Strix Rufipes Research Articles

Food habits of Rufous-legged Owl in a protected area of south-central Chile affected by mixed wildfire

Abstract The diet of Rufous-legged Owl, Strix rufipes, a small raptor present in an Andean protected area, is described here. During the fall of 2017, 44 pellets were collected in the study area, being subsequently analyzed. The occurrence of small mammal prey items in pellets was compared with capture frequencies with live-trapping through Sherman traps. Regarding occurrence frequencies in the diet, arthropods were the most frequent (49.34%), followed by mammals (39.31%), birds (7.86%) and reptiles (3.37%). However, in terms of biomass, mammals had the highest biomass contribution. The observed frequency of consumed preys showed a random pattern, according to the captures of small mammals obtained with Sherman traps. The role of wildfire in the composition of prey in the observed trophic spectrum of these forest owls is also discussed.

New Nesting Records and Breeding Ecology Observations of Rufous-Legged Owls in the Mediterranean Temperate Forest of Central Chile

ABSTRACT The Rufous-legged Owl (Strix rufipes) is the southernmost Strix owl species and its breeding ecology remains little known. We report new observations on the species' breeding ecology, including clutch size, egg size, duration of the incubation and nestling periods, and nestling diet. We conducted our observations on nests found during the summers of 1999 through 2004 in a forestry landscape of central Chile, dominated by Monterey pine (Pinus radiata) plantations with intermixed fragments of native southern beech (Nothofagus) forests. Clutch size was two eggs (n = 2 nests), with one egg larger than the other (mean = 48.8 × 40.1 mm). The incubation period was 30 d and the nestling period 34 d. We analyzed 10 pellets from nestling owls and identified 45 prey items, mostly dominated by large beetles, grasshoppers, and rodents (native and exotic). This information, though based on a limited number of nests, provides baseline ecological data that can inform future studies.

Effect of Forest Cover on Raptor Abundance in Exotic Forest Plantations in Chile

Habitat specialists, such as forest raptors, are generally more likely to suffer from the impacts of large-scale forestry. One of the most characteristic and controversial aspects of many industrial plantation systems is the use of clearcutting as a harvesting method, which generates a mosaic of highly contrasting land cover types, such as wooded areas adjacent to zones practically devoid of vegetation. We explored the effect of forest cover on the abundance of habitat-generalist and forest-specialist raptors in South-central Chile. During the 2016 to 2018 breeding seasons, we conducted 584 playback surveys at 149 sampling points centred on 3×3km plots within 9×9km squares. The Rufous-legged Owl Strix rufipes, a forest specialist, showed a positive relationship with forest cover at the local scale. However, we found no significant relationships for other forest specialists in this study. Most habitat-generalist species showed a negative or non-linear relationship with forest cover, with greater species abundances observed in landscapes with intermediate levels of forest and open areas. Interestingly, the models with the highest statistical support included total forest cover (native forest + plantations) as a predictor, suggesting that the habitat-generalist species did not significantly discriminate between natural and artificial forests. Our results show that both generalist and forest-specialist raptors can use landscapes dominated by exotic plantations in South-central Chile.—Santander, F., Alvarado O., S. & Estades, C.F. (2021). Effect of forest cover on raptor abundance in exotic forest plantations in Chile. Ardeola, 68: 391-408.

Behavioral Responses of Wild Rodents to Owl Calls in an Austral Temperate Forest.

Simple SummaryGrowing human populations are challenging scientists to find effective ways to control and mitigate human–wildlife conflict while preserving biodiversity. It has been reported that predator odor and calls can drive away rodents, but little is known about species-specific responses of prey. For these reasons, we compared the behavioral changes of common rodent species inhabiting the Chilean temperate forest (Abrothrix spp., the long-tailed pygmy rice rat Oligoryzomys longicaudatus and the black rat Rattus rattus) when exposed to two different native predator calls (the austral pygmy owl Glaucidium nana and the rufous-legged owl Strix rufipes) and a control (no predator calls). Our results showed that all rodent species modified their behavior in the presence of predator calls, but the effects were species dependent. These findings point to the need to carefully study target rodent species instead of applying a general control plan for all rodent species.Ecologically based rodent management strategies are arising as a sustainable approach to rodent control, allowing us to preserve biodiversity while safeguarding human economic activities. Despite predator signals being known to generally repel rodents, few field-based studies have compared the behavioral effects of several predators on different prey species, especially in Neotropical ecosystems. Here, we used camera traps to study the behavior of rodent species native to the Chilean temperate forest (Abrothrix spp., long-tailed pygmy rice rat Oligoryzomys longicaudatus) and an introduced rodent (black rat Rattus rattus). Using playbacks of raptor calls, we experimentally exposed rodents to three predation risk treatments: austral pygmy owl calls (Glaucidium nana), rufous-legged owl calls (Strix rufipes) and a control treatment (absence of owl calls). We evaluated the effects of the treatments on the time allocated to three behaviors: feeding time, locomotor activity and vigilance. Moonlight and vegetation cover were also considered in the analyses, as they can modify perceived predation risk. Results showed that predator calls and environmental factors modified prey behavior depending not only on the predator species, but also on the rodent species. Consequently, owl playbacks could be regarded as a promising rodent control tool, knowing that future studies would be critical to deeply understand differences between species in order to select the most effective predator cues.

