Tyrannus Savana Research Articles

Projected population- and season-dependent impacts of climate change on a migratory songbird in South America

Migratory birds depend on resources located in distantly separated ecosystems, potentially making them vulnerable to rapid environmental changes across their range. Yet, we understand little about how such changes may impact birds in different migratory systems, in large part because of a lack of individual-level research throughout their annual cycle and on different continents. The Fork-tailed Flycatcher (Tyrannus savana) is a widely distributed Neotropical bird, whose nominate subspecies is composed of populations that breed at tropical and south-temperate latitudes of South America and then spend the non-breeding season in northern South America. Using movement data collected with light-level geolocators on individual migratory Fork-tailed Flycatchers from breeding populations at tropical and south-temperate latitudes, we evaluated whether different flycatcher populations vary in their vulnerability to future climate change. Results suggest that populations breeding at south-temperate and tropical latitudes will lose at least 22% of their breeding area, with most losses of south-temperate breeding areas occurring in the northern portions of those areas. Both south-temperate breeders and tropical breeders will also lose non-breeding area, with south-temperate breeders experiencing a loss of over a third of their non-breeding area, whereas tropical breeders will lose up to ~16% of that area. These results are the first to demonstrate population- and season-dependent risks to climate change for a migratory bird breeding in the Neotropics, and suggest that mitigating the impacts of climate change for birds in South America will require conservation planning that accounts for both seasonal and regional processes.

Egg shape variation across the distribution of the partially migratory fork‐tailed flycatcher Tyrannus savana

The evolution of egg shape across birds has been associated with breeding ecology, body shape constraints and nest microclimate, among other factors. We model the effects of migratory status, climate, clutch size and egg volume on egg shape variation over the distribution of fork‐tailed flycatchers Tyrannus savana. Although migratory status and climatic variables appear to be influencing intraspecific egg shape, these effects are not significant when accounting for nest identity as a random factor (i.e. eggs from the same clutch are more similar than to other clutches). Moreover, the differences that we observe in egg shape are not explained by variation in egg size. Finally, within a breeding population of migratory fork‐tailed flycatchers, egg shape does not vary with respect to egg‐laying order and/or female wing length (standardized by weight). Egg shape is highly variable within populations of fork‐tailed flycatchers but not within clutches, suggesting that female traits, apart from migratory status and wing morphology, constrain egg shape variation.

New avian hosts for Taphropiestes plaumanni (Coleoptera: Cavognathidae) and the record of nestlings skin lesions and body deterioration associated with parasitism

We collected data during three consecutive breeding seasons (2015-2018) to assess the effects of Taphropiestes plaumanni (Coleoptera: Cavognathidae) on its bird hosts in a native forest of central eastern Argentina. We monitored bird nests for T. plaumanni in 207 nests of Masked Gnatcatcher (Polioptila dumicola, Polioptilidae), 302 nests of Vermilion Flycatcher (Pyrocephalus rubinus, Tyrannidae), 55 nests of Blue-and-yellow Tanager (Pipraeidea bonariensis, Thraupidae), 99 nests of Small-billed Elaenia (Elaenia parvirostris, Tyrannidae), 23 nests of Yellow-browed Tyrant (Satrapa icterophrys, Tyrannidae), and other passerine species nesting in the same forest patches. We found 13 nests in which nestlings showed evidences of parasitism of which four species are new hosts for this parasite (Vermilion Flycatcher, Masked Gnatcatcher, Red-crested Cardinal Paroaria coronata, Thraupidae, and Fork-tailed Flycatcher Tyrannus savana). Skin lesions caused by T. plaumanni larvae consisted in lacerations and crusts on the belly and chest areas. In one parasitized nest of Vermilion Flycatcher and one parasitized nest of Masked Gnatcatcher we observed the death of nestlings after being parasitized. This study adds new species to the list of hosts for this parasite, reports nestling skin lesions in nests with T. plaumanni parasitism, and reports for the first time the death of parasitized nestlings.

