Owl Pellets Research Articles

Holocene stability and recent dramatic changes in micromammalian communities of northwestern Patagonia

Micromammalian fossil sequences of two classical archaeological sites, Cueva Traful I (CTI) and Cueva Epullán Grande (LL), both in the province of Neuquén, northwestern Patagonia, Argentina, were studied. These sequences cover the entire Holocene, with assemblages mainly composed by rodent and marsupial remains accumulated by owls. Both sites are located near the ecotone fringes of the major vegetation units currently present in Patagonia: Forest-Patagonian steppe (CTI) and Patagonian steppe-Monte desert (LL). Comparisons between fossil and recent owl pellet samples in a regional approach indicated that micromammal communities remained stable over the major part of the last 10 ka, with some minor expansion of desert adapted taxa to the west since the middle Holocene, and a dramatic change in the assemblages during the last 100–150 years. Two alternative but not contradictory explanations can be presented to interpret the stable period. First, climate-environmental changes were not of sufficient magnitude to produce a clear reorganization of micromammal communities. Forest did not invade CTI surroundings, and Monte did not reach around LL. Second, the basic structure of northwestern Patagonian steppe micromammal communities was resilient to minor or moderate climate-environmental changes. The strong shift depicted in the studied sequences in very recent times (100–150 years) can be linked to human impact on the regional environment. This change involves a deep restructuration of small mammal communities ranging from virtual extirpations of some species to dramatic increments of opportunistic taxa. A century of sheep overgrazing, coupled with the introduction of exotic shrubs, was the main factor driving the configuration of present small mammal assemblages in northwestern Patagonia.

Range extension of Cavia tschudii Fitzinger, 1867 (Mammalia: Caviidae) and first record in Catamarca, northwestern Argentina

We report the first record of the genus Cavia and the species Cavia tschudii (Rodentia, Caviidae) in Catamarca province, northwestern Argentina, which represents a range extension of about 110 km southward for the species. The cranial and dental remains were recovered from an owl pellet sample found in eastern slopes of the Ambato range, at 1600 m elevation, in a highland grasslands-Chaco Serrano ecotone. According to the environmental continuity along the Ambato range, we suggest that the presence of C. tschudii in southernmost Catamarca and northern La Rioja province is likely.

Applying abundance/biomass comparisons on a small mammal assemblage from Barn owl (Tyto alba) pellets (Mount Soratte, central Italy): a cautionary note

Abundance/biomass comparisons (or ABC curves) allow to obtain information on the level of (anthropogenic or natural) disturbance that may sensu lato affect specific communities. In order to verify the general validity of the ABC curves, we applied these comparisons to a small mammal dataset obtained by a sample of Barn owl (Tyto alba) pellets collected in a nature reserve of central Italy (Monte Soratte). From 43 pellets, we obtained 111 individuals belonging to 11 shrews and rodents spe- cies. Microtus savii, Apodemus sylvaticus, and Apodemus flavicollis were the species most frequently preyed upon by owls. Indices such as absolute (and normalized) species richness and Shannon-Wiener diversity consistently showed higher values than those obtained in similar studies in central Italy, highlighting the complex structure of this assemblage occurring in a landscape with low anthropiza- tion. From ABC curves, abundance was slightly lower than biomass, even though differences between paired cumula- tive frequencies were not significant. This pattern suggests that the small mammal community in our study area features a low level of disturbance. Nevertheless, whereas in undisturbed assemblages a higher biomass in ABC curves indicate a higher frequency of larger species at higher trophic level, in small mammal assemblages such as those revealed by owl pellets, large-sized species are her- bivorous, synanthropic and typical of disturbed habitats. Accordingly, we caution that in disturbed habitats an increase of small mammals with high body mass may results in ABC curves with biomass higher than abundance. Our results therefore suggest that there might be relevant exceptions to the general patterns so far developed for ABC curves.