BLOOD PARASITE INFECTIONS IN STRIGIFORMES AND PSITTACIFORMES SPECIES IN CAPTIVITY WITH A NEW RECORD OF POTENTIAL FATAL BLOOD PARASITE TRANSMISSION TO PARROTS

Although parrot species are infrequently infected by hemoparasites in the wild, some fatal infections have been reported in captive individuals. Conversely birds of prey are frequently infected by hemoparasites. In this study, 193 captive birds from Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) centers in Madrid, Spain, belonging to orders Psittaciformes, Accipitriformes, Strigiformes, and Falconiformes, were blood-sampled in search of parasite infections. Molecular and microscopic analyses were conducted to detect parasites of the following genera: Haemoproteus, Plasmodium, Leucocytozoon, Trypanosoma, Babesia, and Lankesterella. Infections by microfilariae and Coccidia were also searched in blood samples. Surprisingly, infections by Haemoproteus syrnii, a common parasite from owls, were detected in the cadavers of two species of parrots, Trichoglossus haematodus and Psittacula cyanocephala. The same haplotype was also detected in the cadavers of two owl species, Tyto alba and Strix rufipes. All these birds were housed and died in the same center. Infections by species of Plasmodium, Leucocytozoon, and Trypanosoma were also found in different species of raptors. Nocturnal raptors (Strigiformes) show significantly higher prevalence of infection by blood parasites than diurnal raptors (Falconiformes and Accipitriformes). In conclusion, a potential fatal transmission of Haemoproteus syrnii, from Strigiformes to Psittaciformes species, is reported and several infections by different blood parasites were detected in birds of prey. These results emphasize the importance of increasing prevention measures to avoid or reduce the transmission of blood parasites among birds from different species housed in these types of centers.

Centrorhynchus nahuelhuapensis n. sp. (Acanthocephala: Centrorhynchidae) from rufous-legged owl (Strix rufipes King) in Patagonia.

Centrorynchus nahuelhuapensis n. sp. is described from the intestine of Strix rufipes, the rufous-legged owl, in Patagonia, Argentina. This species is characterized by the presence of 31-33 hook rows with 16-17 hooks per row, distributed as follows: 5 true hooks, 4 transitional hooks with 4 alate processes, more evident in the first three, 7-8 spiniform hooks, and three cement glands. It differs from most members of the genus by having a filiform body, the arrangement and size of the hooks, the number of cement glands, and egg size. Part of the SSU and LSU genes were sequenced and compared to those in GenBank. Sequences are most similar to other species of Centrorhynchus, supporting their placement within this genus. We present the first molecular study for a species of Centrorhynchus from South America. Additionally, it is the second species of the genus described in Argentina, and the first species of a terrestrial acanthocephalan from a bird in Patagonia.

