Fig 1.
The stationary periods (greater or equal to 2 days) of 64 whinchats tracked with geolocators from their primary non-breeding grounds in Nigeria (blue) and Liberia (red) in several years.
Fig 2.
The breeding range of Nigerian (blue shaded polygon) and Liberian (red shaded polygon) whinchats tracked with geolocators.
Minimum convex polygons using their breeding locations are plotted. Locations are plotted with one standard error of estimated latitude and longitude assuming the same sun elevation angle as measured on the main non-breeding site (most error bars are too small to be visible at this scale).
Fig 3.
The three (19%) Liberian birds and 13 (27%) Nigerian birds that used sub-Saharan sites away from their main non-breeding location (where they were tagged and retrapped a year later).
Three Nigerian birds (6%) used two sites before crossing the Sahara. Each plotted point is the location of an additional non-breeding site, with filled points indicating a further second location (i.e., three non-breeding locations in total for the individual). Locations are plotted with one standard error of estimated latitude and longitude assuming the same sun elevation angle as measured on the main non-breeding site.
Table 1.
Summary statistics for migration characteristics of 64 Liberian and Nigerian whinchats.
Fig 4.
Predicted values from a mixed model of total migration distance (sum of all great circle distances between stationary periods for spring and autumn respectively).
With country and season as main effects, including individual bird tracked as a random effect, marginal R2 = 0.29, N = 51 birds and 92 complete spring or autumn migrations. The interaction term country*season was not significant.
Fig 5.
Predicted values from a mixed model of number of stopovers, with country and season as main effects, including individual bird tracked as a random effect, and testing the interaction of country*season.
Marginal R2 = 0.16, N = 51 birds and 92 complete spring or autumn migrations. The interaction term is marginally significant, with the main significant difference being between Liberia and Nigeria spring birds.
Fig 6.
Predicted values from a mixed model of longitude of stopover, with country and season as main effects, including individual bird tracked as a random effect, and testing the interaction of country*season.
Marginal R2 = 0.52, N = 41 birds and 159 stopovers. The interaction term is marginally significant: a larger increase in longitude for autumn vs spring for Nigerian birds, compared to Liberian birds.
Fig 7.
Predicted values from a mixed model of overall migration duration, with country and season as main effects, controlling for breeding latitude (predicted values set to mean breeding latitude of 55.7 degrees), including individual bird tracked as a random effect, and testing the interaction of country*season.
Marginal R2 = 0.15, N = 51 birds and 92 complete distances. All bars are significantly different apart from Liberia spring and autumn. Note the data here starts migration from the last sub-Saharan non-breeding site where multiple non-breeding sites were used and finishes when the bird returns to the main non-breeding site, where the bird was tagged.
Fig 8.
Predicted values from a mixed model of speed of travel during a migratory leg (excluding sub-Saharan movements), with country and season as main effects, including individual bird tracked as a random effect, and testing the interaction of country*season.
Marginal R2 = 0.03, N = 64 birds and 279 complete migration legs. The interaction term is significant with main difference being the greater decrease in speed between spring and autumn migrations for Nigeria birds.
Fig 9.
Predicted values from a mixed model of stopover duration, with country and season as main effects, including individual bird tracked as a random effect, and testing the interaction of country*season.
Marginal R2 = 0.24, N = 64 birds and 186 stopovers. Only the autumn Nigeria bar is significantly different. Note the data here excludes all stationary periods south of the Sahara in spring.