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The identification of migratory pathways is critical to understanding potential risks affecting migratory birds. The Great Lakes are an important stopover area along the migratory pathway of millions of nocturnally migrating songbirds. However, large expanses of open water can act as a geographic barrier to migrating songbirds resulting in flight “detours” and increased mortality. We recorded nocturnal flight calls (NFCs) of migratory warblers (one species and one species group) and sparrows (three species) at four sites along the Ohio coastline of Lake Erie during two spring migratory seasons. One pair of coastal and offshore sites was located in the central basin, another pair of coastal and offshore sites was located in the western basin with its associated island archipelago connecting Ohio with Ontario. Acoustic monitoring of NFCs suggested that (1) fewer birds were recorded aloft over offshore, open water sites compared to closely associated coastal sites; (2) sparrows apparently were more influenced by location in the Lake Erie basin than warblers. In summary, although many warbler and sparrow migrants cross Lake Erie, the lake appears to be a barrier for at least some members of the studied species groups. However, consistent with previous studies, the western basin appears more amenable to a lake crossing, particularly for sparrows. While interpretation of NFC data should be done with caution, our findings suggest differential passage over Lake Erie by nocturnal songbird migrants.

Migratory birds encounter the Great Lakes while moving through eastern North America toward breeding grounds to the North, which offers a good opportunity to study variation in migratory behavior as birds face a potentially influencing topographical feature. Using passive infrared technology, we documented the direction of relatively low-flying, nocturnal, mostly passerine migration in spring along the southern coast of Lake Erie's western basin. We examined the extent to which spring migrants flew across Lake Erie as a continuation of the inland, northeasterly broad front migratory direction, as determined by weather radar and infrared observations, or displayed a tendency to deviate to more closely follow the direction of the coastline. We found that an estimated 62% of all low-flying migrants deviated their flight directions toward the coast of Lake Erie at 2 coastal sites, Cedar Point and Ottawa, which were characterized by northwest–southeast oriented coastlines. Migrants at a third coastal location, Maumee Bay, which has a more east–west oriented coastline, did not display similarly deviated flight directions. We found that even when winds were energetically favorable for a lake crossing, many migrants still routinely displayed deviated flight directions that approached paralleling the coastline. Further, the mean flight direction at one site, Ottawa, shifted more in the direction of the coastline as the night progressed, suggesting that time of night could influence the shift to a more coastal flight direction. The data indicate that the western basin of Lake Erie acts as a salient topographical feature influencing the flight directions of nocturnal migrants. The data further suggest that birds are making active decisions while in flight, based on current environmental and physiological conditions, about whether to continue to cross Lake Erie or take a coastal detour.

Migrating birds often encounter ecological barriers to fueling and other costs that can influence their flight directions. During spring migration, many migrants deviate westward along the southern coast of Lake Erie’s western basin instead of continuing to fly the more northerly, broad-front direction and crossing the lake. The goal of this study was to determine if migrants arriving at the same locations along the southern coast of Lake Erie in autumn, after having now already flown over the lake, would similarly respond to the coastal features despite the different decision making, adaptive profile. During the fall migrations of 2015–2017, flight directions of individual migrants, overwhelmingly passerines, were recorded by an infrared camera from three coastal sites along the southern coast of Lake Erie’s western basin. The regional broad-front direction of migration was taken from the WSR Doppler weather radar located near Cleveland, Ohio. Across multiple analyses, no differences in flight directions were observed either across the three observation sites or with respect to the broad-front direction. Generally, migrants flew in a south-southwesterly direction irrespective of location. Further, we found no differences in the flight directions of migrants early in the night compared to later in the night, suggesting that the energetic state did not substantially impact flight directions. In contrast to spring migration, the ecological boundary on Lake Erie’s southern coast was not associated with any change in the flight directions of songbirds during fall migration, suggesting that migratory context is a critical factor determining how migrants may respond to environmental, topographic features. Las aves migratorias, con frecuencia encuentran barreras para el reabastecimiento de energía y otros costos que pueden influenciar las direcciones del vuelo. Durante la migración de primavera, muchos migrantes se desvían hacia el oeste a lo largo de la costa sur de la cuenca occidental del Lago Erie, en lugar de continuar volando hacia el norte directamente para cruzar el lago. El objetivo de este estudio fue determinar si los migrantes que llegan a las mismas localidades de la costa sur del lago Erie en otoño, después de haber volado por encima del lago, responden similarmente a las características de la costa, a pesar del perfil adaptativo en la toma de decisiones. Durante las migraciones de otoño de 2015–2017, registramos las direcciones de vuelo de migrantes individuales, principalmente paseriformes, utilizando las cámaras infrarrojas de tres localidades costeras a lo largo de la costa sur de la cuenca occidental del lago Erie. La dirección regional de frente amplio de la migración fue medida a través del radar climático Doppler WSR, ubicado cerca de Cleveland, Ohio. A trav es de múltiples análisis, no observamos diferencias en las direcciones del vuelo, ni utilizando los datos de los tres sitios de observación, ni la dirección de frente amplio. En general, los migrantes volaron con dirección sur-suroeste independientemente de la ubicación. Adicionalmente, no encontramos diferencias en las direcciones de vuelo de migrantes desplazándose temprano o tarde en la noche, lo cual sugiere que el estatus energético no afecta sustancialmente las direcciones del vuelo. En contraste con la migración de primavera, los límites ecológicos en la costa sur del lago Erie no estuvieron asociados con ningún cambio en las direcciones del vuelo de las aves cantoras durante la migración de otoño, sugiriendo que el contexto migratorio es un factor crítico que determina como los migrantes responden a las características ambientales de la topografía.

