Delayed song maturation and territorial aggression in a songbird

Rapid effects of estrogens on behavior: environmental modulation and molecular mechanisms

Estradiol can modulate neural activity and behavior via both genomic and nongenomic mechanisms. Environmental cues have a major impact on the relative importance of these signaling pathways with significant consequences for behavior. First we consider how photoperiod modulates nongenomic estrogen signaling on behavior. Intriguingly, short days permit rapid effects of estrogens on aggression in both rodents and song sparrows. This highlights the importance of considering photoperiod as a variable in laboratory research. Next we review evidence for rapid effects of estradiol on ecologically-relevant behaviors including aggression, copulation, communication, and learning. We also address the impact of endocrine disruptors on estrogen signaling, such as those found in corncob bedding used in rodent research. Finally, we examine the biochemical mechanisms that may mediate rapid estrogen action on behavior in males and females. A common theme across these topics is that the effects of estrogens on social behaviors vary across different environmental conditions.

Learn it now, sing it later? Field and laboratory studies on song repertoire acquisition and song use in nightingales

In many bird species, song changes with age. The mechanisms that account for such changes are only partially understood. Common nightingales Luscinia megarhynchos change the size and composition of their repertoire between their first and second breeding season. To inquire into mechanisms involved in such changes, we compared the singing of 1-year-old and older free-living nightingales. Older males have more song types in common than have 1-year olds. Certain song types frequently sung by older birds did not (or only rarely) occur in the repertoire of yearlings ('mature' song types). We conducted learning experiments with hand-reared nightingales to address reasons for the lack of mature song types. The acquisition success of mature songs was as good as that of control songs (commonly sung by both age groups). However, the analysis of song type use revealed that all yearlings sang common song types more often than mature types. This indicates that the absence of certain song types in the repertoires of free-living yearlings cannot be accounted for by learning and/or motor constraints during song learning. Moreover, our results suggest that in communication networks, animals may restrict the actual use of their signal repertoire to a certain subset depending on the context.