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| Males of most migratory organisms, including
many birds, precede female conspecifics on their journey
to the breeding areas. Several hypotheses have been
proposed to explain the evolution of protandrous
migration, yet they have rarely been tested at the interspecific
level. Here, we provide correlational support for
the ‘‘mate opportunity’’ hypothesis, which assumes that
selection favours protandry in polygynous species where
males gain significant fitness benefits from arriving earlier
than females. Drawing on phenological data collected
at two northern European stopover sites, we show
that the time-lag in spring passage between males and
females of five Palearctic migratory songbird species is
positively associated with levels of extrapair paternity
available from the literature. This suggests that males
arrive relatively more in advance of females in species
with high sperm competition where sexual selection
through female choice is intense. Thus, protandry may
arise from selection on the relative arrival timing of
males and females rather than from selection within one
of the sexes. | |
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