Aegolius Funereus Research Articles

Notes on the reproduction, breeding biology and ethology of the Eurasian pygmy owl (Glaucidium passerinum) in Slovakia

Notes on the reproduction, breeding biology and ethology of the Eurasian pygmy owl (Glaucidium passerinum) in Slovakia

Bad News and Good News: Population Changes of Finnish Owls During 1982–2007

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.

Conservation of Tengmalm's Owl and Sichuan Wood Owl in Lianhuashan Mountain, Gansu, China

Conservation of Tengmalm's Owl and Sichuan Wood Owl in Lianhuashan Mountain, Gansu, China

First Nest Records of the Boreal OwlAegolius funereusin Nova Scotia, Canada

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.

Multiple predators induce risk reduction in coexisting vole species

Large predators may affect the hunting efficiency of smaller ones directly by decreasing their numbers, or indirectly by altering their behaviour. Either way this may have positive effects on the density of shared prey. Using large outdoor enclosures, we experimentally studied whether the presence of the Tengmalm's owl Aegolius funereus affects the hunting efficiency of the smallest member of the vole‐eating predator guild, the least weasel Mustela nivalis, as measured by population responses of coexisting prey species, the field vole Microtus agrestis and the sibling vole M. levis. We compared the density and survival probability of vole populations exposed to no predation, weasel predation or combined predation by a weasel and an owl. The combined predation of both owl and weasel did not result in obvious changes in the density of sibling and field vole populations compared to the control populations without predators, while predation by least weasel alone decreased the densities of sibling voles and induced a similar trend in field vole densities. Survival of field voles was not affected by predator treatment while sibling vole survival was lower in predator treated populations than in control populations. Our results suggest that weasels are intimidated by avian predators, but without changing the effects of predators on competitive situations between the two vole species. Non‐lethal effects of intraguild predation therefore will not necessarily change competitive interactions between shared prey species.

Parental Investment of Female Tengmalm's OwlsAegolius funereus: Correlation with Varying Food Abundance and Reproductive Success

Abstract. The effects of food abundance, reproductive success and age of nestlings on parental care in female Tengmalm's Owls were tested in this study. The behaviour of female owls was monitored by a camera system from hatching to fledging at 12 nests in 2004 and 2006 in the Ore Mountains, Czech Republic. Food abundance and reproductive success (the latter measured at the end of female's attendance of the brood) were higher in 2004 than in 2006. Females remained for a significantly longer time with their nestlings at the nests in 2004 (24.8 ± 2.4 days) than in 2006 (22.2 ± 0.9 days). During the attendance period, they were leaving the nest for several short trips each night; the duration of these trips, the total time spent outside the nest per night, and the number of trips per night did not differ between years. However, these variables did increase with increasing age of the young (though the number of trips per night increased only during the last week of the females' stay on the nests). Two types of...

Diet and Prey Consumption Rates of Nesting Boreal Owls, <em>Aegolius funereus</em>, in Alaska

Dietary composition and prey consumption rates of nesting Boreal Owls, Aegolius funereus, were investigated during 2004–2006 using two methods. Dietary composition was determined during nest visits through examination of 1882 fresh remains containing at least 11 mammalian and 15 avian species. Consumption rates were calculated based on laboratory examination of seven prey detritus bricks following fledging, yielding 1051 items of five different taxa. During 2003–2006, small mammal snap-trapping was conducted in the vicinity of occupied nest boxes, and relative abundance of potential prey items was estimated. A total of 4020 trap-nights yielded 695 small mammal captures of eight species. Consumption rates of nestling owls ranged from 22.0 to 29.7 g of food per day, averaging 24.2 g (SD = 1.8). Comparisons between availability of small mammals (as indicated by snap-trapping) and consumption (as indicated by nest visits and analysis of prey detritus bricks) showed that Boreal Owls are generally preying on mammals proportionate to their occurrence.

Do Tengmalm’s Owls alter parental feeding effort under varying conditions of main prey availability?

We studied the diet composition and behavioural responses to variable food conditions in Tengmalm’s Owls (Aegolius funereus). The abundance of main prey (voles and mice) of owls was higher in the Ore Mountains, Czech Republic, than in the Kauhava region, Finland. We monitored nests continuously by a camera system to estimate the feeding frequency and to identify prey items provided to nestlings. We recorded 990 prey deliveries at six nests in the Ore Mountains and 1,679 prey deliveries at nine nests in the Kauhava region. Mice (Apodemus) and voles (Microtus and Clethrionomys) were the main foods of owls in the Ore Mountains, whereas voles (Clethrionomys and Microtus) and shrews (Sorex) were the main foods in the Kauhava region. In consequence, on average smaller prey items were brought to nestlings at the Finnish site. However, both absolute and relative (per one nestling) feeding frequency was higher in the Kauhava region, and the biomass available to individual nestlings did not differ between the two areas. Moreover, the Finnish and Czech pairs produced about the same number of fledglings. Our results suggest that male owls are able to maintain the amount of food required for chicks by switching to alternative prey, and to increase their prey delivery rates under conditions of reduced abundance of main food.