Many species of birds that normally migrate during the night have been observed engaging in so-called morning flights during the early morning. The results of previous studies have supported the hypothesis that one function of morning flights is to compensate for wind drift that birds experienced during the night. Our objective was to further explore this hypothesis in a unique geographic context. We determined the orientation of morning flights along the southern shore of Lake Erie's western basin during the spring migrations of 2016 and 2017. This orientation was then compared to the observed orientation of nocturnal migration. Additionally, the orientation of the birds engaged in morning flights following nights with drifting winds was compared to that of birds following nights with non-drifting winds. The morning flights of most birds at our observation site were oriented to the west-northwest, following the southern coast of Lake Erie. Given that nocturnal migration was oriented generally east of north, the orientation of morning flight necessarily reflected compensation for accumulated, seasonal wind drift resulting from prevailingly westerly winds. However, the orientation of morning flights was similar following nights with drifting and non-drifting winds, suggesting that birds on any given morning were not necessarily re-orienting as an immediate response to drift that occurred the previous night. Given the topographical characteristics of our observation area, the west-northwest movement of birds in our study is likely best explained as a more complex interaction that could include some combination of compensation for wind drift, a search for suitable stopover habitat, flying in a direction that minimizes any loss in progressing northward toward the migratory goal, and avoidance of a lake crossing. Muchas especies de aves que migran normalmente durante la noche han sido observadas iniciando los llamados vuelos de la mañana durante tempranas horas del día. Resultados de estudios previos han soportado la hipótesis que una función de los vuelos de la mañana es para compensar por la deriva del viento que las aves han experimentado durante la noche. Nuestro objetivo era explorar mas a fondo esta hipótesis en un contexto geográfico único. Determinamos la orientación de los vuelos de la mañana a lo largo de la costa sur de la Cuenca occidental del lago Erie durante las migraciones de primavera de 2016 y 2017. Esta orientación fue comparada con la orientación observada de la migración nocturna. Adicionalmente comparamos la orientación de las aves que iniciaron vuelos en la mañana posterior a noches con vientos a la deriva con las de aves después de noches sin vientos a la deriva. Los vuelos de la mañana de la mayoría de las aves en nuestro sitio de observación estuvieron orientados hacia el oeste-noroeste, siguiendo la costa sur del lago Erie. Dado que la migración nocturna fue orientada generalmente al este del norte, la orientación de los vuelos de la mañana necesariamente reflejan compensación por la acumulación de la deriva por los vientos estacionales resultado de vientos principalmente hacia el oeste. Sin embargo, la orientación de los vuelos de la mañana fue similar posterior a noches con vientos de deriva a las noches sin vientos de deriva, sugiriendo que las aves en una mañana cualquiera no necesariamente estaban re-orientándose como respuesta inmediata a la deriva ocurrida la noche anterior. Dadas las características topográficas de nuestra área de observación, los movimientos hacia el oeste-noroeste de las aves en nuestro estudio están mejor explicadas por una interacción mas compleja que puede incluir una combinación de la compensación por la deriva por el viento, una búsqueda de hábitats de parada adecuados, vuelos en una dirección que minimiza la perdida del progreso norte hacia el objetivo migratorio y evitar cruzamientos del lago.

