Tyto Furcata Research Articles

Monitoring the feeding and parental care behavior of a pair of free-living owls (Tyto furcata) in the nest during the reproductive period in Rio de Janeiro, Brazil.

The American Barn Owl (Tyto furcata) lives in urban, periurban and wild environments and feeds mainly on small rodents, meaning it has great importance in the biological control of pests. The aim of this work was to describe the reproductive, parental and eating habits of a pair of American barn owls naturally living outside a residence in the urban area of the municipality of Campos dos Goytacazes, Rio de Janeiro state, Brazil. A wood box was installed on an outside wall of the home, monitored by a video camera. A spreadsheet was created to keep track of the observations recorded. The female laid four eggs, and after an incubation period of 30-32 days all the eggs hatched, but only two chicks survived after cannibalism among the chicks. Initially, the male provided the food to the chicks and the female remained in the nest caring for the brood. After approximately a month, the female also began to leave the nest and return with prey, which was offered to the chicks, with the male also continuing this behavior. The chicks left the nest in September, 2017. The data obtained show the existence of cooperation and division of tasks between male and female owls during the reproductive period.

Trophic ecology of Geranoaetus polyosoma and Tyto furcata in an Atacama Desert agricultural landscape

Trophic ecology of Geranoaetus polyosoma and Tyto furcata in an Atacama Desert agricultural landscape

Owl-Neck-Spine-Inspired, Additively Manufactured, Joint Assemblies with Shape Memory Alloy Wire Actuators.

Nature provides a considerable number of good examples for simple and very efficient joint assemblies. One example is the enormously flexible cervical spine of American barn owls, which consists of 14 cervical vertebrae. Each pair of vertebrae produces a comparatively small individual movement in order to provide a large overall movement of the entire cervical spine. The biomimetic replication of such joints is difficult due to the delicate and geometric unrestricted joint shapes as well as the muscles that have to be mimicked. Using X-ray as well as micro-computed tomography images and with the utilisation of additive manufacturing, it was possible to produce the owl neck vertebrae in scaled-up form, to analyse them and then to transfer them into technically usable joint assemblies. The muscle substitution of these joints was realised by smart materials actuators in the form of shape memory alloy wire actuators. This actuator technology is outstanding for its muscle-like movement and for its high-energy density. The disadvantage of this wire actuator technology is the low rate of contraction, which means that a large length of wire has to be installed to generate adequate movement. For this reason, the actuator wires were integrated into additively manufactured carrier components to mimic biological joints. This resulted in joint designs that compensate for the disadvantages of the small contraction of the actuators by intelligently installing large wire lengths on comparatively small installation spaces, while also providing a sufficient force output. With the help of a test rig, the developed technical joint variants are examined and evaluated. This demonstrated the technical applicability of this biomimetic joints.

Muscle architecture of the hindlimb of Tyto furcata (Aves Strigiformes): Highlights in owl morphology.

The American barn owl is a nocturnal bird of prey in which hind limb movements are a key factor in obtaining food; however, the architectural properties of its hind limb muscles have not been studied. This study sought to identify functional trends in the Tyto furcata hindlimb muscles by studying muscular architecture. The architectural parameters of the selected hip, knee, ankle, and digit muscles were studied in three specimens of the Tyto furcata and joint muscular proportions with an additional dataset were calculated. Previously published information on Asio otus was used for comparison. The flexor muscles of the digits had the highest muscle mass. Regarding architectural parameters, the main flexor of the digits (flexor digitorum longus) and the muscles that extend the knee and ankle joints (femorotibialis and gastrocnemius) showed a high physiological cross-sectional area (PCSA) and short fibers, allowing powerful digit flexion and knee and ankle extension. These mentioned features are in accordance with hunting behavior, in which prey capture is not only closely linked to the flexion of the digits but also to the movements of the ankle. During hunting, the distal hind limb is flexed and then fully extended at the moment of contact with the prey, whereas the digits are close to grasping the prey. The hip muscles showed a predominance of extensors over flexors, which were more massive, with parallel fibers and without tendons or short fibers. These features lead to a higher capacity to generate velocity to the detriment of forces, as indicated by the high values of the architectural index, their relatively low PCSA, and short or intermediate fiber length, which enhance the control of the joint positions and muscle length. Compared to Asio otus, Tyto furcata showed longer fibers; however, the relationship between fiber length and PCSA was similar for both species.

