Sampling owls in a reliable and standardized way is not easy given their nocturnal habits. Playback is a widely employed technique to survey owls. We assessed the influence of wind speed, temperature, air humidity, and moon phase on the response rate of the Tropical Screech Owl Megascops choliba and the Burrowing Owl Athene cunicularia in southeast Brazil. Tropical Screech Owl occurs in scrubland and wooded habitats, whereas the Burrowing Owl inhabits open grasslands to grassland savannah. Sixteen survey points were systematically distributed in four different landscape types, ranging from open grassland to woodland savannah. Field work was conducted in 2004 from June to December, the reproductive season of the two owl species. Our study design consisted of eight field expeditions of five nights each; four expeditions occurred under full moon and four under new moon conditions. At each survey station, we performed a broadcast/listening sequence involving several calls and vocalizations from each species, starting with Tropical Screech Owl (the smaller species). From 112 sample periods for each species within their respective preferred habitats, we obtained 54 responses from Tropical Screech Owl (48% response rate) and 30 responses (27% response rate) from Burrowing Owl. We found that the response rate of Tropical Screech Owl increased under conditions of higher temperature and air humidity, while the response rate of Burrowing Owl was higher during full moon nights.

We offer a protocol for conducting standardized nocturnal broadcast (playback) surveys on Little Owls Athene noctua across the range of the species. Based on differing objectives of researchers, two intensity levels of survey efforts are outlined: (1) demographic and density studies, and (2) presence and general distribution surveys. Both survey programs utilize the same field method, but vary in the number of visits required across the survey area. Objectives and definitions for these survey programs, and criteria for determining occupancy, reproduction, and turnover rates to support demographic and monitoring studies are given. The recommended survey period coincides with the breeding season, and depending on the latitude (and elevation), is approximately from 1 February — 30 April in western-Europe, and 1 March — 31 May in eastern Europe, Middle East, and Asia. Surveys are to be conducted from sunset to midnight and from two hours before sunrise to sunrise. Survey stations are located 500 m apart from one another along transects, or in a grid network. The tape-recorded call sequence consists of a 2-min track played three times, with each broadcast track separated by silent periods of 1 min each. The observer listens for 5 min after the last sequence. Thus a maximum of 13 min is spent at each survey station. Positions of all responding owls are recorded on a field map. While Little Owls have a repertoire of 22 vocalizations, two calls, the hoot (“ghuk”) and the “chewing” call, are used by males in territorial contests and are the calls recommended for use in this protocol. Broadcast vocalizations should be played at volume and clarity levels consistent with that of wild owls. For demographic and density studies, we recommend 4 visits across each of the survey routes (and associated survey stations) to gain responses from >95% of the territorial owls. For nest-box programs where the objectives are demographic status and trends, and where the majority of owl territories are already known, survey efforts described in this protocol are used to fill in gaps and offer thorough and systematic coverage of the entire study area. For presence and general distributional surveys, we suggest a 1-visit survey be conducted. While a 1-visit strategy will not detect some of the owls actually present, the outcome of these surveys will illuminate general distributions of owls and highlight areas for further study. We anticipate that this protocol will be updated occasionally, following a normal scientific peer-review process. In particular, we urge additional research on the detection probability of territorial owls to provide clarification as to the number of visits needed to accurately determine the numbers of owls present in a given area. Prior observations have indicated a potential for differential responses from owls in high density populations (higher response rates) compared to owls residing in low density situations, and this needs further research.

Visual observations of nocturnal species such as owls can be difficult. Knowledge of vocalizations associated with particular behaviours is therefore an extremely useful tool in studying owls in the field. For this purpose, I studied the vocalizations and behaviours of the Great Horned Owl Bubo virginianus, collecting observations on a female human-imprinted individual and wild pairs. Spectrographically, Great Horned Owl calls were divided into three main categories: hoots, chitters, and squawks. These categories were further subdivided into five types of hoots, four types of chitters, and five types of squawks based on inflection, number of syllables, duration, pitch, volume, and behavioural context. Two types of non-vocal communication were also distinguished: hisses and bill clacking. Although owl vocalizations are generally considered innate and variation between individuals should not differ in basic makeup and behavioural context, further verification on wild owls is encouraged.

