Tyto Furcata Research Articles

Use of blood clotting assays to assess potential anticoagulant rodenticide exposure and effects in free-ranging birds of prey

Non-target wildlife, particularly birds of prey, are widely exposed to and acutely poisoned by anticoagulant rodenticides (ARs). An unresolved issue surrounding such exposure, however, is the potential for sublethal effects. In particular, the consequences of AR exposure and resulting coagulopathy on health and survival of unintentionally exposed animals, which often encounter a multitude of anthropogenic stressors, are understudied. In a wildlife rehabilitation setting, AR intoxication may be masked by more obvious injuries related to collision with vehicles or electrocution, thereby obfuscating proximate from ultimate cause of mortality. An assessment of coagulation function of admitted wildlife may provide a means of identifying animals exhibiting sublethal coagulopathy, and ultimately ensuring provision of appropriate and swift treatment. In conjunction with routine diagnostics for injury and disease, we performed two blood clotting assays (prothrombin time, Russell's viper venom time) affected by vitamin K-dependent coagulopathy of samples from six species of live raptors admitted to a rehabilitation facility. We also measured clotting time in pre-fledgling barn owl chicks (Tyto furcata) from 10 nest sites in Lower Mainland Canada. Prolonged clotting time or failure to form a clot altogether was observed in 23.0% of 61 sampled raptors admitted to the rehabilitation facility. This is a biologically significant proportion of individuals given the fortuitous and likely biased nature by which raptors are found and admitted to rehabilitation facilities. In contrast, there was little evidence of coagulopathy in 19 pre-fledgling barn owl chicks. The utility of avian coagulation tests for diagnosing AR exposure is promising, yet there remains a need to establish species specific reference values and standardize assay methodologies among testing facilities.

Kocuria tytonicola, new bacteria from the preen glands of American barn owls (Tyto furcata)

Although birds are hosts to a large number of microorganisms, microbes have rarely been found in avian oil glands. Here, we report on two strains of a new bacterial species from the preen oil of American barn owls (Tyto furcata). Phenotypic as well as genotypic methods placed the isolates to the genus Kocuria. Strains are non-fastidious, non-lipophilic Gram-positive cocci and can be unambiguously discriminated from their closest relative Kocuria rhizophila DSM 11926T. In phylogenetic trees, the owl bacteria formed a distinct cluster which was clearly separated from all other known Kocuria species. The same conclusion was drawn from MALDI-TOF MS analyses. Once again, the new bacterial strains were very similar to one another, but exhibited substantial differences when compared to the most closely related species. Besides, the results of the biochemical tests, optimum growth conditions and pigmentation differed from closely related Kocuria spp. Finally, ANIb values of less than 87% provided striking evidence that the isolates recovered from American barn owls represent a hitherto undescribed species, for which we propose the name Kocuria tytonicola sp. nov. The type strain is 489T (DSM 104133T=LMG 29945T, taxonumber TA00340).

EvoDevo in owl ear asymmetry—The little owl (Athene noctua)

Owls are well adapted to nocturnal hunting. This includes vision tuned to low level light conditions, silent flight, and asymmetrical ears. Asymmetrical ears facilitate sound localization and evolved up to seven times independently in the evolutionary history of owls. However, there are also owl species with a crepuscular or diurnal lifestyle, like the little owl (Athene noctua), that have symmetrical ears as adults. Here we show that a small, but significant ear asymmetry occurs in the embryonic development of little owls, despite the presence of symmetrical ears in adults. In the asymmetric period, the left ear opening is bigger in area than its counterpart on the right. The asymmetry in the little owl occurs in the same stages at which the asymmetry in the barn owl (Tyto furcata) develops, but in the little owl the asymmetry vanishes shortly before hatching. Asymmetries in the size of the ear openings are also found in the adults of other owl species, most of them belonging to the genus Strix. We interpret our finding as an indication of a secondarily evolved diurnal activity in little owls. Further, ear asymmetry might be more deeply rooted in the evolution of owls than previously assumed.