Effects of episodic bamboo mast seeding on top predators in the southern Andes

AbstractWoody bamboos that undergo masting on a cyclic basis constitute large‐scale endogenous disturbances in forests of America, Africa and Asia, driving long‐ and short‐term effects on community structure and dynamics. Among the transient effects of these nonequilibrial phenomena are rodent outbreaks whose potential bottom‐up consequences on top predators have never been explored. We investigated the effects of unpredictable rodent outbreaks on the assemblage of nocturnal raptors of the southern Andes after a large‐scale (>140 000 ha), spatially heterogeneous, Chusquea culeou masting event in north Argentine Patagonia. We compared owl numbers and behaviours between pre‐masting (2009) and post‐masting (2011) at subsidized (outbreaking rodents) and unsubsidized (normal rodents) contiguous sites. Both generalist (opportunistic forest resident) and rodent‐specialist (forest‐facultative) owls were monitored, with emphasis on the resident territorial rufous‐legged owl (Strix rufipes). The resident owls behaved as predicted, perceiving the rodent increases soon and gathering at subsidized sites, while apparently relaxing territoriality. Contrary to our predictions, later at the rodent outbreak phase, resident territorial owls turned inconspicuous, coinciding – causally or not – with an irruption of forest‐facultative barn owls (Tyto alba tuidara), and influx of some open country short‐eared owls (Asio flammeus suinda, some of which took a chance to breed in the woods). Considering the whole rodent outbreak period, besides significant changes in owls’ numbers, we recorded a notable adjustment in owls’ foraging modes in response to food surplus (consuming prey heads only), and null interference behaviours among all observed species. This study provides a first quantitative assessment of the effects of bamboo episodic masting on top carnivores globally, and contributes novel data on the indirect effects of these events in forests of South America.

Detection and vocalisations of three owl species (Strigiformes) in temperate rainforests of southern Chile

ABSTRACTConspecific broadcasts are effective to increase detection of owls. To determine the most appropriate time of the year to survey owls, we played conspecific owl vocalisations monthly in a temperate rainforest of southern Chile. From 12 broadcast points surveyed we recorded detections of Glaucidium nana, Strix rufipes and Tyto alba. Glaucidium nana presented a bimodal detection curve throughout the year and we recorded two regular vocalisations in response to broadcasting: contact pair call and territorial call. Strix rufipes and T. alba both showed a peak of detection between February and May. Strix rufipes presented three vocalisations: territorial call, contact pair call and female contact pair call while T. alba uttered two vocalisations: territorial call and twittering call. We recommend surveys during the end of the breeding season (austral summer–autumn) when detection is higher in most owls. Surveys should also take into consideration the variability of the vocalisations and include covariates in monitoring to evaluate occupancy/detection models.

Observations of a Tree-cavity Nest of the Rufous-legged Owl and Predation of an Owl Nestling by a Chimango Caracara in Andean Temperate Forests

Observations of a Tree-cavity Nest of the Rufous-legged Owl and Predation of an Owl Nestling by a Chimango Caracara in Andean Temperate Forests

Beyond species richness: an empirical test of top predators as surrogates for functional diversity and endemism

Using surrogate species to monitor the status of target biodiversity in areas undergoing exceptional habitat loss requires extending the traditional assessment of surrogates for taxonomic diversity to validating surrogates for functional diversity. This validation will be critical to inform about broader ecosystem processes and stability. We compared the surrogacy reliability of the habitat‐specialist Rufous‐legged Owl (Strix rufipes) and the habitat‐generalist Austral Pygmy‐Owl (Glaucidium nana), and we examined potential underlying mechanisms for surrogacy relationships in Andean temperate forests, a global biodiversity hotspot in southern Chile. During 2011–2013, we conducted 1,145 owl surveys, 505 vegetation surveys, and 505 avian point‐transect surveys across 101 sites comprising a range of conditions from degraded forest habitat to structurally complex old‐growth forest stands. The habitat‐specialistS. rufipeswas a reliable surrogate for all avian biodiversity measures, including avian endemism and functional diversity measures (degree of community specialization and density of large‐tree users, understory users, and cavity‐nesters). On the contrary, the habitat‐generalistG. nanadid not function as a surrogate. With increasing occurrence ofS. rufipes, the density of target specialized biodiversity (species, guilds, and communities) increased nonlinearly and peaked at the least degraded sites. This specialist aggregation might be driven by stand structural complexity available in older, more stable, forests. These results suggest that management actions tailored to promote occurrence of habitat‐specialist owls, such as theS. rufipes, may result in enhanced density of endemic species, specialized communities, and likely ecosystem stability.

