Changes in the food of British Barn Owls (Tyto alba) between 1974 and 1997

Comparison of the results of a 1993–97 Barn Owl Tyto alba pellet survey with those of a similar survey from 1956–74 showed that Barn Owl diet had changed significantly. The primary differences were a widespread decrease in the percentage of Common Shrew Sorex araneus, combined with an increase in Pygmy Shrew Sorex minutus. The percentage of Wood and Yellow‐necked mice Apodemus sylvaticus and A. flavicollis and Bank Vole Clethrionomys glareolus in the diet also increased. Changes in Barn Owl diet since 1974 were independent of land‐class group, but were dependent upon region. This was due primarily to a large increase in the percentage of Apodemus spp. in Eastern England. Whilst the percentage of Pygmy Shrew in Barn Owl diet showed significant regional variation, there was no significant variation between land‐class groups. The diversity of Barn Owl diet increased between 1974 and 1997, although it was still lower in 1997 than earlier in the century. This increase was dependent upon region, but independent of land‐class group. The combined results of both surveys showed significant interland‐class group variation in dietary diversity. Changes in diet are discussed in relation to the intensification of agriculture and other changes in land management since the 1970s. The effects on Barn Owls of these changes in prey abundance are discussed, particularly in relation to the decline in Barn Owl numbers during the twentieth century.     

Breeding biology of the Barn Owl Tyto alba in central Mali

Data were obtained on 178 clutches of African Barn Owls in central Mali from four breeding seasons during 1979–1983. Significantly more clutches were laid in 1979–1980 and significantly fewer in 1980– 1981 than the average for the 4 years and there were significantly more clutches laid in the middle period of the annual breeding season. The egg volume was significantly smaller at the beginning of the breeding season and significantly larger in the middle than the overall mean with eggs of second clutches being larger than those of first clutches. The clutch size was 605 eggs of which 479 hatched. The number of young fledged per successful nest was 319 and was 1 83 for all nesting attempts. The month was the only variable shown to affect significantly the clutch size, eggs hatched and fledging rate, the highest success rates being associated with the middle of the breeding period. The average interval between the hatching of eggs was 2–31 days. Survival rates (47'1%) to fledging were significantly affected by year (1981–1982 being the least) and month (mid-season birds the best). The order of hatching significantly affected age at death or disappearance, the first-hatched birds surviving the longest. The year significantly affected age at fledging, the young from the year in which most clutches were laid leaving the nest at the youngest age and those associated with the year having the least number of clutches remaining in the nest the longest. The month of hatching also affected fledging age, birds at the extremes of the breeding season fledging at older ages. The discussion compares these data with those from elsewhere.     

Covariation between plumage colour polymorphism and diet in the Barn Owl Tyto alba

Several hypotheses might explain the evolution and maintenance of colour morphs within animal populations. The 'alternative foraging strategy' hypothesis states that alternative colour morphs exploit different ecological niches. This hypothesis predicts that morphs differ in diet, either because foraging success on alternative prey species is morph-dependent or because differently coloured individuals exploit alternative habitats. I examined this prediction in the Barn Owl Tyto alba , a bird that varies in plumage coloration continuously from dark reddish-brown to white. On the European continent, Owls are light-coloured (subspecies T. a. alba ) in the south and reddish-brown ( T. a. guttata ) in the north; in central Europe the two subspecies interbreed, generating many colour variants. If plumage coloration indicates alternative foraging strategies, in sympatry dark- and light-coloured owls should consume prey species that are typical of the diets of T. a. guttata and T. a. alba in allopatry, respectively. In line with this prediction, both in allopatry and in sympatry in Switzerland T. a. guttata fed primarily upon Common Voles Microtus arvalis and T. a. alba upon Wood Mice Apodemus spp. Statistical analyses suggest that morph-dependent diet did not arise from a non-random habitat distribution of owls with respect to plumage coloration. This suggests that foraging success upon alternative prey is morph-dependent.     

Direction of movements in Hungarian Barn Owls (Tyto alba): gene flow and barriers

Abstract. An analysis of dispersal directions of the barn owl showed that all individuals immigrating to Hungary came from W‐NW‐N. It was shown that immigrating owls breed in Hungary. There is no prevailing direction in emigration from Hungary. The time of fledging does not influence the direction of movement and there is no difference between sexes concerning dispersal direction. The percentages of emigrating owls is greater than that of immigrating ones. These percentages did not differ in relation to most of the analysed countries (Germany, Italy, Switzerland, Poland and countries of the former Yugoslavia and Czechoslovakia) but it differed in relation to Austria. The degree and direction of introgression into and from the transition zone and the recent distribution of the phenotypes are discussed based on the comparative analysis of published European data. These suggest that the subspecies Tyto alba alba and Tyto alba guttata disappear by introgression, to form a phenotypically very variable species.     

Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

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.     

