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1.  The deterrent effect of bird song in territory defense 
Behavioral Ecology  2008;20(1):200-206.
Using the responses of territory owners to playback to infer the territorial function of acoustic signals is common practice. However, difficulties with interpreting the results of such experiments have obscured our understanding of territorial signalling. For instance, a stronger response to playback is often interpreted as more aggressive, but there is no consensus as to whether this should be in response to the least or most threatening simulated intruder. Rather than following a gradual increase or decrease, the relationship between signal intensity and response strength may instead describe a peaked curve. We manipulated banded wren (Thryophilus pleurostictus) songs to simulate low-, median-, and high-performance singers and used these songs as stimuli in playback experiments. Banded wrens were less likely to approach the high-performance stimulus compared with the low- and median-performance stimuli. However, the birds that did approach the high-performance stimulus sang more than those that approached the low-performance stimulus. In addition, birds were more likely to match the songs when exposed to the median- and high-performance stimuli compared with the low-performance stimuli, and song matching predicted approach behavior. These results are in accordance with theoretical models of aggressive encounters in which low-performance opponents are challenged without further assessment. Median- and high-performance opponents, however, may require further assessment, and the latter may be perceived as too intimidating for approach.
doi:10.1093/beheco/arn135
PMCID: PMC2662740  PMID: 19337589
assessment; playback; sexual selection; song; territory defense
2.  The deterrent effect of bird song in territory defense 
Using the responses of territory owners to playback to infer the territorial function of acoustic signals is common practice. However, difficulties with interpreting the results of such experiments have obscured our understanding of territorial signaling. For instance, a stronger response to playback is often interpreted as more aggressive, but there is no consensus as to whether this should be in response to the least or most threatening simulated intruder. Rather than following a gradual increase or decrease, the relationship between signal intensity and response strength may instead describe a peaked curve. We manipulated banded wren (Thryophilus pleurostictus) songs to simulate low, median and high performance singers and used these songs as stimuli in playback experiments. Banded wrens were less likely to approach the high performance stimulus compared to the low and median performance stimuli. However, the birds that did approach the high performance stimulus sang more than those that approached the low performance stimulus. In addition, birds were more likely to match the songs when exposed to the median and high performance stimuli compared to the low performance stimuli and song matching predicted approach behavior. These results are in accordance with theoretical models of aggressive encounters in which low performance opponents are challenged without further assessment. Median and high performance opponents however, may require further assessment and the latter may be perceived as too intimidating for approach.
doi:10.1093/beheco/arn135
PMCID: PMC2662740  PMID: 19337589
playback; song; territory defense; sexual selection; assessment
3.  Song matching, overlapping, and switching in the banded wren: the sender’s perspective 
Interpreting receiver responses to on-territory playback of aggressive signals is problematic. One solution is to combine such receiver-perspective experiments with a sender-perspective experiment that allows subjects to demonstrate how their choice of singing strategies is associated with their approach behavior. Here we report the results of a sender-perspective study on the banded wren (Thryothorus pleurostictus), and combine information on context and results of previous receiver-perspective experiments to clarify function. Territorial males were presented with a 5-min playback consisting of song types present in their repertoire. We assessed the degree to which the subjects’ song matching rate, overlapping rate, and song-type versatility were correlated with their approach latency, closeness of approach, latency to first retreat, and time spent close to the speaker. Male age, breeding stage, and features of the playback stimuli were also considered. Song matching was associated with rapid and close approach, consistent with the receiver-perspective interpretation of type matching as a conventional signal of aggressive motivation. Overlapping was associated with earlier retreat, and together with the aversive receiver response to our previous overlapping playback experiment suggests that overlapping is a defensive withdrawal signal. High versatility was associated with slower first retreat from the speaker and high levels of reciprocal matching between subject and playback. Males with fledglings sang with particularly low versatility and approached the speaker aggressively, whereas males with nestlings overlapped more and retreated quickly. Finally, older males matched more but overlapped less.
PMCID: PMC2288572  PMID: 18392112
Aggressive motivation; playback design; path analysis; signal function; singing versatility; song-type repertoires

Results 1-3 (3)