Simon Boel Pedersen

Habitat‐induced degradation of sound signals: Quantifying the effects of communication sounds and bird location on blur ratio, excess attenuation, and signal‐to‐noise ratio in blackbird song

The habitat‐induced degradation of the full song of the blackbird (Turdus merula) was quantified by measuring excess attenuation, reduction of the signal‐to‐noise ratio, and blur ratio, the latter measure representing the degree of blurring of amplitude and frequency patterns over time. All three measures were calculated from changes of the amplitude functions (i.e., envelopes) of the degraded songs using a new technique which allowed a compensation for the contribution of the background noise to the amplitude values. Representative songs were broadcast in a deciduous forest without leaves and rerecorded. Speakers and microphones were placed at typical blackbird emitter and receiver positions. Analyses showed that the three degradation measures were mutually correlated, and that they varied with log distance. Their variation suggests that the broadcast song could be detected across more than four, and discriminated across more than two territories. The song’s high‐pitched twitter sounds were degraded more rapidly than its low‐pitched motif sounds. Motif sounds with a constant frequency projected best. The effect of microphone height was pronounced, especially on motif sounds, whereas the effect of speaker height was negligible. Degradation was inversely proportional to microphone height. Changing the reception site from a low to a high position reduced the degradation by the same amount as by approaching the sound source across one‐half or one‐whole territory. This suggests that the main reason for a male to sing from a high perch is to improve the singer’s ability to hear responses to its songs, rather than to maximize the transmission distance. The difference in degradation between low and high microphone heights may explain why females, which tend to perch on low brush, disregard certain degradable components of the song.

Song and information about aggressive responses of blackbirds, Turdus merula: evidence from interactive playback experiments with territory owners

Abstract A combination of normal (one-way), interactive (two-way) and randomized ‘interactive’ (one-way) playback experiments were used to examine whether territorial blackbird males can use song to communicate varied information about their short-term intentions in agonistic situations. The study supports earlier analyses suggesting that low intensity song (LI) is least likely to be followed by attacks by the singer, whereas high intensity song (HI) is intermediate and strangled song (SS) is most likely to be followed by attacks. With normal playback, LI released the weakest, and HI and SS the strongest aggressive responses. Interactive playback, i.e. changing between LI, HI and SS in a natural way with the behaviour of the test bird, released evon stronger responses. Randomized ‘interactive’ playback, i.e. changing between LI, HI and SS independently of the behaviour of the test birds, released weaker responses than interactive playback. This indicates that the naturalness, rather than the variation of the sound stimulation, caused the strong responses to the latter. The results from interactive playback support the idea that SS indicates the most aggressive response of the singer. The escalations represented by the changes from HI to SS were apparent, however, only when the changes in song type were interactive. In other words, the interaction between the song type and the behaviour of the test bird was essential for the communicative value of SS. It is suggested that the adaptive significance of communicating such varied information about aggression lies in its relative safety and energy efficiency. Bluffing as a widespread strategy may have been prevented because the differences between the three types of song in production costs and how conspicuous they make the singer make bluffing more costly.

The signal function of overlapping singing in male robins

Songbirds can vary the timing of song production with respect to other singing individuals on a song-by-song timescale, for example birds may overlap songs or alternate singing and thereby avoid overlap. Playback was used to study the information contained in such timing of song exchanges in territorial male robins, Erithacus rubecula. The results are consistent with the idea that interacting with a singer either by overlapping or alternating is a way of indicating the intended receiver whereas non-interactive (loop) playback does not give this information. Furthermore, an overlapping pattern of singing generally elicited responses characteristic of highly aroused males. In robins this is shown by a rapid approach and change to an almost continuous, low amplitude pattern of singing referred to as twittering. Thus overlapping could be taken as indicating a high degree of arousal or a willingness to escalate. The response changed during the experimental period, with twittering responses becoming more common regardless of playback treatment. This result is consistent with experimental males having gathered information from interactions between playback and their neighbours in previous trials, that is, they collected information by eavesdropping. ? 1997 The Association for the Study of Animal Behaviour

The signal value of matched singing in great tits: evidence from interactive playback experiments

Male songbirds engaged in song duels can interactively vary a number of aspects of their song output to match one another. Evidence is presented from playback experiments that allow interactive signalling between the experimenter and territorial male great tits, Parus major. There were two main results. First, the singing behaviour elicited by interactive playback differed from that elicited by non-interactive (loop) playback, but measures of approach response showed no significant difference. Second, the changes in singing behaviour were consistent with the idea that matching provides successively more precise indications of the intended receiver, from relatively imprecise when just matching song type, to very precise when matching song type, strophe length and delay.

Degradation of wren Troglodytes troglodytes song: Implications for information transfer and ranging

The effects of bird song imply a transfer of information between conspecifics. This communication channel is constrained by habitat-induced degradation. Many studies suggest that birds can utilize features of degraded song to assess relative distance to the signaller (ranging). The degradation of transmitted song in the wren Troglodytes troglodytes is quantified to assess the opportunities offered in received song for both information transfer and ranging. This quantification incorporates three measurable aspects of degradation: signal-to-noise ratio; excess attenuation; blur ratio. Each aspect varies more-or-less predictably with transmission distance, i.e., a criterion for ranging. Significant effects of speaker and microphone elevation indicate a potential for birds to optimize both the opportunity for information transfer and ranging by considering perch location. Song elements are the smallest units of a song being defined as a continuous trace on a sonagram. Main and second-order effects of element ...

Is the Signal Value of Overlapping Different from That of Alternating during Matched Singing in Great Tits

Interactive playback experiments to singing male Great Tits Parus major were used to compare the effects of overlapping their songs with alternating playback which avoided such overlapping. The results showed that the means of measures of approach response and amount of song sung did not differ significantly between the two treatments. However, the variation in song length (phrases/song) differed significantly, being largest during overlapping. The lack of overall differences in average response between the two treatments is evidence against the idea that males may escalate threat by changing from an alternating to an overlapping pattern of singing. On the other hand, the difference in variation in song length supports the idea and is in accordance with classical ethological theory that an escalation of threat will not necessary result in an increased counter threat, but rather in an increased variation of the counter threat. The variation in song length during overlapping may have resulted from test males using a number of different ways of responding to the escalated threat of overlapping.

Mesoscopic decoherence in Aharonov-Bohm rings

We study electron decoherence by measuring the temperature dependence of Aharonov-Bohm (AB) oscillations in quasi-one-dimensional rings, etched in a high-mobility

Rainforests as concert halls for birds: Are reverberations improving sound transmission of long song elements?

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OBSERVATION OF QUANTUM ASYMMETRY IN AN AHARONOV-BOHM RING

heterostructure. The oscillation amplitude is influenced both by phase breaking and by thermal averaging. Thermal averaging is important when the temperature approaches the energy scale on which the AB oscillations shift their phase. For the phase breaking, it is demonstrated that the damping of the oscillation amplitude is proportional to the length of the interfering paths. For temperatures T from 0.3 to 4 K we find the phase-coherence length

Nonfasting Mild-to-Moderate Hypertriglyceridemia and Risk of Acute Pancreatitis

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