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Alexandre Roulin - One of the best experts on this subject based on the ideXlab platform.
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Tawny Owl strix aluco as an indicator of barn Owl tyto alba breeding biology and the effect of winter severity on barn Owl reproduction
Ibis, 2014Co-Authors: Alexandre Chausson, Isabelle Henry, Bertrand Ducret, Bettina Almasi, Alexandre RoulinAbstract:In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre-breeding food conditions and winter severity on between-year variations in population size and reproductive performance. To estimate pre-breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.
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pleiotropy in the melanocortin system expression levels of this system are associated with melanogenesis and pigmentation in the Tawny Owl strix aluco
Molecular Ecology, 2013Co-Authors: Guillaume Emaresi, Pierre Bize, Annelyse Ducrest, Hannes Richter, Celine Simon, Alexandre RoulinAbstract:The adaptive function of melanin-based coloration is a long-standing debate. A recent genetic model suggested that pleiotropy could account for covariations between pigmentation, behaviour, morphology, physiology and life history traits. We explored whether the expression levels of genes belonging to the melanocortin system (MC1R, POMC, PC1/3, PC2 and the antagonist ASIP), which have many pleiotropic effects, are associated with melanogenesis (through variation in the expression of the genes MITF, SLC7A11, TYR, TYRP1) and in turn melanin-based coloration. We considered the Tawny Owl (Strix aluco) because individuals vary continuously from light to dark reddish, and thus, colour variation is likely to stem from differences in the levels of gene expression. We measured gene expression in feather bases collected in nestlings at the time of melanin production. As expected, the melanocortin system was associated with the expression of melanogenic genes and pigmentation. Offspring of darker reddish fathers expressed PC1/3 to lower levels but tended to express PC2 to higher levels. The convertase enzyme PC1/3 cleaves the POMC prohormone to obtain ACTH, while the convertase enzyme PC2 cleaves ACTH to produce α-melanin-stimulating hormone (α-MSH). ACTH regulates glucocorticoids, hormones that modulate stress responses, while α-MSH induces eumelanogenesis. We therefore conclude that the melanocortin system, through the convertase enzymes PC1/3 and PC2, may account for part of the interindividual variation in melanin-based coloration in nestling Tawny Owls. Pleiotropy may thus account for the covariation between phenotypic traits involved in social interactions (here pigmentation) and life history, morphology, behaviour and physiology.
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Melanin-based colour polymorphism signals aggressive personality in nest and territory defence in the Tawny Owl (Strix aluco)
Behavioral Ecology and Sociobiology, 2013Co-Authors: Arnaud Silva, Valentijn Brink, Guillaume Emaresi, Ester Luzio, Pierre Bize, Amélie N. Dreiss, Alexandre RoulinAbstract:Nest and territory defence are risky and potentially dangerous behaviours. If the resolution of life history trade-offs differs between individuals, the level of defence may also vary among individuals. Because melanin-based colour traits can be associated with life history strategies, differently coloured individuals may display different nest and territory defence strategies. We investigated this issue in the colour polymorphic Tawny Owl ( Strix aluco ) for which plumage varies from dark to light reddish melanic. Accordingly, we found that (1) our presence induced a greater response (flying around) from dark-coloured than light-coloured females and (2) dark reddish males suffered lower nest predation rates than light-coloured males. In experimentally enlarged broods, the probability that females reacted after we played back the hoot calls of a stranger male was higher if these females were lighter reddish; the opposite pattern was found in experimentally reduced broods with dark parents being more reactive than light parents. Finally, darker females alarmed more frequently when paired with a light than with a dark male, suggesting that partners adjust their behaviour to each other. We also tested whether colouration is used as a signal by conspecifics to adjust the level of their defensive behaviour. Accordingly, breeding females responded more vigorously to a dark than a light reddish stuffed Tawny Owl placed beside their nest. We conclude that melanin-based colouration is a signal of alternative nest and territory defence behaviour that depends on ecological factors.
G J M Hirons - One of the best experts on this subject based on the ideXlab platform.