No phylogeographic structure in the circumpolar snowy owl (Bubo scandiacus)

The snowy owl (Bubo scandiacus) is a nomadic species with a circumpolar distribution. It has recently declined in the western Palearctic and may thus be worthy of special consideration for conservation. We investigated genetic structure in three well separated geographic regions within the snowy owls’ breeding range. We sequenced two mitochondrial genes; the control region and cytochrome b, and two Z-chromosome introns; VLDLR-9 and BRM-15. We found no phylogeographic structure among the sampled regions, indicating high levels of gene flow in the recent past and possibly still today. Intra-population diversity did not vary between regions for the control region, but for Cyt b, North American birds had higher haplotype diversity than Scandinavian and eastern Siberian birds. Western Palearctic birds do not seem to be genetically deprived or inbred. Genetic diversity in the snowy owl was not lower than Scandinavian populations of three other owl species: tawny owls (Strix aluco), Tengmalm’s owls (Aegolius funereus) and eagle owls (Bubo bubo).

Survey of Blood Parasites in Two Forest Owls, Northern Saw-whet Owls and Flammulated Owls, of Western North America

Except for a few studies in the eastern United States, little has been published on hemoparasites in owls. We surveyed the blood parasites of 108 Northern Saw-whet Owls (Aegolius acadicus) and 24 Flammulated Owls (Otus flammeolus) in Idaho during autumn migration in 1999 and 2000. We also surveyed 15 Flammulated Owls (FLOW) during breeding season in Utah from 2000. Leucocytozoon ziemanni, Haemoproteus syrnii, Haemoproteus noctuae, and Trypanosoma avium were identified. The overall prevalence of infection was 53% (78/147) and for the combined species, prevalences of Haemoproteus, Leucocytozoon, and Trypanosoma species were 20%, 39%, and 4%, respectively. Northern Saw-whet Owls (NSWO) had an overall prevalence of 51% (55/108), with prevalences of 6%, 47%, and 4% by hemoparasite genus, respectively. Flammulated Owls had an overall prevalence of 59% (23/39), with prevalences of 56%, 18%, and 5% by genus, respectively. This study provides baseline hematozoa information for two boreal owl species.

Post-Fledging Estimation of Annual Productivity in Boreal Owls Based on Prey Detritus Mass

ESTIMACION POST-EMPLUMAMIENTO DE LA PRODUCTIVIDAD ANUAL EN AEGOLIUS FUNEREUS BASADA EN EL PESO DE LOS RESTOS DE PRESAS Se monitorearon nidos artificiales de Aegolius funereus del interior de Alaska en primavera y verano de 2005 y 2006, y se registro el exito de emplumamiento. En septiembre y octubre, se colectaron restos de presas en 23 nidos artificiales donde las lechuzas habian realizado intentos de nidificacion previos en el ano. Los pesos secos de los restos de las presas estuvieron correlacionados significativamente con las tasas de emplumamiento (regresion lineal, P < 0.05). Esto sugiere que el peso del conglomerado de los restos de las presas puede ser usado como una alternativa a las observaciones directas de las tasas de emplumamiento, permitiendo documentar datos importantes sobre la productividad anual cuando no pueden realizarse conteos directos. Mediante evaluaciones adicionales, este metodo puede ser util para estimar la productividad en otras especies de lechuza que nidifican en cavidades.

Survival of male Tengmalm’s owls increases with cover of old forest in their territory

The loss and fragmentation of forest habitats have been considered to pose a worldwide threat to the viability of forest-dwelling animals, especially to species that occupy old forests. We investigated whether the annual survival of sedentary male Tengmalm's owls Aegolius funereus was associated with the cover of old coniferous forests in Finland. Survival and recapture probabilities varied annually with density changes in populations of the main prey (Microtus voles). When this variation was controlled for, and relationships between survival and proportions of the three different forest age classes (old-growth, middle-aged, and young) were modeled separately, the old-growth model was the most parsimonious. Survival increased with the cover of old forest, although the extent of old forest within owl territories was relatively small (mean approximately 12%, range 2-37%). This association, however, varied among years and appeared especially in years of increasing vole abundance. At such times, old forests may sustain high populations of bank voles Clethrionomys glareolus, shrews and small passerines. In addition, old forests may serve as refuges against large avian predator species, such as Ural owls Strix uralensis and goshawks Accipiter gentilis. Our results suggest that changes in habitat quality created by agriculture and forestry may have the potential to reduce adult survival, an essential component of fitness and population viability.

