Sobre la historia de los cantos de las aves o los cantos de las aves como historia / About the history of the songs of birds or the songs of birds as history

Resumen Igual que es posible trazar una historia de los cantos de las aves, de su recepción por y su relación con los seres humanos, también se puede especular sobre si esos cantos pueden funcionar como historia, viva, sonora, en qué grado y modos, así como en qué diferiría esa historia aviar de la humana o si podría enriquecerla. Muchas aves, después de todo, transmiten y aprenden sus cantos unas de otras, construyen sobre ellos y los complican, recogiendo otros sonidos que asumen e incorporan, sonidos humanos incluidos. Crean así paisajes sonoros que no siempre quedan de fondo: en ocasiones, reclaman su relevancia y toman el primer plano, en la historia y como historia.

Abstract Just as it is possible to trace a history of the songs of birds, of their reception by human beings, and of how humans relate to them, it is also possible to speculate on whether these songs can function as history, a living, resounding history, to which degree and in which ways. As well as on how that avian story would differ from the human one, or if it could enrich it. Many birds, after all, learn their songs from each other, they build on and complicate them, picking up other sounds they incorporate, human sounds included. Thus, they create soundscapes that are not always in the background: sometimes, they claim their relevance and take the foreground, in history and as history.

Differences in predatory pressure on terrestrial snails by birds and mammals.

The evolution of shell polymorphism in terrestrial snails is a classic textbook example of the effect of natural selection in which avian and mammalian predation represents an important selective force on gene frequency. However, many questions about predation remain unclear, especially in the case of mammals. We collected 2000 specimens from eight terrestrial gastropod species to investigate the predation pressure exerted by birds and mice on snails. We found evidence of avian and mammalian predation in 26.5% and 36.8% of the shells. Both birds and mammals were selective with respect to snail species, size and morphs. Birds preferred the brown-lipped banded snail Cepaea nemoralis (L.) and mice preferred the burgundy snail Helix pomatia L. Mice avoided pink mid-banded C. nemoralis and preferred brown mid-banded morphs, which were neglected by birds. In contrast to mice, birds chose larger individuals. Significant differences in their predatory pressure can influence the evolution and maintenance of shell size and polymorphism of shell colouration in snails.