The use of Barn Owl Tyto alba pellets to assess population change in small mammals

Capsule Barn Owl pellets can be used to assess population changes in small mammals though with certain important reservations.Aims To conduct a large-scale, long-term analysis of pellets regurgitated by Barn Owls collected from a defined area of countryside within the UK south Midlands and compare results with those of other studies that have used pellet analysis to investigate the diet of Barn Owls.Methods Over 61 000 Barn Owl pellets collected over 20 years in the south Midlands of England were analyzed.Results We recorded a steady increase in the proportion of Field Voles in pellets over time at the expense of Wood Mice, and a positive relationship between various rainfall measures and the proportion of Field Voles in pellets. We suggest that the conclusions of previous studies of the diet of Barn Owls have often been predicated on inconsistent or untenable assumptions.Conclusion We challenge some of the premises on which Barn Owl pellet analyses have traditionally been based. We do not think that either a shortage of Field Voles in pellets, or of pellets containing the remains of more, smaller prey items, are indicative of foraging difficulty. Barn Owl pellets can be used to assess population changes in small mammals, so long as possible causes of bias, which we discuss, are acknowledged.

Small mammals (Didelphimorphia, Rodentia and Chiroptera) from Pampean Region, Argentina

We studied small mammal assemblages recovered from owl pellets collected at 11 locations throughout the Argentina’s Pampean Region. We identified 21 species, including two marsupials, one bat, and 18 rodents. From the analysis of this dataset, we could distinguish three main groups of small mammals that currently inhabit the Pampean Region: 1) a group of taxa related to Pampean agroecosystems (Calomys spp., Akodon azarae, and Oligoryzomys flavescens); 2) a group of Brazilian species (Cavia aperea, Oxymycterus rufus, Necromys lasiurus, Necromys obscurus, Holochilus brasiliensis, and Monodelphis dimidiata); and 3) a group including species from Patagonia, Espinal and Monte phytogeographic provinces (Microcavia australis, Oligoryzomys longicaudatus, Eligmodontia typus, Graomys griseoflavus, and Akodon molinae). In addition, we documented the first record of a species of the large-bodied group of Calomys in Buenos Aires province, expanding its distribution ca. 420 km southward.

Owl pellet dispersal by wind: Observations and experimentations

Pellets produced and accumulated by owls are subject to biological and atmospherical agents, and may be dispersed before their disaggregation. Observations on dispersion of Athene cunicularia and Tyto alba (Aves, Strigiformes) pellets were performed in a natural environment (Pampean region, Argentina) and in a wind tunnel. Ten burrows were visited, and the distances of pellets and isolated bones from the burrow entrance holes were registered. Intact pellets predominated between 0 and 1 m from the entrance holes. Partially disaggregated and disaggregated pellets showed similar distributions. In two burrows, the transport of new pellets and incorporated bones was observed during one month. Only in a few cases were the pellets mobilized and reoriented according to the predominant winds. Substrate features or the presence of vegetation favored fixing of their positions and prevented their mobility. Many of the pellets suffered total disaggregation or burial within the first 20 days to 1 month. Evaluated isolated bones showed a greater representation of mandibles and long bones, as well as skeletal elements with low susceptibility to wind transport. Pellets evaluated in the wind tunnel, at low wind speed (2.70 m/s), were mobilized very short distances. At high wind speed (4.70 m/s), transport distance was greater. The distances travelled could be related to their initial orientation at the beginning of the experiments, as those that were placed at 90° to the wind flow showed greater transport. The observations showed that there were some differences in mobility between pellets of A. cunicularia and T. alba, as A. cunicularia were more susceptible to transport at each wind speed, likely attributed to their smaller size. Wind increased bone dispersion from partially disaggregated pellets, causing the loss of some of them.

Expanding discourse repertoires with hybridity

In “Hybrid discourse practice and science learning” Kamberelis and Wehunt present a theoretically rich argument about the potential of hybrid discourses for science learning. These discourses draw from different forms of “talk, social practice, and material practices” to create interactions that are “intertextually complex” and “interactionally dynamic.” The hybrid discourse practices are described as involving the dynamic interplay of at least three key elements: “the lamination of multiple cultural frames, the shifting relations between people and their discourse, and the shifting power relations between and among people.” Each of these elements requires a respective unit of analysis and are often mutually reinforcing. The authors present a theoretically cogent argument for the study of hybrid discourse practices and identify the potential such discourses may have for science education. This theoretical development leads to an analysis of spoken and written discourse around a set of educational events concerning the investigation of owl pellets by two fifth grade students, their classmates, and teacher. Two discourse segments are presented and analyzed by the authors in detail. The first is a discourse analysis of the dissection of the owl pellet by two students, Kyle and Max. The second analysis examines the science report of these same two students. In this article, I pose a number of questions about the study with the hope that by doing so I expand the conversation around the insightful analysis presented.

