The communicative value of complex singing in passerine birds

Birdsong is one of the most complex signals in the animal world, as it may consist of many different sounds grouped according to certain rules. Singing acts as a distant signal, indicating, e.g., the species and gender identity of the singer. However, territorial songbirds also use singing as an interactive social signal during territorial disputes, as well while interacting with female. In these contexts, males vary the type and timing of their songs to convey graded information about their motivational state, and those variations can play a role in communication. In this review, we considered how male songbirds vary their singing in territorial context. To study such variations, researchers usually simulated territorial intrusion by broadcasting conspecific singing in territories, including singing modified in a manner necessary for the researcher. For comparison, we considered briefly how singing vary in intersexual context. The author of the paper focuses on the role of singing complexity in communication. Therefore, not all known context-dependent changes in singing are considered, but only those related to “complexity”: the diversity of song/sound types and the transitional patterns of different song/sound types in the course of singing. Our review has shown that males change their singing when they detect environmental changes such as the appearance of a female or a competitor as follows: 1) song rate increases, 2) syllable rate increases, 3) song-type switching rate increases, 4) song-type diversity increases (i.e., the observed repertoire size), and 5) longer and more complex songs are predominantly used. In some species, the song bout organization may also change, but the data is still scarce. Typically, one or more, but not all the aforementioned acoustic behaviors have been found in a given song-bird species. All these behaviors (tactics) come down to a single strategy, namely: maximizing the acoustic diversity over a short period of time (e.g., several minutes), that is, increasing the number of different song and/or note types. The proximate causes of how the increased acoustic diversity work in the territorial competition context might lie in a sensory, or perceptual bias of the receiver. Namely, habituation should occur to repeated presentation of the same song type faster than to presentation of different song types. Therefore, by vocalizing more diversely, males more effectively influence the signal recipient’s behavior.

Re-reading Henrik Ibsen’s A Doll’s House: A Modern Feminist Perspective

This article aims to present a re-reading of Henrik Ibsen’s A Doll’s House from a feminist perspective. Ibsen’s play is a pioneering feminist play, and he is credited for creating the first real feminist character in the history of theatre. The central female characters are analyzed, and the article also addresses the attitude of society towards women and how they struggle to prove themselves. Feminist literary criticism and feminism constitute the conceptual framework of the paper. In this play, Nora Helmer is under the illusion that her married life is perfect and that she owns what she deserves. Torvald, her husband calls her a ‘twittering lark’, ‘squirrel’, ‘song-bird’, and she is pleased with it. However, her illusion shatters when she faces the reality of finding herself being treated like a doll. As soon as she realizes that there exists an individual self of her, she revolts. She leaves the house, challenging the social institutions which contribute to women’s subjugation. Nora protests against the ill-treatment towards her by society for her willingness to get her right back, for her self-respect, and for finding herself.

Singing patterns of the Oriental Magpie Robin Copsychus saularis Linn.

Oriental Magpie Robin is a song bird that resides in some tropical regions of Asia. The present work was attempted to provide a detailed study of the territorial singing of this species in the area of Biratnagar (Nepal). Songs of Oriental Magpie Robin was recorded by using a digital voice recorder (Olympus VN-8700PC) for one hour without break at seven selected sites in Biratnagar. Recorded songs were converted in the form of spectrogram by using avisoft. Seven Oriental Magpie Robins, belonging to seven different study sites of Biratnagar were taken as subjects and have been abbreviated as Bird A, B, C, D, E, F and G respectively. It was very surprising that there was not even a single motif which was matching among any of the birds. Out of 1782 song samples recorded from seven individuals, 328 types of songs were identified. These songs were composed of 3 to 18 types of elements.

Ultraviolet-reflective film applied to windows reduces the likelihood of collisions for two species of songbird

Perhaps a billion birds die annually from colliding with residential and commercial windows. Therefore, there is a societal need to develop technologies that reduce window collisions by birds. Many current window films that are applied to the external surface of windows have human-visible patterns that are not esthetically preferable. BirdShades have developed a short wavelength (ultraviolet) reflective film that appears as a slight tint to the human eye but should be highly visible to many bird species that see in this spectral range. We performed flight tunnel tests of whether the BirdShades external window film reduced the likelihood that two species of song bird (zebra finch, Taeniopygia guttata and brown-headed cowbird, Molothrus ater) collide with windows during daylight. We paid particular attention to simulate the lighting conditions that birds will experience while flying during the day. Our results indicate a 75–90% reduction in the likelihood of collision with BirdShades-treated compared with control windows, in forced choice trials. In more ecologically relevant comparison between trials where all windows were either treated or control windows, the estimated reduction in probability of collision was 30–50%. Further, both bird species slow their flight by approximately 25% when approaching windows treated with the BirdShades film, thereby reducing the force of collisions if they were to happen. Therefore, we conclude that the BirdShades external window film will be effective in reducing the risk of and damage caused to populations and property by birds’ collision with windows. As this ultraviolet-reflective film has no human-visible patterning to it, the product might be an esthetically more acceptable low cost solution to reducing bird-window collisions. Further, we call for testing of other mitigation technologies in lighting and ecological conditions that are more similar to what birds experience in real human-built environments and make suggestions for testing standards to assess collision-reducing technologies.

Sounds of Nature in the City: No Evidence of Bird Song Improving Stress Recovery

: Noise from city traffic is one of the most significant environmental stressors. Natural soundscapes, such as bird songs, have been suggested to potentially mitigate or mask noise. All previous studies on masking noise use self-evaluation data rather than physiological data. In this study, while respondents (n = 117) watched a 360° virtual reality (VR) photograph of a park, they were exposed to different soundscapes and mild electrical shocks. The soundscapes—“bird song”, “bird song and traffic noise”, and “traffic noise”—were played during a 10 min recovery period while their skin conductance levels were assessed as a measure of arousal/stress. No significant difference in stress recovery was found between the soundscapes although a tendency for less stress in “bird song” and more stress in “traffic noise” was noted. All three soundscapes, however, significantly reduced stress. This result could be attributed to the stress-reducing effect of the visual VR environment, to the noise levels being higher than 47 dBA (a level known to make masking ineffective), or to the respondents finding bird songs stressful. Reduction of stress in cities using masking with natural sounds requires further studies with not only larger samples but also sufficient methods to detect potential sex differences.