Strix Aluco Research Articles

Variation and Acoustic Stability in the Call Duration of Tawny Owl Strix aluco Males

Variation and Acoustic Stability in the Call Duration of Tawny Owl Strix aluco Males

The Multi-Functional Use of Large Tree Cavities by Arboreal Vertebrates in a Temperate Broadleaved Forest of Eastern Europe.

Tree cavities offer protected shelters and resources for arboreal vertebrates worldwide. In general, cavities with larger openings are better accessible for predators and are avoided by smaller species for breeding, but can still be attractive for occasional use. The current study explores the diversity of functional use types and species interactions at the largest available tree cavities (entrance width ≥ 10 cm) in a temperate European forest with a low number of large cavity-breeding species. Year-round camera observations at 9 cavities (range 0.7-3.5 years) revealed 34 visiting species of birds and mammals, including non-cavity-breeding species. The top predator threatening other large-cavity users was European pine marten (Martes martes), which regularly visited each cavity year-round, on average every 0.7 months. Tawny owl (Strix aluco) was the only species successfully breeding in cavities, arguably because of its ability to defend the nests. However, other species visited cavities at an average rate of 1.5 visits per day, making predominantly short visits (less than 30 s) interpreted as exploration, searching for food, or inspecting for the presence of owls (mobbing). Making short visits and time segregation with predators was a behavioural strategy to exploit cavities for most species. These results confirm that, similarly to other keystone structures (large arboreal nests, ground burrows, etc.), large tree cavities attract a significant part of the arboreal vertebrate community and enrich their habitats. To sustain these functions in wooded ecosystems, management should provide a surplus of available cavities and diversity of their characteristics even when the apparent number of breeding species is low.

Antipredator responses of bats during short boreal nights with variable climatic conditions

Abstract The threat of predation can influence the behavior of animals. To minimize the impact of predation, animals rely on antipredatory responses and effectively balance these responses with other activities to maximize survival. Boreal bats are nocturnal animals that must forage within a narrow time frame during short, light summer nights with unpredictable weather. Despite having no specialized predators, boreal bats are still subject to predation. However, whether they express antipredatory responses has not been established. We studied antipredatory responses and responses to climatic conditions in boreal bats in 2 settings: 1) during roost emergence; and 2) during foraging within Tawny Owl territories and at locations with no Tawny Owl sightings. Acoustic data were collected at 23 roosts and 10 foraging grounds. Two controlled predation threats were used—playbacks of Tawny Owl calls and fledgling calls. Fledgling calls were only played during roost emergence. In both experiments, music and no treatment were used as controls. We also incorporated weather variables in the model. According to our results, bats tend to delay their emergence by 16 min when Tawny Owl calls were played outside the roost, but this effect was not noticeable when weather variables were included. There was no difference in exit time when music or fledgling sounds were played. While foraging, bats reduced their activity in Tawny Owl territories when calls of owls or music were played compared to no treatment. These results suggest that bats might display variable antipredatory responses, but weather influences behavior of bats more than predation risk, highlighting the importance of energy-saving strategies at northerly latitudes.

Sex allocation is color morph-specific and associated with fledging condition in a wild bird.

Melanin-based color polymorphism is predicted to evolve and maintain through differential fitness of morphs in different environments, and several empirical studies indicate that life history strategies, physiology, and behavior vary among color morphs. Sex allocation theory predicts that parents should adjust their sex allocation based on differential costs of raising sons and daughters, and therefore, color morphs are expected to modify their brood sex ratio decisions. In color polymorphic tawny owls (Strix aluco), the pheomelanistic brown morph is associated with higher energy requirements, faster growth, and higher parental effort than the gray morph. As hypothesized, we find that brown tawny owl mothers produced more daughters in early broods and more males in late broods, whereas gray mothers did the opposite. At fledging, daughters of early broods and of brown mothers were heavier than those of late broods or gray mothers. Hence, larger and more costly daughters appeared to benefit more than males from being born to brown mothers early in the season. Brown mothers breeding later in the season produced more cheap sons, while gray mothers face fewer challenges under limited resources and favor daughters. These findings suggest that environmental conditions influence brood sex allocation strategies of genetically determined color morphs differently.