Once regarded as Britain's most abundant owl species, Barn Owl Tyto alba numbers declined substantially from 1850 to 1950. While more recent surveys suggest that numbers may now have stabilized, breeding range declines and the species' unfavourable European conservation status have resulted in its inclusion on the Birds of Conservation Concern Amber List. As existing schemes were not suited to monitoring the abundance of low density, nocturnal species, the Barn Owl Monitoring Programme (BOMP) was established by the British Trust for Ornithology in 2000, assisted by the Wildlife Conservation Partnership. Under BOMP methodology, approximately 600 potential breeding sites (c. 10% of the national population) located throughout the British Isles are visited by volunteer observers each year who record owl occupancy and productivity. These data are used to assess long-term trends, and the results from the first six years of data collection (2000–05) are presented in this paper. As expected, given the short time-span of data collection, there was no strong evidence for a significant temporal trend in either occupancy or productivity. Habitat type appears to play a significant role in determining both occupancy rates and productivity. A greater proportion of sites in areas of natural or semi-natural grassland were occupied by Barn Owls and broods produced at these sites were significantly larger than those produced in pastoral or arable habitats. Areas of rough grassland are likely to support greater numbers of small mammals, particularly voles Microtus spp., providing more food for adults and nestlings. There was some evidence to suggest that occupancy rates were higher towards the western part of the country, possibly due to the milder winter conditions in these areas.

The Philippine Archipelago is widely acknowledged as one of the world's major biodiversity and endemism ‘hot-spots’. However, as a result of a burgeoning human population increase and resultant destruction and exploitation of the native forests over the past half century, the Philippines has gone from being one of the most biologically rich areas on earth, to one of the most endangered. Nowhere else in the world has this decline taken place so rapidly. Once, the Philippines had virtually a 100% forest cover, now this figure is down to less than 10%. The significance of this to Philippine owls cannot be overstated. This country has more threatened owls than any other part of the world, and of the 16 species recorded from this archipelago, 14 are almost totally dependent upon this habitat. Unless something is done quickly to protect the last few remaining forest remnants and replant those lost, virtually all of the Philippine owls, and certainly the endemic species, will soon join the New Zealand Laughing Owl Sceloglaux albifacies in the ranks of extinct birds. In an attempt to rectify this situation the World Owl Trust signed a Memorandum of Agreement with the Philippine Government to manage the ‘Philippine Owl Conservation Programme’ as part of the overall ‘Philippine Biodiversity Conservation Programme’ overseen by Fauna & Flora International. This has been very successful in carrying out field research, education and conservation-breeding programmes focused on some of the threatened taxa. Another major objective is to involve the local people in conservation initiatives by means of education, providing employment and alternative life-styles.

The density and reproduction of Long-eared Owls Asio otus were studied in a 5000 ha study area of Havelland, Brandenburg, Germany from 1984 through 2007. Locations of territorial Long-eared Owls were mapped from the end of January until the end of April, counts of fledged young were made from mid-May until August. Long-eared Owls nested in conifer groupings or isolated woods in the agricultural landscape. Nearly all nesting took place in nests of crows Corvidae, mainly in Scots Pine Pinus sylvestris trees. A total of 867 breeding attempts were recorded; 335 (36.6%) pairs were successful in fledging 1468 young. The reproductive output was 1.57 fledglings for all pairs that attempted to nest, and 4.31 fledglings per successful pair. Average population density for the 24 years was 72.7 breeding pair/100 km² (range 40–118 breeding pair/100 km²). For the time frame of 1984–2007 there was no trend in the number of breeding pairs or in the number of young fledged. After 1990, when conservation-focused farming in the nature reserve began, the number of young fledged increased significantly. Grassland management is considered a principal conservation measure for Long-eared Owls in Brandenburg.

By 1979, the Barn Owl Tyto alba had almost disappeared from the province of Friesland, northern Netherlands. With the placement of nest boxes and by specific forms of landscape restoration, the minimum breeding population of 8 pairs increased to 573 pairs in 2007. In this paper I compare the increase of the breeding Barn Owls across the three landscape types in Friesland, based on soil type sand, peat and clay. Each of these three soil types was divided into 15 categories of openness: open (1–5), partly-open (6–10) and closed landscapes with many trees and bushes (11–15). Each year, a large group of volunteers ensured that all nest boxes (up to 1470 in 2007) were inspected. The increase first became apparent in the sandy soil region with the breeding density exceeding the 1 pair/100 km² threshold in 1982. This threshold was crossed on peat soils in 1985 and on clay soils in 1990. During the population incline, increasing numbers of nest boxes were made available so that nest sites were never in short supply. The population increase on all soil types stabilized as of 2000. In the peak vole year of 2004 the population density was 25.5 pair/100 km² on sand, 20.1 pair/100 km² on peat, and 10.9 pair/100 km² on clay. To our surprise during the population increase Barn Owls did not show clear preferences for a particular degree of landscape openness on any soil type. To explain the highest densities of pairs that eventually established on sandy soils, the habitat type that is least open, I suggest that food conditions are more constant in the most heterogeneous landscape (sandy soils) which leads to the highest reproductive success. Only in good vole years did reproduction in the clay and peat areas exceeds that of sandy soils.

