Travel rate for migrating swifts in relation to latitude.

<p>Daily travel rate in relation to latitude calculated for 3-day segments for six migrating swifts for periods of actual travel during (A) autumn and (B) spring migration, respectively. The curves show second degree polynomial fitted to the data: (A) U_trav = 155.5+15.6 Lat –0.29 Lat², with maximum travel rate at latitude 27.1°N; (B) U_trav = 278.4+19.3 Lat –0.39 Lat², with maximum travel rate at latitude 24.8°N.</p

Migration tracks of swifts.

<p>(A) Autumn migration tracks for 6 individuals where filled circles represent 3-day average positions and filled yellow circles represent stopover periods when the bird did not move (2 days or more). Dotted lines indicate lack of data around autumn equinox. (B) Spring migration tracks for the same birds as in (A).</p

Average key numbers of migration for swifts <i>Apus apus</i> as recorded using light-level geolocators, N = 6.

<p>Average key numbers of migration for swifts <i>Apus apus</i> as recorded using light-level geolocators, N = 6.</p

Wind assistance for six swifts <i>Apus apus</i> during spring migration calculated for four different pressure levels (925, 850, 700 and 500 hPa, respectively) representing altitudes 750 m, 1500 m, 3000 m and 5000 m, respectively.

<p>Tailwinds are shown in normal font and headwinds are shown in bold font.</p>*<p>Did not make stopover in Liberia.</p