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.     

Context-Specific Reweighting of Auditory Spatial Cues following Altered Experience during Development

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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.     

Conditional association between melanism and personality in Israeli Barn Owls

Capsule Boldness defines the extent to which animals are willing to take risks in the presence of a predator. Late, but not early, in the breeding season, Israeli nestling Barn Owls displaying larger black feather spots were more docile, feigned death longer and had a lower breathing rate when handled than smaller-spotted nestlings. Larger-spotted breeding females were less docile if heavy but more more docile if light. The covariation between personality (boldness vs. timid) and melanin-based colouration is therefore conditional on environmental factors.     

Weighting of Spatial and Spectro-Temporal Cues for Auditory Scene Analysis by Human Listeners

The auditory system creates a neuronal representation of the acoustic world based on spectral and temporal cues present at the listener''s ears, including cues that potentially signal the locations of sounds. Discrimination of concurrent sounds from multiple sources is especially challenging. The current study is part of an effort to better understand the neuronal mechanisms governing this process, which has been termed “auditory scene analysis”. In particular, we are interested in spatial release from masking by which spatial cues can segregate signals from other competing sounds, thereby overcoming the tendency of overlapping spectra and/or common temporal envelopes to fuse signals with maskers. We studied detection of pulsed tones in free-field conditions in the presence of concurrent multi-tone non-speech maskers. In “energetic” masking conditions, in which the frequencies of maskers fell within the ±1/3-octave band containing the signal, spatial release from masking at low frequencies (∼600 Hz) was found to be about 10 dB. In contrast, negligible spatial release from energetic masking was seen at high frequencies (∼4000 Hz). We observed robust spatial release from masking in broadband “informational” masking conditions, in which listeners could confuse signal with masker even though there was no spectral overlap. Substantial spatial release was observed in conditions in which the onsets of the signal and all masker components were synchronized, and spatial release was even greater under asynchronous conditions. Spatial cues limited to high frequencies (>1500 Hz), which could have included interaural level differences and the better-ear effect, produced only limited improvement in signal detection. Substantially greater improvement was seen for low-frequency sounds, for which interaural time differences are the dominant spatial cue.     

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.     

Multiplicative Auditory Spatial Receptive Fields Created by a Hierarchy of Population Codes

A multiplicative combination of tuning to interaural time difference (ITD) and interaural level difference (ILD) contributes to the generation of spatially selective auditory neurons in the owl''s midbrain. Previous analyses of multiplicative responses in the owl have not taken into consideration the frequency-dependence of ITD and ILD cues that occur under natural listening conditions. Here, we present a model for the responses of ITD- and ILD-sensitive neurons in the barn owl''s inferior colliculus which satisfies constraints raised by experimental data on frequency convergence, multiplicative interaction of ITD and ILD, and response properties of afferent neurons. We propose that multiplication between ITD- and ILD-dependent signals occurs only within frequency channels and that frequency integration occurs using a linear-threshold mechanism. The model reproduces the experimentally observed nonlinear responses to ITD and ILD in the inferior colliculus, with greater accuracy than previous models. We show that linear-threshold frequency integration allows the system to represent multiple sound sources with natural sound localization cues, whereas multiplicative frequency integration does not. Nonlinear responses in the owl''s inferior colliculus can thus be generated using a combination of cellular and network mechanisms, showing that multiple elements of previous theories can be combined in a single system.     

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.     

Geographic and temporal variation in the consumption of bats by European Barn Owls

Capsule We report a review of the occurrence of bats in the Barn Owl diet Tyto alba in Europe. Based on 802 studies reporting 4.02 million prey items identified in pellets, 4949 were bats (0.12%). We found that bat predation decreased during the last 150 years, is more frequent on islands than mainland, and is higher in eastern than western Europe and in southern than northern Europe. Although Barn Owls usually capture bats opportunistically, they can sometimes specialize on them.     