We monitored the dynamics of owls, raptors and corvids within the 3400 ha of the Amsterdam Water Supply Dunes in the western Netherlands from 1961 through 2007. In the 1930s and 1950s, afforestation projects were initiated. In 1961 the first Tawny Owl nest was found, from whence the population increased steadily to stabilize in the 1970s at c. 24 pairs. Tawny Owl dynamics were affected by competition for nest sites with Jackdaws Corvus monedula and depredation by Northern Goshawks Accipiter gentilis. Jackdaws were able to take over nest boxes from egg laying and incubating Tawny Owls, reducing the letter's breeding success. Tawny Owl numbers and breeding success were negatively correlated with Jackdaw numbers (R² = 0.556 and R² = 0.592, respectively). After the first nest in 1993, Goshawk numbers rapidly increased to 10–11 pairs in 1999. The number of Jackdaw breeding pairs correlated negatively with the number of Goshawks (R² = 0.661). Goshawks apparently limited Jackdaw numbers, which led to an improvement of Tawny Owl breeding success. However, post-fledging mortality of Tawny Owl from Goshawk predation was also significant, reducing local recruitment in the Tawny Owl breeding population.

Information on the Collared Scops Owl Otus lettia in Thailand is extremely limited and this study examined its nesting ecology. From August 2006 – September 2007, 23 nests were found and observed in Chanthaburi Province. The breeding season for the Collared Scops Owl started in early January and continued until the end of April. The majority of nest sites were a tree cavity with the opening facing skyward. The average nest height was 3.4 m (SD 1.7) from the ground; average size of the nest entrance was 16 (SD 6.1) cm × 28 (SD 17.4) cm; cavity dimensions were 17 (SD 6.1) cm wide, 24 (SD 8.9) cm long, and depth was 24 (SD 28.5) cm. The average crown cover in the nest area was 43%. The majority of the land used around the nest site was agricultural land. The number of eggs laid per nest was 1–4, with a majority of the nests containing three eggs, and the hatching rate was 60%. The average weight of hatched chicks was 13 (SD 1.6) g and the fledgling weight was 88 (SD 7.6) g. The nesting success was 52% (12 of 23 nests), the survival rate (to fledging) was 65% and mortality rate was Inversely related to chick age.

Starting in 1983, nest boxes for Barn Owls Tyto alba were erected as part of a biological pest control program to deal with rodents, in Kibbutz Sde Eliyahu, and later in other agricultural fields and plantations in the Beit She'an valley, Israel. More than a decade ago, the nest box scheme was extended to include other agricultural areas in the valley, and grew from 14 boxes on 3 km² in 1983 to about 300 boxes on 90 km² throughout the entire Beit She'an valley in 2007. Here we present the results of a study during the 2002 through 2006 breeding seasons, in which 156 to 243 nest boxes were monitored each season. Mean occupation of nest boxes during the study was 53.5% (SE 2.1, n = 248), and a total of 596 breeding attempts were recorded, of which 85.2% successfully fledged at least one young. Yearly occupation of nest boxes varied significantly between the years, ranging from 48.1% to 73.5%. The occupancy rate of first-year nest boxes was lower than that of those available for two or more years. The occupancy rate and the number of nestlings per box (per year) were positively correlated to the distance to the closest nest box and negatively correlated to the number of nest boxes within a 500 m radius. Similar to other studies in the world, the erection of nest boxes for Barn Owls in agricultural fields proved extremely successful in the Beit She'an valley, with 86.7% (n = 248) of nest boxes being occupied at least once during the five-year study period. This high occupancy rate demonstrates not only that natural nesting sites were lacking, but also that nest boxes can be used to increase Barn Owl populations in agricultural areas, both for conservation and for biological pest control.

In Finland, monitoring of ‘common’ birds of prey is based on two projects run by the Finnish Ringing Centre: the Raptor Grid (since 1982) and Raptor Questionnaire (since 1986). The Raptor Grid has produced sufficient data for analysing population trends in six of ten owl species. The overall trend during 1982–2007 was significantly negative in the Eagle Owl Bubo bubo (-2.2% per year), Long-eared Owl Asio otus (-4.7%) and Tengmalm's Owl Aegolius funereus (-3.1%), and significantly positive in the Ural Owl Strix uralensis ( 1%); no significant trend was detected in the Pygmy Owl Glaucidium passerinum or Tawny Owl Strix aluco. The Eagle Owl population increased to the middle of 1990s, but has since decreased by 5% per year. The decrease coincides with the closing of 90% of local open rubbish dumps, which offered a stable and rich food supply to the Eagle Owls. The decrease in the Tengmalm's Owls can partly be attributed to the decrease in the amount of old forest. The Pygmy Owl population increased steeply (>5% per year) during 1994–2003, then crashed following a mass invasion and has since started to recover. The geographical distribution of the Raptor Grid study plots is not suitable for monitoring the northern nomadic species like the Snowy Owl Bubo scandiacus, Northern Hawk-Owl Surnia ulula, Great Grey Owl Strix nebulosa and Short-eared Owl Asio flammeus. Annual totals of active nests and occupied territories reported with the Raptor Questionnaire do not indicate any long-term population changes of these species. However, intensive cooperation over larger areas across national boundaries in northern Europe is urgently needed for reliable monitoring of these nomadic owls.