Tawny Owls Strix aluco from a southern European population differ in size and degree of reverse sexual dimorphism from northern European counterparts

ABSTRACT Tawny Owls in southern Europe were trapped and measured. Compared to males, the females were larger, heavier, and more greyish in colour, but there was a large biometric overlap. The variable with the highest Storer’s dimorphism index (SDI) was weight, though our population had one of the smallest dimorphisms observed in Europe for weight. It has been proposed that differences in diet could lead to differing behaviour and, in consequence, the observed dimorphism degree (SDI) by natural selection.

Assessing Contamination Profiles in Livers from Road-Killed Owls.

Raptors are recognized as valuable sentinel species for monitoring environmental contaminants owing to their foraging behavior across terrestrial and aquatic food webs and their high trophic position. The present study monitored environmental contaminants in livers from road-killed owls to evaluate differences in the exposure patterns due to factors such as species, age, and sex of individuals. Carcasses of road-killed individuals of eagle owl (Bubo bubo), long-eared owl (Asio otus), little owl (Athene noctua), tawny owl (Strix aluco), and barn owl (Tyto alba) were collected in Alentejo (Portugal). Eighty-one organic contaminants were analyzed, including organochlorine pesticides (OCPs), per- and polyfluoroalkyl substances (PFAS), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals, in-use pesticides, and organophosphate esters (OPEs). Overall, 21 contaminants were detected. In all species ∑OCPs were prevalent at concentrations from 3.24 to 4480 ng/g wet weight, followed by perfluorooctane sulfonic acid (PFOS), the only PFASs detected (from 2.88 to 848 ng/g wet wt) and ∑PCBs (1.98-2010 ng/g wet wt); ∑PAHs were ubiquitous but detected at the lowest concentrations (7.35-123 ng/g wet wt). Differences among species were observed according to principal component analysis. Eagle owl and long-eared owl presented the highest levels of ∑OCPs, ∑PCBs, and PFOS, consistent with its higher trophic position, while ∑PAHs prevailed in tawny owl, barn owl, and little owl, related to their frequent use of urban areas for nesting and roadsides for hunting. Adults presented higher concentrations of ∑OCPs and ∑PCBs than juveniles, while no differences were observed for PFOS and ∑PAHs. Pharmaceuticals, in-use pesticides, and OPEs were not detected. Overall, the present study shows specific contamination patterns in five species with similar diet but with differences in habitat preferences. Environ Toxicol Chem 2024;43:821-832. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Genomic basis of melanin-associated phenotypes suggests colour-specific environmental adaptations in tawny owls.

Feathers comprise a series of evolutionary innovations but also harbour colour, a key biological trait known to co-vary with life history or complex traits. Those relationships are particularly true in melanin-based pigmentation species due to known pleiotropic effects of the melanocortin pathway - originating from melanin-associated phenotypes. Here, we explore the molecular basis of melanin colouration and expected co-variation at the molecular level in the melanin-based, colour polymorphic system of the tawny owl (Strix aluco). An extensive body of literature has revealed that grey and brown tawny owl colour morphs differ in a series of life history and behavioural traits. Thus, it is plausible to expect co-variation also at molecular level between colour morphs. To investigate this possibility, we assembled the first draft genome of the species against which we mapped ddRADseq reads from 220 grey and 150 brown morphs - representing 10 years of pedigree data from a population in Southern Finland - and explored genome-wide associations with colour phenotype. Our results revealed putative molecular signatures of cold adaptation strongly associated with the grey phenotype, namely, a non-synonymous substitution in MCHR1, plus 2 substitutions in non-coding regions of FTCD and FAM135A whose genotype combinations obtained a predictive power of up to 100% (predicting grey colour). These suggest a molecular basis of cold environment adaptations predicted to be grey-morph specific. Our results potentially reveal part of the molecular machinery of melanin-associated phenotypes and provide novel insights towards understanding the functional genomics of colour polymorphism in melanin-based pigmented species.

