Data from: An assay to investigate factors influencing initial orientation in nocturnally fledging seabirds.

The first solitary migration of juvenile birds is difficult to study
because of a low juvenile survival rates and sometimes long delays in
return to the breeding grounds. Consequently, little is known about this
crucial life event for many bird species, in particular the sensory
guidance mechanisms facilitating the first migratory journey. Initial
orientation during the first migration is a key measure to investigate
these mechanisms. Here, we developed an assay to measure initial
orientation as flight direction upon first take-off in nocturnally
fledging juvenile seabirds. We dorsally deployed a coloured LED on
juvenile birds to allow researchers to observe the vanishing bearings of
individuals as they flew out to sea. Additionally, we co-deployed either a
small Neodymium magnet or glass bead (control) on top of the bird’s head
to investigate the use of magnetoreception, previously unexplored in this
early life stage.   We used this assay to observe the first
flight of Manx shearwaters (Puffinus puffinus) and found that they did not
orient towards their wintering ground straight after taking off. Further,
we did not find an effect of the magnetic treatment on juveniles’ flight
direction, though whether this is due to the birds not using
magnetoreception, other salient cues being available or
a lack of motivation to orient to the migratory beeline is
unclear. We were, however, able to identify wind direction and topography
as drivers of first flight direction in Manx shearwaters, which fledged
with wind component between a crosswind and a tailwind and directed their
maiden flight towards the sea and away from the land.   
This novel assay will facilitate the study of the maiden flight of
nocturnally fledging birds and will help advance the study of sensory
guidance mechanisms underpinning migratory orientation in a wide range of
taxa, including species which are traditionally challenging to
study.