Until the end of the 20th century, the distribution of the Ural Owl Strix uralensis was limited to the Carpathian Mountain area of southwestern Ukraine. The abundance and distribution of Ural Owls in the Ukrainian Roztochchya area was investigated in 2005 and 2007; the density of owls was found to be 1.7–2.0 pairs/10 km². The species was a very rare vagrant in this area at the beginning of 1990s. The population of the owl has expanded in the past decade and it is now a common species in almost all of western Ukraine. The first indication of a change in the owl population was through an increase in the number of wintering specimens (including those killed on roads). The Ural Owl prefers old beech and rarely uses mixed forests in newly settled forest areas.

The Northern Saw-whet Owl Aegolius acadicus (NSWO) can be found year-round on Its North American breeding range, but considerable numbers migrate south in autumn, with banding data documenting migration movements over 1000 km. Although the timing and routes of migration are better known in eastern North America, there is some evidence of a general movement from Manitoba, Ontario and Minnesota around Lake Superior to Wisconsin, and then south and/or east. We examined NSWO calling indices from annual auditory surveys in Manitoba, Canada (1991–2006) and from another study site over 770 km southeast in Wisconsin, USA (1986–2007) for covarlance as evidence of a spring migration in central North America. In Manitoba and Wisconsin, NSWO calling showed a consistent pattern of regular periodicity, with peak calling every 2–7 years (average 3–5). Likewise, NSWO prey (small mammal) abundance in southeastern Manitoba surveys (1986–2006) showed a periodicity of 2–7 years. NSWO calling, both in Manitoba and Wisconsin, covarled significantly with small mammal abundance in southeastern Manitoba. NSWO indices in Manitoba covarled nearly significantly with the same year in Wisconsin, and significantly with the lag year in Wisconsin suggesting a spring migration takes place in central North America that is influenced by prey availability. This study highlights the need for more extensive analyses of long-term data from owl and prey surveys and for spring owl migration banding to better understand NSWO migration in North America.

A nine year search for the first nesting Boreal Owls Aegolius funereus in Nova Scotia, Canada culminated in the discovery of two nests in Cape Breton Highlands National Park of Canada in 2004. In 2005, one nest north of the Park and another nest on mainland Nova Scotia were also found. Nest start dates ranged from 20 March to 3 June over the two years; only the nest with the latest start date failed entirely, the other nests fledged two or three young each. Nests were in boreal forest, with Balsam Fir Abies balsamea and White Birch Betula papyrifera normally dominating. These findings extend the known breeding distribution of the Boreal Owl eastwards by approximately 450 km at the latitude found.

The distribution of owls in Syria was investigated during a larger project to plot the distribution of small mammals in the country. Owl pellets were collected from 92 localities representing most of the habitats in Syria; during this work, seven species of owl were observed (Little Owl Athene noctua, Barn Owl Tyto alba, Eagle Owl Bubo bubo, Tawny Owl Strix aluco, Striated Scops Owl Otus brucei, Eurasian Scops Owl Otus scops and Long-eared Owl Asio otus). Little Owl and Barn Owl were the most common owls. Owl distributions were mapped based on recent observations and published records. Threats affecting owl populations in Syria include trade for taxidermy or traditional use, secondary poisoning by insecticides and rodenticides and habitat destruction.

The Ural Owl Strix uralensis meets its westernmost distribution in Hedmark County, southeast Norway. Since 1979 we have provided the species with nest boxes in this region. A total of 80 nest boxes were put out in prime Ural Owl habitat, starting with 9 in 1979, 18 in 1982 and 53 in 1985. Two more nest boxes put up by others, and four made by ourselves, were later added, giving a total 86 nest-box localities. The nest boxes were checked up to 2004, when 28 nest boxes were moved to western (n = 8) and central (n = 20) Sweden. We have analysed the results for 25 seasons from 1980 to 2004. For comparison, the results for the 20 nest boxes in central Sweden for the seasons 2005–07 have been included. The Norwegian nest boxes offered a total of 1429 nest-box years. Since all boxes were not inspected each year, the total number of observation-years was 847 (59.3%). Ural Owls only used 4 nest boxes for breeding, occupied for the first time 1, 1, 1 and 10 years respectively after the boxes were put up. The four boxes were used for a total of 19 breedings. In central Sweden, 9 out of 20 nest boxes were used by Ural Owls for breeding (n = 6) or breeding initiations (n = 3), for a total use of 8 of 56 nest-box years. The Ural Owl nest-box use in Norway (1.3% of nest-box years) is very low compared to central Sweden (14.3% of nest-box years). Telemetry studies of Ural Owl hunting behaviour in 1989–90 (unpubl.) showed that the nest boxes were indeed placed in prime Ural Owl habitat. Despite this, there was no increase in Ural Owl nest-box breeding in Norway during the study period. We conclude that Ural Owls are not limited by nest sites at the species' westernmost borderline and hypothesize that food availability during winter is a more likely factor limiting the species.