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body weight gonad development and moult in the Tawny Owl strix alum
Journal of Zoology, 2009Co-Authors: G J M Hirons, A R Hardy, P I StanleyAbstract:Gonad development, moult and seasonal changes in body weight and composition in the Tawny Owl Strix aluco were studied by examining the carcasses of 369 Owls (mostly road casualties) supplemented by 112 weights of live birds. In breeding females laying was preceded by the accumulation of fat and to a lesser extent protein which meant that they weighed more at this time (February/March) than at any other. Females declined in weight after laying but were still heavy during incubation. In contrast, males and non-breeding females did not increase in weight before the start of the breeding season. Juveniles reached or even exceeded adult weight well before independence due to the deposition of fat. Even after the exclusion of diseased or contaminated individuals, 9·4% of the birds examined were identified as starving; most of these were in the autumn and were probably newly-independent young wandering in search of territories. In both sexes gonad maturation was of brief duration coinciding with the period (mid-March to mid-April) in which eggs are normally laid. Ovarian growth was biphasic. In the three months prior to the breeding season ovarian condition in different birds was positively correlated with body weight and it appeared that the largest ovarian follicles of females in poor condition failed to attain the size from which rapid growth to final ovulation occurs. in males testis size in the breeding season was correlated with pectoral muscle weight (an index to protein condition) but not body weight. The majority of adults commenced wing moult in June. The average duration of primary moult was estimated to be 77 days. Healthy birds replaced the primaries of both wings at the same rate but most diseased birds moulted asymmetrically and/or out of season. First-year birds renewed their body feathers between September and November. In the Tawny Owl territory establishment, breeding and moult are temporally separated.
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the effects of territorial behaviour on the stability and dispersion of Tawny Owl strix aluco populations
Journal of Zoology, 2009Co-Authors: G J M HironsAbstract:The effect of territorial behaviour on the density and stability of Tawny Owl (Strix aluco (L.)) populations was studied in three habitats during 1971–74: deciduous woodland (Wytham, near Oxford), mixed farmland (south Warwickshire) and conifer plantations (Dumfries). Territory size was determined by plotting the position of territorial challenges (hoots) of males; these were individually recognizable. In all three areas, pairs of Owls maintained contiguous territories which changed little in size and configuration from year to year. In Wytham, this was in spite of wide fluctuations in the abundance of rodent prey. Territory size was most variable on farmland (17–74 ha) where it was inversely correlated with the area of closed woodland contained within territories. The mean size of territories was significantly smaller in the deciduous woodland (18.2 ha) than the coniferous woodland (46.1 ha) or farmland (37.4 ha). This variation was probably ultimately related to the availability of prey in different habitats. In Wytham, the annual rate of disappearance of territory-holding males was around 15% and, except after a poor breeding season, birds which disappeared or were removed from their territories were replaced rapidly. Territory boundaries remained the same after replacement and the number and spatial configuration of territories (around 30) was similar to that found 14 years earlier. There is some evidence that individual pairs would be able to raise more young if they could defend larger territories than is possible at the current population size. Recoveries of birds ringed nationally indicate that Owls survive less well without territories, and that young suffer heavy mortality in their first autumn. The proportion of young recovered was highest in years when many were ringed. Examination of 276 corpses (mostly road casualties) suggests that many young starve soon after becoming independent. These observations support the idea that the stability of Tawny Owl populations results from the territorial behaviour of residents acting to produce subsequent mortality among birds unable to establish their own territories. This regulation probably applies over wide areas and a variety of habitats.
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the importance of body reserves for successful reproduction in the Tawny Owl strix aluco
Journal of Zoology, 2009Co-Authors: G J M HironsAbstract:One-quarter of Tawny Owl nests fail to hatch young, mainly because the eggs are chilled and/or deserted. In 1973–74 automatic photography was employed at four nests near Oxford to relate the incubation behaviour of females to the ration of prey supplied to them by their mates. The eggs did not hatch in two nests and young fledged from only one of the others. Females were less attentive at the nests which failed during incubation and on average received less prey, but even at successful nests there were some nights when the female was supplied with less than her estimated daily food requirement. Female Tawny Owls accumulate large reserves of fat and protein before laying. These buffer against any temporary inability of the male to provide sufficient food during incubation, and enable the female to stay on the nest rather than hunt for herself and risk the eggs becoming chilled. When prey are scarce, many females do not lay at all, and the ultimate factor determining whether breeding takes place may be the female's ability to acquire body reserves sufficient to provide a chance of breeding successfully.
