Selective disappearance based on navigational efficiency in a long-lived seabird

Whilst efficient movement through space is thought to increase the fitness
of long-distance migrants, evidence that selection acts upon such traits
remains elusive. Here, using 228 migratory tracks collected from 102 adult
breeding common terns (Sterna hirundo) aged 3 – 22 years, we find evidence
that older terns navigate more efficiently than younger terns, and that
efficient navigation leads to a reduced migration duration and earlier
arrival at the breeding and wintering grounds.  We additionally
find that the age-specificity of navigational efficiency in adult breeding
birds cannot be explained by within-individual change with age (i.e.
learning), suggesting the selective disappearance of less navigationally
efficient individuals.  This suggests that, at least in common
terns, learning of navigational skills may be largely absent in adulthood,
and limited to the pre-breeding phase of life where tracking is more
difficult. We propose that selection might explain parts of the
age-specificity of navigational performance observed in migratory taxa
more generally; discuss the causes and evolutionary implications of
variation in navigational traits and the selective agents acting upon
them; and highlight the necessity of longitudinal studies when considering
changes in behaviour with age.