Dietary ecology of two migrant flycatchers in habitats with and without cattle during the breeding season in central Argentina

Food selection is a key aspect of a bird's life history strategy, so understanding how birds respond to variation in food abundance is relevant to evaluating their general ecology and survival, and also the potential consequences of the degradation of environments impacted by livestock. We studied the dietary ecology of Vermilion Flycatchers (VEFL) and Fork-tailed Flycatchers (FTFL), two insectivores and Neotropical austral migrants, during their breeding season. We worked in areas with and without cattle ranching in the Espinal biome of La Pampa, Argentina. We found different arthropod prey abundance for both flycatchers according to arthropod orders and/or study sites, suggesting that livestock may impact food abundance. Both consumed similar prey and positively selected for hymenopterans and coleopterans, and FTFL also positively selected for orthopterans. VEFL selected nest sites with a lower abundance of heteropterans and FTFL selected sites with a higher abundance of coleopterans. Additionally, VEFL nest survival was negatively related to the abundance of hemipterans and FTFL nest survival was positively related to the abundance of coleopterans. This study helps fill gaps on the general ecology of species that breed in rangelands, and highlights the importance of similar studies to formulate effective conservation planning for the Espinal biome.

The 46th Annual Report of the California Bird Records Committee: 2020 Records

From its last report through 2020, the California Bird Records Committee reached decisions on 206 records involving 195 individuals of 67 species and two species groups, endorsing 180 records of 169 individuals. Especially notable records detailed in this report include those of California’s third Common Crane (Grus grus), third Bristle-thighed Curlew (Numenius tahitiensis), third Marsh Sandpiper (Tringa stagnatalis), third Eurasian Skylark (Alauda arvensis), fourth Chuck-will’s-widow (Antrostomus carolinensis), and fourth Fork-tailed Flycatcher (Tyrannus savanna).

A trophic niche shift in a South American migrant: Stable nitrogen isotope signatures in feathers of Fork-tailed Flycatchers (Tyrannus savana)

Understanding how diet and life history strategies interact is important for exploring constraints of available nutrition on energetically expensive life history events in wild animals (i.e., reproduction, annual migration, molt). Previous research on migratory birds breeding in the Northern Hemisphere has demonstrated trophic niche shifts from invertebrates to fruit in order to fuel spring migration. We examined whether a trophic niche shift occurred in a Neotropical austral migrant, the Fork-tailed Flycatcher (Tyrannus savana savana), prior to spring migration by measuring stable nitrogen isotopes in feathers. We found that the austral migrant subspecies T. s. savana did appear to shift in diet from a higher to a lower trophic level (consistent in pattern with a shift from a higher to a lower ratio of invertebrates to fruit) but the shift occurred earlier than expected if it was preparation for migration. A sympatric sedentary subspecies occupying the same habitat (T. s. monachus) appeared to forage only at the lower trophic level during its annual molt and showed no evidence of a trophic niche shift; however, the molt of the 2 subspecies occurs at slightly different times of year. The timing of the trophic niche shift leads us to conclude that a higher trophic level diet early in molt is not related to preparation for spring migration but that it may be related to seasonal changes in food availability as the wet season concludes. A remaining challenge for understanding the ecological consequences of trophic niche shifts is to find ways to empirically measure trade-offs between different diets across energetically expensive life history events and compare these between taxa with differing life history strategies.

Sonations in Migratory and Non-migratory Fork-tailed Flycatchers (Tyrannus savana).