Biotic interactions improve prediction of boreal bird distributions at macro‐scales

ABSTRACTAim The role of biotic interactions in influencing species distributions at macro‐scales remains poorly understood. Here we test whether predictions of distributions for four boreal owl species at two macro‐scales (10 × 10 km and 40 × 40 km grid resolutions) are improved by incorporating interactions with woodpeckers into climate envelope models.Location Finland, northern Europe.Methods Distribution data for four owl and six woodpecker species, along with data for six land cover and three climatic variables, were collated from 2861 10 × 10 km grid cells. Generalized additive models were calibrated using a 50% random sample of the species data from western Finland, and by repeating this procedure 20 times for each of the four owl species. Models were fitted using three sets of explanatory variables: (1) climate only; (2) climate and land cover; and (3) climate, land cover and two woodpecker interaction variables. Models were evaluated using three approaches: (1) examination of explained deviance; (2) four‐fold cross‐validation using the model calibration data; and (3) comparison of predicted and observed values for independent grid cells in eastern Finland. The model accuracy for approaches (2) and (3) was measured using the area under the curve of a receiver operating characteristic plot.Results At 10‐km resolution, inclusion of the distribution of woodpeckers as a predictor variable significantly improved the explanatory power, cross‐validation statistics and the predictive accuracy of the models. Inclusion of land cover led to similar improvements at 10‐km resolution, although these improvements were less apparent at 40‐km resolution for both land cover and biotic interactions.Main conclusions Predictions of species distributions at macro‐scales may be significantly improved by incorporating biotic interactions and land cover variables into models. Our results are important for models used to predict the impacts of climate change, and emphasize the need for comprehensive evaluation of the reliability of species–climate impact models.

Interspecific competition limits larders of pygmy owls Glaucidium passerinum

To test whether competitive and predatory interactions limit larder size we erected pygmy owl Glaucidium passerinum nest-boxes for hoarding with 45 mm entrance diameter near and far (2 km) from Tengmalm’s owl Aegolius funereus nest-boxes with 80 mm entrance diameter during early autumn. We found larders of pygmy owls in similar frequency in both near and far plots (41 vs. 42% of plots), but in near plots the number and biomass of cached prey by pygmy owls were lower. These results suggest that there is competition for food between these two owl species and/or that food caching behaviour of pygmy owls is disturbed by larger Tengmalm’s owls.

High Connectivity and Minimal Genetic Structure Among North American Boreal Owl (Aegolius Funereus) Populations, Regardless of Habitat Matrix

AbstractHabitat connectivity and corridors are often assumed to be critical for the persistence of patchily distributed populations, but empirical evidence for this assumption is scarce. We assessed the importance of connectivity among habitat patches for dispersal by a mature-forest obligate, the Boreal Owl (Aegolius funereus). Boreal Owls demonstrated a lack of genetic structure (θ = 0.004 ± 0.002 [SE]) among subpopulations, regardless of matrix type and extent, which indicates that unforested matrix does not act as a barrier to dispersal for this vagile species. We found only slightly higher genetic distances (Cavalli-Sforza chord distances ranged from 0.015 to 0.025) among patchily distributed Rocky Mountain subpopulations as compared with largely contiguous boreal-forest subpopulations (0.013 to 0.019) and no evidence of a genetic split across the expansive high plains of Wyoming. Even the most isolated subalpine patches are connected via gene flow. As northern boreal forests continue to experience intensive harvest of mature stands, geographic dispersion of Boreal Owl habitat may begin to more closely resemble that found in the Rocky Mountains. We suggest that decreased connectivity poses much less of a threat to continued abundance of this mature-forest obligate than overall loss of nesting and foraging habitat. Assessment of the importance of corridors and connectivity should be conducted on a species-by-species basis, given the variation in response of species to discontinuity of habitat, even among closely related taxa or guilds.Alta Conectividad y Estructura Genética Mínima entre Poblaciones Norteamericanas de Aegolius funereus, Independientemente de la Matriz del Hábitat

Age-Dependent Response of Migrant and Resident Aegolius Owl Species to Small Rodent Population Fluctuations in the Eastern Canadian Boreal Forest

ABSTRACT We investigated the relationship between late summer abundance of small rodents and fall migrant abundance of two nocturnal avian predators, the Boreal Owl (Aegolius funereus) and the Northern Saw-whet Owl (A. acadicus), during their fall movement/migration. In the eastern Canadian boreal forest, Boreal Owls are considered resident (with irruptive movements to the south thought to occur during periods of low prey availability), and Northern Saw-whet Owls migratory. Data on late summer abundance of small rodents collected between 1995 and 2004 were used to develop an index of prey availability. Data on the number and age of irrupting/migrating owls were collected between 1996–2004 (mid-September to late October) using audiolures and mist nets. Our study revealed strong evidence of (1) a negative relationship between the abundance of small rodents and movement of Boreal Owls and (2) a positive relationship between the abundance of small rodents and the number of migrating juveniles and second year ...