Pequenos mamíferos (Didelphimorphia, Chiroptera e Rodentia) em egagropilos de Tyto furcata (coruja-das-igrejas) (Aves, Tytonidae) do sul do Brasil

A análise e identificação de pequenos mamíferos em egagropilos de coruja, em especial do gênero Tyto, são consideradas uma ferramenta útil e complementar na mastozoologia. No entanto, poucos estudos deste tipo têm sido desenvolvidos no sul do Brasil. Foram analisados os fragmentos cranianos e mandibulares de pequenos mamíferos encontrados em egagropilos de Tyto furcata coletados em sete localidades dos três estados do sul do país. Ao todo, foram contabilizados 2.382 indivíduos pertencentes a 29 táxons, incluindo cinco marsupiais (Didelphidae; 1,39% dos indivíduos), quatro quirópteros (Molossidae, Phyllostomidae e Vespertilionidae; 0,25%) e 20 roedores (Cricetidae, Muridae, Caviidae e Echimyidae; 98,36%). Os roedores Akodon spp., Oligoryzomys sp. e Mus musculus foram os táxons mais comuns. A amostra inclui espécies com poucos registros para o sul do Brasil, como Bibimys sp., Calomys tener e Wilfredomys oenax. A riqueza de pequenos mamíferos obtida nessas amostras corrobora a utilidade e importância da análise de egagropilos de aves de rapina. Ainda assim, são necessários estudos mais detalhados sobre a morfologia e identificação das espécies, como de Akodon e Oligoryzomys, considerando-se a natureza fragmentária do material nos egagropilos.

Tyto furcata(Tytonidae: Strigiformes) pellets: tools to access the richness of small mammals of a poorly known Caatinga area in northeast Brazil

AbstractOwls are efficient predators and are widely distributed around the globe. Remains of undigested prey is regurgitated by these birds in the form of pellets, and these are a valuable source of information about prey communities and the diet of owls. In this study, the composition of mammals present in the diet of owls that inhabit different caves was evaluated through the analysis of their pellets. We found 373 pellets from seven caves, and small mammals composed at least 80% of the diet of these birds in all caves. The mammal composition found in the pellets showed a richness of 26 distinct taxa including 12 rodents, three marsupials and 11 bats. In this work, we highlight the richness of small mammals in a poorly known Caatinga area. We also highlight the importance of morphology and taxonomy in supporting this kind of research, which relies upon vertebrate parts as its source of information for identification. Finally, we reiterate the efficiency of the study of owl pellets as a rapid approach for assessing local mammal richness and as a complementary method in studies of diversity and conservation.

Effect of environmental factors on the abundance variations of two native rodents in agricultural systems of Buenos Aires, Argentina

AbstractOur aim was to assess the effect of environmental factors on short temporal abundance variations of the two most abundant native rodents of agricultural agroecosystems, Akodon azarae and Calomys laucha. We conducted a 3‐year longitudinal sampling of rodents, and recorded meteorological data such as temperature and precipitation, predation rate by Leopardus geoffroyi, Tyto furcata and Athene cunicularia, vegetation cover and height, characteristics of cropfields and their borders. The effect of these factors on rodent abundance was evaluated through generalized linear mixed models. Abundance variations of both rodent species were explained by characteristics of both cropfields and their borders. At the studied temporal scale, meteorological variables did not have a direct effect on abundance variations, but probably influenced through vegetation characteristics and were expressed in seasonal variations. For A. azarae there was also an effect of predation by L. geoffroyi (positive) and T. furcata (negative), while predation by A. cunicularia did not contribute to explain abundance variations of any species.

Spatial, road geometric and biotic factors associated with Barn Owl mortality along an interstate highway

Highway programmes typically focus on reducing vehicle collisions with large mammals because of economic or safety reasons, while overlooking the millions of birds that die annually from traffic. We studied wildlife–vehicle collisions along an interstate highway in southern Idaho, USA, with among the highest reported rates of American Barn Owl Tyto furcata road mortality. Carcass data from systematic and ad hoc surveys conducted in 2004–2006 and 2013–2015 were used to explore the extent to which spatial, road geometric and biotic factors explained Barn Owl–vehicle collisions. Barn Owls outnumbered all other identified vertebrate species of roadkill and represented > 25% of individuals and 73.6% of road‐killed birds. At a 1‐km highway segment scale, the number of dead Barn Owls decreased with increasing numbers of human structures, cumulative length of secondary roads near the highway and width of the highway median. The number of dead Barn Owls increased with higher commercial average annual daily traffic (CAADT), small mammal abundance index and grass rather than shrubs in the roadside verge. The small mammal abundance index was also greater in roadsides with grass vs. mixed shrubs, suggesting that Barn Owls may be attracted to grassy portions of the highway with more abundant small mammals for hunting prey. When assessed at a 3‐km highway segment scale, the number of dead Barn Owls again increased, with higher CAADT as well as with greater numbers of dairy farms. At a 5‐km scale, the number of dead Barn Owls increased with a greater percentage of cropland near the highway. Although human conversion of the environment from natural shrub‐steppe to irrigated agriculture in this region of Idaho has probably enhanced habitat for Barns Owls, it simultaneously has increased risk for owl–vehicle collisions where an interstate highway traverses the altered landscape. We review some approaches for highway mitigation and suggest that reducing wildlife–vehicle collisions involving Barn Owls may contribute to the persistence of this species.

