The broad spectrum of species studied at Helgoland
and the long-term nature of the dataset provide unique
confirmation that the trend towards earlier spring passage
in migrating birds is an even more general phenomenon in
western and northern European migrants than previously
thought. This is valid, in contrast to some recent investigations
(Sokolov et al. 1998; Both & Visser 2001;
Tryjanowski et al. 2002), for both short/medium-distance
and long-distance migrants. The correlation with climate
change during the last four decades, particularly with the
change in spring temperature and, to a greater extent, the
change in the NAO index, is striking. Namely, in view of
the fact that daily trapping totals are variable owing to, for
example, mass migration or arrested migration