Vocal interaction between Tawny Owl (Strix aluco) and Ural Owl (Strix uralensis) in the Middle Volga

The work studied the co-vocalization of Tawny Owl and Ural Owl. Researched primarily using digital voice recorders. Co-vocalization was revealed only in spring. This is due to the breeding season of birds. The roll call of two species of owls was recorded 2 h 30 min after sunset. Co-vocalization was always observed from 21:00 to 22:00 hours. Duration of co-vocalization of the Tawny Owl and the Ural Owl ranged from several sec to 6 min. During periods of co-vocalization, the Tawny Owl managed to produce twice as many calls as the Ural Owl. The Tawny Owl was the first to start calling, and later the calls of the Ural Owl joined it. The Tawny Owl stopped vocalizing, and the Ural Owl continued to call after it. The calls of each of the two owl species in shared habitats were recorded primarily at different times. More often, the Tawny Owl began vocalization 30 min after the Ural Owl stopped calling. The natural and climatic conditions of the area in which co-vocalization was noted were studied. Co-vocalizations were observed in the temperature range from +3 to +7°C. Joint calls were recorded at wind strength from 4 to 7 m/s, at cloud cover from 40 to 90%, at pressure from 734 to 744 mm Hg.

Distribution of the Quill Mite Bubophilus aluconis Parasitising Western Palaearctic Owls Belonging to the Genus Strix.

Background: The paper presents the results of studies on the distribution of the parasitic quill mite species Bubophilus aluconis (Acariformes: Syringophilidae) in the feather quills of the Western Palaearctic owls of the genus Strix, that is, tawny owl S. aluco, collected in Poland and Sweden, the Ural owl S. uralensis, from Poland, Sweden, and Finland, and the great grey owl S. nebulosa, from Sweden and Finland. The two latter species are new hosts for B. aluconis. Methods: Feather samples of the tawny owl, Ural owl, and great grey owl used in this study come from Prof. Marian Cieślak's private collection, which contains feathers of Western Palearctic birds of prey and owls. Each of the 77 tawny owl, 75 Ural owl, and 55 great grey owl specimens are represented either by whole dry wings or a full complement of flight feathers (primaries (P) and secondaries (S)) and tails (rectrices (R)). Particular types of feathers were coded as follows: Ps, Ss, R, primary greater upperwing coverts (PGUppC), secondary greater upperwing coverts (SGUppC), primary greater underwing coverts (PGUndrC), secondary greater underwing coverts (SGUndrC), uppertail coverts (UppTC), and undertail coverts (UndrTC). Results: The prevalence was relatively low for all of the examined birds, that is, 12% for S. uralensis (N = 79), 2.6% for S. aluco (N = 77), and 3.6% for S. nebulosa (N = 55). In total, we examined 37,260 flight feathers and coverts. The mite B. aluconis occupied only the inner S of the tawny owl, secondary greater under and upperwing coverts of the great grey owl, and inner Ss, primary and secondary upperwing coverts, UndrTC, and coverts from the scapulars of the Ural owl. Conclusion: We hypothesise that the absence of these parasites in the examined P, S, and R suggests that these feather types might be unsuitable for the mites due to their thick quill walls, preventing successful feeding.

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.

Small mammals near Janowiec nad Wisłą (middle-eastern Poland) on the basis of prey composition of the tawny owl Strix aluco and long-eared owl Asio otus

At two sites near Janowiec nad Wisłą (middle-eastern Poland) the species composition of a small mammal community in the diet of the tawny owl Strix aluco and long-eared owl Asio otus has been examined. The bones of 128 mammals have been extracted from S. aluco pellets gathered in the years 2014-2015, whereas 401 mammals have been extracted from A. otus pellets collected in the years 2023-2024. Dominant species in the diet of S. aluco (the site bordering woodland) were Clethrionomys glareolus (31.3%), Apodemus agrarius (16.4%) and Apodemus flavicollis (12.5%), while in the case of A. otus (the site bordering open landscape) Microtus arvalis (55.1%) appeared most frequent. Altogether 16 species were recorded representing: Soricomorpha (4), Chiroptera (1), Rodentia (10) and Carnivora (1). Two bats caught as prey belonged to the species of Myotis nattereri, common in this part of Poland. Most interesting species were Crocidura leucodon, whose recorded sites are near its range limit, and Muscardinus avellanarius – the species infrequently recorded in central and eastern Poland.