Highway Network Expansion in Andean Patagonia: a Warning Notice From Rufous-legged Owls

As part of the economic and population growth of Patagonia, several dust/gravel roads crossing well preserved Andean forests are being converted into paved highways. The potential effects of these changes on forest wildlife have been little studied. The Rufous-legged Owl (Strix rufipes) was dominant among road-killed birds in our survey of a 27-km section of highway running through forests of Nahuel Huapi National Park, in Argentine Patagonia. Fatalities were not evenly distributed along the surveyed length of the road, so we investigated whether landscape features, roadside slope on both sides of the highway, demography, and/or season explained the aggregation pattern. Patterns of distribution of the road-killed owls were explained by owl abundance and age-class, time of year, and hour, and were weakly related to canopy closure; roadside slope on both sides was unrelated to abundance of fatalities. Traffic-related deaths were likely the primary cause of non-natural mortality of Rufous-legged Owls (especially for young individuals) in the study area. Examination of carcasses indicated that most owls were killed by turbulence behind large vehicles and that deaths occurred early in the night. Semitrailer trucks capable of carrying large loads, which peak in numbers between dusk and midnight, likely caused most fatalities. A way to reduce owl mortality could be to schedule truck traffic outside the hours when owls are most active at hunting around paved roads crossing natural forests, at least during late winter and spring seasons. Because transportation networks encourage future development that will affect the environment in a variety of ways, it is critical to retain roadless and near-roadless (i.e., having only dirt or gravel roads with slow-moving traffic) portions of the southern Andes to preserve their natural landscapes.

Occurrence patterns and niche relationships of sympatric owls in South American temperate forests: A multi-scale approach

Habitat-specialists have narrower niches, but achieve higher or similar peak performance (e.g. occurrence probability, ψ) than habitat-generalists along resource gradients that may be selected from the stand- to landscape-levels. Understanding the relationship between niche width and ψ of forest owls will facilitate the development of appropriate management recommendations for their conservation. We assessed ψ of the threatened habitat-specialist rufous-legged owls (Strix rufipes) and habitat-generalist austral pygmy-owls (Glaucidium nana) across three spatial scales, and tested whether they differed in resource utilization and peak ψ in temperate forests of southern Chile. We conducted 1145 broadcast surveys at 101 sites and used multi-season occupancy models, accounting for imperfect detection, to estimate ψ. For S. rufipes, ψ ranged between 0.05 and 1 across sites, and was positively associated with the variability (standard deviation, SD) in diameter at breast height (DBH) of trees and bamboo understory density. For G. nana, ψ ranged between 0.67 and 0.98, and was positively associated with forest-patch shape index (irregularity and edge effects) and forest cover at 180ha, although the parameter estimates were imprecise. Relative to G. nana, S. rufipes had lower total resource utilization due to lower ψ over gradients of all covariates, but achieved similar peak ψ for resources related with stand-level forest complexity and forest stability at the landscape scale. Occurrence of habitat-specialist owls will be promoted if multi-aged stands with a variety of tree sizes (SD of DBH=19.9±9cm), including large old-growth trees, with relatively high bamboo cover (34.2±26.6%), are retained. Landscapes with forest cover >63.5% would also favor occurrence by habitat-specialist owls.

Factors associated with the detectability of owls in South American temperate forests: Implications for nocturnal raptor monitoring

Owls occur at relatively low densities and are cryptic; thus, monitoring programs that estimate variation in detectability will improve inferences about their presence. We investigated temporal and abiotic sources of variation associated with detection probabilities of rufous-legged owls (Strix rufipes), a threatened forest specialist, and austral pygmy-owls (Glaucidium nana), a habitat generalist, in temperate forests of southern Chile. We also assessed whether detection of 1 species was related to the detection of the other species. During 2011–2013, we conducted 1,145 broadcast surveys at 101 sampling units established along an elevational gradient located inside and outside protected areas. We used a multi-season occupancy framework for modeling occupancy (ψ) and detection (p), and ranked models using an information-theoretic approach. We recorded 292 detections of rufous-legged owls and 334 detections of austral pygmy-owls. Occupancy was positively associated with elevation for rufous-legged owls but constant (i.e., did not vary with covariates) for pygmy-owls. Detectability for both owls increased with greater moonlight and decreased with environmental noise, and for pygmy-owls greater wind speed decreased detectability. The probability of detecting pygmy-owls increased nonlinearly with number of days since the start of surveys and peaked during the latest surveys of the season (23 Jan–7 Feb). Detection of both species was positively correlated with the detection of the other species. We suggest both species should be surveyed simultaneously for a minimum of 3–4 times during a season, survey stations should be located away from noise, and observers should record the moon phase and weather conditions for each survey. © 2014 The Wildlife Society.

