Gyrfalcon Falco rusticolus post-glacial colonization and extreme long-term use of nest-sites in Greenland

Gyrfalcons Falco rusticolus use the same nest-sites over long periods of time, and in the cold dry climate of Greenland, guano and other nest debris decay slowly. Nineteen guano samples and three feathers were collected from 13 Gyrfalcon nests with stratified faecal accumulation in central-west and northwest Greenland. Samples were C-14 dated, with the oldest guano sample dating to c. 2740-2360 calendar years (cal yr) before present (BP) and three others were probably > 1000 cal yr BP. Feather samples ranged from 670 to 60 cal yr BP. Although the estimated age of material was correlated with sample depth, both sample depth and guano thickness gave a much less reliable prediction of sample age than use of radiocarbon dating on which the margin of error was less. Older samples were obtained from sites farther from the current Greenland Ice Sheet and at higher elevations, while younger samples were closer to the current ice sheet and at lower elevations. Values for delta C-13 showed that Gyrfalcons nesting farther from the Greenland Ice Sheet had a more marine diet, whereas those nesting closer to the ice sheet (= further inland) fed on a more terrestrial diet. The duration of nest-site use by Gyrfalcons is a probable indicator of both the time at which colonization occurred and the palaeoenvironmental conditions and patterns of glacial retreat. Nowhere before has such extreme long-term to present use of raptor nest-sites been documented.