„Podłe życie miałem”. "Puszczyk" Stefana Grabińskiego wobec modernistycznego dekadentyzmu

“I Had a Rough Life:” Stefan Grabiński’s Puszczyk and the Decadent Movement in Modernism The article is an attempt to analyze Puszczyk [Tawny Owl], Stefan Grabiński’s first fantastic horror novella, thus introducing this little-known work into the study of pessimistic attitudes prevailing during Modernism, i.e. at the turn of the 19th and 20th centuries. The research is placed in the context of selected approaches to decadence as one of the leading philosophical movements of the era and one which perfectly reflected the mood and melancholic attitudes of the time when the literary work was created. The novella is shown to have the most characteristic features of decadence and corresponds with the general atmosphere and poetics of Polish modernism. Decadence is understood here as an “attitude towards culture, society, civilization, and a certain way of thinking about them” that focuses on “fall, disintegration, or decline.”

<i>Strix aluco</i>’s scavenging observation on <i>Myocastor</i> coypus in Italy

Documentation of cases of scavenging by Tawny Owl Strix aluco on coypu Myocastor coypus in Italy; highlighting this particular type of feeding behaviour by the species

Camouflage efficiency in a colour-polymorphic predator is dependent on environmental variation and snow presence in the wild.

Colour polymorphism can be maintained by colour morph-specific benefits across environmental conditions. Currently, the amount and the duration of snow cover during winter decrease especially in northern latitudes, which can alter the potential for camouflage of animals with light and dark morphs. Tawny owls, Strix aluco, are colour-polymorphic avian predators with dark (brown) and light (grey) colour morphs, where the grey morph is presumed to enjoy camouflage benefits under snowy conditions. We studied the camouflage potential of morphs in two tawny owls potential using passerines' probability to mob in the wild during winter with and without snow. For comparison with other seasons, we also repeated the experiment during spring and autumn. We found that grey tawny owls have a lower probability of being mobbed than the brown tawny owls only during snowy winters. The two colour morphs therefore experience differential benefits across snow conditions, which may help to maintain colour morphs in the population, although further warming of winter climate will reduce the potential for camouflage for grey tawny owls in northern latitudes.

Unsupervised discrimination of male Tawny owls (Strix aluco) individual calls using robust measurements of the acoustic signal

ABSTRACT Vocal individuality has been widely documented in the Tawny owl (Strix aluco); however, all statistical tools employed thus far to discriminate individual vocalisations have relied on prior knowledge regarding number and identity of individuals. In this study, we tested the effectiveness of four unsupervised clustering algorithms in distinguishing among eight Tawny owl males, solely based on acoustic characteristics of their vocalisations. We also employed both traditional bound-based and robust measurements of acoustic signal to compare their efficacy. We finally evaluated the applicability of this method in identifying the number and distribution of the remaining males recorded in our study area. Three of the four unsupervised techniques had a high rate of success in discriminating among vocalisations of the eight males. In all cases, the best results were obtained using robust measurements. However, when extending the analysis to the remaining unknown males recorded, the highest rate of misclassification errors made results more difficult to interpret. Our study provided a useful tool to discriminate male Tawny owls when only their call recordings are available. Furthermore, this method could be extended to other nocturnal and vociferous species, representing one of the few existing approaches for unsupervised classification of individuals based on acoustic features.