We examined 11 Eagle Owl Bubo bubo nests in Mongolia during 2004–06. Five nests were located in cliffs, three in rock columns, two in sandy precipices and one on a rock ledge. Mean height (above ground) of the nest site structure was 7.6 (SD 5.9) m and height of nest entrance was 3.1 (SD 2.5) m. Mean clutch size was 1.7 (SD 0.9) and the number of fledglings was 1.5 (SD 0.5). Nest structure or entrance height did not correlate with the number of eggs laid (r = 0.1, r = 0.4) or young fledged (r = 0.001, r = 0.1). We identified 276 prey from pellets and remains from nests or nearby perches. Pellets averaged 63.5 (SD 14.2) by 22.2 (SD 4.1) mm and weighed 10.6 (SD 4.6) g when collected. Seventeen species of birds were taken as prey, and represented 32.2% of prey biomass (26.1% by frequency), while 13 mammal species constituted 67.8% of the biomass (72.2% by frequency). The most frequent avian prey was the Eurasian Sparrowhawk Accipiter nisus; the most frequent mammalian prey was the Mongolian Five-toed Jerboa Allactaga sibirica. Amphibians and beetles together represented a very small percentage (0.23%) of the diet biomass.

Random-stratified spring nocturnal surveys using tape playback were conducted for Eastern Screech Owls Megascops asio from 2004 through 2007 in Winnipeg, Manitoba, Canada, at the northern periphery of its range. Surveys were stratified by (1) human density, (2) riparian vs. non-riparian habitat, and 3) the presence or absence of suburban greenspace. A total of 120 transects (each 1.75 km long) were surveyed, with 55 Eastern Screech Owls detected. Eastern Screech Owl densities peaked in moderate to high-density suburban areas (>20 persons/ha), where 36 (66%) detections occurred, and were lowest in wildlands (<1 pair/ha), where no detections occurred. Fifty-one (93%) Eastern Screech Owls were detected in riparian areas. Only 20 (36%) Eastern Screech Owls were detected in suburban greenspaces. In 4 years I located a total of 46 successful Eastern Screech Owl nests, 6 failed nests, and 37 territories with non-breeding owls. Excluding repeat cavity uses, a total of 61 nest sites and territory centres were located, of which 38 (62.3%) were in natural cavities, 21 (34.4%) in nest boxes, and 2 (3.3%) at sites where cavity choice was undetermined. Fledging dates ranged from 28 May – 3 July (mean 15 June, SE 1.4) over the 4-year period. Eastern Screech Owls were closely tied to riparian habitat, and showed larger average brood sizes and earlier average fledging dates in moderate and high-density suburban areas than in low-density suburban and rural areas.

Habitat selection of the Eurasian Scops Owl Otus scops was studied in Ljubljansko barje (central Slovenia, 180 km²) where abiotic conditions, especially climate, could be considered suboptimal for this xerothermophilic species. Data on the number and distribution of calling males were gathered in May and June 2004–06 using the playback method. A total of 137 calling males were counted (29 in 2004, 66 in 2005, 42 in 2006). To avoid pseudo-replication, 72 non-overlapping sites were selected for habitat analysis. Habitat within 250-m radius plots surrounding owl sites was compared with 136 unoccupied and non-overlapping sites. Within plots, 14 habitat variables were measured. Discriminating variables between occupied and non-occupied sites were identified with stepwise logistic regression. Scops Owl occupation was positively associated with the number of tree lines, and slightly negative with the surface area of woodland and settlements. Scops Owls preferred sites with a higher than average proportion of traditional orchards, tree lines, scrub, unimproved meadows, and tree plantations. Tree plantations were only used by owls during 2005, when the number of calling males was highest. All males were unpaired, perhaps indicating inexperienced or late-arriving males outcompeted to marginal habitat. Conservation actions needed to maintain this population of Scops Owl at the northern border of its breeding range include: (1) preserve and rejuvenate traditional orchards and isolated trees in farmyards, (2) encourage renovation of old houses and their farmyards and discourage high density housing, (3) protect and restore tree lines and copses, (4) enlarge the proportion of unimproved meadows, and (5) limit the increase of cropland and the use of biocides.