Pellet contents of the Barn Owl,Tyto alba,near Samandag,Turkey

Summary

Weights and standard measurements are given of 568 individuals of 52 bird species ringed in various localities in Turkey in July and August 1973. The Melodious Warbler, Hippolais polyglotta, was recorded in Turkey for the first time.     

Corticosterone Promotes Scramble Competition Over Sibling Negotiation in Barn Owl Nestlings (Tyto alba)

In species with parental care, siblings compete for access to food resources. Typically, they vocally signal their level of need to each other and to parents, and jostle for the position in the nest where parents deliver food. Although food shortage and social interactions are stressful, little is known about the effect of stress on the way siblings resolve the conflict over how food is shared among them. Because glucocorticoid hormones mediate physiological and behavioral responses to stressors, we tested whether corticosterone, the main glucocorticoid in birds, modulates physical and vocal signaling used by barn owl siblings (Tyto alba) to compete for food. Although corticosterone-implanted (cort-) nestlings and placebo-nestlings were similarly successful to monopolize food, they employed different behavioral strategies. Compared to placebo-nestlings, cort-individuals reduced the rate of vocally communicating with their siblings (but not with their parents) but were positioned closer to the nest-box entrance where parents predictably deliver food. Therefore, corticosterone induced nestlings to increase their effort in physical competition for the best nest position at the expense of investment in sib?Csib communication without modifying vocal begging signals directed to parents. This suggests that in the barn owl stress alters nestlings?? behavior and corticosterone could mediate the trade-off between scramble competition and vocal sib?Csib communication. We conclude that stressful environments may prevent the evolution of sib?Csib communication as a way to resolve family conflicts peacefully.     

Genetic divergence analysis of the Common Barn Owl Tyto alba (Scopoli, 1769) and the Short-eared Owl Asio flammeus (Pontoppidan, 1763) from southern Chile using COI sequence

In this paper new mitochondrial COI sequences of Common Barn Owl Tyto alba (Scopoli, 1769) and Short-eared Owl Asio flammeus (Pontoppidan, 1763) from southern Chile are reported and compared with sequences from other parts of the World. The intraspecific genetic divergence (mean p-distance) was 4.6 to 5.5% for the Common Barn Owl in comparison with specimens from northern Europe and Australasia and 3.1% for the Short-eared Owl with respect to samples from north America, northern Europe and northern Asia. Phylogenetic analyses revealed three distinctive groups for the Common Barn Owl: (i) South America (Chile and Argentina) plus Central and North America, (ii) northern Europe and (iii) Australasia, and two distinctive groups for the Short-eared Owl: (i) South America (Chile and Argentina) and (ii) north America plus northern Europe and northern Asia. The level of genetic divergence observed in both species exceeds the upper limit of intraspecific comparisons reported previously for Strigiformes. Therefore, this suggests that further research is needed to assess the taxonomic status, particularly for the Chilean populations that, to date, have been identified as belonging to these species through traditional taxonomy.     

Multiple Paternity in Polyandrous Barn Owls (Tyto alba)

In polyandrous species females produce successive clutches with several males. Female barn owls (Tyto alba) often desert their offspring and mate to produce a 2^nd annual brood with a second male. We tested whether copulating during chick rearing at the 1^st annual brood increases the male''s likelihood to obtain paternity at the 2^nd annual breeding attempt of his female mate in case she deserts their brood to produce a second brood with a different male. Using molecular paternity analyses we found that 2 out of 26 (8%) second annual broods of deserting females contained in total 6 extra-pair young out of 15 nestlings. These young were all sired by the male with whom the female had produced the 1^st annual brood. In contrast, none of the 49 1^st annual breeding attempts (219 offspring) and of the 20 2^nd annual breeding attempts (93 offspring) of non-deserting females contained extra-pair young. We suggest that female desertion can select male counter-strategies to increase paternity and hence individual fitness. Alternatively, females may copulate with the 1^st male to derive genetic benefits, since he is usually of higher quality than the 2^nd male which is commonly a yearling individual.     

Wing and tail myology of Tyto furcata (Aves,Tytonidae)

Barn Owls (Tytonidae) are nocturnal raptors with the largest geographical distribution among Strigiformes. Several osteological, morphometrical, and biomechanical studies of this species were performed by previous authors. Nevertheless, the myology of forelimb and tail of the Barn Owls is virtually unknown. This study is the first detailed myological study performed on the wing and tail of the American Barn Owl (Tyto furcata). A total of 11 specimens were dissected and their morphology and muscle masses were described. Although T. furcata has the wing and tail myological pattern present in other species of Strigiformes, some peculiarities were observed including a difference in the attachment of m. pectoralis propatagialis due to the lack of the os prominence, and the presence of an osseous arch in the radius that seems to widen the anchorage area of the mm. pronator profundus, extensor longus alulae, and extensor longus digiti majoris. Furthermore, the m. biceps brachii has an unusual extra belly that flexes the forearm. The interosseous muscles have a small size and lacks ossified tendons. This feature may be indicative of a lower specialization in the elevation and flexion of the digiti majoris. Forelimb and tail muscle mass account for 10.66 and 0.24% of the total body mass, respectively. Forelimb muscle mass value is similar to the nocturnal (Strigiformes) and diurnal (Falconidae and Accipitridae) raptors, while the tail value is lower than in the diurnal raptors (Falconidae and Accipitridae). The myological differences with other birds of prey are here interpreted in association with their “parachuting” hunting style. This work complements our knowledge of the axial musculature of the American Barn owls, and provides important information for future studies related to functional morphology and ecomorphology.     

