Migration is energetically costly, and many passerines prepare for and maintain migration with hyperphagia and increased fuel or fat reserves. During spring migration, as they approach their breeding ...grounds, passerines may deposit fat in excess of what is needed to complete migration. Individuals may carry excess fuel reserves as insurance against potentially poor environmental conditions in early spring (insurance hypothesis). If this is true, individuals arriving early at northern stopover locations or their breeding grounds should have greater energy reserves than later arrivals. Alternatively, passerines may arrive in spring with excess fat to help offset the demands of breeding (breeding performance hypothesis). Given the energetic requirements of egg production, females may arrive with greater reserves than males if excess fat directly or indirectly offsets breeding costs. We analyzed the energetic condition of 12 warbler species mist-netted during migration from 1999 to 2012 at Braddock Bay Bird Observatory, Monroe County, New York, USA. This northern stopover location is near the breeding range (in relation to total migratory distance) for most of the parulid species we examined and, therefore, is a likely location to show carryover effects between migration and breeding. In 11 of the 12 species, energetic condition was greater in the spring than in the fall for both sexes; and in all 12 species, condition was greater in females than in males in both seasons. Contrary to the insurance hypothesis, condition increased with arrival date for most species during spring migration. Although better condition in females supports the breeding performance hypothesis, the presence of this difference in both seasons suggests that additional factors influence energetic condition in parulids. Given that males arrive in better condition in the spring than when they depart in the fall, individuals of both sexes may carry excess energy reserves during spring migration to potentially use for reproductive efforts.
Most passerines use fat to fuel migration and pause at stopover sites to rest or refuel. Moreover, during spring migration, en route to breeding grounds, passerines may deposit “excess” fat as either ...insurance against unpredictable environmental conditions or in anticipation of breeding. We analyzed the energetic condition of Hermit Thrush (Catharus guttatus), Swainson's Thrush (C. ustulatus), and Veery (C. fuscescens) during spring and autumn migration at the Braddock Bay Bird Observatory (Rochester, New York, USA). We used path analysis to determine if the “spring fatter” or insurance hypotheses could help explain some of the variation in energetic condition in Catharus thrushes by designing and analyzing biologically plausible models of the potential effects of season, capture date, hour captured, and age on energetic condition during stopover. While path models differed among species and seasons, capture (or arrival) date was the strongest predictor of energetic condition; contrary to the insurance hypothesis condition increased with date during both seasons for all species. Hour of capture predicted much less variation in condition but was consistently positive (when significant). In long-distance migrants (i.e., Swainson's Thrush and Veery), less experienced or young migrants exhibited better condition than adults regardless of arriving later, which was revealed by including a direct path between age and condition and an indirect path mediated via capture date to control for potential differences in arrival timing related to age. Despite being closely related, we found only a few patterns in common among Swainson's Thrush, Hermit Thrush, and Veery. We suspect differences in phenology, flight, morphology, and migratory strategy may play a significant role in the differences among these species. La mayoría de las aves paserinas utilizan la grasa para impulsar la migración y los sitios de escala para descansar o recargarse. Por ejemplo, durante la migración de primavera, camino a las zonas de reproducción, las aves paserinas pueden formar depósitos de grasa ya sea como seguro contra condiciones ambientales impredecibles o en anticipación a la reproducción. Analizamos la condición energética de los zorzales Catharus guttatus, C. ustulatus, y C. fuscescens durante las migraciones de primavera y de otoño en Braddock Bay Bird Observatory (Rochester, New York, USA). Utilizamos análisis de trayectorias para determinar si la hipotésis de “más gordo en primavera” o la hipótesis de aseguramiento podrían explicar parte de la variación en la condición energética de zorzales Catharus al diseñar y analizar modelos biológicamente posibles de efectos potenciales de estacionalidad, fecha de captura, hora de captura y edad en la condición energética durante su escala. Aunque los modelos de trayectoria difirieron entre especies y estaciones, la fecha de captura (o llegada) fue el predictor más importante de condición energética y esta condición se incrementó a lo largo de ambas estaciones para todas las especies. La hora de captura predijo mucha menos variación pero fue consistentemente positiva (cuando fue significativa). En aves migratorias de larga distancia (como los zorzales C. ustulatus y C. fuscescens), las aves migratorias con menos experiencia o más jóvenes mostraban mejor condición que los adultos aunque llegaran más tarde, lo que fue revelado al incluir una trayectoria directa entre la edad y la condición y una trayectoria indirecta mediada por la fecha de captura para controlar por diferencias potenciales en el tiempo de llegada relacionadas a la edad. A pesar de su relación cercana, encontramos solo unos pocos patrones relacionados entre los zorzales C. guttatus, C. ustulatus, y C. fuscescens. Sospechamos que diferencias en fenología, vuelo, morfología y estrategia migratoria pueden jugar un papel importante en las diferencias entre estas especies. Palabras clave: análisis de confirmación de trayectoria, aves canoras, ecología de escala, hipótesis de aseguramiento, hipótesis de “más gordo en primavera”, migración, modelado de ecuaciones estructurales.