Rufous-legged Owl (Strix rufipes) and Austral Pygmy Owl (Glaucidium nanum) stand use in a gradient of disrupted and old growth Andean temperate forests, Chile

We studied how human induced structural changes in forests affect stand use of the Rufous-legged Owl (forest-specialist) and the Austral Pygmy Owl (forest-facultative), in a gradient from lowland disrupted forests to protected Andean forests in Chile. We also tested if the calls of one species influenced the calling behaviour of the other. We detected a total of 34 Rufous-legged Owls and 21 Austral Pygmy Owls during the four seasons. Rufous-legged Owls were found principally in old growth Araucaria-Nothofagus stands (32.4%), and Pygmy Owls in old growth evergreen stands (52.4%). For both species there was a seasonal effect on call response, with a drop in responses in autumn and winter. Our models suggested that Rufous-legged Owls inhabit a more specific range of habitat characteristics than Pygmy Owls. The former selected stands with tall trees, relatively low tree density, and high bamboo density. Pygmy Owls selected stands with tall trees and relatively high tree density. There was no evidence that either species influenced the calling behaviour of the other, suggesting no negative association between use of a territory by the two species. Our results emphasize the importance of structural components of old growth forests for both species, but also the relevance of stands surrounding protected areas. Estudiamos cómo los cambios estructurales en el bosque, inducidos por el ser humano, afectan el uso de hábitat del concón (especialista de bosque) y del chuncho (facultativo de bosque), en un gradiente desde bosques perturbados en zonas bajas hasta bosques andinos protegidos de Chile. También evaluamos si los llamados de una especie influencian el comportamiento de vocalización de la otra. Detectamos un total de 34 concones y 21 chunchos para las cuatro estaciones del año. Los concones fueron registrados principalmente en bosques antiguos de Araucaria-Nothofagus (32.4%), y los chunchos en bosques antiguos siempre-verdes (52.4%). Para ambas especies hubo una disminución de la actividad en otoño e invierno. Nuestros modelos sugirieron que el concón tiene requerimientos de hábitat más específicos que el chuncho. El concón seleccionó bosques con árboles altos y en baja densidad relativa, y una alta densidad de quila. Por su parte, el chuncho seleccionó bosques con árboles altos y en alta densidad relativa. No hubo evidencia de que los llamados de una especie afectaran las respuestas de la otra, sugiriendo que no existe una asociación negativa en el uso de un mismo territorio por ellas. Los resultados enfatizan la importancia de los elementos estructurales de los bosques antiguos para ambas especies pero, a su vez, la relevancia de los bosques periféricos a áreas protegidas.

Multi-ethnic bird guide of the sub-Antarctic forests of South America

The subantarctic forests of South America are the world’s southernmost forested ecosystems. The birds have sung in these austral forests for millions of years; the Yahgan and Mapuche peoples have handed down their bird stories from generation to generation for hundreds of years. In Multi-ethnic Bird Guide of the Subantarctic Forests of South America, Ricardo Rozzi and his collaborators present a unique combination of bird guide and cultural ethnography. The book includes entries on fifty bird species of southern Chile and Argentina, among them the Magellanic Woodpecker, Rufous-Legged Owl, Ringed Kingfisher, Buff-Necked Ibis, Giant Hummingbird, and Andean Condor. Each bird is named in Yahgan, Mapudungun, Spanish, English, and scientific nomenclature, followed by a description, full color photographs, the bird’s distribution map, habitat and lifestyle, and its history in the region. Each entry is augmented further with indigenous accounts of the bird in history and folklore. “Highly original in its approach of combining information on natural history and biodiversity with information on the region’s human cultural and linguistic diversity.”—Chris Elphick, coauthor of The Sibley Guide to Bird Life and Behavior

Diet of the Rufous-legged Owl (Strix rufipes) at the Northern Limit of its Distribution in Chile

We quantified the diet of the Rufous-legged Owl (Strix rufipes) by analysing 63 pellets collected during 2003 and 2005 in a small coastal sclerophyllous forest stand at the northern limit of its distribution in Chile (31–32° S). The diet comprised small mammals (frequency = 57.8%, biomass = 99.3%), crustaceans (frequency = 1.7%, biomass = 0.1%), and insects (frequency = 40.5%, biomass = 0.6%). We identified at least 10 small mammal species in these pellets of which Bennett's chinchilla rat (Abrocoma bennetti; frequency = 12.4%) and long-tailed pygmy rice rat (Oligoryzomys longicaudatus; frequency = 7.4%) were the most frequently occurring mammalian prey remains. Terrestrial small mammals accounted for 21.5% by frequency of all individuals and 49.1% of the total biomass; scansorial/arboreal small mammals accounted for only 13.2% of all individual prey and 17.2% of total biomass.