Home ranges of 11 Little Owls Athene noctua were studied using radio telemetry in agricultural landscapes of eastern Poland during the breeding seasons of 2000–03. Owls were tracked from the time of egg laying until the young dispersed (15 April – 22 August). Areas of use were determined for three periods: egg laying and incubation period (15 April –17 May), nestling period (8 May – 28 June), and fledgling period (29 June – 22 August). During the egg laying and incubation period use areas were on average 18 ha (SD 20, 2.5–65.3, n = 9), during the nestling period 27.5 ha (SD 28.2, 1.9–95.0, n = 18), during the fledgling period 9.0 ha (SD 9.4, 1.8–34.1, n = 11). Combining data for all owls from all breeding season periods, the area of use was 1.8–95.0 ha (average 19.9 ha, SD = 23.2, n = 38). The majority of owl locations were recorded in fields (64%, mainly cereals). Fewer locations were in fields with row crops (12%, sugar beets, potatoes), on buildings (11%), gardens and orchards (9%), meadows and pastures (2%), roads (1%) trees and bushes (1%). During the breeding season, the growth of vegetation limited the access that owls had to the ground. Little Owls spent 85–95% of their time at places where vegetation height did not exceed 20 cm.

Locomotion is costly and should therefore serve a purpose according to the principle of optimal behaviour. In this light, we studied variation in nocturnal activity of radio-tagged Little Owls Athene noctua in Denmark where, after a decline of at least 30 years, the species is threatened with extinction. The study is based on 143 one-hour surveys of breeding and 274 surveys of non-breeding Little Owls (27 territorial individuals on 14 territories). Working effort is calculated as the total linear distance between all observed consecutive telemetry fixes during one-hour surveys (Minimum Flight Distance, MFD). The effort peaked during the post-hatching dependency period with males flying longer distances and having fewer inactivity periods than females. This might suggest that also after hatching, males provide more food to the nest than females. Non-breeding owls were completely inactive in 13% of all surveys. Probability of inactivity increased with heavy rain and was highest in the middle of the night. During the non-breeding season, MFD of active owls varied with a peak in March and a low in December, possibly reflecting seasonal variation in metabolic needs and social activity. During the non-breeding season, MFD was slightly higher for males than for females, possibly reflecting lower energetic flight costs due to lower weight, and were highest at the beginning and end of nights.

Snowy Owl Bubo scandiacus nest mounds from Barrow, Alaska, were characterized measuring several variables from 114 nests and 2280 random mounds. Mound height appeared to be the most important trait, as nest mounds averaged about 1 m tall, and were significantly different from random mounds in all years. Generally circular nest bowls (n = 91) were dug by females and averaged 47.5 × 44.0 × 9.6 cm (length × width × depth). Mound vegetation did not conceal Incubating or brooding Snowy Owls. Tall nest mounds were advantageous in that they were drier (thinner snow cover which melted earlier allowing females to dig nest bowls), windier (relief from mosquitoes and cooler in summer) and allowed nesting owls greater vigilance against predators.

We surveyed the Ural Owl Strix uralensis macroura from 1993 to 2007 to determine the geographic range of the species in Croatia and to provide information on its density and habitat preferences. We conducted playback surveys at 365 survey points within 19 plots (total survey area 1070 km²) systematically covering all of the major forest types in Croatia. Surveys were also carried out at 144 calling stations arranged in transects and at 133 stations scattered over larger areas. Playback surveys were conducted twice at stations in plots and along transects, and once at scattered stations. A total of 234 Ural Owl territories were located. We estimate the total population of the Ural Owl in Croatia to be 700–1000 pairs, and include an updated map of its distribution. The owls occurred in Dinaric fir—beech forests, montane beech, Sessile Oak Quercus petraea and Common Oak Quercus robur forests. The majority of the population, around 80%, was located in Mountain Croatia, where mixed Dinaric fir—beech forests predominated, at densities ranging from 1.1 to 5.4 pairs/10 km² (average 2.3 pairs/10 km²). The highest density was found in the Plitvice Lakes National Park, in forests that have not been commercially logged for more than 50 years. Approximately 20% of the total population was found in the western part of Lowland Croatia, in the zone of beech and Sessile Oak-hornbeam forests, with average density of 0.9 pairs/ km², as well as in Common Oak forests, with density of 0.7 pairs/10 km². In Mediterranean Croatia the Ural Owl was found only in the mountainous zone of thermophile beech forests. There we recorded a density of 0.3 pairs/km² and estimate the population at 15–25 breeding pairs constituting approximately 2% of total population in Croatia.