Can migrating Tengmalm's Owls Aegolius funereus be reliably sexed in autumn using simple morphometric measurements?

I investigate whether three standard, easily‐taken body measurements (wing length, tail length and mass) can be used in combination to determine accurately the sex of Tengmalm's Owls Aegolius funereus in autumn. A total of 135 migratory Tengmalm's Owls, caught in autumn 1999 on a small island between Sweden and Finland, were weighed, measured and accurately sexed using PCR‐based molecular techniques. While females were on average larger than males, discriminant analysis using wing length, tail length and mass could not satisfactorily classify males and females. Ringers are advised not to use these common morphometric measurements to sex individual Tengmalm's Owls in autumn, as the degree of overlap is too great, and even the largest and smallest individuals might be incorrectly sexed.

HIGH CONNECTIVITY AND MINIMAL GENETIC STRUCTURE AMONG NORTH AMERICAN BOREAL OWL (AEGOLIUS FUNEREUS) POPULATIONS, REGARDLESS OF HABITAT MATRIX

Abstract Habitat connectivity and corridors are often assumed to be critical for the persistence of patchily distributed populations, but empirical evidence for this assumption is scarce. We assessed the importance of connectivity among habitat patches for dispersal by a mature-forest obligate, the Boreal Owl (Aegolius funereus). Boreal Owls demonstrated a lack of genetic structure (θ = 0.004 ± 0.002 [SE]) among subpopulations, regardless of matrix type and extent, which indicates that unforested matrix does not act as a barrier to dispersal for this vagile species. We found only slightly higher genetic distances (Cavalli-Sforza chord distances ranged from 0.015 to 0.025) among patchily distributed Rocky Mountain subpopulations as compared with largely contiguous boreal-forest subpopulations (0.013 to 0.019) and no evidence of a genetic split across the expansive high plains of Wyoming. Even the most isolated subalpine patches are connected via gene flow. As northern boreal forests continue to experience ...

Two New Late Pleistocene Avifaunas From New Mexico

Abstract We report two new late Pleistocene avifaunas from New Mexico, recovered from Sandia Cave during archaeological excavations by F. Hibben in the 1930s and the nearby Marmot Cave excavated in 2000. The fossil assemblage from Sandia Cave consists of at least 30 taxa, including seven extralimital and two extinct species, Coragyps occidentalis (extinct vulture) and Ectopistes migratorius (Passenger Pigeon). The avifauna from Marmot Cave is limited to eight taxa shared with Sandia Cave. Two new records of Gymnogyps californianus (California Condor) are reported from these sites, as well as new records of Lagopus sp. (ptarmigan), Aegolius funereus (Boreal Owl), and Micrathene whitneyi (Elf Owl) from New Mexico. Two new radiocarbon dates on fossil G. californianus from Sandia and Marmot cave are reported at 10 795 ± 50 and 25 090 ± 220 14C years before present (B.P.), respectively. These collections provide further evidence for mixed avian communities in New Mexico during the late Pleistocene and are similar to other cave avifaunas of comparable age from the Great Basin and Rocky Mountain regions. The birds from Sandia Cave that are shared with other fossil avifaunas include species currently found in arctic tundra, boreal, and steppe habitats, as well as open, xeric communities. This collection provides additional evidence for widespread steppe-tundra, shrub, and subalpine forest environments at lower elevations of western North America during the late Pleistocene.

New Coleoptera records from owl nests in Nova Scotia, Canada

A preliminary study of boreal owl, Aegolius funereus richardsoni (Bonaparte), and northern sawwhet owl, Aegolius acadicus acadicus (Gmelin), nests from Nova Scotia, Canada revealed the presence of 14 species of Coleoptera, several of which represent significant extensions of their known ranges. Atheta (Datomicra) celata (Erichson) is newly recorded for North America; Atheta irrita Casey is newly recorded for Canada and eastern North America; Atheta pseudocrenuliventris Klimaszewski, and Hylota ochracea Casey are newly recorded for Nova Scotia; and Gnathoncus barbatus Bousquet and Laplante, Carcinops pumilo (Erichson), and Phyllodrepa floralis (Paykull) are newly recorded for Cape Breton Island. Gnathoncus barbatus, H. ochracea, A. irrita, A. pseudocrenuliventris, and Corticarina cavicollis (Mannerheim) are all recorded for the first time from bird nests. One new synonym Atheta (Datomicra) celata (Erichson, 1837) [= Datomicra wrangeli Casey 1911. syn nov. ] is designated. Additional new records of A. irrita from Québec are also reported. Attention is drawn to the limited state of knowledge of this specialized beetle fauna and to the high proportion (50%) of adventive species which were found in these environments.