Dear territory or dear partner? Causes and consequences of breeding dispersal in a highly territorial bird of prey with a strong pair bond

Territorial species are unlikely to show extensive movements between breeding seasons. This is especially true for long-lived species, which often have strong pair bonding and can occupy the same territory for years. However, also in such species, individuals may face situations that can lead to a territory shift. Here, we use a comprehensive dataset documenting 40 years of breeding behavior in tawny owl (Strix aluco) – a long-lived species with high site tenacity and mate fidelity – to examine the factors affecting the decisions whether or not to move to another breeding territory and how far, as well as the fitness consequences thereof. We found that the likelihood and distance of movement in either sexes is strongly associated with a change of partner, indicating that mate loss may cause breeding dispersal. Moreover, mate change, not movement to a new territory, had negative effects on subsequent reproductive performance: individuals that changed partner were more likely to skip reproduction in the subsequent year and, in those cases they bred, they produced smaller clutches and raised fewer offspring. Our findings indicate that tawny owls change territory almost exclusively when searching for a new partner and that mate change has profound consequences on their subsequent breeding performance. Overall, our study provides evidence that in tawny owls territoriality and monogamy are associated and strongly linked to fitness, but mate fidelity may be more important than site fidelity, likely because sexes are involved in specific tasks and their cooperation ensures breeding success and, consequently, increases fitness.Significance statementBreeding dispersal, the movement of individuals between breeding sites, can entail high costs for animal fitness, especially for territorial species, which display strong site fidelity. We studied the factors associated with breeding dispersal and the consequences on breeding performances in tawny owl (Strix aluco), a highly territorial species. We found that tawny owls moved more frequently to another breeding territory when the mate died. Either sexes showed an equal probability to move, but the effect was stronger in females than in males after a mate change. Moreover, owls that changed partner showed delayed reproduction, smaller clutch and a higher probability to skip reproduction. Our findings show that in tawny owls territoriality and monogamy are associated and strongly linked to fitness, but mate fidelity may be more important than site fidelity, likely because sexes share the costs of holding the territory.

The Diversity of Small Mammals along a Large River Valley Revealed from Pellets of Tawny Owl Strix aluco.

The Vistula River is one of the largest European semi-natural rivers of high ecological value that functions as an ecological corridor. To assess the structure of small mammal communities along the Vistula River, an analysis of the diet of an opportunistic predator, the tawny owl Strix aluco, was used. A total of 6355 individuals of 19 species were found, including 5 soricomorph species, 12 rodents, 1 carnivore, and 1 bat species. Tawny owls most frequently caught Apodemus agrarius, Clethrionomys glareolus, Apodemus flavicollis, and Microtus arvalis. Rodents dominated small mammal communities (90%), followed by soricomorphs (8%), and the share of Chiroptera was significant (2%). Using Ward's method in cluster analysis, three clusters of sites with similar mammal communities were identified. The cluster that included 17 study sites with the dominance of agriculture habitats was inhabited by diverse mammal communities with a high number of species. In the cluster composed of three suburban forest sites, mammal communities had the lowest diversity, although the high species richness and the highest shares of the forest species (A. flavicollis, C. glareolus, and Nyctalus noctula). Mammal communities in the cluster were composed of three urban sites were dominated by A. agrarius and M. arvalis. The study indicates the high species richness of small mammals in floodplains of the Vistula River and the adjacent areas in central Poland. The floodplain offers suitable habitats for species associated with forests, water bodies, agricultural land, and developed areas. The data collected confirms earlier model predictions about the presence of well-connected local populations of forest mammals along the Vistula River.

Per- and poly-fluoroalkyl substances in Tawny Owl (Strix aluco) feathers from Trøndelag, Norway