The Rocky Mountains as a dispersal barrier between barn owl (Tyto alba) populations in North America

AbstractAimGeological barriers within a species range play a key role in shaping patterns of genetic variation by restricting gene flow. Mountain ranges are particularly imposing barriers responsible for creating genetic differentiation across multiple taxa, from small amphibians to large mammals and birds. Here, we examined the population structure of North American barn owls (Tyto alba) and investigated whether the Rocky Mountains influence gene flow and dispersal at the continental scale.LocationContinental North America.MethodsWe collected 292 museum samples covering the species range, genotyped them at 20 microsatellite markers and sequenced 410 bp of the mitochondrial gene ND6. Population and landscape genetics tools were used to study range‐wide patterns of structure and identify gene flow barriers. Ring recapture data were also analysed to investigate individual movement patterns and frequency of exchanges between both sides of the Rocky Mountains.ResultsWe found faint overall genetic structure, which is consistent with barn owl's high mobility across its continuous range. Nonetheless, we identified two distinct genetic groups on the western and eastern regions of the Rocky Mountains with a likely contact point through the narrow southern pass between them and the Sierra Madre Occidental in Mexico. Accordingly, most recaptured barn owls remain on the same side of the mountains. The Rockies appear to significantly isolate the populations in the west, which, as a consequence, display lower genetic diversity than their counterparts to the east.Main conclusionsThe Rocky Mountains appear to constrain barn owl dispersal and gene flow. Our study supports the hypothesis that regional landscape barriers can shape gene flow and population structure even in highly mobile organisms.

Comprehensive molecular phylogeny of barn owls and relatives (Family: Tytonidae), and their six major Pleistocene radiations

The owl family Tytonidae comprises two genera: Phodilus, limited to the forests of central Africa and South-East Asia, and the ubiquitous Tyto. The genus Tyto is majorly represented by the cosmopolitan Common Barn Owl group, with more than 30 subspecies worldwide. Discrete differences in body size and plumage colouration have led to the classification of this family into many species and subspecies, but the taxonomic status and phylogenetic relationships between taxa remain unclear, and in some groups controversial. Although several previous studies attempted to resolve this problem, they have been limited in their taxonomic and geographical coverage, or have relied on restricted molecular evidence and low sample sizes. Based on the most comprehensive sampling to date (16 out of 17 Tyto species, and one out of three Phodilus species), a multi-locus approach using seven mitochondrial and two nuclear markers, and taking advantage of field data and museum collections available worldwide, our main questions in this study were: (1) what are the phylogenetic relationships and classification status of the whole family; (2) when and where did the most important speciation events occur? We confirm that the Common Barn Owl, Tyto alba is divided into three main evolutionary units: the American Barn Owl, T. furcata; the Western Barn Owl, T. alba; and the Eastern Barn Owl, T. javanica, and suggest a Late Miocene (ca. 6 mya) Australasian and African origin of the group. Our results are supported by fossil age information, given that the most recent common ancestor between the Tytonidae genera Phodilus and Tyto was probably from the Oligocene (ca. 28 mya) of Australasia. We finally reveal six major Pleistocene radiations of Tyto, all resulting in wide-range distributions.

Response adaptation in the barn owl's auditory space map.