Jon E. Brommer - One of the best experts on this subject based on the ideXlab platform.
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Blood parasites mediate morph-specific maintenance costs in a colour polymorphic wild bird.
Journal of Evolutionary Biology, 2011Co-Authors: Patrik Karell, Kari Ahola, Teuvo Karstinen, Heikki Kolunen, Heli Siitari, Jon E. BrommerAbstract:Parasites can mediate profound negative effects on host fitness. Colour polymorphism has been suggested to covary genetically with intrinsic physiological properties. Tawny Owl colour polymorphism is highly heritable with two main morphs, grey and brown. We show that experimental medication acts to reduce blood parasites and that medicated grey females maintain body mass during breeding, whereas medicated brown females decline in body mass similar to control females of both morphs. We find no effect of medication on general immunoglobulin levels, antigen-specific humoral response or H/L ratio. In the descriptive data, both morphs have similar blood parasite infection rates, but blood parasite infection is associated with decreased body mass in brown but not in grey females. We conclude that blood parasite infection primarily has somatic costs, which differ between the two highly heritable Tawny Owl colour morphs with more pronounced costs in the grey (little pigmented) morph than in the brown (heavily pigmented) morph. Because our descriptive results imply the opposite pattern, our findings highlight the need of experimental manipulation when studying heritable variation in hosts’ response to parasitism.
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population dynamics in a cyclic environment consequences of cyclic food abundance on Tawny Owl reproduction and survival
Journal of Animal Ecology, 2009Co-Authors: Patrik Karell, Kari Ahola, Teuvo Karstinen, Aniko Zolei, Jon E. BrommerAbstract:1. Understanding which factors regulate population dynamics may help us to understand how a population would respond to environmental change, and why some populations are declining. 2. In southern Finland, vole abundance shows a three-phased cycle of low, increase and decrease phases, but these have been fading out in recent years. During five such cycles (1981-1995), all Tawny Owls Strix aluco were censused in a 250-km(2) study area, and their reproduction and survival were monitored. 3. Males and females showed similar dynamics, but experienced breeders recruited more offspring and had higher survival than first breeders. Offspring recruitment, but not survival of breeding individuals varied in accordance with vole abundance. 4. The population's numerical response to prey abundance was primarily due to first-breeding individuals entering the population in the increase phase when immigration was the highest. First-breeding birds were younger, but experienced breeders were older in more favourable vole years. 5. A stage-specific matrix population model integrating survival and fecundity showed that, despite obvious variation in fecundity between vole cycle phases, this variation had limited importance for overall Tawny Owl population dynamics, but that the survival of experienced breeders during the low phase is most important for population growth. 6. Model and data agreed that the vole cycle drives the dynamics of this avian predator by limiting the recruitment of new breeders during the low phase. Population dynamics hence differ not only from the classic example of the species in a more temperate region in the UK where the number of territories is stable across years, but also from the dynamics of other avian vole predators in Fennoscandia where the recurring crash in vole abundance drastically lowers adult survival thereby creating vacancies.
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Tawny Owl reproduction and offspring sex ratios under variable food conditions
Journal of Ornithology, 2007Co-Authors: Jaana Kekkonen, Patrik Karell, Heikki Kolunen, Hannu Pietiainen, Jon E. BrommerAbstract:Tawny Owl reproduction and offspring sex ratios have been considered to depend on the abundance of small voles. We studied reproductive performance (laying date, clutch and brood size) during 1995–2003 and offspring sex ratios from 1999 to 2003 in relation to the abundance of small voles and food delivered to the nest in a Tawny Owl population in southern Finland. Abundance of small voles (field and bank voles) was based on trappings in the field, and estimates of food delivery was based on diet analysis of food remains in the nest boxes. In this population, reproductive output was not related to the abundance of small voles. Analysis of food delivered to the nest showed that the prey weight per offspring varied more than twofold between years and revealed that this difference was mainly related to the proportion of water voles in the diet. Only the number of water voles correlated with laying dates. Offspring sex ratios were weakly male biased (55%) but did not differ from parity. Sex ratios were not related to the abundance of small voles, and we found no evidence that parents delivered more food to nests with proportionally more offspring of the larger (female) sex. Our results underline the notion that populations may differ in their sex allocation pattern, and suggest such differences may be due to diet.