Many passerines regularly use flight calls to communicate during migration. However, flight-calling is inconsistent throughout the day, with a markedly lower degree of calling by free-flying ...individuals during the early evening hours and with peaks in calling typically around dawn. Based on these observations, we hypothesized that individual flight call response would vary by time of day, and the likelihood to respond would be lower at dusk than during the daytime. We tested daytime and dusk flight call responsiveness of captive American Redstarts (Setophaga ruticilla) and Magnolia Warblers (S. magnolia) during spring migration at the Braddock Bay Bird Observatory (near Rochester, New York, USA). We played a conspecific flight call sound stimulus for individual birds placed inside a soundproof recording studio and recorded their acoustic responses. In our experiment, American Redstarts and Magnolia Warblers were significantly less likely to give flight call responses at dusk than the individuals tested during the daytime. The almost absent responsiveness to flight calls at dusk suggests that these species either minimally communicate with one another during take-off or do not use flight calls as a source of communication at this time. These results have important implications for detection and quantitative bioacoustics migration monitoring. They also demonstrate the need for additional studies in temporal flight-calling behavior.
Most passerines use fat to fuel migration and pause at stopover sites to rest or refuel. Moreover, during spring migration, en route to breeding grounds, passerines may deposit "excess" fat as either ...insurance against unpredictable environmental conditions or in anticipation of breeding. We analyzed the energetic condition of Hermit Thrush (Catharus guttatus), Swainson's Thrush (C. ustulatus), and Veery (C. fuscescens) during spring and autumn migration at the Braddock Bay Bird Observatory (Rochester, New York, USA). We used path analysis to determine if the "spring fatter" or insurance hypotheses could help explain some of the variation in energetic condition in Catharus thrushes by designing and analyzing biologically plausible models of the potential effects of season, capture date, hour captured, and age on energetic condition during stopover. While path models differed among species and seasons, capture (or arrival) date was the strongest predictor of energetic condition; contrary to the insurance hypothesis condition increased with date during both seasons for all species. Hour of capture predicted much less variation in condition but was consistently positive (when significant). In long-distance migrants (i.e., Swainson's Thrush and Veery), less experienced or young migrants exhibited better condition than adults regardless of arriving later, which was revealed by including a direct path between age and condition and an indirect path mediated via capture date to control for potential differences in arrival timing related to age. Despite being closely related, we found only a few patterns in common among Swainson's Thrush, Hermit Thrush, and Veery. We suspect differences in phenology, flight, morphology, and migratory strategy may play a significant role in the differences among these species.
The interaction and hierarchy of celestial and magnetic compass cues used by migratory songbirds for orientation has long been the topic of an intense debate. We have previously shown that migratory ...Savannah sparrows, Passerculus sandwichensis, use polarized light cues near the horizon at sunrise and sunset to recalibrate their magnetic compass. Birds exposed to a +/-90 deg. shifted artificial polarization pattern at sunrise or sunset recalibrated their magnetic compass, but only when given full access to celestial cues, including polarized light cues near the horizon. In the current study, we carried out cue conflict experiments with white-throated sparrows, Zonotrichia albicollis, during both spring and autumn migration in a transition zone between the species' breeding and wintering areas on the south shore of Lake Ontario. We show that white-throated sparrows also recalibrate their magnetic compass by polarized light cues at sunrise and sunset. Sunrise exposure to an artificial polarization pattern shifted relative to the natural magnetic field or exposure to a shift of the magnetic field relative to the natural sky both led to recalibration of the magnetic compass, demonstrating that artificial polarizing filters do not create an anomalous, unnatural orientation response. Our results further indicate that there is no evidence for a difference in compass hierarchy between different phases of migration, confirming previous work showing that polarized light cues near the horizon at sunrise and sunset provide the primary calibration reference both in the beginning and at the end of migration.