Sonations are sounds that animals produce with structures other than the vocal apparatus for communication. In birds, many sonations are usually produced with modified flight feathers through diverse kinematic mechanisms. For instance, aeroelastic fluttering of feathers produces tonal sound when airflow exceeds a threshold velocity and induces flight feathers to oscillate at a constant frequency. The Fork-tailed flycatcher (Tyrannus savana) is a Neotropical bird with both migratory and year-round resident subspecies that differ in the shape of the outer primary feathers of their wings. By integrating behavioral observations, audio recordings, and high-speed videos, we find that male Fork-tailed flycatchers produce sonations with their outer primary feathers P8-10, and possibly P7. These sounds are produced during different behavioral contexts including: the pre-dawn display, intraspecific territorial disputes, when attacking potential nest predators, and when escaping. By placing feathers in a wind tunnel, we elicited flutter at frequencies that matched the acoustic signature of sounds recorded in the wild, indicating that the kinematic mechanism responsible for sound production is aeroelastic flutter. Video of wild birds indicated that sonations were produced during the downstroke. Finally, the feathers of migratory (T.s.savana) and year-round resident (T.s.monachus) Fork-tailed flycatchers flutter in feather locations that differ in shape between the subspecies, and these shape differences between the subspecies result in sounds produced at different frequencies.

Speciation Associated with Shifts in Migratory Behavior in an Avian Radiation.

Migratory animals move up to thousands of kilometers every year [1]. Losses of migration (i.e., migratory drop-offs) occur when individuals of a migratory species stop migrating and establish founder sedentary populations, a phenomenon documented in birds [2-5] and butterflies [6]. In theory, losses-and also gains-of migration might promote speciation if sedentary and migratory populations become reproductively isolated [7-9]. Because migratory and sedentary strategies involve alternative physiological, behavioral, and morphological traits [10-13], divergence along multiple axes of organismal function is expected to accompany switches in migratory behavior, potentially accelerating speciation. We present evidence of speciation driven by a migratory drop-off in the fork-tailed flycatcher (Tyrannus savana) resulting in reproductive isolation likely driven by changes in breeding schedules (allochronic speciation [13-15]) and geographic isolation of breeding grounds (allopatric speciation [16]). Phylogenetic analyses across New World flycatchers (Tyrannidae) showed that an association between speciation and drop-offs is also observable at a macroevolutionary scale. Loss of migration was significantly more frequent than its gain, and speciation rates of migratory and partially migratory lineages (i.e., species having both migratory and sedentary populations) exceeded those of sedentary lineages. Models of trait evolution indicated that partial migration is an intermediate step between migratory and sedentary states in this family. Given that partial migration is widespread across migratory animals (e.g., of all migratory birds, ca. 51% are partially migratory [5]), speciation via switches in migratory behavior might be an important yet overlooked mechanism of animal diversification.

Nest-site selection and breeding success of two neotropical austral migrant birds in a semiarid forest: A comparison of sites with and without livestock

Understanding the mechanisms underpinning nest-site selection offers novel insights about selective forces shaping the breeding ecology of birds, and provides vital information for conservation planning. We evaluated and compared nest-site selection and breeding success of Vermilion Flycatchers (VEFL) and Fork-tailed Flycatchers (FTFL) in areas with and without livestock in the Espinal biome of La Pampa Province, Argentina. VEFL selected nest sites with greater tree cover, whereas FTFL nested in taller trees with narrower trunks. We found a weak positive effect of nest height, diameter of nest-support branches and the absence of livestock on VEFL nest survival, and a weak positive effect of nest orientation on FTFL nest survival. However, although some habitat characteristics varied between the two areas, nest site characteristics of both species in areas with and without livestock did not differ significantly. The nest survival was 12.7% for VEFL and 28.7% for FTFL, and did not differ significantly between these two flycatchers. The breeding ecology of these birds has likely been molded by a broad suite of selective pressures, such as severe weather, brood parasites and predators that characterize habitats in central Argentina.