Patrik Karell - One of the best experts on this subject based on the ideXlab platform.
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Mammalian nest predation induces small-scale nest site switching in territorial Tawny Owl (Strix aluco) females
Ornis Fennica, 2020Co-Authors: Patrik Karell, Peter Ericsson, Daniel Ericsson, Kent Haglund, Chiara Morosinotto, Lars Ove NilssonAbstract:Nest predation is a major factor affecting fitness in birds. Individuals are expected to respond to nest predation by selecting safe nesting sites and by moving away from risky sites. Thereby, perceived risk or experience of predation should lead to shifts in nest site selection. Experimental studies on behavioural and life-history consequences of nest predation have traditionally manipulated the risk of predation and studied the immediate consequences thereof. Fewer studies have however analysed the behavioural consequences of perceived predation risk to future breeding events and we know little about how sedentary territorial species respond to nest predation. We experimentally manipulated Tawny Owl (Strix aluco) breeding nest site choice by providing an additional alternative nest box within the territory, nearby the original nesting sites. The new nest box was provided either after a successful reproductive event (control group), or following a failed reproductive event caused by a nest predator (i.e. pine marten Martes martes, predated group). We show that Tawny Owls generally switched to the alternative nest site in the current breeding season when the nest was predated in the previous year, whereas they used the same nest after a successful breeding. We found no effects of previous predation experience on the probability to breed nor on clutch size. We conclude that small scale movement within the territory are used by Tawny Owls to minimize predation risk and that the Owls use information on past predation events and nest failure to optimize their breeding decision in the following season. (Less)
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Blood parasites mediate morph-specific maintenance costs in a colour polymorphic wild bird.
Journal of Evolutionary Biology, 2011Co-Authors: Patrik Karell, Kari Ahola, Teuvo Karstinen, Heikki Kolunen, Heli Siitari, Jon E. BrommerAbstract:Parasites can mediate profound negative effects on host fitness. Colour polymorphism has been suggested to covary genetically with intrinsic physiological properties. Tawny Owl colour polymorphism is highly heritable with two main morphs, grey and brown. We show that experimental medication acts to reduce blood parasites and that medicated grey females maintain body mass during breeding, whereas medicated brown females decline in body mass similar to control females of both morphs. We find no effect of medication on general immunoglobulin levels, antigen-specific humoral response or H/L ratio. In the descriptive data, both morphs have similar blood parasite infection rates, but blood parasite infection is associated with decreased body mass in brown but not in grey females. We conclude that blood parasite infection primarily has somatic costs, which differ between the two highly heritable Tawny Owl colour morphs with more pronounced costs in the grey (little pigmented) morph than in the brown (heavily pigmented) morph. Because our descriptive results imply the opposite pattern, our findings highlight the need of experimental manipulation when studying heritable variation in hosts’ response to parasitism.
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population dynamics in a cyclic environment consequences of cyclic food abundance on Tawny Owl reproduction and survival
Journal of Animal Ecology, 2009Co-Authors: Patrik Karell, Kari Ahola, Teuvo Karstinen, Aniko Zolei, Jon E. BrommerAbstract:1. Understanding which factors regulate population dynamics may help us to understand how a population would respond to environmental change, and why some populations are declining. 2. In southern Finland, vole abundance shows a three-phased cycle of low, increase and decrease phases, but these have been fading out in recent years. During five such cycles (1981-1995), all Tawny Owls Strix aluco were censused in a 250-km(2) study area, and their reproduction and survival were monitored. 3. Males and females showed similar dynamics, but experienced breeders recruited more offspring and had higher survival than first breeders. Offspring recruitment, but not survival of breeding individuals varied in accordance with vole abundance. 4. The population's numerical response to prey abundance was primarily due to first-breeding individuals entering the population in the increase phase when immigration was the highest. First-breeding birds were younger, but experienced breeders were older in more favourable vole years. 5. A stage-specific matrix population model integrating survival and fecundity showed that, despite obvious variation in fecundity between vole cycle phases, this variation had limited importance for overall Tawny Owl population dynamics, but that the survival of experienced breeders during the low phase is most important for population growth. 6. Model and data agreed that the vole cycle drives the dynamics of this avian predator by limiting the recruitment of new breeders during the low phase. Population dynamics hence differ not only from the classic example of the species in a more temperate region in the UK where the number of territories is stable across years, but also from the dynamics of other avian vole predators in Fennoscandia where the recurring crash in vole abundance drastically lowers adult survival thereby creating vacancies.
