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

• Published in: Animal Biotelemetry
• Main Authors: Katie J. Harrington, James A. Fahlbusch, Roland Langrock, Jean-François Therrien, Jennifer L. Houtz, Birgitte I. McDonald
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2020
• Subjects: Falconid; Hidden Markov model; Migratory prey; Seabirds; South Atlantic; Vectorial dynamic body acceleration; Ecology; QH540-549.5; Animal biochemistry; QP501-801; Saunders; Saunders Island
• Online Access: https://doi.org/10.1186/s40317-020-00214-y; https://doaj.org/article/763c089f15334075b20f58bdd031fb46

Abstract Background Animals need adaptive strategies to cope with seasonal changes in prey availability to survive and reproduce, which can include migrating, prey-switching, or reducing metabolic needs. Human settlements can disrupt spatiotemporal patterning in resource availability, which can affect animals’ foraging success, particularly for juveniles who are behaviorally developing and learning efficient foraging skills. Here, we investigate behavioral responses of juvenile striated caracaras, a near-threatened scavenging falconid, to seasonally migratory seabird prey and a farm settlement on Saunders Island, Falklands. We deployed accelerometer–GPS dataloggers (n = 27) to measure seasonal differences in daily and hourly vectorial dynamic body acceleration (VeDBA; an activity index measured in gravitational g) and space use, and investigated seasonal variation in body mass of the tagged subset and an additional 65 caracaras. Results Juvenile caracaras were overall similarly active in winter and summer. However, during winter, caracaras made the most of limited daylight by increasing average daytime activity (winter males: 0.16 ± 0.03 g, summer males: 0.09 ± 0.01 g, winter females: 0.12 ± 0.02 g, summer females: 0.08 ± 0.01 g). During winter, both sexes increased the percentage of daylight spent in high activity (winter males: 35 ± 5%, summer males: 21 ± 3%, winter females: 25 ± 6%, summer females: 16 ± 3%, p < 0.001) and ranged nearly 4 times farther (95% kernel density estimate winter: 2.36 ± 0.96 km2, summer: 0.61 ± 0.20 km2; p < 0.001). Furthermore, on a daily scale, males were 21% more active than females year-round (24-h average VeDBA: males 0.07 ± 0.01 g, females 0.06 ± 0.01 g; p < 0.01). We did not observe a significant seasonal difference in mass. Conclusion That caracaras’ daily activity and body mass did not vary between seasons suggests that wintering birds on Saunders are meeting resource requirements despite the absence of seasonally migratory prey. We hypothesize that human subsidies ...