During 2003–07, the moult of four captive Northern Hawk Owls Surnia ulula was studied in Poznań Zoological Garden (Poland). The aviary was under daily observation and all breeding events were recorded. It was recognized that captive conditions differ from that in the wild (food availability, expended energy — especially by males, and stress) but the study of captive owls allowed a detailed study of moult in relation to the breeding cycle of Northern Hawk Owls. Identification of dated moulted feathers enabled us to reconstruct the moult process of primaries, secondaries and rectrices. During this study the four birds had different breeding status: single, paired without breeding, paired with unsuccessful or successful breeding. In nine cases, the moult corresponded to patterns described in literature. In every case all primaries and rectrices were renewed each season. Males started moulting 3–11 days earlier than females and shed all secondaries every year while females replaced from 50–100% of secondaries annually. Rate of moult was not related to ambient temperature. During a successful breeding season, the moult of both sexes was two-phased: a short first phase with low moult intensity lasting until young owlets left the nest box followed by a longer, more intense second phase. Breeding females (egg laying and incubation) started to moult a few weeks earlier than non-breeding females but completed moult at approximately the same date. In contrast, breeding and non-breeding males had similar patterns of moulting intensity.

For 97 owl taxa from 15 of the larger genera (some monotyplc taxa are not represented) a molecular phylogeny was Inferred from a combined dataset of nucleotide sequences of mitochondrial cytochrome b and nuclear RAG-1 genes. The molecular phylogeny can be used to create a taxonomic framework, which agrees with cladistics. Strigiformes are divided Into two families: Tytonldae and Strigidae. The Tytonldae are subdivided into the subfamilies Tytoninae (with Tyto) and Phodilinae (with Phodilus). The Strigidae cluster in three subfamilies: Striginae, Surniinae and Ninoxinae (with the genera Ninox, and possibly the monotypic Uroglaux and Sceloglaux). The Surniinae are subdivided in three tribes Surnini (with Surnia, Glaucidium and Taenloglaux), Athenini (with Athene) and Aegolini (with Aegolius). The Striginae are subdivided into six tribes: Bubonini (with Bubo including the former Nyctea, Ketupa and Scotopelia), Strigini (with Strix and Jubula), Pulsatrigini (with Pulsatrix and Lophostrix), Megascopini (with Megascops and Psiloscops), Otini (with Otus and Mimizuku) and Asionini (with Asio, Ptilopsis and possibly the monotypic Nesaslo and Pseudoscops).

Long-eared Owl Asio otus nestlings usually depart from their nests at approximately 22 days of age, and cannot fly until approximately 35 days of age. Corticosterone has been Implicated as a mechanism Influencing nest departure in many avian species. We sampled corticosterone concentrations in wild nestling and nest-departed Long-eared Owl chicks to determine if this stress hormone Influenced nest departure. Baseline corticosterone titres were found to be similar in nest-bound and nest-departed young (10.69 ± 1.37 vs. 9.29 ± 1.58 ng/ml respectively), suggesting that stress was not the trigger for nest departure. Nest-bound chicks however did show lower stress-induced titres levels than nest-departed chicks (14.62 ± 1.98 vs. 21.58 ± 2.22 ng/ml, respectively). This suggests that nest-bound chicks may have a blunted response, perhaps due to age-related developmental constraints influencing corticosterone secretion.

From January to May 2006, 130 Tawny Owls were reported dead along the coastal areas of southern Norway. Of these, 79 were collected for a museum collection, most from the counties Vest-Agder (27), Aust-Agder (37), Telemark (9) and Vestfold (4). One owl was found starving, and was nurtured back to life. Of 67 sexable specimens, there were 34 males and 33 females. Nine of the birds were ringed, 5 females, 3 males and one unsexed bird. Five ringed owls were juveniles (in their second calendar year), while four ringed were old adults (calendar year 6–12). Of 79 aged owls, 51 (64.6%) were juveniles, while 28 (35.4%) were adults (third calendar year or older). Weight and body measurements were taken from all individuals as far as the carcasses allowed. The famine followed a very good breeding year of Tawny Owls along the southern coast of Norway in 2005, with high numbers of wood mice Apodemus sylvaticus until frost and snowfall in November. The following winter was cold, followed by heavy snowfall on 20–21 January 2006. Snow depth increased steadily through February and March, reaching about 1 m in the coastal areas of Agder around 10 March. Tawny Owls started dying in February (n = 7), but most owls were found in March (n = 52). Many owls found in April (n = 17) were more or less decomposed, many probably having died in March. Young and old birds seemed to die at a similar rate through spring. Neither was there any sex difference in mortality rates.

Long-eared Owls Asio otus were flushed and captured from communal winter roosts and nesting seasons to assess both initial and stress-induced corticosterone concentrations. We examined blood samples from 16 males and 8 females in the winter, and 16 males and 11 females in the breeding season. Corticosterone concentrations after flushing owls in either season were not correlated with the elapsed time from initial flush to capture, suggesting that these birds did not interpret flushing as stressful. In contrast, 30 min of handling and restraint during both seasons elicited robust increases in plasma cortlcosterone concentrations that did not differ by sex. Although stress-induced corticosterone levels did not differ seasonally, baseline levels were 50% lower during the winter compared to breeding, suggesting the breeding season is a more stressful time. These results indicate that capture techniques used in this study with Long-eared Owls were only stressful when successful, and that initial corticosterone concentrations vary seasonally.