Selective Attention Modulates Human Auditory Brainstem Responses: Relative Contributions of Frequency and Spatial Cues

Selective attention is the mechanism that allows focusing one’s attention on a particular stimulus while filtering out a range of other stimuli, for instance, on a single conversation in a noisy room. Attending to one sound source rather than another changes activity in the human auditory cortex, but it is unclear whether attention to different acoustic features, such as voice pitch and speaker location, modulates subcortical activity. Studies using a dichotic listening paradigm indicated that auditory brainstem processing may be modulated by the direction of attention. We investigated whether endogenous selective attention to one of two speech signals affects amplitude and phase locking in auditory brainstem responses when the signals were either discriminable by frequency content alone, or by frequency content and spatial location. Frequency-following responses to the speech sounds were significantly modulated in both conditions. The modulation was specific to the task-relevant frequency band. The effect was stronger when both frequency and spatial information were available. Patterns of response were variable between participants, and were correlated with psychophysical discriminability of the stimuli, suggesting that the modulation was biologically relevant. Our results demonstrate that auditory brainstem responses are susceptible to efferent modulation related to behavioral goals. Furthermore they suggest that mechanisms of selective attention actively shape activity at early subcortical processing stages according to task relevance and based on frequency and spatial cues.     

Auditory Perception of Hawks and Owls for Passerine Alarm Calls

The auditory perception of eight species of raptors was examined to test the hypothesis of Marler (1955) that these avian predators are unable to locate certain songbird alarm calls. In particular, Marler proposed that mobbing calls have characteristics that enhance their locatability and that these characteristics are absent in the high-frequency 'seet' calls given by individual songbirds. To test this hypothesis, the behavioral responses of four species of owls and four species of hawks, housed at two different raptor rehabilitation sites, to tape recorded alarm calls were examined. Each raptor was exposed to a random order of 10 trials of mobbing calls and 10 trials of a seet call. Responses were scored based upon head angle orientations. Hawks and owls responded more often and more accurately to mobbing calls than to seet calls. In general, owls responded to significantly more calls than hawks. The results are consistent with Marler's hypothesis that raptors have difficulty locating passerine seet calls. Nevertheless, future studies should test mobbing calls that vary in their frequency and duration ( Ficken & Popp 1996 ) to determine whether some mobbing calls are more difficult to locate than others.     

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.     

非人灵长类社会等级现象的研究进展

等级结构在群居生活种类中普遍存在,在非人灵长类尤为突出。该主要对近年来有关灵长类等级现象的研究结果进行分析综述,认为等级现象与个体的年龄、性别、母亲的顺位以及呆在群内时间长短等自身因素相关,也反映在个体之间的攻击、理毛、爬跨和近距等社会交往行为中。等级结构在不同动物中又不尽相同,故研究中需要对具体物种做具体分析。等级现象的存在,不仅有利于动物群体的生存,而且对动物个体也是有利的。     

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.     

Landscape and Climatic Variations Shaped Secondary Contacts amid Barn Owls of the Western Palearctic

The combined actions of climatic variations and landscape barriers shape the history of natural populations. When organisms follow their shifting niches, obstacles in the landscape can lead to the splitting of populations, on which evolution will then act independently. When two such populations are reunited, secondary contact occurs in a broad range of admixture patterns, from narrow hybrid zones to the complete dissolution of lineages. A previous study suggested that barn owls colonized the Western Palearctic after the last glaciation in a ring-like fashion around the Mediterranean Sea, and conjectured an admixture zone in the Balkans. Here, we take advantage of whole-genome sequences of 94 individuals across the Western Palearctic to reveal the complex history of the species in the region using observational and modeling approaches. Even though our results confirm that two distinct lineages colonized the region, one in Europe and one in the Levant, they suggest that it predates the last glaciation and identify a secondary contact zone between the two in Anatolia. We also show that barn owls recolonized Europe after the glaciation from two distinct glacial refugia: a previously identified western one in Iberia and a new eastern one in Italy. Both glacial lineages now communicate via eastern Europe, in a wide and permeable contact zone. This complex history of populations enlightens the taxonomy of Tyto alba in the region, highlights the key role played by mountain ranges and large water bodies as barriers and illustrates the power of population genomics in uncovering intricate demographic patterns.     

Strong decline in the consumption of invertebrates by Barn Owls from 1860 to 2012 in Europe

Capsule The analysis of 616 papers about the diet of the European Barn Owl Tyto alba showed that 9678 invertebrates were captured out of 3.13 million prey items (0.31%). The consumption of invertebrates strongly decreased between 1860 and 2012. This further demonstrates that the Barn Owl diet changed to a large extent during the last 150 years.     

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.