Small mammal remains from Cueva Huenul 1, northern Patagonia, Argentina: Taphonomy and paleoenvironments since the Late Pleistocene

Small mammal samples from the archaeological sequence of Cueva Huenul 1 (CH1, 36°56′45″S, 69°47′32″W, Neuquén Province, Argentina) are described, and taphonomic and paleoenvironmental conditions assessed. This site is located near the steppe-monte ecotone in the northernmost Patagonia. Small mammal remains (NISP=1426, MNE=1409, MNI=87) were recovered from Late Pleistocene (13,800–11,800 14C BP), Early Holocene (9500 14C BP) and Late Holocene layers (1400 14C BP). Taphonomic analysis indicates that the CH1 assemblage is an archaeofaunistic owl pellet accumulation. It has a good post-depositional preservation since it was rapidly incorporated in the sedimentary matrix, although it previously experienced trampling action. From latest Pleistocene to Late Holocene, the assemblages are mainly composed by the sigmodontines Eligmodontia spp. and Phyllotis xanthopygus, and the caviomorphs Microcavia australis and Ctenomys sp., suggesting in overall terms a marked ecological stability. CHl is one of the few sites where the Pleistocene–Holocene transition is represented by faunal evidence. The latest Pleistocene sample spanning 13,800 and 11,800 14C BP indicate scrub steppe with substantial open ground and rocky exposition; one Early Holocene sample (9500 14C BP) suggests a more heterogeneous environment as evidenced by the first occurrence of Akodon iniscatus and Euneomys chinchilloides. In this context, CH1 assemblages do not reflect the small mammal community reworking that putatively accompanied the Pleistocene–Holocene transition.

Rodent-Prey Content in Long-Term Samples of Barn Owl (Tyto alba) Pellets from the Northwestern United States Reflects Local Agricultural Change

Rodent prey contained in two temporally distinct collections of Barn Owl (Tyto alba) pellets from the same roost in southeastern Washington state (USA) differ in terms of taxonomic abundances. Deer mice (Peromyscus maniculatus) dominate the fauna in the pellet sample deposited while much of the landscape was productive wheat field, and voles (Microtus spp.) are a distant second. The fauna in the pellet sample deposited after 20% of the surrounding landscape was placed in soil bank and converted to a grass non-producing field is dominated by voles with deer mice a close second. The coincident changes in local vegetation and in the rodent fauna are causally as well as temporally interrelated. Previous local studies have focused on the agricultural economics of coincident shifts in agricultural practices and rodent faunas. Results presented here indicate potential benefits to owl faunas of changes in agricultural practices and suggest that study of curated owl pellet faunas collected decades ago may reveal much about the long-term history of anthropogenic influences on rodent faunas.

Strontium isotopes and human mobility in prehistoric Denmark

The principles behind the strontium isotopic system are an important tool for archaeologists tracing human migration and patterns of movement in prehistory. However, there are several scientific challenges of analytical nature, as well as those which relate to unknown parameters inherent to the interpretation of such data. One prerequisite is the knowledge of the range of strontium isotopic ratios that best characterize the bioavailable fractions of a particular area of interest. The study reported here attempts to establish a baseline for strontium isotope signatures valuable for Denmark (excluding the island of Bornholm) and particularly for the use in archaeological investigations. We present strontium isotope ratios of bones and teeth from modern mice contained in owl pellets, of snail shells, and of archaeological fauna samples. We compare these ratios with median strontium isotope signatures characterizing human enamel populations from archaeological sites within Denmark. The fauna samples reported here range from 87Sr/86Sr = 0.70717 to 0.71185 with an average of 0.70919, and human enamel defines a range from 87Sr/86Sr = 0.7086 to 0.7110 with an average of 0.7098. In both datasets, we observe a small difference between the baseline values for the western (Jutland) and eastern (Funen, Zealand, and the southern islands) parts of Denmark. We therefore propose two slightly different baseline ranges with a partial overlap for the isotopic signatures of bioavailable strontium fractions within Denmark, namely a range of 87Sr/86Sr = 0.7078–0.7098 for the western area and a range of 87Sr/86Sr = 0.7089–0.7108 for the eastern parts.