Diet Composition of a Pair of Tyto furcata pratincola (American Barn Owl) in an Urban Park and Natural Area Fragment in South Florida

Tyto furcata pratincola (American Barn Owl) is a widespread bird of prey with great adaptability that can be found in partially urbanized areas. We examined the prey composition of a pair of American Barn Owls through dissection and analysis of a subset of cast pellets found at a roost site in an urban park in South Florida by comparing hair, bone, and teeth to online identification guides and museum specimens. The main identified prey species were rodents, with Sigmodon hispidus (Hispid Cotton Rat) accounting for 63.0% of all prey identified. Within the home range of these owls were 9 known colonies of endangered and common species of bats, but no evidence of depredation was found in the pellet analysis. Other small mammals, reptiles, and invertebrates made up the remainder of the diet, which is consistent with other similar studies in more natural settings.

New records of small mammals in American barn owl, Tyto furcata pellets from southeastern Ecuador

El análisis de egagrópilas de búhos es una alternativa eficiente para evaluar la composición de la comunidad de pequeños mamíferos. En Ecuador, existen análisis previos de egagrópilas de la lechuza de campanario americana, Tyto furcata en las tierras bajas del Pacífico y en los valles interandinos, resaltando un alto consumo de roedores. Describimos por primera vez la dieta de T. furcata en la región amazónica, sureste del Ecuador, resaltando la abundancia y distribución de los mamíferos presa. Colectamos egagrópilas de un individuo de T. furcata en Paquisha, cuenca del río Nangaritza, ladera oeste de la Cordillera del Cóndor. Disgregamos las egagrópilas, separamos huesos y otros restos de presas. Usamos las estructuras únicas como los cráneos y pares de mandíbulas para identificar y estimar el número mínimo de individuos de presa. Identificamos las presas usando claves taxonómicas y por comparación con material de referencia museológico. Encontramos principalmente pequeños mamíferos como presas: 2 didelphidos y 5 cricétidos. El ratón colilargo delicado, Oligoryzomys delicatus, es el registro más austral de su distribución; la marmosa esbelta de Bishop, Marmosops bishopi, es el primer registro en la provincia de Zamora Chinchipe. El ratón campestre de las Yungas, Akodon aerosus y O. delicatus fueron las presas más abundantes, por lo que podemos sugerir como comunes en la localidad. El análisis de las egagrópilas de T. furcata fue eficiente para registrar la diversidad de pequeños mamíferos en esta área previamente poco estudiada. Los cráneos encontrados aumentaron el material museológico, antes poco representado para algunas especies y también en la provincia. Finalmente destacamos a T. furcata como depredador de estos pequeños mamíferos, un aspecto importante de la historia natural del ave y de las presas.

New reports of parasitism by Synhimantus (Dispharynx) nasuta (Rudolphi, 1819) (Nematoda: Acuariidae) in wild birds in Brazil.

The aim of this study was to register the first occurrence of Synhimantus (Dispharynx) nasuta (Nematoda: Acuariidae) in some species of wild birds in Brazil. In addition, the aim was to deepen the knowledge about the morphology of this species through analysis using scanning electron microscopy. Nematodes were collected in wild birds of the species Turdus leucomelas, T. rufiventris, Mimus saturninus, Pitangus sulphuratus, Megascops choliba, Tyto furcata, and Falco sparverius. The morphological and morphometric data observed in the nematodes prove that these parasites are S. (D.) nasuta. This study also provides morphological data from light microscopy and scanning electron microscopy (SEM), as well as the morphometry of this nematode in each host species. Therefore, the current study confirms the first record of this nematode in F. sparverius and T. furcata in South America and, at the same time, these findings expand the host range of this parasite species worldwide, through the first records in M. choliba, M. saturninus, T. leucomelas and T. rufiventris.