Growth of nestling Barn Owls Tyto alba in central Mali

Data on growth of 276 young Barn Owls were analysed with respect to the effects of year and month of hatching, hatch order and brood order. Growth characteristics considered were weight; lengths of culmen, tarsus, central tail feathers and quill of third outermost primary; standard wing length; and wing span. For weight the growth constant K was 0151 and time t ₁₀- t ₉₀ was 32-2 days. Least-squares analyses showed that gain in weight and culmen and tarsus length were affected by month of hatching with young hatched in the middle part of the breeding season showing the most rapid growth. Hatch order affected gain in weight. Differences in growth rates of all these characters were not, however, reflected in differences in weight or length at fledging except for the effects of brood on weight with second broods fledging at significantly lighter weights than first ones. Predictive equations for character against age are provided for all linear measurements. All characters examined attained apparent asymptotes before fledging except tail and standard wing length.     

Prey taken by the Barn Owl in England and Wales

The increase in air traffic brings with it an evergrowing bird-strike hazard; the risks to life and property make this an urgent problem worthy of the closest investigation. The author, reporting on a study of gull movements around Edinburgh Airport, suggests that a useful ‘bird forecast'’could be based on a knowledge of the birds''daily and seasonal feeding and roosting habits.     

The prey of the Barn owl (Tyto alba alba) in East Norfolk

Some 5000 Barn owl pellets, collected from sites in East Norfolk during the past decade, have been examined. The most important prey species, by weight, were the Field vole (Microtus agrestis) 52%, the Brown rat (Rattus norvegicus) 17%, and the Common shrew (Sorex araneus) 12%. The prey varies over different habitats; Wood mice (Apodemus sylvaticus) and Bank vole (Clethrionomys glareolus) forming a higher proportion in localities with hedges, scrub and woodland than in open grasslands. These results are comparable with those of other recent work. However, when compared with studies conducted over 30 years ago, it would appear that the Field vole now constitutes a higher proportion, and the Brown rat a lower proportion, of the prey taken.     

四川都江堰东方草鸮的繁殖记录

<正>东方草鸮(Tyto longimembris)隶属于鸮形目草鸮科,共有6个亚种的分化,我国分布的2个亚种为T.l.chinensis和T.l.pithecops。东方草鸮在我国主要分布于西南和华南(chinensis)以及台湾(pithecops),国外分布于印度次大陆、东南亚、菲律宾、新几内亚岛和澳大利亚(del Hoyo et al.1999,郑光美2011)。在《中国鸟类分类与分布名录》(第二版)中,东方草鸮的分布区并不包括四川省。实际上,早在2000年时就曾有报道称在四川省南充市高坪区发现草鸮的分布(胡锦矗2000),一直未能引起关注。有关东方草鸮繁殖生物学的资料,大多来自国外的     

Habitat selection by a predator of rodent pests is resilient to wildfire in a vineyard agroecosystem

Conservation of uncultivated habitats can increase the potential for ecosystem services in agroecosystems, but these lands are also susceptible to wildfires in the arid western United States. In Napa Valley, California, abundant rodent pests and an interest in integrated pest management have led wine producers to use nest boxes to attract Barn Owls (Tyto furcata) to winegrape vineyards. The viability of this practice as a method to control rodent pests depends heavily on the amount of hunting effort that Barn Owls expend in vineyards, which is known to be influenced by the amount of uncultivated land cover types surrounding the nest box. Wildfires burned nearly 60,000 ha of mainly urban and uncultivated lands surrounding Napa Valley in 2017, altering Barn Owl habitats. We compared GPS tracking data from 32 Barn Owls nesting in 24 individual nest boxes before and after the fires to analyze their hunting habitat selection. Owls with burned areas available to them after the fires had home ranges that shifted toward the fires, but selection was not strongly associated with burned areas. Though there was some spatial use of burned areas, selection of land cover types was similar for birds before and after the fires and in burned and unburned areas. The strongest selection was for areas closest to the nest box, and most recorded locations were in grassland, though selection indicated that owls used land cover types in proportion to their availability. Overall, habitat selection was resilient to changes caused by wildfires. These results are important for farmers who use nest boxes as a means of rodent control, which may be affected after dramatic disturbance events, especially as wildfires increase in the western United States.