Data from: Sex-specific arrival times on the breeding grounds: hybridizing migratory skuas provide empirical support for the role of sex ratios

In migratory animals, protandry (earlier arrival of males on the breeding
grounds) prevails over protogyny (females preceding males). In theory, sex
differences in timing of arrival should be driven by the operational sex
ratio, shifting toward protogyny in female-biased populations. However,
empirical support for this hypothesis is, to date, lacking. To test this
hypothesis, we analyzed arrival data from three populations of the
long-distance migratory south polar skua (Catharacta maccormicki). These
populations differed in their operational sex ratio caused by the
unidirectional hybridization of male south polar skuas with female brown
skuas (Catharacta antarctica lonnbergi). We found that arrival times were
protandrous in allopatry, shifting toward protogyny in female-biased
populations when breeding in sympatry. This unique observation is
consistent with theoretical predictions that sex-specific arrival times
should be influenced by sex ratio and that protogyny should be observed in
populations with female-biased operational sex ratio.