Small mammals in the diet of barn owls, Tyto alba (Aves: Strigiformes) along the mid-Araguaia river in central Brazil

We collected and analyzed 286 Barn owl, Tyto alba (Scopoli, 1769), pellets from two nests in different environments along the mid-Araguaia River in central Brazil. Our analyses revealed that these owls feed mainly on small mammals, especially rodents. Owls from the riverbanks at Fazenda Santa Fé had a more diverse diet, preying mainly on rodents that typically inhabit riparian grasslands - Holochilus sciureus Wagner, 1842 - and forests - Hylaeamys megacephalus (Fischer, 1814) and Oecomys spp., which probably also occur in forest borders or clearings. On the other hand, owls from an agroecosystem at Fazenda Lago Verde preyed mostly on rodent species common in these agrarian fields, Calomys tocantinsi Bonvicino, Lima & Almeida, 2003. Additionally, we compared small mammal richness estimates based on the analysis of owl pellets with estimates from live-trapping in the same areas. Owl pellets revealed two rodent species undetected by live traps - Euryoryzomys sp. and Rattus rattus (Linnaeus, 1758) - and four rodent species were trapped, but not found in owl pellets - Oecomys roberti Thomas, 1904, Pseudoryzomys simplex (Winge, 1887), Rhipidomys ipukensis Rocha, B.M.A. Costa & L.P. Costa, 2011, and Makalata didelphoides (Desmarest, 1817). Traps yielded higher species richness, but these two methods complement each other for surveying small rodents.

Didelphimorphia and Rodentia (Mammalia) from Sierras de Tecka and surrounding areas, northwestern Chubut, Argentina

The small mammal fauna from northwestern Chubut Province (Argentina) is poorly known. We herein report small mammal assemblages from three new localities: Sierras de Tecka, an extra-Andean system elevated 900 m.a.sl.; Estancia La Mimosa on the Tecka river valley (at ca. 650 m.a.sl.); and Arroyo Pescado (at ca. 620 m.a.sl.) 40 km north of the other sites. Specimens were recovered from disaggregated owl pellets. Total species richness includes 16 native (13 sigmodontine and two caviomorph rodents, and one marsupial) and one introduced species. Estancia La Mimosa had the highest richness (n = 14), while Arroyo Pescado the lowest (n = 11). Four species were only recorded at Estancia La Mimosa (Akodon iniscatus, Calomys musculinus, Oligoryzomys longicaudatus and Mus musculus), two in Sierras de Tecka (Notiomys edwardsii and Microcavia australis) and one in Arroyo Pescado (Geoxus valdivianus). This work also adds new localities for Akodon iniscatus, Geoxus valdivianus, Lestodelphys halli and Notiomys edwardsii in western Chubut Province.

Mammalia, Rodentia, Sigmodontinae Wagner, 1843: new Locality records, filling gaps and geographic distribution maps from La Rioja province, northwestern Argentina

Sigmodontine rodents are well represented in northwestern Argentina, but information regarding their distribution in La Rioja is scarce. We add new information for seven species from seven localities in the Famatina range. These new records were obtained using both captures and owl pellet analysis. We cite the first record of Neotomys ebriosus in La Rioja. The collection locality is unusual for this species because of its low altitude and xeric conditions. Other notable results include the second record of Abrothrix andinus and of the genus Oligoryzomys at the province.