Small mammal taphonomy and palaeoecological Holocene interpretations in the Andean piedmont (southern Mendoza province, Argentina)

ABSTRACT Salamanca cave (southern Mendoza province) is in the Andean piedmont, a transitional area in which small mammal communities may have been affected by climatic pulses. The site yields three archaeological components covering from the early to the late-Holocene with a mid-Holocene occupational and sedimentological hiatus. Taphonomic analyses of the small mammal assemblages indicate that barn owls (Tyto furcata) were the main accumulation agent, ensuring accurate palaeoecological inferences. Taxonomic composition of the site shows the dominance of Eligmodontia sp. followed by Thylamys pallidior, Phyllotis cf. P. vaccarum-pehuenche and Ctenomys sp., all of them indicative of shrubland and bare ground habitats. Palaeoclimatic inferences indicate a trend to warmer temperatures from the lower to the upper component with a slight increase in humidity in the middle component. This humid pulse is also supported by post-depositional taphonomic processes. The taxonomic structure and abundance of small mammals do not show deep changes amongst the three archaeological components, following the general trend observed in other archaeological sites from the Pampean region, southern Mendoza province and the arid and semi-arid zones of north Patagonia, in which changes in the taxonomic composition of small mammal communities are almost absent since Pleistocene–Holocene transition to late Holocene.

A Comparison of Aerodynamic Parameters in Two Subspecies of the American Barn Owl (Tyto furcata).

Simple SummaryMorphology and function depend on the ecological niche in which an animal lives. Barn owls, occurring on all continents, occupy a nocturnal niche. These birds prey mainly on small rodents but include other small vertebrates and invertebrates in the diet. The size of the barn-owl species and subspecies varies considerably. The American continent harbors the species Tyto furcata. The body mass of the subspecies in North America (T.f.pratincola) is about a factor of two higher than that of the subspecies living on the Galapagos archipelago (T.f.puncatissima). We asked how this difference translates into aerodynamic parameters. The key question was whether there is so-called similarity scaling or not. In other words, whether important aerodynamic parameters scale according to body mass. This is called isometric scaling. Deviation from isometric scaling is called allometric scaling. If we use the subspecies from the continent as a reference, we find that the Galapagos barn owl has relatively larger wings than expected from isometric scaling. This translates into a lower wing loading in punctatissima than in pratincola. A lower wing loading means higher maneuverability. We speculate that the higher maneuverability allows the Galapagos owl to catch smaller prey, especially insects.Aerodynamic parameters, such as wing loading, are important indicators of flight maneuverability. We studied two subspecies of the American Barn owl (Tyto furcata), the North American subspecies, T.f.pratincola, and the Galapagos subspecies, T.f.punctatissima, with respect to aerodynamic parameters and compared our findings with those in other owl and bird species. The body mass of T.f.pratincola is about two times higher than that of T.f.punctatissima. Wing loading between the two subspecies scales allometrically. Wing loading in T.f.pratincola is about 50% higher than in T.f.punctatissima. The scaling of wing length is not statistically different from the prediction for isometric scaling. By contrast, the wing chord in T.f.punctatissima is larger than predicted by isometric scaling, as is the wing area. The scaling of wing loading observed here for T.f.punctatissima differs considerably from the scaling in other owl and bird species as available in the literature. We speculate that the allometric scaling helps T.f.punctatissima to catch smaller prey such, as insects that are found in many pellets of T.f.punctatissima, despite the fact that in both subspecies, small rodents make up most of the diet.

