Birdsong Overlapping: Random Coincidence or Acoustic Interactions.

Birdsong overlapping may either indicate communicative interaction between birds or be a simple coincidence. We developed a program that allowed us to mathematically modulate the independent singing of birds with a given level of song rate. This permitted us to statistically evaluate whether song overlapping is a random coincidence or real acoustic interactions between birds. Analysis of automatic recording (Song Meter SM4) of singing detected the cases of reliable acoustic interactions between both conspecific and heterospecific individuals. They account for 6% of the total singing time. The most numerous and actively singing chaffinches (in the case of singing of several individuals) suppress the singing of other species. The singing of a single chaffinch, on the other hand, can provoke the singing of other species, involving previously silent neighbors in song duels. It is possible that it is the acoustic interactions that are responsible for maintaining the structure of the population at the end of the breeding season.

Seasonal Dynamics of Testosterone and Corticosterone in Predatory Birds as Exemplified by the Northern Goshawk (Accipiter gentilis).

Testosterone and corticosterone are steroid hormones that regulate various aspects of bird behavior. The dynamics of blood level of these hormones depending on the stage of the life cycle have been studied in many species. It has been shown for both sexes that the levels of both hormones rise during the breeding season. We have studied changes in the level of these hormones in the northern goshawk (Accipiter gentilis) during a year. This has been the first study of this type on northern goshawk. We collected blood samples from 16 adult northern goshawks kept in pairs in aviaries in the VITASFERA Rare Bird Species Breeding Center. The testosterone level rises in males during the period of lekking and mating (March-June); however, there is no synchronous increase in females. The corticosterone level generally remains high throughout the year in both sexes. Since these are the only data on the northern goshawk, it cannot be concluded whether this is characteristic of the species as a whole or only for captive birds.

[Formation of passerine (Passeriformes) vocalization in ontogeny: the current state of the problem].

It the acoustic signal system of birds, songs and calls are distinguished. Up to the late 1970s, the attention of researchers was focused primarily on studying the process of song formation; the patterns of the call system formation remained virtually unstudied. In this field, the prevailing notion was that, since all calls are hereditary, their formation in the repertoire of all birds is similar. This notion was based on non-passerine birds, for which calls constitute most of the vocal communication. Most calls can, indeed, be formed without learning, even in nestlings raised in isolation. Yet some calls remain and are transferred in populations only through learning. The stages of sound repertoire development reflect crucial reorganizations of the acoustic behaviour of nestlings and are distinctly recognizable in most of the studied birds. The first three stages coincide with the periods of postnatal development of altricial birds distinguished by researchers from other fields (based on morphological, behavioural, and physiological characters). These are the early nestling, later nestling, and post-nestling periods. Two more periods may, however, be distinguished in the formation of vocalization: the fourth, confined to the period of hormonal reorganization of the organism during the autumn moult, and the fifth, coinciding with the beginning of the first reproductive cycle of the young bird. The formation of calls in representatives of different systematic groups (to families inclusive) can follow three principal paths: independent, successive, or explosive. Data on the development of the specific repertoire of acoustic signals in ontogeny can serve as a reliable taxonomic criterion, assisting in reconstructing and specifying phylogenetic relationships between different bird lineages.