Study site and study species
We studied four migrant bird species, Chaffinches (Fringilla
coelebs ), Dunnocks (Prunella modularis ), Song thrushes
(Turdus philomelos ) and Northern wheatears (Oenanthe
oenanthe , Wheatear hereafter), on the Island of Helgoland (54 ̵̊11’N, 07
°55’E), 50 km off the German North Sea coast. Chaffinches and Dunnocks
are diurnal migrants whereas Song thrushes and Wheatears are nocturnal
migrants. The birds were caught during daylight hours in the spring
(March and April) of 2019. All birds sampled are assumed to be migrants,
as only a few (or no) pairs of these species breed on Helgoland
(Dierschke et al. 2011).