Hotspots and Season Related to Wildlife Roadkill in the Amazonia–Cerrado Transition

The construction of new roads opens access to native environments, resulting in changes to the landscape. These roads cause the death of native wildlife due to collisions with vehicles, which is the main cause of human-induced vertebrate death. This work aimed to investigate the spatial distribution of roadkills on the BR-163 highway, Mato Grosso, Brazil, an Amazonia–Cerrado transition zone, to identify roadkill hotspots. The study area consisted of 244 km of road. Twenty-five trips were made totaling 6100 km of surveyed roadway between 2008 and 2011. A total of 1005 individuals from 65 species was recorded in this study. Mammals were the most affected, both in number of individuals and species, followed by birds, reptiles, and amphibians. The species with the highest roadkill rates were Cerdocyon thous and Tyto furcata. Identified endangered mammals included Myrmecophaga tridactyla, Chrysocyon brachyurus, Priodontes maximus, Speothos venaticus, Tapirus terrestris, Pteronura brasiliensis, and Ateles marginatus. The highest rates of roadkill were recorded during the wet season. The location and number of hotspots varied among classes and were related to different environmental variables such as waterbodies, forest fragments, and agricultural areas. Roadkills may be a major threat for vulnerable species and should therefore be studied to define conservation plans for local species and road traffic.

Banding records of nestling barn owls reveal optimal timing for nest box maintenance in California

AbstractAmerican barn owls (Tyto furcata) often rely on nest box networks for breeding, especially within agricultural landscapes. Nest boxes are commonly installed for pest management purposes and require regular maintenance, such as removal of pellet debris and repairs, to remain functional and safe for breeding owls. Ideally, nest box maintenance should be conducted before the breeding season begins to minimize nest disturbance. The timing of the barn owl breeding season is especially important to understand in California, USA, which has a high diversity of ecoregions and expansive latitudinal range. Our objective was to describe the barn owl breeding season throughout California using nestling records to assist with data‐driven management recommendations. We queried 96 years of barn owl nestling banding records (n = 22,670) from the United States Geological Survey Bird Banding Lab to estimate egg laying dates across California and summarized 39 years of intake records (n = 1,741) from the California Raptor Center in the Central Valley. Our results suggest that barn owls typically begin to lay eggs in California in winter months; the median egg laying date for the state was 20 February. Based on these reports, planning for barn owl nest box maintenance to begin in fall (Sep–Nov) would align with the season that breeding activity and nest disturbance may be lowest, especially in the Central Valley and Southern Coast ecoregions.

Trypanosoma cruzi, beyond the dogma of non-infection in birds.

Trypanosoma cruzi is a protozoan parasite responsible for Chagas disease affecting seven million people. The disease cycle is maintained between Triatominae insects and Mammalia hosts; a refractory effect against infection was noted in birds, but only verified in poultry. This paper presents a new host record for T. cruzi, the American barn-owl (Tyto furcata). Trypanosoma cruzi DTU II molecular evidence was found in heart, intestine, liver, and breast suggesting an established chronic infection based on the parasite DNA presence in multiple organs but absent in spleen, as in the murine model and chronically infected raccoons (Procyon lotor). For birds, the parasite rejection was explained based on the complement and high body temperature, but these mechanisms vary greatly among the members of the avian class. Therefore, there is a need to investigate whether more bird species can become infected, and if T. furcata has a role in disseminating, transmitting and/or maintaining the parasite.

