Moult of Malayan Barn Owls Tyto alba

Moult in Malayan Barn Owls Tyto alba was studied in two pairs of wild collected captive birds and from feathers taken from nest sites throughout peninsular Malaysia.
Post-juvenile captive birds moulted nearly to completion prior to first breeding, beginning with P6 at a mean age of 301.5 days. This contrasted with the only other study of moult in captive Barn Ow-Is in Germany when moult began at an age of 400 days, and then continued for a protracted period of two years separated by a suspension of moult during the normal breeding season.
The complex sequence of moult in primaries and secondaries both in the Malayan and German birds was similar.
Moult among adult Malayan birds in the wild showed a broad and somebyhat irregular seasonal trend With lower incidence during peak breeding periods.     

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.     

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.     

The feeding and breeding ecology of Barn Owls Tyto alba in Peninsular Malaysia

Barn Owls have only recently colonized Peninsular Malaysia, nesting in the roof spaces of houses in oil palm estates and feeding on the rats which inhabit these plantations. Pellet analysis showed that the prey spectrum was confined almost entirely to three species of the genus Rattus which are the major pests of oil palm. There was no annual variation in diet. Breeding showed a broad seasonality but occurred in all months of the year. Mean clutch and brood sizes of 6.6 and 4.6 respectively were recorded, most pairs producing two broods a year although on two occasions three were raised. Overall hatching success was 69.0% with first clutches more successful (79.9%) than second (57.3%). First broods fledged 86.1% and second broods 69.1% of young fledged. Comparison of growth rates of different sized broods suggested that there is a physiological maximum at which all broods proceed irrespective of brood size. The behaviour al changes needed in hunting techniques when colonizing dense plantations rather than the more usual open habitat of Barn Owls is discussed. The breeding strategy seems to be one of producing large clutches and broods, and frequent breeding attempts in a habitat with a high potential carrying capacity.     

The importance of micro-habitat in the breeding of Barn Owls Tyto alba

Capsule?Habitat parameters associated with 706 Barn Owl (Tyto alba) nesting boxes in Israel were analysed. Pairs bred in 259 of the boxes. The intensity of agricultural practices at nestbox sites were shown to have only a weak effect on aspects of Barn Owl breeding in this region.     

Mortality causes in British Barn Owls Tyto alba, with a discussion of aldrin-dieldrin poisoning

During 1963-89, 627 Barn Owl Tyto alba carcasses were received for autopsy and chemical analysis. Much larger numbers were received per month outside the breeding season than within it, with peaks in autumn (mainly juveniles) and late winter (adults and juveniles).
The main causes of recorded deaths were collisions (mostly with road traffic) and starvation. No great seasonal variation occurred in the main causes of recorded deaths and starved juveniles were reported even in summer. Most starved males weighed less than 240 g, and most starved females less than 250 g.
Another important cause of mortality in eastern arable counties, at least to 1977, was poisoning by organochlorine pesticides, especially aldrin/dieldrin. Levels of HEOD (the metabolized product of aldrin/dieldrin) in the livers of birds that had apparently died of aldrin/ dieldrin poisoning were in the range 6–44 ppm (geometric mean 14 ppm). Pesticide victims formed up to 40% of all dead Barn Owls obtained from some eastern counties during 1963-77. By 1987-89, HEOD levels in Barn Owls in eastern counties had fallen to less than 1.6 ppm, and no deaths from organochlorine poisoning were recorded.
Organochlorine pesticides almost certainly contributed to population decline in eastern England evident in the 1950s and 1960s, and reductions in the use of these chemicals may have allowed a subsequent increase, apparent over the last 10–15 years.     

Factors determining the frequency and productivity of double brooding of Barn Owls Tyto alba

Capsule: Early nesting Barn Owls Tyto alba and those that switched nest sites fledged most chicks overall because they could fit two, more productive, nesting attempts into a breeding season.

Aims: To determine the frequency and productivity of double broods in Barn Owls, and for double brooders, to determine what affects the probability of nest switching and how that affects productivity.