Fat reserves influence the orientation of migrating songbirds at ecological barriers, such as expansive water crossings. Upon encountering a body of water, fat migrants usually cross the barrier ...exhibiting 'forward' migration in a seasonally appropriate direction. In contrast, lean birds often exhibit temporary 'reverse' orientation away from the water, possibly to lead them to suitable habitats for refueling. Most examples of reverse orientation are restricted to autumn migration and, in North America, are largely limited to transcontinental migrants prior to crossing the Gulf of Mexico. Little is known about the orientation of lean birds after crossing an ecological barrier or on the way to their breeding grounds. We examined the effect of fat stores on migratory orientation of both long- and short-distance migrants before and after a water crossing near their breeding grounds; Catharus thrushes (Swainson's and gray-cheeked thrushes, C. ustulatus and C. minimus) and white-throated sparrows Zonotrichiaalbicollis were tested for orientation at the south shore of Lake Ontario during spring and autumn. During both spring and autumn, fat birds oriented in a seasonally appropriate, forward direction. Lean thrushes showed a tendency for reverse orientation upon encountering water in the spring and axial, shoreline orientation after crossing water in the autumn. Lean sparrows were not consistently oriented in any direction during either season. The responses of lean birds may be attributable to their stopover ecology and seasonally-dependent habitat quality.
Geographic relocations of migratory passerines have shown that adults can compensate for physical displacements; juveniles on their first migration, however, use an innate clock-and-compass strategy ...and are unable to compensate for displacement. We examined the effects of changes in magnetic inclination and intensity on orientation of adult and juvenile Australian Silvereyes (Zosterops l. lateralis) to learn if geomagnetic cues are used by a migratory passerine for geographic positioning. Silvereyes, captured in breeding areas in Tasmania, were physically transported to a location along their migratory route and assessed for orientation during autumn migration. Adults and juveniles exhibited seasonally appropriate, northeasterly orientation (19° and 23° east of magnetic North, respectively) when tested under the natural geomagnetic field. Birds were then exposed to changes in the magnetic field that simulated either southern (SimS) or northern (SimN) locations near the beginning and end, respectively, of their migratory route. Inexperienced juveniles continued to show seasonally appropriate orientation (3° and 358°, respectively) in both SimS and SimN magnetic fields. Adults, in contrast, exhibited changes in orientation but only when the experimental magnetic field was consistent with a geographical displacement that should require compensatory orientation (i.e., SimN). Adults exposed to a SimS magnetic field continued to show seasonally-appropriate orientation to the North (0°). However, adults exposed to magnetic fields simulating locations beyond their wintering areas (SimN) altered their orientation significantly, orienting bimodally and perpendicular (123°–303°) to their seasonally appropriate migratory direction. These results are consistent with the presence of an age- or experience-dependent magnetic geographic position sense in migratory Australian Silvereyes.
Experimental research on the orientation of migratory songbirds is traditionally conducted using orientation funnels or automatic registration cages that record the directional activity of individual ...birds on paper or a computer. Most traditionally used funnel and cage designs do not permit investigators to observe detailed behavior of the birds and, therefore, we have gained little insight into the actual behavior of birds while they are exhibiting migratory restlessness and making directional choices. Such behavior can only be studied by direct observation or by video filming. Here, we present BirdOriTrack, a video-tracking program for extracting time-resolved, positional data of birds (and potentially other animal species) to determine their orientation relative to the center of a circular cage/funnel. With relatively inexpensive cameras, recording equipment, and cages, orientation experiments can easily be conducted and analyzed using BirdOriTrack. The program is designed to be flexible, allowing analysis of orientation behavior of birds of any size in different cage designs and in both controlled laboratory settings and field-based studies. To demonstrate the program's utility, we show the results of preliminary field experiments on several species of migratory birds captured at a migration monitoring station. BirdOriTrack is freely available at http://canmove.lu.se/birdoritrack. Tradicionalmente la investigación experimental sobre la orientación de aves migratorias se ha realizado usando embudos de orientación o cajas de registro automático, que graban la direccionalidad de la actividad individual de las aves en un papel o un computador. La mayoría de diseños tradicionales de embudos y cajas no permiten a los investigadores observar detalles del comportamiento del aves mientras éstas exhiben inquietud migratoria y toman decisiones direccionales. Éste comportamiento solo puede ser estudiado por observaciones directas o filmaciones. Aquí presentamos BirdOriTrack, un programa de video seguimiento para extraer datos temporales de posiciones de aves (y potencialmente otras especies de animales) para determinar su orientación relativa al centro de una caja o embudo circular. Con BirdOriTrack, experimentos de orientación pueden ser fácilmente realizados y analizados usando cámaras de costo relativamente bajo, equipo de grabación y cajas. El programa esta diseñado para ser flexible, permitiendo análisis del comportamiento de orientación de aves de cualquier tamaño en distintos diseños de cajas y tanto en ambientes controlados de laboratorio, como en estudios de campo. Para demostrar la utilidad del programa, mostramos los resultados de un experimento de campo preliminar en varias especies migratorias de aves capturadas en una estación de monitoreo de migración. BirdOriTrack está disponible de manera gratuita en http://canmove.lu.se/birdoritrack.