Small mammals in the diet of Barn Owls (Tyto furcata) in an urban area in Rio de Janeiro state, Brazil, with a new record of the dwarf mouse opossum (Cryptonanus)

Abstract Several studies emphasize the use of owl pellets in small mammal inventories in natural areas harboring high richness of rare species, but few Brazilian Atlantic forest localities have been surveyed by this method. The present study documents the species composition and abundance of small mammals in the diet of Tyto furcata in an urban area of the municipality of Campos dos Goytacazes, Rio de Janeiro, Brazil, remarking on a new record of the dwarf mouse opossum genus Cryptonanus in the Atlantic forest. We analyzed 265 pellets regurgitated by a pair of T. furcata from November 2016 to September 2017 found in a nesting box. Analysis of the samples enabled finding a total of 596 individuals of four small mammal species. Mus musculus was predominant among the prey items (98.3%), while the native rodents Necromys lasiurus (1.3%) and Holochilus brasiliensis (0,17%) were much rarer. A single specimen of Cryptonanus sp. was identified among the diet items based on distinctive dental characters. The identification of this genus in the present study represents the second record in the state of Rio de Janeiro, and the sixth in the Atlantic Forest biome, suggesting that this marsupial occupies a wider ecological and biogeographic range. The present study underscores the relevance of owl pellets for small mammal surveys, even in urban and highly disturbed areas.

Habitat selection by a predator of rodent pests is resilient to wildfire in a vineyard agroecosystem.

Conservation of uncultivated habitats can increase the potential for ecosystem services in agroecosystems, but these lands are also susceptible to wildfires in the arid western United States. In Napa Valley, California, abundant rodent pests and an interest in integrated pest management have led wine producers to use nest boxes to attract Barn Owls (Tyto furcata) to winegrape vineyards. The viability of this practice as a method to control rodent pests depends heavily on the amount of hunting effort that Barn Owls expend in vineyards, which is known to be influenced by the amount of uncultivated land cover types surrounding the nest box. Wildfires burned nearly 60,000 ha of mainly urban and uncultivated lands surrounding Napa Valley in 2017, altering Barn Owl habitats. We compared GPS tracking data from 32 Barn Owls nesting in 24 individual nest boxes before and after the fires to analyze their hunting habitat selection. Owls with burned areas available to them after the fires had home ranges that shifted toward the fires, but selection was not strongly associated with burned areas. Though there was some spatial use of burned areas, selection of land cover types was similar for birds before and after the fires and in burned and unburned areas. The strongest selection was for areas closest to the nest box, and most recorded locations were in grassland, though selection indicated that owls used land cover types in proportion to their availability. Overall, habitat selection was resilient to changes caused by wildfires. These results are important for farmers who use nest boxes as a means of rodent control, which may be affected after dramatic disturbance events, especially as wildfires increase in the western United States.

Environmental values of California winegrape growers and the use of barn owl nest boxes as a tool for integrated pest management

Synthetic pesticides from agriculture pose threats to biodiversity, and the adoption of alternative pest management is vital to meet rising crop demands while protecting native species. For example, the use of nest boxes for barn owls (Tyto furcata and T. alba) may help control rodent pests and reduce the use of rodenticides. However, the environmental perceptions of farmers and how receptive they are to alternative pest management practices remains uncertain. Traditionally, agricultural policies and programs have focused largely on the economic self-interest of farmers, but these narrow approaches have proven insufficient to describe and predict conservation behaviors, and the study of environmental value orientations (EVOs) may better explain farmers’ adoption of novel wildlife-friendly practices. The study of EVOs can help identify people as “mutualists”, meaning those who value the environment for its own sake, and “utilitarians,” meaning those who value the environment for the services it can provide. We surveyed 71 California winegrape growers in order to better understand how their underlying environmental values relate to the use of barn owl boxes and other sustainable practices. Overall, most winegrape growers had mutualist value orientations (64%). However, there was a disconnect between the use of barn owl boxes and EVOs, with most respondents (80%) reporting the use of owl boxes regardless of underlying values. This opens the door for future research to examine whether this is true of other wildlife-friendly farming practices.