Avian studies have shown that food quality (amino acid load) can act as a limiting factor in reproduction and possibly breeding density. In owls, the role of food quality may have been largely overlooked due to the strong effect of food quantity. I examined evidence of food quality limitation in owl reproduction from four sets of data: (1) population data in Tawny Owls and diurnal birds of prey in a degenerate forest, (2) post-laying breast muscle conditions of Tawny Owls Strix aluco and Sparrowhawks Accipiter nisus which strongly relied on internal amino acid stores during egg formation, (3) amino acid deficiency-related embryo anomaly data in failed eggs of Barn Owls Tyto alba, Little Owls Athene noctua, and two reference species, and (4) growth of Tawny Owl chicks experimentally fed with day-old chickens or mice. The Tawny Owl population was found to be stable whereas sympatric bird of prey species greatly declined; breeding female Tawny Owls (n = 5) did not show a decline of breast muscle tissue as was found in Sparrowhawks. Embryo mortality from amino acid deficiency was estimated at 63% and 12% in Barn Owls and Little Owls, respectively. Growth rate of Tawny Owl chicks did not relate to food type. I conclude that egg amino acid investments can affect embryo viability in owls, but mainly in relation to reproductive strategy instead of environment. I hypothesize that owls can obtain additional amino acids from their caecal bacteria, which are lacking in birds of prey, and thereby are less dependent on amino acid availability in the food chain to acquire the amino acids needed for egg formation and chick growth.

In this literature review, I examined 475 publications with information on the global diet of the Long-eared Owl Asio otus. Data within 312 publications were entered into a database, and quantitative diet data were available from 194 of these publications. The composite data set identified 477 different prey: 180 mammal, 191 bird, 15 reptile, 7 amphibian, and 1 fish species, and 83 invertebrate groupings. In 798 prey lists reflecting 813 033 prey items, small mammals accounted for 93.3% and birds for 6.4% of the vertebrate prey. Prey ranged from 1–500 g, with the vast majority of prey consisting of species ≤50 g. Twenty-three species predominate the prey in at least one species list. Diet composition at the family level was similar in different regions, but considerable differences were shown at the species level.

Diet composition of the Barn Owl Tyto alba was studied in agricultural landscapes in Thessaly, Greece, for 3 years (2003–05). A total of 852 Rattus spp. individuals were identified from 10 065 pellets, which accounted for 2.9% by frequency and 27.4% by biomass of 29 061 prey items. Rattus spp. were more numerous in Barn Owl pellets during winter months than in summer. We suggest that this difference was due to a shift in relative prey availability and an increased need for energy by the Barn Owl during the colder months. Comparisons between Thessaly and 15 other areas showed differences in prey availability between islands and mainland Greece. Microtus spp. were absent from all island diets except one, and some islands had greater species richness.

We examined 250 pellets of Long-eared Owls Asio otus in 2006 and 2007 from winter roost sites in southeastern Iran. In contrast to the diet of wintering owls (e.g. mainly small mammals) reported elsewhere in the world, the diet of wintering Long-eared Owls at Zabol was predominantly larger rodents (c. 150 g). Specifically, big-size rodents, including the Indian Gerbil Tatera indica, and a Bandikoot Rat Nesokia indica made up 72.9% of the total biomass in the diet of the owls at Zabol. In addition to small mammal and bird species found in Long-eared Owl pellets from other regions, we found Meriones spp. and Gerbillus spp. (both are types of Gerbils) that, thus far, had not been reported in the diet of this owl.

Male Barn Owls Tyto alba delivered significantly more male than female Field Voles Microtus agrestis to their mates and nestlings in spring. The male bias was evident both in the prey stored at the nest and in the skeletal remains of prey in pellets taken from the nest. The sex ratio in voles caught by trapping showed a slight female bias. Analysis of pellets produced by the male barn owls at their roosts at the same time, showed the same biased sex ratio of voles, demonstrating that selection of male voles occurred at capture and was not a result of differences between prey delivered to the nest and those consumed by the males. The mean weights of trapped male and female voles in spring were 23.4 g (SE 0.5) and 18.5 g (SE 0.4) respectively. During winter when voles were not breeding the sex ratio in pellets of male and female owls was close to unity. This suggests that the increased aggressiveness and/or activity levels of male voles associated with territorial behaviour and breeding in spring led to an increase in their detection rate by owls hunting by use of auditory cues. Thus the selection for male voles was the result of an increased encounter rate rather than optimal foraging based on the greater body mass of male voles. In spring the owls caught significantly more Field Voles than Wood Mice Apodemus sylvaticus than predicted from the relative abundances of the two species in the field. It is suggested this was the result of the greater ability of Wood Mice to detect the owls and their greater agility in evading capture.