Cerulean Warblers (Setophaga cerulea) are among the fastest declining Nearctic-Neotropical migrant wood-warblers (Parulidae) in North America. Despite ongoing conservation efforts, little is known about their non-breeding distribution. In June 2016-2018, we deployed geolocators (n = 30) on adult male Cerulean Warblers in Indiana, USA, to track annual movements of individuals. Recovered geolocators (n = 4) showed that Cerulean Warblers occurred broadly throughout northern South America. Autumn migration lasted 44-71 days (n = 4), whereas spring migration lasted 37-41 days (n = 3). The average migration distance was 5268 km. During autumn migration, Cerulean Warblers made 1-4 stopovers (i.e., ≥2 days; n = 4) and 1-2 stopovers during spring migration (n = 3). When crossing the Gulf of Mexico during autumn migration, two birds stopped over after crossing, but not beforehand. Two others navigated through the Caribbean rather than crossing the Gulf of Mexico. During spring migration, one individual stopped after crossing, one individual stopped before crossing, and one individual stopped before and after crossing the Gulf of Mexico. No birds migrated through the Caribbean Islands during spring migration. These results represent novel information describing annual movements of individual Cerulean Warblers and will inform conservation efforts for this declining species.

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Space use information can be integral in the creation of effective conservation and management strategies.  However, avian territories (defended areas) are studied far more frequently than home ranges (entire use areas), and few studies have compared the two areas.  This is the case for the cerulean warbler Setophaga cerulea , a declining Neotropical migrant songbird.  There is an extensive record of cerulean warbler territory estimates, while the home range has only recently been explored.  Studies of these space use areas differ in their sampling techniques, estimation techniques, and location.  Consequently, comparison of both space use areas is difficult.  We used radio telemetry to delineate cerulean warbler diurnal space use areas in southern Indiana.  The primary objective of this study was to describe the relationship between the home range and territory.  Kernel density home range estimates of sampled adult male cerulean warblers ( n = 14, mean ± SE = 2.33 ± 0.29 hectares) were significantly larger (0.54 ± 0.18 ha, P = 0.006) than territory estimates of the same group of individuals ( n = 14, mean ± SE = 1.79 ± 0.39 hectares; P = 0.006).  Minimum convex polygon home range estimates of the same group of birds ( n = 14, mean ± SE = 3.45 ± 0.55 hectares) were also significantly larger (1.38 ± 0.19 ha, P < 0.001) than territory estimates ( n = 14, mean ± SE = 2.07 ± 0.58 hectares).  Additionally, territory estimates described here are considerably larger than other published estimates for this species, which were delineated using spot mapping methods.  Cerulean warbler home ranges contain territorial and extra-territorial space, and the latter has not been studied in detail.  Area and habitat requirements likely vary throughout this species’ range, and regional conservation management might benefit from study in peripheral space use areas.

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