Response adaptation is the change of the firing rate of neurons induced by a preceding stimulus. It can be found in many sensory systems and throughout the auditory pathway. We investigated response adaptation in the external nucleus of the inferior colliculus (ICX) of barn owls ( Tyto furcata), a nocturnal bird of prey and specialist in sound localization. Individual neurons in the ICX represent locations in auditory space by maximally responding to combinations of interaural time and level differences (ITD and ILD). Neuronal responses were recorded extracellularly under ketamine-diazepam anesthesia. Response adaptation was observed in three double stimulation paradigms. In two paradigms, the same binaural parameters for both stimuli were chosen. A variation of the level of the second stimulus yielded a level increase sufficient to compensate for adaptation around 5 dB. Introducing a silent interstimulus interval (ISI) resulted in recovery from adaptation. The time course of recovery was followed by varying the ISI, and full recovery was found after an ISI of 50 ms. In a third paradigm, the ITD of the second stimulus was varied to investigate the representation of ITD under adaptive conditions. We found that adaptation led to an increased precision and improved selectivity while the best ITD was stable. These changes of representation remained for longer ISIs than were needed to recover from response adaptation at the best ITD. Stimuli with non-best ITDs could also induce similar adaptive effects if the neurons responded to these ITDs. NEW & NOTEWORTHY We demonstrate and characterize response adaptation in neurons of the auditory space map in the barn owl's midbrain with acoustic double-stimulation paradigms. An increase of the second level by 5 dB compensated for the observed adaptive effect. Recovery from adaptation was faster than in upstream nuclei of the auditory pathway. Our results also show that response adaptation might improve precision and selectivity in the representation of interaural time difference.

Development of ear asymmetry in the American barn owl (Tyto furcata pratincola)

Owls are known for their nocturnal hunting capability. Many owl species are able to localize prey in complete darkness just by hearing. Sound localization of strictly nocturnal owls is improved by asymmetrically arranged outer ears. According to Norberg (1977), who worked with adult owls, asymmetrical ears evolved at least four times independently among owls. What is unknown so far is how the ear asymmetry develops in the embryo. Here we examine the embryonic development of ear asymmetry in the American barn owl (Tyto furcata pratincola) in the frame of the 42 stages suggested by Köppl et al. (2005). In this species, the left ear opening in the skin is located higher than its counterpart on the right. Micro-CT scans show that in an anatomically defined coordinate system, the ear openings initially appear symmetrically as does the skull as well as the eyes, the nasal openings, the stapes and the squamosum. The ear openings are initially located ventrally in the skull. Soon after their appearance, the ear openings start to move dorso-occipitally. At the developmental stages 36–39, the left ear opening moves faster than the right one. In this way, an ear asymmetry develops within a few developmental stages. The skull and the other anatomical markers remain symmetrical. Thus, these data show that the soft tissue asymmetry in the barn owl develops already before hatching. It will be interesting to compare the time course described here with the time course of development in owl species with bony ear asymmetries.

Habitat use by barn owls across a rural to urban gradient and an assessment of stressors including, habitat loss, rodenticide exposure and road mortality

Urbanization and agricultural intensification resulting in habitat loss is having a profound negative effect on grassland and farmland birds worldwide. Barn owls (Tyto furcata), as a species, have been affected by this intensification. To evaluate how urbanization and agricultural intensification affects barn owls we sought to address: 1) how human land use influences barn owl hunting behavior and diet, and 2) do habitat and prey choice influence the likelihood of barn owls consuming anticoagulant rodenticide (AR) exposed prey. We radio tagged 11 owls across the rural-urban landscape gradient in the Lower Mainland, British Columbia, and collected sufficient location data on 10barn owls. We found that the 95% kernel home-ranges ranged from 1.0 to 28.5km2 (n=10) and were positively correlated with the proportion of urban land use within home-ranges. Barn owls across all landscapes selected roadside grass verges significantly more than other habitat types within home-ranges, which may reflect the loss of grassland associated agriculture in the region. The risk of consuming AR exposed prey was highest in roadside grass verges compared to other habitat types. However, the overall likelihood of consuming AR exposed prey significantly decreased when the proportion of grass patches within home-ranges increased, which suggests smaller linear grass sections are more likely to contain AR exposed small mammal prey. These results highlight the need to retain and enhance hunting habitat for barn owls during urban development and to mitigate the risk of barn owl road mortality along major highways.

Phylogeny, biogeography, and diversification of barn owls (Aves: Strigiformes)

The existence of substantial morphological variation has resulted in the description of numerous subspecies of the cosmopolitan barn owl, Tyto alba. However, preliminary studies have revealed a high degree of genetic variation between Old and New World barn owls, suggesting that the T. alba complex may consist of several species. We present a comprehensive study of its taxonomy and propose a spatiotemporal framework to explain the origin and patterns of dispersal and diversification within these cosmopolitan owls. We used a Bayesian relaxed molecular clock approach to assess the timing of diversification. To evaluate the biogeographical pattern, we considered dispersal in addition to temporal connectivity between areas. Finally, we used ecological niche modelling to evaluate their ecological niches. Our phylogenetic analyses suggest that barn owls of the Old and New World show a high degree of genetic divergence, and the barn owls of South and South-east Asia (Tyto alba stertens and Tyto alba javanica) cluster with the Australian barn owl Tyto delicatula. We propose to treat the T. alba complex as three species: T. alba (Africa, Europe), Tyto furcata (New World), and Tyto javanica (Australasia). The dating analyses indicate that the early divergence among the species of the T. alba complex took place in the Middle Miocene and we hypothesize that a common ancestor of the T. alba complex lived in Africa. A potential scenario suggests that T. alba dispersed to Europe and south-western Asia during the interglacial periods of the Miocene/Pliocene, and dispersed into the New World either via an eastern Asian route or a western north Atlantic one.

