Harrington Katie J, Pole-Evans Suzan, Reeves Micky, Bechard Marc, Bobowski Melissa, Barber David R, Rexer-Huber Kalinka, Lecomte Nicolas, Bildstein Keith L
1Acopian Center for Conservation Learning, Hawk Mountain Sanctuary, 410 Summer Valley Road, Orwigsburg, PA 17961 USA.
2Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039 USA.
Mov Ecol. 2018 Mar 30;6:4. doi: 10.1186/s40462-018-0122-8. eCollection 2018.
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 () 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.
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 km [mean ± SD]), whereas those at the human-subsidized site in winter maintained larger 95% kernel core areas (3.8 ± 4.6 km). 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.
Our results suggest that seasonal shifts in food resource availability drive seasonal micro-migrations in a farm-island population of striated caracaras, and that farm sites can be critical in providing nutritional resources for caracaras when naturally occurring marine-subsidized resources become less available. Our results have important implications for striated caracara spatial ecology and conservation, as increased winter survival could improve the status of this globally Near-Threatened population.
食物可获得性的季节性变化对自由放养的猛禽种群小规模移动的影响程度相对较少受到研究。在此，我们描述了福克兰群岛一个农场岛屿上条纹卡拉鹰（）种群的季节性“微迁徙”，这是对海鸟尸体可获得性季节性变化的响应。我们在桑德斯岛给450多只个体戴上脚环，在17只个体上部署了存档和卫星GPS数据记录器，并监测了桑德斯岛上两个觅食区域内及之间的移动情况，一个是靠近海鸟聚居地的“海洋补贴”地点，另一个是东南部16公里处的人为“人类补贴”农场地点。
在2010年至2015年的67个观察日期间，在南半球夏季，在海洋补贴地点重新观察到的312只戴环条纹卡拉鹰比冬季更多，并且每日重新观察到的总数在春季与夏季、夏季与冬季、秋季与春季以及秋季与冬季之间存在显著差异。在南半球冬季，在人类补贴地点重新观察到的数量比夏季多，并且每日重新观察到的总数在所有双季比较中均存在显著差异。重新观察结果表明，在同一冬季，197只鸟中至少有12只（6.1%）在人类补贴和海洋补贴地点之间至少移动了一次，335只鸟中有15只（4.5%）在春季这样做了，164只鸟在夏季没有这样做，297只鸟中有16只（5.4%）在秋季这样做了。夏季在海洋补贴地点佩戴存档GPS数据记录器的个体保持高度本地化的95%核核心区域（0.55±0.12公里[平均值±标准差]），而冬季在人类补贴地点的个体保持更大的95%核核心区域（3.8±4.6公里）。在桑德斯岛西北偏西80公里处已知的条纹卡拉鹰繁殖聚居地过夏的6只卫星标记个体中，有2只随后在冬季在人类补贴地点被重新观察到。
我们的结果表明，食物资源可获得性的季节性变化驱动了农场岛屿条纹卡拉鹰种群的季节性微迁徙，并且当自然出现的海洋补贴资源变得不那么可获得时，农场地点对于为条纹卡拉鹰提供营养资源可能至关重要。我们的结果对条纹卡拉鹰的空间生态学和保护具有重要意义，因为冬季存活率的提高可能改善这个全球近危种群的状况。