ECOLOGÍA URBANA DE AVES: RELACIÓN DE LAS PLANTAS, CLIMA Y RUIDO CON LA BIODIVERSIDAD DE AVES EN LA CIUDAD DE IQUITOS, PERÚ

La ecología urbana brinda directrices a las políticas de desarrollo urbano, para que las sociedades humanas vivan en ambientes más saludables y naturales. Las aves son buenas indicadoras de los ecosistemas naturales, por tal razón con el objetivo de determinar la relación de las plantas, clima y ruido con la biodiversidad de aves urbanas de la ciudad de Iquitos (Perú), se utilizó el método de conteo por puntos en seis de las principales plazas de la ciudad. El diseño de muestreo en cada plaza consistió de cuatro puntos de observación, y se colectó información durante tres días consecutivos, desde las 6:00 a 9:00 h y 16:00 a 18:00 h. La riqueza de aves fue de 50 especies, con mayor abundancia de Columba livia, Coragyps atratus y Tyrannus savana, y la riqueza de plantas fue de 19 especies, con dominancia de Adonidia merrillii, Elaeis oleifera, Livistona chinensis y Ficus benjamina. La temperatura ambiental entre las plazas no difieren, pero si la temperatura del suelo, humedad relativa y ruido. Hay relación del índice de abundancia de aves carnívoras con la riqueza de especies de plantas en general, plantas nativas y riqueza de árboles. La presencia de plantas, sobre todo de árboles altos proporcionaría mayor oferta de alimento, sitios de perchado y de nidificación a las especies de aves carnívoras. A mayor número de estas especies de aves en un ambiente urbano mayor será el avance hacia una ciudad verde.

Drivers of wing shape in a widespread Neotropical bird: a dual role of sex-specific and migration-related functions

A large body of research has shown how avian morphology is shaped by specific behavioral repertoires and life history traits. Yet, the majority of such research has been conducted on birds breeding at north-temperate latitudes. We tested the hypothesis that functional wing traits of Fork-tailed Flycatchers (Tyrannus savana), which migrate within South America, vary predictably between non-migratory and migratory flycatchers. Additionally, due to sex-specific differences in this species (e.g., males perform courtship displays), we explored sex-related variation in wing shape. We applied classic measures of wing shape (e.g., wing loading, length, aspect ratio, pointedness), as well as landmark-based morphometric analysis to describe the wing morphology of Fork-tailed Flycatchers from breeding populations across South America. We found that migratory flycatchers tend to have more pointed wings than non-migratory flycatchers. Additionally, we found that males have wings that are significantly longer, more pointed, with a higher aspect ratio and that are more swept than those of females, regardless of whether they migrate or not. Overall, our results suggest that wing shape of Fork-tailed Flycatchers is the result of a complex set of tradeoffs shaped by selective pressures exerted on both sexes (i.e., the need to forage on the wing, evade predators and migrate efficiently), as well as sex-specific behaviors (e.g., the need for males to execute acrobatic displays).

Ecological determinants ofTyrannusflycatcher nestling growth at north- and south-temperate latitudes

ABSTRACT An organism's life history strategy is made up of a suite of physiological, behavioral, and ecological traits, which vary at both the interspecific and intraspecific levels in accordance with selective pressures operating on individuals. For birds, 2 primary ecological factors have been proposed to explain intraspecific and interspecific variation in nestling growth: nest predation and food availability. Individual nestling growth rates have important consequences for overall fitness because growth speed could influence subsequent reproductive performance and survival. We studied the relationship between ecological factors (i.e. precipitation level and predation rate) and nestling growth patterns of 2 New World flycatcher species (Tyrannidae) of the genus Tyrannus (Fork-tailed Flycatcher [T. savana] and Scissor-tailed Flycatcher [T. forficatus]) breeding at south- and north-temperate latitudes. We tested the hypothesis that nestling growth rates are driven by nest predation rates and predicted th...

Relationship between arrival timing and breeding success of intra-tropical migratory Fork-tailed Flycatchers (Tyrannus savana)

Relationship between arrival timing and breeding success of intra-tropical migratory Fork-tailed Flycatchers (<i>Tyrannus savana</i>)

Utilização de poleiros artificiais por aves em áreas de restauração ecológica dos biomas Cerrado e Mata Atlântica no Brasil

