Figure 2
Normal migratory directions of white-throated sparrows (WTSPs) in southern Ontario in spring determined by three methods.
(a) Map assignment of deuterium isotope ratios extracted from tail feathers grown during the breeding season. Black dots show the capture (lower right) site, Long Point Bird Observatory (LPBO), and displacement (upper left) site in Saskatchewan. The values on the right scale represent the number of birds in the sample that were isotopically consistent with a cell of the same colour in the map representing a likely origin at 2:1 odds (Supplementary Material). Black rectangle shows the spatial extent of the Motus automated-telemetry array (zoomed in on (b)). (b) Migratory flight tracks (black arrows) detected by radio-tracking in southern Ontario by the Motus automated-telemetry array (black crosses). Note that from 8 birds released at the capture site at LPBO, six were successfully radio-tracked, two of which showed identical flight directions. (c) Emlen funnel data obtained from a sub-sample (n = 17) of later displaced birds tested at the capture site, LPBO. Black dots at the circle’s perimeter: individual mean directions. The arrow shows mean group vector flanked by its 95% confidence interval (solid lines). The dashed circles indicate the minimum length of the group mean vector needed for significance according to the Rayleigh test45 (inner circle, P = 0.05; outer, P = 0.01). Combined, all three methods indicate that WTSPs migrating through LPBO are heading generally North most probably towards breeding and/or natal sites in central Ontario. Maps were created using the R46 (version 3.2.4, https://www.r-project.org/), package ‘ggmap’. The circular diagram was created by Inkscape (version 0.91, https://inkscape.org/).
