Subject: Correction: Owl Conservation and Research News -- 29 September 2020

Owl Conservation & Research News
A summary of recent owl publications, conservation and conference and news.

Note: Submissions are edited for length, but not necessarily for grammar.

Corrected version: some of the author links were incorrect in the previous version.
Korpimäki, E. 2020: Highlights from a long-term study of Tengmalm’s Owls: cyclic fluctuations in vole abundance govern mating systems, population dynamics and demography. - British Birds 113: 316–333.
Main results from the 47-year study of Tengmalm’s owls Aegolius funereus in western Finland were as follows. Breeding densities of owls increased with density estimates of main foods (Microtus and bank voles). The annual mean laying date of the owl population was postponed by one month in poor vole years, and clutch sizes were 2-3 eggs less and numbers of fledglings 2-3 owlets less than in good vole years. Ten to twenty percent of males was simultaneously polygynous in good vole years, whereas successive polyandry of female owls was mostly recorded in the increase phase of the vole cycle with improving food conditions during the summer. Natal dispersal of females was twice more extensive and breeding dispersal distances of females were longer in the decrease than in the increase phase of the vole cycle. Long-distance autumn movements of hatch-year owls and adult females were also responses to the lack of food in the previous breeding areas. Over-winter survival of male parents increased with the augmenting abundances of the main food supply in the preceding autumn. The proportion of nests that produced recruits in the increase phase of the vole cycle was three times as high as in the decrease phase and twice as high as in the low phase of the vole cycle. These results indicated a remarkably better survival of owlets hatched in the improving rather than in deteriorating or poor food conditions.
Click here for the full-text article.
Korpimäki, E., Hongisto, K., Masoero, G. & Laaksonen, T. 2020: The difference between generalist and specialist: the effects of wide fluctuations in main food abundance on numbers and reproduction of two co-existing predators. – Journal of Avian Biology doi: 10.1111/jav.02508.
Pygmy owls Glaucidium passerinum have less vole-specialized diets than Tengmalm’s owls Aegolius funereus, both of which mainly subsist on temporally fluctuating food resources (voles). We studied breeding densities and reproduction of pygmy and Tengmalm’s owls during 2002-2019. Breeding densities of pygmy owls increased with augmenting densities of voles in the previous autumn, whereas breeding densities of Tengmalm’s owls increased with higher vole densities in both the previous autumn and the current spring. In years of vole scarcity, pygmy owl females started egg-laying earlier than Tengmalm’s owls, whereas in years of vole abundance Tengmalm’s owl females laid eggs one month earlier than pygmy owl females. The yearly mean clutch size and number of fledglings produced of both pygmy and Tengmalm’s owls increased with abundance of voles in the current spring. Pygmy owls laid large clutches and produced large broods in years of both high and low vole abundance, whereas Tengmalm’s owls were able to do so only in years of high vole abundance. Pygmy owls were able to raise on average 73% of the eggs to fledglings whereas Tengmalm’s owls only 44%. The generalist foraging strategy of Pygmy owls including flexible switching from main prey to alternative prey (small birds) appeared to be more productive than the vole-specialized foraging strategy of Tengmalm’s owls.
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Baroni, D., Korpimäki, E., Selonen, V. & Laaksonen, T. 2020: Tree cavity abundance and beyond: Nesting and food storing sites of the pygmy owl in managed boreal forests. – Forest Ecology and Management 460: 117818
We studied the abundance of suitable cavities and the preferences for different cavity characteristics in two managed forest landscapes in south-western and central-western Finland (300 km apart) for forest-dwelling Eurasian Pygmy Owls Glaucidium passerinum. They require tree cavities for both nesting and food hoarding. We found that natural cavities were scarce in the landscape (6.5/km2) but abundance of natural cavities per se did not appear to limit the owl breeding density, as suggested by a low occupancy rate in both natural cavities and nest-boxes. Owls cleaned the cavities that were filled with nest material of other birds, which provides a greater number of possible cavities to choose from. Cavities whose characteristics prevent the nest from being reached by predators (mainly pine martens) were clearly preferred, as the owls select cavities with more than 5 cm width of the front wall and the nest was at depth of 15-30 cm from cavity entrance. The entrance hole orientation or the height of the cavity from the ground did not affect cavity occupancy by pygmy owls for nesting. None of the characteristics of the cavities that we surveyed affected their use for food hoarding. While the number of cavities per se may not limit the nesting of the owls, they may be limited by suitable habitat with abundant food supply around available cavities, or by lack of cavities in suitable habitats. They also need more cavities in the winter than in the summer, as each individual needs one or more cavities for hoarding food to survive over winter.