Predation of birds by the Barn Owl (Tyto furcata Temminck, 1827) in four envi-ronments in southern Santa Fe province, Argentina

ABSTRACT
 In this paper we present the birds that make up the diet of Tyto furcata in four environments in the south of the province of Santa Fe, where previous data were practically nonexistent. From this contribution, 37 individuals corresponding to three Orders and 10 Families could be established as part of the diet of this raptor. The family with the most predated representatives was Thraupidae (n=19) with three genera: Sicalis, Zonotrichia and Sporophila. The average body size of the prey was 17cm. The peri-urban/suburban (AP/S) environment had the greatest diversity of prey consumed. In all environments, the highest abundance occurred in the warm seasons (spring-summer), corresponding to the decrease in micromammal populations. This type of study demonstrates the effectiveness of pellet analysis as a tool to know the existing species in highly anthropized environments.
 
 RESUMEN
 En este trabajo se presentan las aves que componen la dieta de Tyto furcata en cuatro ambientes del sur de la provincia de Santa Fe, donde los datos anteriores eran prácticamente inexistentes. A partir de este aporte se pudo establecer que 37 individuos correspondientes a tres órdenes y 10 familias forman parte de la dieta de esta rapaz. La familia con más representantes depredados fue Thraupidae (n=19) con tres géneros: Sicalis, Zonotrichia y Sporophila. El tamaño medio del cuerpo de las presas fue de 17 cm. El entorno periurbano/suburbano (PA/S) presentó la mayor diversidad de presas consumidas. En todos los entornos, la mayor abundancia se produjo en las estaciones cálidas (primavera-verano), lo que se corresponde con la disminución de las poblaciones de micromamíferos. Este tipo de estudio demuestra la eficacia del análisis de egagrópilas como herramienta para conocer las especies existentes en ambientes altamente antropizados.

Birefringence Analyses Reveal Differences in Supramolecular Characteristics of Corneal Stromal Collagen Fibrils Between Falconiformes and Strigiformes.

This study aimed to assess the birefringent properties of corneal stromal collagen fibrils in birds of the orders Falconiformes (diurnal) and Strigiformes (predominantly nocturnal) to compare their supramolecular organizations. In total, 22 corneas of Falconiformes (Caracara plancus, n=8; Rupornis magnirostris, n=10; and Falco sparverius, n=4) and 28 of Strigiformes (Tyto furcata, n=16; Pseudoscops clamator, n=6; and Athene cunicularia, n=6) were processed histotechnically into 8-μm thick sections. Corneal optical retardation (OR) values related to the form and intrinsic fractions of the total birefringence of collagen fibrils were measured using a polarized light microscope equipped with phase compensators. In addition, the coherence coefficients that inform the local orientation of the fibrils were calculated through video image analysis. All assessments were conducted both in the anterior and posterior stroma of the cornea. Differences were significant when P<0.05. The results showed supraorganizational differences between fibrils in the anterior stroma of Falconiformes and Strigiformes. The OR values were greater (P<0.0001) for Falconiformes, indicating that the corneas of these birds contain more collagen fibrils or more aggregated collagen fibrils. In contrast, the coherence coefficients were higher (P=0.016) for Strigiformes, indicating that the corneal collagen fibers in these birds are highly aligned and have few undulations. A multivariate data matrix constructed for Euclidean distance calculations showed that the dissimilarity between Falconiformes and Strigiformes corneas, in terms of the supraorganization of stromal collagen fibrils, was 4.56%. In conclusion, it is possible that the supraorganizational differences reported in this study may be sources of variation in the visual quality of Falconiformes and Strigiformes. This study provides the necessary evidence to encourage further research associating corneal optical performance to supramolecular characteristics of corneal stromal collagen.