Diet of the Rufous‐legged Owl (Strix rufipes, Strigiformes) in an Andean Nothofagus–Araucaria forest, southern Chile

We quantified the diet of the Rufous‐legged Owl (Strix rufipes) by analyzing 40 pellets collected during the austral autumn 2001, 2003 and 2004 in an Andean Nothofagus–Araucaria forest, southern Chile. Five small mammal species, two passerine birds, insects of two orders, four scorpions and a snail were identified in the pellets. Although insects were the most numerous prey (72.4% of all prey items), small mammals constituted most of the biomass (89.2%). The arboreal small mammals Dromiciops gliroides and Irenomys tarsalis were the most frequently consumed prey (10.4% and 6.3% of all individuals; 37.7% and 28% of total biomass, respectively). The scansorial Oligoryzomys longicaudatus accounted for almost 3% of all items and 7% of total biomass. Terrestrial small mammals accounted for only 1% of all individual prey and 3.6% of total biomass. Our results were similar to those reported for Rufous‐legged Owls inhabiting Valdivian rainforests, which suggest that this owl species is conservative in its food habits throughout the southern temperate forest, hunting mostly arboreal and scansorial small mammals. Resumen La dieta del concón (Strix rufipes) fue cuantificada sobre la base de 40 regurgitados colectados durante los otoños de 2001, 2003 y 2004 en un bosque andino de Nothofagus–Araucaria en el sur de Chile. Cinco especies de micromamíferos, dos aves paserinas, dos órdenes de insectos, cuatro escorpiones y un caracol fueron identificados en los regurgitados. Aunque los insectos fueron las presas más numerosas (72.4% de todas las presas individuales), los micromamíferos constituyeron la mayor parte de la biomasa (89.2%). Los micromamíferos arborícolas Dromiciops gliroides e Irenomys tarsalis fueron las presas más consumidas (10.4% y 6.3% de todas las presas; 37.7% y 28% de la biomasa total, respectivamente). Oligoryzomys longicaudatus, un roedor trepador, constituyó casi el 3% de todas las presas y 7% de la biomasa total. Los micromamíferos terrestres alcanzaron sólo el 1% de todas las presas y 3.6% de la biomasa total. Nuestros resultados fueron similares con aquellos documentados para concones que habitan el bosque Valdiviano del sur de Chile, sugiriendo que la especie es conservadora en sus hábitos tróficos a lo largo del bosque templado austral, cazando principalmente micromamíferos arborícolas y trepadores.

Habitat, relative abundance, and diet of rufous-legged owls (Strix rufipesKing) in temperate forest remnants of southern Chile

Abstract:We report the first quantitative information on the relative abundance of rufous-legged owls (Strix rufipes King) in six secondary and five old-growth rainforest remnants of southern Chile...

A New Species of Owl from the Pleistocene of Rancho La Brea, California

Upon a recent examination of the owl bones in the Los Angeles Museum collections from Rancho La Brea, certain unusual specimens came to the writer's attention. All are of a size easily to be confused with slender bones of Bubo virginianus and, in fact, were found among the elements which had been so assigned in the first general survey of the collection. The specimens may be separated from those of the Horned Owl, however, on the basis of the same characters which distinguish members of the genus Strix from Bubo. Comparisons were made also with Scotiaptex, Nyctea and Asio of North America and Pulsatrix, Rhinoptynx and Ciccaba from the south.' The fossil, however, most closely accords with Strix, though it is larger than either North American species of that genus. Furthermore, from such information as can be gained from the literature on the subject, and from Dr. Wetmore who has kindly measured Strix rufipes for the writer, it is apparently larger than any other species of that genus or of the genus Ciccaba, which resembles Strix in many characters. Nine of the principal skeletal elements have been identified and are fairly well represented, the number of available specimens totalling fifty-six. With regard to the pelvis, the variation within the genus Strix and the similarities between Strix and Bubo in general characters make difficult a separation of the pelves of these two genera; this fact coupled with the somewhat fragmentary condition of the La Brea specimens has made it impossible to identify this element of the fossil form. This is the case also with the ulna. No furcula, cranium, or lower mandible of the fossil species is available; these elements are but poorly represented and the few specimens of large owl which occur in the collection appear to belong to Bubo. No attempt has been made to identify the radius, vertebrae, ribs or phalanges. In describing the species, a tarsometatarsus has been selected as the type because of completeness of the specimen and the diagnostic features of the element. The other available elements are discussed as referred material. The photographs of the type specimen were made by Mr. H. Wm. Menke.