Seks jesienny ptaków i jego konsekwencje

Many bird species of the temperate climatic zone show in autumn behaviors of a clear sexual character – they engage in sexual display similar to the spring one. Males sing, defend territories, form pairs, and attempt copulation. Some species build nests and on very rare occasions lay eggs. Their testosterone level is very low as compared that during the spring display, but it is sufficiently high to elicit the costly sexual behavior. This raises a question why and in to what way this behavior is favored by natural selection. Birds paired in autumn and supporting territory can start breeding earlier in spring and, consequently, they can lay larger clutches, increase nest survival, and raise more broods in the season. Nests built during the autumn display by birds that are sedentary in winter can be used for roosting at night and thereby reduce the winter mortality of their owners. The autumn display is the first attempt to select a breeding site in the best possible habitat.