Multi‐year nest box occupancy and short‐term resilience to wildfire disturbance by barn owls in a vineyard agroecosystem

AbstractLandscape composition can strongly affect the delivery of ecosystem services in agroecosystems. Conserving uncultivated habitats can support ecosystem services, but in Mediterranean biomes, these lands can also increase the area susceptible to wildfires. In the world‐renowned wine‐producing region of Napa Valley, California, wine grape growers install nest boxes to attract American barn owls (Tyto furcata), which may reduce rodent crop damage. Annual monitoring of 273 nest boxes began in 2015, and devastating wildfires burned approximately 60,000 ha in the region in 2017, including homes and businesses, as well as some vineyards and uncultivated land. The goal of this study was to determine whether changes in nest box occupancy were attributed to wildfires, nest box design, land cover type, or some combination of these variables. Occupancy surveys before and after these wildfires revealed changes in habitat selection at the nest scale. Occupancy increased during the study, reaching its highest point after the fires. Owls were found breeding in recently burned areas that were previously unoccupied and modeling results showed that nest box occupancy had a positive relationship with burned areas, particularly with edges of the fire perimeter. Barn owls also consistently showed a strong preference for taller nest boxes that were surrounded by more grassland than other land cover types and a moderate selection for wooden over plastic boxes. These results illustrate an incentive for the conservation of uncultivated habitat, particularly grassland, in vineyard ecosystems, and they provide an example of a mobile pest predator’s response to wildfire disturbance. In this case, results suggest an agroecosystem service made resilient to wildfire by the owls’ selection of burned and uncultivated habitats.

Effects of habitat on prey delivery rate and prey species composition of breeding barn owls in winegrape vineyards

The provision of habitat for natural enemies of agricultural pests is common in integrated pest management approaches but has rarely been examined for vertebrate predators controlling vertebrate pests. To mitigate the economic and environmental costs of removing rodent pests in vineyards in Napa Valley, California, winegrape producers have installed nest boxes to attract American barn owls (Tyto furcata) to their properties. A rigorous estimate of how many rodents barn owls remove from the landscape is a necessary first step to understanding the overall impact of barn owls on rodent pest populations, and this study provides an estimate of rodent removal and prey composition by using remote nest box cameras. In addition, we tested hypotheses for how habitat may influence prey delivery rates and composition. Videography indicated that each barn owl chick received on average of 191 ± 10.01 prey items before fledging the nest box and that the amount of grassland habitat near the nest box and the proportion of deliveries of smaller prey were positive predictors of prey delivery rate. Prey composition was dominated by voles, gophers, and mice, and their relative proportions were associated with the composition of habitats near a nest box. Specifically, oak savannah was positively associated with the proportion of gophers and negatively associated with voles, and grassland was positively associated with voles. Further research on prey delivery should focus on the possible roles of rodent abundance, adult owl quality, and additional metrics of habitat structure.

Evolution of wing length and melanin‐based coloration in insular populations of a cosmopolitan raptor

AbstractAimInsular populations face different conditions than those living on continents, thus, resulting in the evolution of typical insular phenotypes, like smaller body sizes or reduced colourations. However, the generality of the so‐called “island rule” has been questioned, and intraspecific analyses on the effects of insularity on cosmopolitan species are lacking. Here, we tested the predictions of the island rule in the cosmopolitan common barn owl group.LocationWorld.TaxonBarn owl species complex.MethodsWe compared wing and bill length, as well as melanin‐based plumage traits, between thousands of insular and continental barn owls living in the Afro‐Palearctic region (Tyto alba), in the Americas (Tyto furcata) and in Australasia (Tyto javanica). We also tested whether the difference between insular and continental populations in these phenotypic traits varies among islands/archipelagos of different size and isolation.ResultsIn all the regions, we found differences between insular and continental owls in all the traits but bill length, with insular populations convergently evolving shorter wings and paler colourations. In addition, the difference in wing size between insular and continental populations is particularly marked on small and remote island systems, while melanin‐based traits are less expressed especially on large islands.Main conclusionsWe thus provide unprecedented evidence that insular conditions drive predictable phenotypic variations, even at the intraspecific level in different biogeographic regions, possibly promoting speciation events. In addition, our results also indicate that selective advantages of a given colouration can arise as the by‐product of positive selection on individuals displaying phenotypic traits which can favour island colonization and are genetically linked to melanization.