Seasonal micro-migration in a farm-island population of striated caracaras (Phalcoboenus australis) in the Falkland Islands

• Published in: Movement Ecology
• Main Authors: Katie J. Harrington, Suzan Pole-Evans, Micky Reeves, Marc Bechard, Melissa Bobowski, David R. Barber, Kalinka Rexer-Huber, Nicolas Lecomte, Keith L. Bildstein
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2018
• Subjects: Movement ecology; Phalcoboenus australis; Island population; Short distance; Seasonal; Space use; Biology (General); QH301-705.5; Austral; Saunders; Saunders Island
• Online Access: https://doi.org/10.1186/s40462-018-0122-8; https://doaj.org/article/90c64707b79e4c869775624088d10117

Abstract Background The extent to which seasonal changes in food availability affect small-scale movements in free-ranging populations of birds of prey is relatively little studied. Here we describe a seasonal “micro-migration” of a farm-island population of striated caracaras (Phalcoboenus australis) in the Falkland Islands in response to seasonal changes in the availability of seabird carcasses. We banded more than 450 individuals on Saunders Island, deployed archival and satellite GPS data loggers on 17 individuals, and monitored movements within and between two feeding areas on Saunders Island, a “marine-subsidized” site near seabird colonies and an anthropogenic “human-subsidized” farm site 16 km to the southeast. Results During 67 observation days between 2010 and 2015, resightings of 312 banded caracaras were greater at the marine-subsidized site during austral summer than winter, and the total daily resightings varied significantly between spring versus summer, summer versus winter, autumn versus spring, and autumn versus winter. Resightings were higher at the human-subsidized site in austral winter than summer and the total daily resightings varied significantly across all bi-seasonal comparisons. Resightings indicated that at least 12 of 197 birds (6.1%) moved between the human- and marine-subsidized sites at least once during the same winter, 15 of 335 birds (4.5%) did so in spring, none of 164 birds did so in summer, and 16 of 297 birds (5.4%) did so in autumn. Individuals fitted with archival GPS data loggers at the marine-subsidized site in summer maintained highly localized 95% kernel core areas (0.55 ± 0.12 km2 [mean ± SD]), whereas those at the human-subsidized site in winter maintained larger 95% kernel core areas (3.8 ± 4.6 km2). Two of 6 satellite-tagged individuals that summered at known caracara breeding colonies 80 km WNW of Saunders Island were subsequently resighted in winter at the human-subsidized site. Conclusion Our results suggest that seasonal shifts in food resource availability ...