Methods: We monitored the first egg date of each nesting attempt, whether it was in a ‘vole year’, whether a breeding attempt was first or a second annual attempt, the number of chicks fledged from each attempt, and whether a pair switched nest sites, if breeding twice, from 602 Barn Owl breeding attempts in an area of lowland England from 1996 to 2007. General linear models were used to determine predictors of the probability that a pair had a second brood and the number of chicks fledged in each nesting attempt, and then for those owls that double brooded, which variables best predicted the probability of switching, and the number of chicks fledged from the second nest. Finally, we tested whether switching resulted in a shorter laying interval and higher annual productivity.

Results: Early nesting birds were more likely to double brood, although this was relaxed in vole years when later nesting birds also double brooded. Productivity (through increased numbers of chicks fledged or reduced chick loss) was higher the earlier a nest occurred, and there were more chicks fledged in good vole years and in second nesting attempts. Productivity, brood depletion, first clutch date and vole years did not determine whether a double brooding pair switched nesting sites. Productivity in the second nest did not change with a switch but productivity increased for early first nests and second nests with a shorter interval between the first and second nest. Switching however decreased nesting interval and nesting interval was also shorter if there were fewer fledglings from the first nest. Overall productivity was higher for pairs that switched.

Conclusions: Double brooding in Barn Owls increased seasonal productivity substantially and its occurrence depended on vole abundance or early nesting. Nest switching between broods may be a strategy for earlier laying of the second brood. Provision of alternative nest sites, close together in a Barn Owl’s home range, may allow earlier re-nesting and so increase productivity.     

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.     

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.     

A preliminary assessment of the relationship between trophic variability in southern African Barn Owls Tyto alba and climate

Avery, D.M. 1999. A preliminary assessment of the relationship between trophic variability in southern African Barn Owls Tyto alba and climate. Ostrich 70 (3&4): 179–186.

The proximate purpose of the study was to investigate the possibility that micromammalian remains from archaeological sites could provide quantified data concerning past climates. Proportions of micromammalian taxa represented in Barn Owl pellets recovered from 111 roost sites in Africa south of 22°S were analysed with climate variables to determine whether there was any relationship between the two. Preliminary results indicate that some taxa, notably the gerbils Gerbillinae and Gerbillurus and mice Mastomys, will be capable of providing such data. It is clear, however, that careful attention must be paid to the compilation of the database and the nature of the evidence being employed. The disturbed nature of much vegetation in the region must be taken into consideration but it is probable that the effects of disturbance can be characterised and therefore discounted.     

Shrews and moles are less often captured by European Barn Owls Tyto alba nowadays than 150 years ago

Capsule: The analysis of 815 papers about the diet of the European Barn Owl Tyto alba showed that the consumption of small mammals that are insectivorous (shrews and moles) declined between 1860 and 2014. This suggests that the impoverished invertebrate communities due to global changes affected a large range of animals up to top predators.     

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.     

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.     

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.     

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.     

Food partitioning between breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in southern Brazil.

I examined the diet of breeding White-tailed Kites (Elanus leucurus; Aves; Accipitridae) and Barn Owls (Tyto alba; Aves; Tytonidae) in an agrarian area of southern Brazil by analyzing regurgitated prey remains. The objective was to evaluate how these raptors, which differ markedly in their hunting activity periods (owls are nocturnal and kites diurnal), share their mammalian food component. 2,087 prey consumed by Barn Owls and 1,276 by White-tailed Kites were identified. They presented a high overlap of food-niches (Piankas index was 0.98). Based on the daily activity period of their main small mammal prey, a lower overlap would be expected. The crepuscular/nocturnal Mus musculus was the main prey for the diet of breeding Barn Owls (81%) and White-tailed Kites (63%). This small exotic rodent provided 63% of the small mammal biomass ingested by owls and 44% by kites. Larger native small mammals were also considered important for the diet of kites, mainly because of their biomass contribution. Although these raptors differ markedly in their hunting activity periods, Barn Owls and White-tailed Kites are very similar predators in southern Brazil, overlapping their diets.