Per- and polyfluoroalkyl substances (PFASs) are contaminants of global concern due to their ubiquitous occurrence in the environment, bioaccumulation and the adverse effects on organisms. Tawny Owls (Strix aluco) are documented to be exposed to increasing concentrations of perfluoroalkyl carboxylic acids (PFCAs), and have been suggested in literature as a key raptor monitoring species. Therefore, non-destructive biomonitoring efforts are of high interest. Thus far, the use of feathers for biomonitoring PFASs in Tawny Owls has not been investigated. In this study, 32 PFASs were analyzed in 49 Tawny Owl body feather samples collected from 2017 to 2020 in Trøndelag, Norway. There were 30 PFASs detected in at least one feather, with the sum concentrations ranging from 31 to 203 ng/g (w.w.). Perfluoroheptanoic acid (PFHpA) (median: 33 ng/g) and perfluorooctane sulfonamidoacetic acid (FOSAA) (median: 18 ng/g) were the two compounds with the highest concentrations. Perfluorooctane sulfonic acid (PFOS), which is banned for production and use in Norway since 2007, was found in all samples (median: 4.14 ng/g), indicating its high persistence. 8 PFASs were detected in at least 50 % of the samples: FOSAA (11–127 ng/g), PFHpA (<0.04–115 ng/g), perfluorobutanesulfonic acid (PFBS) (<0.28–21 ng/g), PFOS (0.23–13 ng/g), perfluorotridecanoic acid (PFTrDA) (0.24–5.15 ng/g), perfluorododecanoic acid (PFDoDA) (<0.28–4.45 ng/g), perfluoroundecanoic acid (PFUnDA) (<0.28–2.33 ng/g), and 1H,1H,2H,2H-perfluorooctanesulfonic acid (6:2 FTSA) (0.07–1.01 ng/g). No significant differences were found for the concentrations of PFASs between calendar years and locations, but a slight increase could be observed in the sum concentration of PFASs (Ʃ32PFASs) over the sampling years. As Tawny Owls are residential owls that usually do not cover great distances, their feathers can be used as a potential alternative matrix for future biomonitoring studies. To our knowledge, this is the first study on the occurrence of 32 PFASs investigated in feathers of a Tawny Owl population.

Continuous low-intensity predation by owls (Strix aluco) on bats (Nyctalus lasiopterus) in Spain and the potential effect on bat colony stability.

Owls prey on bats, but information on owl predation is scarce, its impact on bat mortality is unclear, and reports on behavioural responses, including roost-switching and fission-fusion behaviour, are equivocal. To study the link between owl predation and anti-predator behaviour in bats, we evaluated seven months of video recordings at roosts and the behaviour of 51 passive integrated transponder (PIT)-tagged bats and bats without tags in a geographically isolated colony of greater noctule bats (Nyctalus lasiopterus) in Spain. We found the tawny owl Strix aluco to almost continuously hunt N. lasiopterus, from perches and on the wing, well after the bats emerged at dusk and when they returned to their roosts. We recorded 39 unsuccessful and three successful attacks. Nonetheless, we found no evidence that owl predation modifies bat behaviour. While the bats constituted only a very small proportion of the owls' diet, owl predation accounted for an estimated 30-40% of bat mortality, which may have a significant impact on small, local or isolated bat populations, in particular, and thereby shape regional bat distributions. We hypothesize that low roost availability may also affect the bats' potential response to predation, which could lead to natural predation having an excessive impact on bat populations.

Changes in over-winter prey availability, rather than winter climate, are associated with a long-term decline in a northern Tawny Owl population

Although the associations between climate, food conditions and reproduction in the wild has been the focus of numerous studies in recent years, we still know little about population level responses to climate and fluctuating food conditions in long-lived species and during longer periods of time. Here, we assessed the relative importance of the abundance of the main prey in winter (small mammals), and winter climate on population size and productivity in a Tawny Owl (Strix aluco) population in southern Finland during a 40-year period. We studied how population trends changed over time and in relation to winter weather and small mammal abundance on three levels: total estimated population size, proportion of breeders and population productivity. We identified declining trends in each population parameter over time, as well as directional changes in climate variables and prey abundance. Overall, small mammal abundance was the foremost predictor in explaining the variation in the number of active territorial pairs (population size). Moreover, both prey abundance and winter temperature significantly affected the proportion of territorial pairs that attempted to breed and thereby total offspring production, which reveals the relevance of winter weather conditions for population productivity. These results provide additional support to the view that changes in climate can modify predator–prey interactions leading to functional changes in the food web.