Seasonal Movements of the Short-Eared Owl (Asio flammeus) in Western North America as Revealed by Satellite Telemetry
The Short-eared Owl (Asio flammeus) is a widespread raptor whose abundance and distribution fluctuates in response to the varying amplitudes of its prey, which are predominately microtines. Previous efforts to describe the seasonal movements of Short-eared Owls have been hindered by few band recoveries and the species' cryptic and irruptive behavior. We attached satellite transmitters to adult Short-eared Owls at breeding areas in western and interior Alaska in June 2009 and July 2010, and tracked their movements for up to 19 mo. Owls initiated long-distance southward movements from Alaska and most followed a corridor east of the Rocky Mountains into the Prairie provinces and Great Plains states. Four owls followed a coastal route west of the Rocky Mountains, including one owl that crossed the Gulf of Alaska. Completed autumn migration distances ranged from 3205–6886 km (mean = 4722 ± 1156 km [SD]). Wintering areas spanned 21° of latitude from central Montana to southern Texas, and 24° of longitude from central California to western Kansas. Subsequent seasonal migrations were generally northward in spring and southward in autumn; these movements were comparatively short-distance (mean = 767.5 ± 517.4 km [SD]) and the owls exhibited low site fidelity. The Short-eared Owls we tracked from two relatively local breeding areas in Alaska used a patchwork of diverse open habitats across a large area of North America, which highlights that effective conservation of this species requires a collaborative, continental-scale focus.
Asio flammeus
es un ave rapaz de amplia distribución cuya abundancia y distribución fluctúa en respuesta a la variabilidad de sus presas, las cuales son predominantemente roedores microtinos. Los esfuerzos previos para describir los movimientos estacionales de A. flammeus se vieron obstaculizados por la recuperación de pocas anillas y por el comportamiento críptico e irruptivo de la especie. Equipamos con transmisores satelitales a individuos adultos de A. flammeus en áreas de cría en el oeste y el interior de Alaska en junio del 2009 y julio del 2010, y seguimos sus movimientos hasta 19 meses. Los búhos iniciaron sus movimientos de larga distancia desde Alaska hacia el sur y la mayoría siguió un corredor ubicado al este de las Montañas Rocosas hacia las provincias de las Praderas y los estados de las Grandes Llanuras. Cuatro individuos siguieron una ruta costera al oeste de las Montañas Rocosas, incluyendo un búho que cruzó el Golfo de Alaska. Las distancias completas de la migración de otoño oscilaron entre 3205 y 6886 km (promedio = 4722 ± 1156 km [DE]). Las áreas de invernada abarcaron desde los 21° de latitud desde el centro de Montana hasta el sur de Tejas y 24° de longitud desde el centro de California hasta el oeste de Kansas. Las migraciones estacionales posteriores fueron en general hacia el norte en primavera y hacia el sur en otoño; comparativamente, estos movimientos fueron de corta distancia (promedio = 767.5 ± 517.4 km [DE]) y los búhos mostraron una baja fidelidad al sitio. Los individuos de A. flammeus seguidos, pertenecientes a dos áreas reproductivas relativamente locales, utilizaron un mosaico diverso de hábitats abiertos a lo largo de una gran área de América del Norte, lo que remarca que la conservación efectiva de esta especie requiere de un enfoque colaborativo a escala continental. [Traducción del equipo editorial]Abstract
Resumen
(A) Autumn movements of 14 Short-eared Owls captured on Seward Peninsula (orange lines) and 12 owls captured at two sites in interior (black lines) Alaska. Yellow dots denote location and duration of stopovers. Triangles denote last known location of partial migratory tracks, and dots denote locations where owls completed migration. (B) Seasonal movements of four Short-eared Owls following first documented winter period. Black and orange lines delineate spring and autumn migration routes, respectively. Other symbols are as for (A). (C) Movements of one owl that remained in southern Idaho for a full year after migrating south from Alaska. For all maps, orthodromes are depicted as straight lines in this gnomonic map projection.
Tracking speeds of Short-eared Owls during local daytime and nighttime hours. More and faster movements occurred at night. To represent movements of flying owls, samples (in parentheses) were limited to vectors of 2–10 hr duration that were bounded by standard quality Argos locations (LC 3, 2, or 1) and represented ground speeds >5 km/hr. The upper range of tracking speeds (35–45 km/hr) represents conservative (straight line) maximum estimates of sustained (2–10 hr) movement rates over the landscape. Boxes span the interquartile range (IQR), whiskers extend to 1.5 times the IQR, means are denoted with diamonds, and medians with horizontal lines.
Long-distance movements (50–80 hr and >500 km) of Short-eared Owls in relation to wind conditions. Positive values represent tailwinds and negative values represent headwinds.
Near-surface (1000 millibar) wind conditions (National Oceanographic and Atmospheric Administration 2016) during the flight of a Short-eared Owl over the Gulf of Alaska. Black dots are Argos satellite tracking locations and white dots are estimated locations for the beginning and end of the open-water crossing. (A) Beginning wind conditions when the owl encountered a low pressure system in the northern Gulf of Alaska and appeared to follow tailwinds around the southern side of the low. (B) Ending wind conditions showing a trough of easterly tailwinds that prevailed as the owl completed the second half of the crossing.
Migratory stopover duration of Short-eared Owls in relation to wind conditions. Positive values represent tailwinds and negative values represent headwinds.
Contributor Notes
Associate Editor: Jeff P. Smith