Click here for the full-text article.
Masoero, G., Laaksonen, T., Morosinotto, C. & Korpimäki, E. 2020: Age and sex differences in numerical responses, dietary shifts and total responses of a generalist predator to population dynamics of main prey. – Oecologia
We studied the effects of fluctuating main prey abundance (voles) in autumn on the age and sex composition of a food-hoarding population of Eurasian pygmy owls Glaucidium passerinum (327 individuals), and on the species composition of their food stores in western Finland during 2003-2017 (629 food stores). Numbers of hatch-year owls (<1-year old) of both sexes and adult (+1-year old) females increased with increasing vole abundance in the environment. During low vole abundance, adult owls stored more small birds and less small mammals than hatch-year owls. Females stored more small mammals than males. The amount of consumed birds (the most important alternative prey), and in particular of crested, willow, great and blue tits, increased with low vole densities. Our results show that numerical, functional and total responses of pygmy owls to the availability of the main prey in winter are shaped by the age and sex composition of the owl population, which both show large spatio-temporal variation in boreal forests.
Click here for the full-text article.
Masoero, G., Laaksonen, T., Morosinotto, C. & Korpimäki, E. 2020: Climate change and perishable food stores of an avian predator: is the freezer still working? – Global Change Biology 2020;00:1–17 DOI: 10.1111/gcb.15250
Species hoarding perishable food for over-winter survival, like owls, are predicted to be particularly susceptible to increasing temperatures. We analyzed the influence of autumn and winter weather, and abundance of main foods (voles), on the food-hoarding behavior of Eurasian pygmy owls (Glaucidium passerinum) during 16 years in Finland. Fewer freeze-thaw events in early autumn delayed the initiation of food-hoarding. Pygmy owls consumed more hoarded food with more frequent freeze-thaw events and a deeper snow cover in autumn and in winter, and lower precipitation in winter. In autumn, the rotting of food hoards increased with precipitation. Hoards already present in early autumn were much more likely to rot than the ones initiated in late autumn. Rotten food hoards were used more in years of low food abundance than in years of high food abundance. Having rotten food hoards in autumn resulted in a lower future recapture probability of female owls. These results indicate that pygmy owls might be partly able to adapt to climate change by delaying food hoarding, but changes in the snow cover, precipitation and frequency of freeze-thaw events might impair their foraging and ultimately decrease local over-winter survival. Therefore, impacts of climate change on wintering food-hoarding owls could be substantial, because their “freezers” may no longer work properly.
Click here for the full-text article.
Miller, R. (2019, October 22). WAfLS 2019 Results Presentation [Video file]. Retrieved August 29, 2020, from
Project WAfLS is an eight-state program designed to assess the population status, trends, and threats against the Short-eared Owl in the western United States. Project WAfLS engages enthusiastic citizen-scientist volunteers to gather critical survey data, enabling a rigorous assessment of the status of this species. The link is for a video presentation of the 2019 results, but the 2020 results will be released in our next newsletter.
Click here for the full-text article.
Bos, J., Schaub, T., Klaasen, R., & Kuiper, M. (Eds.). (2020). International Hen Harrier and Short-eared Owl Meeting 2019. Retrieved September 25, 2020
Short-eared Owls and Hen Harriers both live in open landscapes throughout the northern hemisphere. Despite their vast distribution range and apparent flexibility regarding breeding habitats, regional populations of both species are decreasing in large parts of Europe. The exact mechanisms leading to the observed population declines are poorly understood, calling for efforts to improve our ecological understanding of these two enigmatic species. The Dutch Montagu’s Harrier Foundation and BirdLife Netherlands organized an international 3-day expert meeting at the University of Groningen, the Netherlands, on the two species on 20-22 March 2019. The meeting brought together 50 experts from 13 countries. The goals of the meeting were to: 1) exchange and update information on status and trends of Hen Harriers and Short-eared Owls in European countries; 2) exchange information on research that has been conducted on the summer and winter ecology of both species in past and recent years; 3) exchange ideas on effective conservation strategies for both species; 4) identify knowledge gaps and explore possibilities for future co-operation in research on and conservation of both species; 5) synthesize a ‘future vision’ for viable populations of both species in Europe. In this booklet you can find the abstracts of all the presentations held during the meeting, including a summary of the general discussion held at the end of meeting, synthesizing the main outcomes.
Click here for the list of abstracts.
The Owls of Europe (in German)