Onion thrips (Thrips tabaci Lindeman) has become a significant pest of cabbage (Brasssica oleracea L.) in regions with a dry continental climate. Thrips-resistant cabbage varieties have been ...developed in breeding programs, but the mechanisms of resistance remain largely unknown. Antixenosis, one of the three resistance mechanisms, may play a role but no plant trait has been identified as a source of antixenosis. A series of studies were conducted to identify resistance mechanisms in this insect—crop interaction and to seek plant traits that were correlated to resistance. In this first article of the series, the result of studying antixenosis and overall resistance of cabbage and the correlation between antixenosis and light reflectance characteristics are reported. There were distinct differences in the overall resistance to thrips between the six cabbage varieties studied. There were more pronounced differences between varieties based on the number of damaged head leaves compared with the use of damage ratings as a measure of overall resistance. Varieties also differed in their level of antixenosis; proportional abundance of thrips adults on head-forming leaves was more closely correlated to overall resistance of cabbage than actual thrips numbers. Some of the variables computed from the recorded reflectance spectra of cabbage were correlated to thrips abundance on head-forming leaves only in the first but not in the second year of this study, suggesting that either spectral characteristics do not affect antixenosis or other variables may affect thrips' responses to spectral cues. Furthermore, multiple spray applications of a kaolin particle-based product significantly changed the light reflectance characteristics of cabbage, but it did not reduce the actual thrips abundance on head-forming leaves.
Site fidelity to breeding and wintering grounds, and even stopover sites, suggests that passerines are capable of accurate navigation during their annual migrations. Geolocator-based studies are ...beginning to demonstrate precise population-specific migratory routes and even some interannual consistency in individual routes. Displacement studies of birds have shown that at least adult birds are capable of goal-oriented movements, likely involving some type of map or geographic position system. In contrast, juveniles on their first migration use a clock-and-compass orientation strategy, with limited knowledge about locations along their migratory routes. Positioning information could come from a variety of cues including visual, olfactory, acoustic, and geomagnetic sources. How information from these systems is integrated and used for avian navigation has yet to be fully articulated. In this review, we (1) define geographic positioning and distinguish the types of navigational strategies that birds could use for orientation, (2) describe sensory cues available to birds for geographic positioning, (3) review the evidence for geographic positioning in birds and methods used to collect that evidence, and (4) discuss ways ornithologists, particularly field ornithologists, can contribute to and advance our knowledge of the navigational abilities of birds. Few studies of avian orientation and navigation mechanisms have been conducted in the Western Hemisphere. To fully understand migratory systems in the Western Hemisphere and develop better conservation policies, information about the orientation and navigation mechanisms used by specific species needs to be integrated with other aspects of their migration ecology and biology. Fidelidad con las localidades de reproducción y zonas de migración e incluso sitios de parada, sugiere que los Passeriformes tienen habilidades de navegación precisa durante las migraciones anuales. Estudios basados en geolocalizadores están comenzando a demostrar, rutas precisas especificas para las poblaciones, e inclusive alguna consistencia interanual en rutas individuales. Estudios de desplazamiento han demostrado que por lo menos aves adultas tienen la habilidad de realizar movimientos orientados hacia los objetivos, probablemente involucrando algún tipo de mapa o sistema de posicionamiento geográfico. En contraste, aves juveniles en su primera etapa de migración usan una estrategia de orientación basada en reloj y compas, con conocimiento limitado acerca de las localidades a lo largo de las rutas de migración. La información sobre el posicionamiento puede provenir de una variedad de señales incluyendo fuentes visuales, olfatorias, acústicas y geomagnéticas. Sin embargo, todavía no ha sido completamente articulado la forma en la cual estos sistemas son integrados y utilizados para la navegación en aves. En esta revisión, (1) definimos el posicionamiento geográfico y diferenciamos entre tipos de estrategias de navegación que las aves potencialmente usan para la orientación, (2) describimos las señales sensoriales disponibles para las aves para el posicionamiento geográfico, (3) hacemos una revisión de la evidencia existente para el posicionamiento global en aves y los métodos utilizados para colectar esta evidencia, y (4) discutimos algunas formas de cómo los ornitólogos, particularmente ornitólogos de campo, pueden contribuir y promover nuestro conocimiento sobre las habilidades de navegación en las aves. En el hemisferio Occidental, se han realizado pocos estudios de orientación en aves y mecanismos de navegación. Para comprender completamente los sistemas de migración en el hemisferio Occidental y desarrollar mejores políticas de conservación, necesitamos integrar la información acerca de los mecanismos de orientación y navegación utilizados por especies especificas, con otros aspectos de la ecología de la migración y biología.
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