Detection of elements and radioactivity in pellets from long-eared owls (Asio otus) inhabiting the city of Belgrade (Serbia)

In this study, we analysed pellets from long-eared owls (Asio otus) collected from four localities in Belgrade (Serbia). The pellets contained the remains of prey, namely voles (Arvicola terrestris) and field mice (Apodemus agrarius). The concentrations of 14 elements (Ca, P, Mg, Na, K, Fe, Zn, Sr, Ba, Mn, Ti, Cu, Si, B) were evaluated in whole pellets and in samples containing only bone tissue, which were dissected from the whole pellet. The increased levels of certain elements, including Mn, Zn, Ba, Cu and radioactive 40K, indicate contamination of the soil by various sources, such as industrial plants and agricultural practices. From the results presented in this article, we suggest that the analysis of owl pellets may indicate the quality of the local environment.

Who ends up in the eagle owl pellets? A new method to assess whether water voles experience different predation risk

Using field methods that provide unbiased estimates of predation risk is challenging for medium and small sized prey. We conducted this study in a simple predator–prey system (Sleneset archipelago, northern Norway) where eagle owls Bubo bubo depend on water vole Arvicola amphibius and other predators are absent, and we tested the prediction that substandard individuals (i.e. with lower body condition) would be exposed to higher predation risk. In summer 2007–2009 we capture-mark-recaptured water voles with passive integrated transponder tags inserted by injection under the skin of the neck. We then searched and scanned the study area for passive transponders in eagle owl pellets and compared the body condition of predated and unknown fate individuals by means of logistic regression models. Substandard water voles had a higher probability of being predated by eagle owl, suggesting that voles in compromised condition were more vulnerable to predation. Therefore natural selection may be at work also through avian ambush predators.

Food habits of genetically identified pine marten (Martes martes) expanding in agricultural lowlands (NW Italy)

We assessed the diet of pine marten (Martes martes) expanding in the heavily human-altered agricultural plain of the River Po, northern Italy. Between February 2008 and November 2009, surveys were carried out twice a week during seasonal sampling sessions of three to four consecutive weeks. To distinguish the faecal samples from those of sympatric carnivores, a polymerase chain reaction-restriction fragment length polymorphism method was applied. The availability of small mammals was assessed by the analysis of 59 barn owl (Tyto alba) pellets. A total of 109 pine marten faeces were analysed. Its diet consisted of fruit, rodents, lagomorphs and birds. Seasonal variation occurred for fruit, which prevailed in summer, and rodents, which were more preyed upon in autumn. In winter, the diet of the pine marten was almost totally based on vertebrates, and lagomorphs were the main source of protein in summer. Use of small mammals differed significantly from their availability, voles, particularly bank vole Myodes glareolus, being preferred to mice (Apodemus sp.) and rats (Rattus sp.). Medium-size mammals formed about 18% of pine marten diet, a value generally reported for high-latitude habitats. In agricultural areas, the pine marten proved to be an opportunistic predator, able to face the reduced availability of small mammals by preying upon medium-size prey and fruit.

Absence of Differential Predation on Rats by Malaysian Barn Owls in Oil Palm Plantations

Barn Owls (Tyto alba javanica) have been widely introduced in Malaysian oil palm plantations to control rodent pests. However, their effectiveness in regulating rodent populations is unknown. We investigated whether Barn Owls selected prey with respect to size and sex classes based on data from 128 pellets of Barn Owls compared to 1292 live-trapped rats in an oil palm plantation in Malaysia. The birds mostly fed on Rattus rattus diardii, the most commonly trapped species. Body mass of prey consumed was predicted based on models derived from measurements from trapped rats. Sex of prey was determined by pelvic measurements with reference to those taken from specimens of known gender. There was no clear selection of prey by Barn Owls in relation to size or sex of prey, and no difference in the body mass of prey between the owls' breeding and nonbreeding seasons. The absence of differential predation in Barn Owls may partly explain the lack of clear evidence that they regulate rodent populations and thus act as successful biological control agents.

