, Switzerland, Germany, Czechia, Slovakia, Sweden, Finland, and Norway. A total of four host specimens from Poland, Switzerland, and Finland were infested by Bubophilus aegolius (index of prevalence IP = 7.3; 95% confidence interval for prevalence (Sterne’s method) CI = 2.5–17.9). In the material consisting of 14 juvenile (in the 1st calendar year) and 41 adults (in the 2nd calendar year or older) birds, only juvenile hosts were infested (IP = 28.6%; CI = 10.4–57.4). Among 3,190 examined feathers (primaries (N = 1,100), secondaries (N = 1,430), rectrices (N = 660), quill mites were found only in four feathers, each feather from a single host specimen: in two small secondaries, S12, S13, and in two middle rectrices R1. This low prevalence may be related to the solitary behaviour of owls and the marginal role of horizontal transfers of parasites between hosts. Hypothetically, the low number of infested feathers on the host indicates low effectiveness (= high mortality) during transmission, where – in each case – only one fertilised female foundress (dispersal stage) was able to transfer from the parent to the offspring and enter a new quill feather. http://www.zoobank.org/urn:lsid:zoobank.org:pub:66025B6E-A126-48FF-8B1A-F618265CA34D