Sanderlings (Calidris alba) of two different age classes at the moment of individual colour-marking at four non-breeding sites that were or were not observed during migration following the capture.

<p>The data file contains data of Sanderlings (<em>Calidris alba</em>) of two different age classes at the moment of capture and individual colour-marking at one of four wintering areas that were or were not observed during migration following the capture. Each individual is indicated with a unique number in column &ldquo;BirdID&rdquo;. The column &ldquo;country&rdquo; indicates which of the four wintering areas (as depicted in Fig. 1 in the manuscript), with GB indicating England, PT indicating Portugal, MR indicating Mauritania and GH indicating Ghana.&nbsp; The &ldquo;age&rdquo; of each bird was either juvenile (&lt;1 year old) or adult (&gt;1 year old). Whether an individual was observed during migration, i.e. at least 2 latitudinal degrees north of its average winter location between 15 March &ndash; 15 October, in the migration period following capture is indicated with a 0 (not observed) or 1 (observed)&nbsp; in the column &ldquo;observed&rdquo;. Further details can be found in the methods section in the manuscript.</p>