Environmental implications of micromammals accumulated close to the MIS 6 to MIS 5 transition at Pinnacle Point Cave 9 (Mossel Bay, Western Cape Province, South Africa)

PP9C is a coastal cave situated on the south coast, Pinnacle Point, Mossel Bay, and contains both archeological deposits, as well as fossil micromammal accumulations. Micromammals were analyzed from facies accumulated close to the transition from MIS (Marine Isotope Stage) 6 to MIS 5, between 130 ± 9 and 120 ± 7 ka. The taphonomy of the assemblages indicates that the majority of micromammals became associated with the site when they were deposited in Spotted eagle owl or Barn owl pellets. Modern comparative studies suggest that these two predator species select a very similar suit of prey species from the available micromammal population and the fossil micromammal assemblages they produce are comparable when tracing palaeoenvironmental change. The fossil assemblages suggest that the period during which the micromammals accumulated was warm and wet, and that the vegetation within the hunting range of the owls accumulating the micromammal assemblages was relatively dense. There is, however, some evidence that at the time of deposition of the older assemblages, conditions were colder, relatively grassier, and may reflect a rather more open environment. This difference may indicate the change from glacial MIS 6 to inter-glacial MIS 5e climatic conditions. These conclusions are supported both by the habitats and habits of the micromammal faunas, as well as by multivariate analysis. E. edwardii and A. namaquensis appear only in the earliest fossil assemblages at PP9C, and their general scarcity suggests that the rocky and open habitat preferred by these two species was never available on a wide scale at Pinnacle Point. The Pinnacle Point fossil sites indicate that the soricid, C. flavescens, was a common component of the local micromammal fauna and occurred in the area during some of MIS 6, and into MIS 5, suggesting that this species was able to adapt to glacial/interglacial cycles, and may utilize drier habitats than commonly reported in the literature. The fossil evidence indicates that C. cyanea, S. infinitesimus and Saccostomys campestris are relative latecomers to the Mossel Bay region. S. campestris appears only in PP9C in surface sediments, and confirms previous suggestions that the arrival of this species to the southern Cape occurred sometime within the Holocene.

Dense-sampling reveals a complex distributional pattern between the southernmost marsupials Lestodelphys and Thylamys in Patagonia, Argentina

Lestodelphys halli and Thylamys pallidior are southernmost representatives of the Order Didelphimorphia. We analyzed their southern distribution compiling locality records south of 42°S (Chubut and Santa Cruz provinces). We found 87 locality records for L. halli and 105 for T. pallidior. The distribution of L. halli reaches the central plateaus of Santa Cruz province but avoids the northeastern corner of the Deseado Massif. We report the southernmost locality for this species. The eastern and southern distribution of T. pallidior follows the courses of major rivers and coastal areas and it was not found at altitudes >700 m. Its southern distribution is more reduced than in L. halli, not reaching latitudes south of 46°S. We have recorded 20 localities of sympatry between both taxa, all of them from owl pellet samples; however, we have not found conclusive evidence of syntopy by trapping at any site. Both marsupials have widespread distribution in south-central Patagonia with two different histories: one, that of L. halli, related to Patagonian steppes and the other one linked to arid and semiarid lowlands represented by T. pallidior.

Mamíferos presentes en la dieta de la Lechuza de Campanario (Tyto alba) en Valdivia, provincia de Guayas, Ecuador

En el sector de Valdivia, cercano al Parque Nacional Machalilla, se encontraron en la pared de un risco, dos refugios de lechuza de campanario (Tyto alba) y al pie del risco y bajo los refugios se encontraron algunas egagrópilas y numerosos restos óseos de los animales que sirven de alimento a esta lechuza. Se identificaron los restos de 8 especies de mamíferos, de los cuales el 85% representan los roedores y el 12.6% los marsupiales.
 La principal especie de mamífero consumida por esta especie de lechuza en el sector de Valdivia, es la rata algodonera peruana (Sigmodon peruanus) representando el 40.2 % del total de mamíferos utilizados como alimento por la lechuza de campanario, seguido por la rata costera amarillenta (Aegialomys xantheolus) con el 33.3 %, luego por la rata espinosa del pacífico (Proechimys decumanus) con el 9.2%, la raposa chica de simons (Marmosa robinsoni simonsi) con el 8%, la raposa (Didelphis sp.) con el 4.6%, la rata transandina (Transandinomys sp.), con el 2.3 %, el conejo silvestre (Sylvilagus brasiliensis) y el murciélago frutero fraternal (Artibeus fraterculus) con el 1.1 % cada uno. La media calculada de individuos registrados en cada egagrópila fue de 2.2.