Data from: Ecological crossovers of sexual signalling in a migratory bird

Environmental shifts may induce sudden reversals in the relative quality or sexual attractiveness of mates (ecological cross-overs) leading to non-directional sexual selection. Studies on such ecological cross-overs induced by environmental shifts during the non-breeding season are particularly rare. We studied the interactive effects between wintering conditions and a male white wing patch on the breeding success of breeding pairs and the local survival of females in a migratory passerine population over a 32-year period. After dry winters, females paired with large-patched males were more likely to survive than those paired with small-patched males, and vice versa after moist winters. Moreover, after dry winters, large-patched males succeeded in attracting females that laid large clutches, while small-patched males bred with females that laid small clutches, and vice versa after moist winters. This phenomenon led to a difference in fledgling numbers only during years with dry winters and high precipitation during the breeding season. The selection on this male trait and its signalling value to females thus depended on a complex interaction between conditions both at the wintering and breeding grounds. We show that it is important to consider conditions during the non-breeding season when examining the effects of sexual ornaments on fitness.