Muscular Arrangement and Muscle Attachment Sites in the Cervical Region of the American Barn Owl (Tyto furcata pratincola).

Owls have the largest head rotation capability amongst vertebrates. Anatomical knowledge of the cervical region is needed to understand the mechanics of these extreme head movements. While data on the morphology of the cervical vertebrae of the barn owl have been provided, this study is aimed to provide an extensive description of the muscle arrangement and the attachment sites of the muscles on the owl’s head-neck region. The major cervical muscles were identified by gross dissection of cadavers of the American barn owl (Tyto furcata pratincola), and their origin, courses, and insertion were traced. In the head-neck region nine superficial larger cervical muscles of the craniocervical, dorsal and ventral subsystems were selected for analysis, and the muscle attachment sites were illustrated in digital models of the skull and cervical vertebrae of the same species as well as visualised in a two-dimensional sketch. In addition, fibre orientation and lengths of the muscles and the nature (fleshy or tendinous) of the attachment sites were determined. Myological data from this study were combined with osteological data of the same species. This improved the anatomical description of the cervical region of this species. The myological description provided in this study is to our best knowledge the most detailed documentation of the cervical muscles in a strigiform species presented so far. Our results show useful information for researchers in the field of functional anatomy, biomechanical modelling and for evolutionary and comparative studies.

Barn Owl pellets (Aves: Tyto furcata) reveal a higher mammalian richness in the Restinga de Jurubatiba National Park, Southeastern Brazil

The northern coast of the state of Rio de Janeiro harbors the largest coastal sandy plains (restingas) of southeastern Brazil, severely threatened due to recent human occupation. In this context, mammal inventories becomes urgent to support biodiversity conservation and management policies. This paper aims to update the knowledge on the mammalian species richness of Restinga de Jurubatiba National Park by analyzing pellets of the Barn owl Tyto furcata. The analyses of 4745 mammalian bone fragments (1739 individuals) revealed the occurrence of 17 species belonging to the orders Rodentia (9 spp.), Didelphimorphia (2 spp.) and Chiroptera (6 spp.). The rodents Mus musculus and Cerradomys goytaca accounted for 77.2% of the total individuals preyed, suggesting that the Barn owl hunts in both disturbed and natural open shrub formations. A compilation of previous records, together with those provided in the present study, indicates the occurrence of 44 species of mammals in the Restinga de Jurubatiba National Park, of which six (13.6%) were exclusively detected in pellets. These new records include species adapted to open formations of the interior of Brazil that were not previously reported in restingas on the basis of voucher-specimens, such as the rodents Necromys lasiurus and Calomys tener, the latter being recorded for the first time in the littoral of Rio de Janeiro state. This study underscores the importance of owl pellet analysis as a complementary and indispensable method for inventorying mammals. The results highlight the Restinga de Jurubatiba National Park as one of the restingas in Southeastern Brazil with the highest number of mammal species.

Gloger's rule in North American Barn Owls

ABSTRACT Studying the geographic variation of phenotypic traits can provide key information about the potential adaptive function of alternative phenotypes. Gloger's rule posits that animals should be dark- vs. light-colored in warm and humid vs. cold and dry habitats, respectively. The rule is based on the assumption that melanin pigments and/or dark coloration confer selective advantages in warm and humid regions. This rule may not apply, however, if genes for color are acting on other traits conferring fitness benefits in specific climes. Covariation between coloration and climate will therefore depend on the relative importance of coloration or melanin pigments and the genetically correlated physiological and behavioral processes that enable an animal to deal with climatic factors. The Barn Owl (Tyto alba) displays three melanin-based plumage traits, and we tested whether geographic variation in these traits at the scale of the North American continent supported Gloger's rule. An analysis of variation...