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Tawny Owl reproduction and offspring sex ratios under variable food conditions
Journal of Ornithology, 2007Co-Authors: Jaana Kekkonen, Patrik Karell, Heikki Kolunen, Hannu Pietiainen, Jon E. BrommerAbstract:Tawny Owl reproduction and offspring sex ratios have been considered to depend on the abundance of small voles. We studied reproductive performance (laying date, clutch and brood size) during 1995–2003 and offspring sex ratios from 1999 to 2003 in relation to the abundance of small voles and food delivered to the nest in a Tawny Owl population in southern Finland. Abundance of small voles (field and bank voles) was based on trappings in the field, and estimates of food delivery was based on diet analysis of food remains in the nest boxes. In this population, reproductive output was not related to the abundance of small voles. Analysis of food delivered to the nest showed that the prey weight per offspring varied more than twofold between years and revealed that this difference was mainly related to the proportion of water voles in the diet. Only the number of water voles correlated with laying dates. Offspring sex ratios were weakly male biased (55%) but did not differ from parity. Sex ratios were not related to the abundance of small voles, and we found no evidence that parents delivered more food to nests with proportionally more offspring of the larger (female) sex. Our results underline the notion that populations may differ in their sex allocation pattern, and suggest such differences may be due to diet.
Paolo Galeotti - One of the best experts on this subject based on the ideXlab platform.
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Fluctuating Asymmetry in Body Traits Increases Predation Risks: Tawny Owl Selection Against Asymmetric Woodmice
Evolutionary Ecology, 2005Co-Authors: Paolo Galeotti, Roberto Sacchi, Vincenzo VicarioAbstract:During the last decade, the study of fluctuating asymmetry (FA) in relation to different fitness aspects has become a popular issue in evolutionary biology. There has been much recent debate in subtle departures from perfect symmetry in bilaterally paired morphological characters, and the extent to which such departure actually reflects aspects of individual quality and fitness. We used data from pellet collection and trapping sessions involving the trophic system Apodemus – Strix aluco, to test the hypothesis that asymmetric woodmice disproportionately fell prey to the Tawny Owl compared with “normal” woodmice. We found that woodmice preyed on by Owls had significantly more asymmetric leg bones than survivors, particularly hind legs, those devoted to jumping. Thus asymmetry in locomotory traits apparently increased predation risks due probably to minor efficiency of asymmetric woodmice in evading predators or to their general low quality. These results suggest that FA affects fitness and consequently may be a good predictor of survival chances for woodmice, i.e. their quality; on the other hand, by removing asymmetric individuals, Tawny Owls can exert a stabilising selection on prey populations.
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patterns of territory size and defence level in rural and urban Tawny Owl strix aluco populations
Journal of Zoology, 1994Co-Authors: Paolo GaleottiAbstract:The effect of different variables on the territory size and defence level of Tawny Owl (Strix aluco L.) populations was studied in two habitats: mixed farmland (1976–1978) and town (1986–1988). Territory size was determined by plotting the position of territorial challenges (hoots) of males which were individually recognizable in most cases. No differences were found in size, defence, number of competitors and biomass between territories in farmland and in town, but territories in town were more fragmented and showed a larger nearest neighbour distance. Size of rural territories was adequately predicted both by some structural habitat features and food supplies, while size of urban territories was affected only by habitat structure and by years of territory occupancy. No effect on territory size by competing neighbours was found in either habitat, thus confirming that behavioural interactions between the owners of territories and potential settlers prevent a decrease of territory size. Defence level of urban territories was affected by 'social’variables (nearest neighbour distance and years of occupancy), structural variables (percentage of poplar grove and diversity), and food supply, while in rural territories only structural variables (fragmentation or natural vegetation) and food supplies affected defence level. This was due to different settlement tactics in the two areas, depending on the extent and quality of suitable habitat.
