Getting into position. A further look at the winter timing of a pair of Belgian swifts in 2012. This is the third instalment of our story about where the Swifts were in December and February.
March is a difficult month for tracking birds using light level dataloggers. From about 15 days either side of the spring equinox on the 20th, the day length is about the same across all latitudes and so no north / south fix is possible. However the timing of local midday is not affected, so longitude (how far east or west) can be calculated.
In the following map I've plotted the locations during March (shown in closed or open black dots) by using the longitude combined with a fabricated latitude derived by simply dividing the first and last fix before and after the equinox by the number of days. The February and April positions are also included to show how this ties in before and after the equinox
Red dots are female positions in February and in April
Black dots are female positions in March
Blue dots are male positions in February and in April
Open dots are male positions in March
[Click map to enlarge]