Table 2. Wind assistance for six swifts Apus apus 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.

	Part 1, Congo-Liberia detour				Part 2, Crossing Sahara Desert				Part 3, Crossing Europe
Swift	925	850	700	500	925	850	700	500	925	850	700	500
7881	0.6	3.0	6.6	6.1	1.1	2.1	4.8	8.3	−4.4	−4.8	−5.2	−7.3
7882	0.5	1.8	7.2	6.3	−1.0	0.9	5.8	9.3	−0.3	0.9	3.6	5.3
7964*					−1.0	−0.8	−2.4	−4.6	−2.8	−4.1	−6.2	−8.4
7968	−0.2	1.8	9.9	6.6	−1.7	1.8	5.9	8.9	−0.2	0.1	−1.0	−6.1
7969	1.5	3.5	6.6	7.4	−0.5	−1.3	−2.7	3.4	−0.9	0.0	−0.3	−2.8
7970	0.5	1.8	8.0	0.6	−1.3	0.5	3.0	4.1	4.7	3.7	3.1	6.7
Mean	0.6	2.4	7.7	5.4	−0.7	0.6	2.4	4.9	−0.6	−0.7	−1.0	−2.1

Tailwinds are shown in normal font and headwinds are shown in bold font.

^*Did not make stopover in Liberia.