Usage and plasticity of sexually selected signals: the role of background noise individual learning and signal amplitude

Lead Research Organisation: University of St Andrews
Department Name: Biology

Abstract

To understand how animals communicate and how their signals evolved, we need to know what information their signals convey and the selective forces that have shaped them. A high proportion of animal communication research has been on vocal signals, with bird song one of the most useful models. Bird song is particularly interesting because, in addition to natural selection acting on sound transmission, it is also subject to sexual selection by female choice and male-male competition. However, it is often forgotten that bird song is a multifaceted behaviour, and one of the most important parameters for transmission, how loud the signal is, has been neglected, although it may have an important role in encoding information. To fill this crucial gap in our knowledge, we propose (1) to investigate whether birds are able to adjust the frequency characteristics of their songs to reduce interference from background noise, and whether such an adaptation is related to song learning, and (2) to determine whether song amplitude is an honest indicator of the current and/or past condition of signalling males. To investigate how adaptation to background noise is achieved, we will use great tits in a song learning experiment in which they will be exposed to different noise profiles. The topic of the information coded in signal amplitude will be addressed in experiments with breeding zebra finches. The results of the project will increase our knowledge of how the environment influences the evolution of sexually selected signals and how this is affected by individual learning processes. It will also help to shed light on which messages can be encoded in the amplitude of a sexually selected signal. In addition to this impact on theory, the proposed research also has applied potential: many habitats are affected by man-made noise and the world is becoming more and more noisy because of progressing urbanisation and increasing local and global traffic. It is therefore of great importance for conservation to find out how adaptable the communication systems of animals are and the extent to which a vocalising animal can cope with interference from noise.

Technical Summary

The advertisement signals of sexually-displaying males are among the most widely studied phenomena in animal behaviour. In particular, many of our current advances in understanding animal communication and sexual selection derive from studies on bird song. The specific purpose of this research proposal is to investigate how sexually selected signals can be affected be environmental influences, how this is related to individual learning and, in addition, to determine the messages that can be encoded in the signal amplitude. Therefore we plan to investigate whether birds are able to adjust the frequency characteristics of their songs to reduce interference from background noise and whether such an adaptation is related to song learning, and (2) determine whether song amplitude is an honest indicator of current and/or past condition of signalling males. To investigate how adaptation to noise is achieved, we will use great tits in a song learning experiments in which they will be exposed to different noise profiles. The topic of information coding in signal amplitude will be addressed in experiments with zebra finches, in which we will test the influence of a male's food intake rate and the effect developmental stress experienced early in life. The results of the project will increase our knowledge of how the environment affects the evolution of sexually selected signals and how this is related to individual learning processes. It will also help to shed light on which messages can be encoded in the amplitude of a sexually selected signal. In addition to this impact on theory, the proposed research also has applied potential: many habitats are affected by anthropogenic noise and the noise levels in many areas are expected to raise dramatically in the near future. It is therefore of great importance for conservation to find out how adaptable the communication systems of animals are and the extent to which a vocalising animal can cope with interference from noise.

Publications

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Description The data collected during the period of this grant yielded several important advances in understanding the role of background noise, individual learning and signal amplitude in the production of bird songs. Of these, the most significant include: 1) the discovery that nutritional stress during the early development of songbirds zebra finches impairs the accuracy of song learning, but not song performance features such as amplitude, duration or repertoire size,. 2) In contrast, the current condition of adult birds influences several performance-related features of song, such as song amplitude and song rate, as well as fundamental frequency. Finally, we showed that 3) the songs of great tits exposed to city-like noise during their first year did not differ in frequency from the songs of their tutors. This suggests that, contrary to prevailing hypotheses, great tits do not adjust the frequency properties of their songs to cope with acoustic masking from background noise.








The data collected during the period of this grant yielded several important advances in understanding the role of background noise, individual learning and signal amplitude in the production of bird songs. Of these, the most significant include: 1) the discovery that nutritional stress during the early development of zebra finches impairs the accuracy of song learning, but not song performance features such as amplitude, duration or repertoire size, 2) In contrast, the current condition of adult birds influences several performance-related features of song, such as song amplitude and song rate, as well as fundamental frequency. Finally, we showed that 3) the songs of great tits exposed to city-like noise during their first year did not differ in frequency from the songs of their tutors. This suggests that, contrary to prevailing hypotheses, great tits do not adjust the frequency properties of their songs to cope with acoustic masking from background noise.
Exploitation Route Our study shows how a multifaceted signal such as bird song may serve as an honest signal of both current and past condition. It also contributes much-needed data to our understanding of how birds adapt their signals to their ever-changing environment to ensure effective signal transmission.
Sectors Environment

 
Description Collaboration in study of zebra finch song at University of Utah, Salt Lake City 
Organisation University of Utah
Country United States 
Sector Academic/University 
PI Contribution My post-doctoral assistant made two trips to Utah to use the facilities there to study the respiratory costs of singing at higher amplitude
Collaborator Contribution Facilities and advice
Impact Zollinger, S. A., Goller, F., & Brumm, H. (2011). Metabolic and respiratory costs of increasing song amplitude in zebra finches. PLoS ONE, 6, e23198.
Start Year 2008
 
Description Continued collaboration with HB after he took up Emmy Noether Fellowship in Germany 
Organisation Max Planck Society
Department Max Planck Institute for Ornithology
Country Germany 
Sector Public 
PI Contribution The research was primarily by my research team but using the facilities and field site in Germany to obtain nestlings for hand rearing after failing to achieve an adequate sample size in the UK through lack of nest box occupancy
Collaborator Contribution Apart from facilities, the collaboration and expertise of the first post-doctoral researcher on this project after he had moved to Germany was critical to the success of the project
Impact Main study still ongoing
Start Year 2007