Scherzinger, W. & Mebs, Th. (2020): Die Eulen Europas. Biologie, Kennzeichen, Bestände. 3rd edition Kosmos-Verlag / Stuttgart; 416 S. > 300 photos, ISBN: 978-3-440-15984-2
Owls are not only fascinating birds, they also impress us with their extraordinary adaptations as "hunters of the night".

In this standard work all 13 species of owls occurring in Europe are presented. It is an identification book, reference work and modern compendium on the diversity of these extraordinary animals.
--Detailed drawings of typical positions, behavioral processes and facial expressions.
--Over 300 brilliant photos for assigning branch clothes, color phases or flight images.
--Updated distribution maps and the latest population estimates for the countries of Europe with a focus on Central Europe.
--Behavior, voice, brood biology and youth development for determination, inventory and the interpretation of own observations.
--Life strategies, hunting techniques, choice of prey and habitat requirements.
--Causes of danger and information on species and biotope protection.

A completely revised and updated standard work for all owl friends, bird watchers, students or professionals.
No online version is available for this book.
Penteriani, V., & Delgado, M. D. (2019). The eagle owl. London: T & ADPoyser.
The Eagle Owl is one of the largest owls in the world, and is considered the most eclectic in terms of habitat, nest site and diet. An undisputed top predator, it can prey on a range of mammals up to the size of a fox, and almost every species of bird, reptile, amphibian and fish, as well as a wide spectrum of invertebrates. Surprisingly, this owl can breed almost anywhere, the female laying her eggs on a variety of natural and artificial structures over an array of altitudes. Despite being so adaptable, however, it is still a vulnerable species, and has suffered widely from persecution as well as other threats including electrocution on power lines, decreasing prey availability, the effects of pesticides and pollutants, and habitat alteration.
No online version is available for this book.
Slaght, J. C. (2020). Owls of the eastern ice: A quest to find and save the world's largest owl. New York, NY: Farrar, Straus and Giroux.
Despite a wingspan of six feet and a height of over two feet, the Blakiston’s fish owl is highly elusive. They are easiest to find in winter, when their tracks mark the snowy banks of the rivers where they feed. They are also endangered. And so, as Slaght and his devoted team set out to locate the owls, they aim to craft a conservation plan that helps ensure the species’ survival. This quest sends them on all-night monitoring missions in freezing tents, mad dashes across thawing rivers, and free-climbs up rotting trees to check nests for precious eggs. They use cutting-edge tracking technology and improvise ingenious traps. And all along, they must keep watch against a run-in with a bear or an Amur tiger. At the heart of Slaght’s story are the fish owls themselves: cunning hunters, devoted parents, singers of eerie duets, and survivors in a harsh and shrinking habitat.

Through this rare glimpse into the everyday life of a field scientist and conservationist, Owls of the Eastern Ice testifies to the determination and creativity essential to scientific advancement and serves as a powerful reminder of the beauty, strength, and vulnerability of the natural world.
No online version is available for this book.
Roulin, A. (2020). Barn Owls: Evolution and Ecology. Cambridge University Press.
With heart-shaped face, buff back and wings, and pure white underparts, the barn owl is a distinctive and much-loved bird which has fascinated people from many cultures throughout history. How did the barn owl colonise the world? What adaptations have made this bird so successful? How is the increasing impact of human disturbance affecting these animals? Answering these questions and more, Roulin brings together the main global perspectives on the evolution, ecology and behaviour of the barn owl and its relatives, discussing topics such as the high reproductive potential, physiology, social and family interaction, pronounced colour variation and global distribution. Accessible and beautifully illustrated, this definitive volume on the barn owl is for researchers, professionals and graduate students in ornithology, animal behaviour, ecology, conservation biology and evolutionary biology, and will also appeal to amateur ornithologists and nature lovers.
No online version is available for this book.
W. Scherzinger (2019): Increasing interest in international research on the "silent" flight of owls (Strigiformes). Eulen-Rundblick 69, 83-89
Since all times the silent flight of owls fascinated – and alarmed – people. Though this phenomenon was associated with the special quality of the owl’s plumage from the very first biological studies, only newest methods of measuring are able to clarify aerodynamic effects, which are associated with the surprising noise damping in detail. Strong motivations for an intensified research on owl flight come from the need of low-noise constructions for airplanes, wind-power rotors or high-speed trains. 

The silent flight is rated as an adaptation for an acoustic localisation of prey, when hunting in full darkness, as well as for a quiet surprise attack on small vertebrates. Due to the large wing in relation to a rather low body-mass, the owl’s wing-load is remarkable low, what enables a slow gliding flight. Hereby the dense, loose and fluffy plumage dampens any flight-sound solely. In addition vibrations and vortices get buffered by super-elastic primaries.

In fact a number of highly specialised feather-structures are primarily significant for the extraordinary silent flight of an owl:
A “comb” of finest, hair-like bristles along the front edge of the outermost; a brushy fringe of bristle-like hairs along the edges of primaries and retrices; a broad seam of long fringes, formed by subtle pennulae, along the edge of the inner vane of primaries, secondaries and tail-feathers; a filamentous contour in all the feathers; and a velvety fluff of tender barbs, interwoven as a light netting.
There is no online link to this article.
Submit your recent owl publications

To submit a research summary for inclusion in this e-newsletter, please send an email to that includes:

-Proper citation for the article (published in the last 12 months; publication need not be in English, but please translate the title into English if it is not already)
-Short English summary of the research (250 words or less) that includes basic results (similar to an abstract, but not the actual abstract so we avoid any copyright infringement)
-Link to the full-text article if it is available online at no charge
-Email address for the corresponding author

-A photo related to the article, if available (it could be of an owl, researcher, location--something to grab attention)

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