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1 September 2012 Determination of Raptor Migratory Patterns Over a Large Landscape
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Abstract

Each autumn, tens of thousands of raptors pass over Hawk Ridge in Duluth, Minnesota, on their southbound migration, but migratory pathways leading to Hawk Ridge are unknown. To address this issue, we counted migrating raptors between mid-August and mid-November 2008 from 24 observation points along eight transects perpendicular to the shoreline between Duluth and the Minnesota-Canadian border. Our goals were to determine migratory pathways over a large area (>2000 km2) and identify how these movements were affected by weather, time of day, season, and characteristics of the landscape. A total of 4303 raptors of 14 different species were counted during the 2008 migration season. Exploratory analyses suggested that migratory raptors concentrated near the northern shoreline of Lake Superior, particularly during midday when winds are westerly. Average migration height differed between soaring raptors (buteos and eagles) and accipiters, with >40% of soaring raptors observed higher than 100 m above the tree canopy and ≥30% of accipiters observed lower than 100 m above the tree canopy. Mixed models analysis identified the significant factors (P < 0.05) associated with total raptor migration: wind direction, time of day, temperature, and antecedent wind (number of days in which the wind did not have a westerly component prior to the observation days; R2  =  0.23). Significant factors associated with soaring-raptor migration included wind direction, time of day, temperature, and seasonal interval (e.g., early or late in the migration season; R2  =  0.17) and those associated with accipiter migration included time of day, temperature, antecedent wind, wind direction, and seasonal interval (R2  =  0.29). With the increasing popularity of wind power development, information is needed regarding avian migratory pathways to avoid bird-turbine conflicts. The methodology and design of this study provided a means to quantify the magnitude, timing, pathways, and weather conditions associated with raptor migration over a large landscape.

Cada otoño, decenas de miles de rapaces sobrevuelan Hawk Ridge en Duluth, Minnesota, en su migración hacia el sur, pero las rutas migratorias que llevan a Hawk Ridge son desconocidas. Para resolver este tema, contamos rapaces migratorias entre mediados de agosto y mediados de noviembre de 2008 en 24 puntos de observación a lo largo de ocho transectas perpendiculares a la línea de costa entre Duluth y la frontera entre Minnesota y Canadá. Nuestros objetivos fueron determinar las rutas migratorias sobre un área extensa (>2000 km2) e identificar cómo estos movimientos se vieron afectados por el clima, la hora del día, la estación y las características del paisaje. Un total de 4303 rapaces de 14 especies diferentes fueron contadas durante la época migratoria de 2008. Análisis exploratorios sugirieron que las rapaces migratorias se concentraron cerca de la línea de costa norte del Lago Superior, particularmente durante el mediodía cuando los vientos tienen dirección oeste. La altura media de migración difirió entre rapaces de vuelo planeado (especies de Buteo y águilas) y accipitéridos, con >40% de rapaces de vuelo planeado observadas a alturas mayores a los 100 m sobre el dosel de los árboles y ≥30% de accipitéridos observados a alturas menores a los 100 m sobre el dosel arbóreo. Modelos de análisis mixtos identificaron los factores significativos (P < 0.05) asociados con la migración de rapaces total: dirección del viento, hora del día, temperatura y viento antecedente (número de días en los que el viento no tuvo un componente oeste previo a los días de observación; R2  =  0.23). Los factores significativos asociados con la migración de rapaces de vuelo planeado incluyeron dirección del viento, hora del día, tempe

Heidi M. Seeland, Gerald J. Niemi, Ronald R. Regal, Anna Peterson, and Carly Lapin "Determination of Raptor Migratory Patterns Over a Large Landscape," Journal of Raptor Research 46(3), 283-295, (1 September 2012). https://doi.org/10.3356/JRR-11-44.1
Received: 6 June 2011; Accepted: 1 March 2012; Published: 1 September 2012
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