A case of partial leucism in the American Barn Owl (Tyto furcata) (Temminck, 1827), from Buenos Aires province, Argentina

The diverse colorations of a birds’ plumage are due to either structural colors or pigments that are synthesized in specialized cells or incorporated through the diet. However, plumage color aberrations can occur; several cases of albinism and leucism have been reported for different bird species and some examples are found in Strigiformes. A specimen of the American Barn Owl (Tyto furcata) with partial leucism was found in Carhué, Buenos Aires province. The plumage of its facial disc, tail and the ventral region was completely white; furthermore, the neck, primaries, and secondaries were pigmented although in a significantly lighter fashion than in normal-phenotype specimens. The rest of the body presented a normal pattern for the species.

The cervical spine of the American barn owl (Tyto furcata pratincola): I. Anatomy of the vertebrae and regionalization in their S-shaped arrangement.

BackgroundOwls possess an extraordinary neck and head mobility. To understand this mobility it is necessary to have an anatomical description of cervical vertebrae with an emphasis on those criteria that are relevant for head positioning. No functional description specific to owls is available.Methodology/Principal findingsX-ray films and micro-CT scans were recorded from American barn owls (Tyto furcata pratincola) and used to obtain three-dimensional head movements and three-dimensional models of the 14 cervical vertebrae (C1−C14). The diameter of the vertebral canal, the zygapophyseal protrusion, the distance between joint centers, and the pitching angle were quantified. Whereas the first two variables are purely osteological characteristics of single vertebrae, the latter two take into account interactions between vertebrae. These variables change in characteristic ways from cranial to caudal. The vertebral canal is wide in the cranial and caudal neck regions, but narrow in the middle, where both the zygapophyseal protrusion and the distance between joint centers are large. Pitching angles are more negative in the cranial and caudal neck regions than in the middle region. Cluster analysis suggested a complex regionalization. Whereas the borders (C1 and C13/C14) formed stable clusters, the other cervical vertebrae were sorted into 4 or 5 additional clusters. The borders of the clusters were influenced by the variables analyzed.Conclusions/SignificanceA statistical analysis was used to evaluate the regionalization of the cervical spine in the barn owl. While earlier measurements have shown that there appear to be three regions of flexibility of the neck, our indicators suggest 3–7 regions. These many regions allow a high degree of flexibility, potentially facilitating the large head turns that barn owls are able to make. The cervical vertebral series of other species should also be investigated using statistical criteria to further characterize morphology and the potential movements associated with it.

Absolute hearing thresholds and critical masking ratios in the European barn owl: a comparison with other owls

Absolute thresholds and critical masking ratios were determined behaviorally for the European barn owl (Tyto alba guttata). It shows an excellent sensitivity throughout its hearing range with a minimum threshold of −14.2 dB sound pressure level at 6.3 kHz, which is similar to the sensitivity found in the American barn owl (Tyto alba pratincola) and some other owls. Both the European and the American barn owl have a high upper-frequency limit of hearing exceeding that in other bird species. Critical masking ratios, that can provide an estimate for the frequency selectivity in the barn owl's hearing system, were determined with a noise of about 0 dB spectrum level. They increased from 19.1 dB at 2 kHz to 29.2 dB at 8 kHz at a rate of 5.1 dB per octave. The corresponding critical ratio bandwidths were 81, 218, 562 and 831 Hz for test-tone frequencies of 2, 4, 6.3 and 8 kHz, respectively. These values indicate, contrary to expectations based on the spatial representation of frequencies on the basilar papilla, increasing bandwidths of auditory filters in the region of the barn owl's auditory fovea. This increase, however, correlates with the increase in the bandwidths of tuning curves in the barn owl's auditory fovea.

Small Mammal Taphonomy: Intraspecific Bone Assemblage Comparison between South and North American Barn Owl,Tyto alba, Populations

Actualistic studies of small mammal taphonomy usually describe interspecific bone patterns of contemporary agents of bone deposition. These studies assume that each agent produces one specific bone pattern. Here we examine intraspecific bone patterning for bone assemblages produced by different barn owl,Tyto alba, populations. We analyse bone completeness and fragmentation patterns produced by this raptor between three Chilean and four North American localities.We found that the barn owl produces variable completeness and fragmentation patterns, suggesting that different raptor populations produce different bone assemblages. Our results suggest a different approach to the study of small mammal taphonomy, and that we should direct our efforts towards describing the variance associated with bone patterns. We should focus our attention on the processes that generate bone assemblages and their associated variability, emphasizing physiological and ecological causes.