The Cerulean Warbler (Setophaga cerulea) is a declining Nearctic-Neotropical migratory species of conservation concern. Implementing full annual cycle conservation strategies to facilitate recovery has been difficult because we know little about the migratory period or connectivity between North American breeding regions and South American non-breeding regions. Between 2014–2017, we deployed geolocators on 282 males at 13 study sites throughout the species’ range with the objectives of a) evaluating the strength of connectivity between breeding and non-breeding regions; b) identifying approximate routes and stopover regions, and c) documenting migration phenology. We retrieved migration data from 28 birds and most (14/15; 93%) Appalachian-breeders overwintered in the Colombian/Venezuelan Andes, whereas 5/7 (71%) breeders from the Ozarks overwintered in the southwestern portion of their non-breeding range in Peru/Ecuador. During spring migration, over a 26 d ± 1.2 (SE) period, birds (n = 23) staged at multiple stopover locations between Panama and southern Mexico. The migratory periods were substantial and approximately equal in duration: 38 ± 2 d (SE) in fall and 42 d ± 2 (SE) in spring. Based on the observed connectivity pattern, conservation of Appalachian breeding populations should focus on forest protection and restoration in premontane/lower montane forests of Colombia and Venezuela, whereas Ozark breeding population conservation should focus efforts in Ecuador and Peru. Additionally, protections of forests used by ceruleans during stopovers throughout Central America and southern Mexico, in southeastern United States coastal areas, and in the Mississippi Alluvial Valley are likely to have high conservation value for this species.

We deployed 257 light-level geolocators on male Cerulean Warblers (Setophaga cerulea) across 12 study sites located throughout the breeding range from 2014–2016. A year after deployments, we recovered geolocator data from 26 birds that were recaptured with Biotrack (Wareham, UK) model ML6340 units or Migrate Technology (Cambridge, UK) model Intigeo-Intigeo-P30Z11-7 units. Biotrack units recorded light levels along with timestamps (in GMT) every two minutes as .lig files, and Migrate units recorded light levels along with timestamps (in GMT) every 5 minutes for 6–13 months as .lux files, both of which we processed and analyzed largely using the R packages "TwGeos and SGAT". Analyses of these light-level data files allow us to estimate approximate latitudes and longitudes based on length of day and twilight times encountered by Cerulean Warblers across their entire annual cycle as they migrate between North and South America. Our geolocation analysis methods are described in "Cerulean Warblers (Setophaga cerulea) exhibit parallel migration patterns and multiple migratory stopovers within the Central American isthmus". 

The data files included with this submission can be opened with Microsoft Excel or any program that opens .csv files.