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Abstract Migratory birds encounter the Great Lakes while moving through eastern North America toward breeding grounds to the North, which offers a good opportunity to study variation in migratory behavior as birds face a potentially influencing topographical feature. Using passive infrared technology, we documented the direction of relatively low-flying, nocturnal, mostly passerine migration in spring along the southern coast of Lake Erie’s western basin. We examined the extent to which spring migrants flew across Lake Erie as a continuation of the inland, northeasterly broad front migratory direction, as determined by weather radar and infrared observations, or displayed a tendency to deviate to more closely follow the direction of the coastline. We found that an estimated 62% of all low-flying migrants deviated their flight directions toward the coast of Lake Erie at 2 coastal sites, Cedar Point and Ottawa, which were characterized by northwest–southeast oriented coastlines. Migrants at a third coastal location, Maumee Bay, which has a more east–west oriented coastline, did not display similarly deviated flight directions. We found that even when winds were energetically favorable for a lake crossing, many migrants still routinely displayed deviated flight directions that approached paralleling the coastline. Further, the mean flight direction at one site, Ottawa, shifted more in the direction of the coastline as the night progressed, suggesting that time of night could influence the shift to a more coastal flight direction. The data indicate that the western basin of Lake Erie acts as a salient topographical feature influencing the flight directions of nocturnal migrants. The data further suggest that birds are making active decisions while in flight, based on current environmental and physiological conditions, about whether to continue to cross Lake Erie or take a coastal detour.

Identifying migratory pathways is critical for understanding the risks affecting migratory birds. Large expanses of open water are a potential challenge during migration because of increased mortality and the energetic cost of flight \"detours.\" Therefore, migratory birds face tradeoffs between the risk assumed by overwater flights and minimizing energy or time. However, it may favor a bird energetically to deviate their flight paths by following coastlines or, in many cases, there may be an optimum detour involving a shortcut across a smaller fraction of the obstacle. We investigated the patterns of nocturnal bird migration in spring at 3 coastal sites and 1 inland site on the southwest coast of Lake Erie by means of a passive infrared device. The directions of the coastlines differed by 35° at the 3 coastal sites, which were 16 km apart. Observations across 50 nights were made from civil sunset through civil sunrise when conditions permitted. Generally, mean track directions of birds observed along the coast differed from the prevailing broad front direction (NNE), suggesting a counterclockwise shift in orientation which may reduce the extent of an overwater flight. The mean track direction differed between sites, suggesting some local influence of the underlying topography on orientation behavior. The propensity of birds to deviate from the broad front direction was significantly higher at coastal sites where the orientation of the coastline has a more northerly component. The results suggest birds actively shifting their migratory orientation in an energetically meaningful way upon arrival to the Lake Erie coast.

Many long-distance migratory songbirds encounter geographic barriers at some point during their annual migrations. Bird migration routes often follow detours where passages across ecological barriers are either avoided entirely or reduced in extent. Numerous early reports of broad front migration crossing coastlines seemingly without taking notice of the transition from land to water contradict more recent observations suggesting important deviations from the standard broad front direction associated with the underlying topography, in particular, the course of coastlines. However, whether and under what conditions nocturnally migrating songbirds would respond to a more modest obstacle such the Great Lakes is less well understood. I used a combination of weather surveillance radar and thermal imaging cameras to capture the direction of spring migration both regionally, as migrants are approaching the southern shore of Lake Erie, and locally along the coast. In the present body of work, I have studied (1) the nocturnal migratory orientation of birds along the southwest coast of Lake Erie during the spring migratory season, (2) the orientation of migrants with respect to the prevailing winds, and (3) the orientation with respect to time of night, which presumably is reflective of differences in the energetic condition of migrants. Along the southwest coast of Lake Erie, the direction of migration differed significantly from the broad front direction approaching Lake Erie, and the probability of a migrant deviating from the broad front direction was higher at sites which presented southeast-northwest oriented coastlines (Cedar Point and Ottawa NWR). Even under energetically favorable winds above Cedar Point and Ottawa some migrants were observed detouring the Lake, and migration in crosswinds increased the likelihood of either coastal flights in easterly winds or crossing flights in westerly winds. Migrants approaching the shore above Ottawa showed a significant increase in the percent of flight bearings deviating along the coast late in the night compared to early in the night, possibly reflective of a decline in motivation to cross as energetic stores become depleted during the night. Migrants approaching the southern shore above Maumee Bay, an east-west oriented coastline, were more consistent with observations made inland, away from any presumptive effects of the coast, and made a Lake crossing regardless of winds aloft or time of night. As a whole, the present dissertation expands the scientific understanding of the phenomenon of coastal migration in the context of an understudied system, the Great Lakes, and in particular Lake Erie.