Artificial perches are widely used in ecological restoration projects; however, the results of these works are yet to be summarized in a review. The goal of the present study was to describe the taxonomic structure of birds that utilized artificial perches, as well as determine the species of birds that most frequently utilized the perches in restoration areas of the Cerrado and Atlantic Forest biomes. We used secondary data obtained from a systematic review of literature available on digital sources. A total of 17 studies were obtained for the two biomes, 15 of which were analyzed. From these studies, 126 bird species were recorded, averaging 19.26 ± 8.30 SD species per study. Five species were categorized as frequent users of artificial perches (Pitangus sulphuratus, Tyrannus melancholicus, Mimus saturninus, Columbina talpacoti, and Tyrannus savana). These birds are predominantly generalist species, which disperse seed under the perches and this feeding habit of this group has implications for the restoration process. The large number of species that utilize artificial perches highlights the importance of these structures in supporting bird diversity, in addition to the promotion of bird ecosystem services.Keywords: nucleation, birdlife, ecosystem services, agroecosystems.

Long-term association of Tyrannus savana and Sturnella superciliaris density with land cover and climatic variables in agroecosystems of Argentina

Agricultural expansion and intensification resulted in important changes in the agricultural landscape of the Pampas region, Argentina. We used linear mixed models to analyze the relationship between environmental variables associated to land use/cover, productivity and climate and changes in densities of two bird species, the Fork-tailed Flycatcher (Tyrannus savana) and the White-browed Blackbird (Sturnella superciliaris). The study area in central Argentina was divided in three agroproductive sub-regions: (1) predominantly agricultural, (2) mixed agricultural– rangeland and (3) mixed agricultural–forested rangeland. Bird populations were sampled annually during 2003–2011 using point-transects along secondary roads (48 transects). Mean estimated density for Fork-tailed Flycatcher was 0.132 ind/ha, increased in the agricultural sub-region and was associated with decreasing forest cover and increasing fallow and weedy fields cover. Mean density of the White-browed Blackbird was 0.045 ind/ha, decreased in the agricultural-rangeland sub-region and increased in landscapes with more perennial pastures, fallow and weedy fields and annual pastures, avoiding sites with more forest cover. Productivity and climatic variables only showed a strong association with White-browed Blackbird density. Our results suggest that land use/cover, productivity and climatic factors are important variables when planning strategies to conserve bird population at a regional level in agroecosystems of Argentina.

Intra-tropical migration and wintering areas of Fork-tailed Flycatchers (Tyrannus savana) breeding in São Paulo, Brazil

Fork-tailed Flycatchers ( Tyrannus s. savana ) breed from central to southern South America from September to January, migrating to northern South America to spend the non-breeding season. However, little is known of the migratory routes, rate, and timing of migration of those that breed in Brazil. In 2013, we attached light-level geolocators to breeding Fork-tailed Flycatchers breeding in Sao Paulo State. Data for six male flycatchers recaptured in 2014 indicates that they exhibited two fall migration strategies. Some individuals migrated northwest to the wintering grounds (primarily Colombia, Venezuela and northern Brazil), while others first spent several weeks in southwestern Brazil before going to the wintering grounds. Mean fall migration rate was 69 km/day (±13.7) during 59 (±13.2) days. Some flycatchers moved during winter, using more than one winter area. Flycatchers initiated spring migration in July and migrated southeast to the breeding grounds at a mean rate of 129 km/day (±19.0) during 27 (±2.8) days. A detailed understanding of the annual cycle of South America's migratory birds is essential to evaluating theoretical questions, such as the evolution of their life history strategies, in addition to applied questions, such as explanations for changes in population size, or their role as disease vectors.

