Breeding sex ratios in two declining diving duck species: between-year variation and changes over six decades

摘要: Sex ratio variation has important consequences for population dynamics and viability. Adult sex is male biased in many duck species, data from wintering areas suggest bias been increasing some European species. However, the reasons changes ratios remain poorly understood, information on among breeding ducks limited. We studied long-term numbers Common Pochard Aythya ferina Tufted Duck fuligula southern Finland, former species being currently assessed as critically endangered latter Finland. In addition, we tested hypothesis that between-year affected by severity of weather conditions areas. The proportion females Ducks decreased 42.9% 1951–1970 to 36.9% 1996–2015, while no statistically significant change was observed (41.8% 39.5%, respectively). Both showed a decline over same period. Severity preceding winter did not affect area.