THE EVOLUTION OF POLYGAMY IN EUROPEAN REED WARBLERS OF THE GENUS ACROCEPHALUS - A COMPARATIVE APPROACH

A comparative survey of mating systems in six European Acrocephalus species revealed that two of the species can be classified as polygamous and four monogamous. Several correlations were then found between mating system and various aspects of behaviour, ecology and morphology. Males of polygamous species invested little or nothing in parental care, whereas males of monogamous species shared it equally with females. Males of polygamous species defended large territories in high productivity marshland ecotones rich in arthropod food. Monogamous males defended smaller territories in less productive marshland, Females of polygamous species fed their young on larger prey collected within territory near the nest. In monogamous species, smaller prey was collected from longer flights often outside territory. Polygamous species also had larger bills as an adaptation to take larger prey. Males of polygamous species had short, simple songs used in territorial defense, whereas males of monogamous species had long, complex songs for mate attraction. These correlations were then used to make predictions about the mating systems or ecology and behaviour of less well known Acrocephalus species. The comparative approach is a useful tool in the continuing investigation into the evolution of polygamy. It suggests that the emancipation of males from biparental care and the constraints of food supply have both been important factors. In Acrocephalus warblers, polygamy is best viewed as a continuum of gradual departure from monogamy in the rich but variable marshlands of Europe.