Demographic variation in timing and intensity of feather molt in migratory Fork‐tailed Flycatchers (Tyrannus s. savana)

Understanding the annual cycle of migratory birds is imperative for evaluating the evolution of life-history strategies and developing effective conservation strategies. Yet, we still know little about the annual cycle of migratory birds that breed at south-temperate latitudes of South America. We aged, sexed, and determined the progression and intensity of body, remige, and rectrix molt of migratory Fork-tailed Flycatchers (Tyrannus s. savana) at breeding sites in southern South America and at wintering sites in northern South America. Molt of both body and flight feathers occurred primarily during the winter. In early winter, a similar proportion of young and adult flycatchers molted remiges and rectrices, but remige molt intensity (number of remiges molting) was greater and primary molt progression (mean primary feather molting) more advanced in adults. In late winter, remige molt intensity and primary molt progression did not differ between age groups. We found no difference between males and females either in the proportion of individuals molting in winter or in the intensity or progress of remige molt. Our results suggest that the nominate subspecies of Fork-tailed Flycatcher undergoes one complete, annual molt on the wintering grounds, and represents the first comprehensive evaluation of molt timing of a migratory New World flycatcher that overwinters in the tropics. Given that breeding, molt, and migration represent three key events in the annual cycle of migratory birds, knowledge of the timing of these events is the first step toward understanding the possible tradeoffs migratory birds face throughout the year. © 2016 Association of Field Ornithologists.

Drivers of clutch-size in Fork-tailed Flycatchers (Tyrannus savana) at temperate and tropical latitudes in South America

Many species of birds exhibit a latitudinal gradient in annual reproductive investment, laying more eggs and producing more nestlings at higher latitudes. However, few studies have evaluated the mechanisms that underlie such patterns and such differences in grassland birds specifically. We monitored nests of Fork-tailed Flycatchers (Tyrannus savana) over two breeding seasons at a tropical site in Bolivia (in 2010–11 and 2011–12) and three breeding seasons at a southern temperate site in Argentina (2010–11, 2011–12 and 2012–13), testing two hypotheses explaining variation in clutch-size among populations: the food-limitation hypothesis and the nest-predation hypothesis. Mean clutch-size and mean brood-size were significantly larger at the temperate study site than at the tropical site. Availability of arthropod food per individual bird was significantly higher at the temperate site. There was no relationship, positive or negative, between rates of nest predation and either clutch-or brood-size, and thus no support for the nest-predation hypothesis. We conclude that food availability explains much of the latitudinal variation in clutch-size in this species. We discuss avenues for future research on the mechanisms underlying geographical variation in the life histories of Neotropical birds.

Five new species of the feather mite genus Trouessartia Canestrini from South America (Acari: Trouessartiidae).

Five new feather mite species of the genus Trouessartia Canestrini are described from South American birds: Trouessartia latiducta sp. nov. from Phylloscartes kronei (Tyrannidae), T. basileuteri sp. nov. from Basileuterus culicivorus (Parulidae), T. sicaliae sp. nov. from Sicalis flaveola (Emberizidae), T. savanae sp. nov. from Tyrannus savana (Tyrannidae), and T. picumni from Picumnus fulvescens (Picidae). The latter species is the first representative of the genus described from a bird of the order Piciformes.

Long-distance bird migration within South America revealed by light-level geolocators

Little is known about the timing of migration, migration routes, and migratory connectivity of most of the >230 species of birds that breed at south temperate latitudes of South America and then migrate toward the tropics to overwinter. We used light-level geolocators to track the migration of 3 male and 3 female Fork-tailed Flycatchers (Tyrannus savana) captured on their breeding territories in Argentina. All birds initiated fall migration between late January and late February, and migrated 45 to 66 km day-1 in a northwesterly direction through central South America to either one or two wintering areas. Five individuals first spent several weeks (in April and May) in western Amazonia (mainly Peru, northwestern Brazil, and southern Colombia) before moving east to spend the rest of the non-breeding season in central Venezuela and northern Brazil. One individual occupied primarily one wintering area in eastern Colombia, northwestern Brazil, and southwestern Venezuela. Fall migration took approximately 7–12 weeks to complete and covered a distance of 2,888–4,105 km. We did not analyze spring migration data because of broad overlap with the austral spring equinox. These results are the first data on wintering locations, migration timing, and routes of individual migrant passerine birds that breed in South America. Given the general lack of similar data for practically all migratory birds that breed in South America, geolocator technology has the potential to revolutionize our understanding of how birds migrate—and the threats they face—on South America's rapidly changing landscape.