Scientific studies: The available writings suggest that responding to call-playback may incur energy costs, disrupt social systems, lead to pair break-ups and cause stress. Some of the more relevant are extracted below:

♪ A study conducted by Professor Martin Wikelski of the University of Illinois on Spotted Antbirds in Panama found that male antbirds increased their testosterone levels and became more aggressive, even in a sexually inactive period, when confronted by a prolonged (2 hrs) playback of recorded sounds made by potential enemies. Professor Wikelski goes on to say “it makes sense for birds to maintain a baseline level of aggression without testosterone, because testosterone has costs, such as higher mortality rates”.[19, 25]
[Similar studies on bush warblers (Cettia diphone) in Japan[21] suggest that adrenocorticosteroid responses to stress may vary according to location (tropics vs temperate regions) and territorial and parental behaviour and results of such experiments may not be generalized.]

There is also "evidence that prolonged high levels of circulating testosterone may incur costs that may potentially reduce lifetime fitness" ~ Avoiding the 'Costs' of Testosterone: Ecological Bases of Hormone-Behavior Interactions by John C Wingfield & others.[18]

♪ Daniel J. Mennill of the University of Illinois led a team that conducted a study on 'female eavesdropping on male song contests in songbirds'[15] using call playback. The results showed that female Black-capped Chickadees eavesdrop on male song contests to make extra-pair mating decisions following simulated playback defeats of their partner. Dr. Mennill also found that “... high-ranking males who lost song contests also lost paternity in their nests.” and “ Finally, our results show that short playback sessions can have long lasting and far-reaching effects on individual fitness.”[15, 22]

Paul McDonald comments on the same study in the Birding Aus forum “The point is that with only a very short playback period (...), the authors triggered females to drastically change their reproductive behaviour. Likewise, it has been shown in many species that other males also eavesdrop on these interactions, and the 'loser' may be prone to more intrusions from adjacent males, as his quality may be inferred to be lower than it actually is following an experimental defeat. Thus, by continually playing calls in the one territory, I suspect birders are effectively simulating the resident bird 'losing' to the tape/mp3 player that it fails to evict from its territory.”[27]

Similar results were obtained by Dr. Jeffrey R. Lucas, Professor, Dept. of Biological Sciences, Purdue University on studies conducted on Carolina Chickadees. He found that it was “very common for us to instigate territory disputes”.. “because responses that we elicit from one neighbor are usually reacted to by other neighbors”. He believes that these increased interactions may potentially have a disruptive effect on social systems. Dr. Lucas's comments were shared on the NEOORN discussion board[6].

♪ Paulo Gama Mota, Director, Museum of Science, University of Coimbra, Portugal conducted a 'test of the effect of male song on female nesting behavior in the Serin (Serinus serinus)' in a field playback experiment. He found that that females who listened daily to playbacks of male songs, during the nest-building stage, spent about 30% more time nest building than females that were not thus exposed. Incidentally, male song is known to “stimulate female reproductive activity, affecting their behavior and physiology, such as follicular growth, nest building and egg laying”.[49]

Several field studies have shown that playback of songs are sufficient stimuli to evoke behavior which normally occurs in response to the singing of another bird (e.g., Weeden and Falls, 1959; Stein, 1963).

♪ Playback experiments conducted by Dr. K. Yasukawa and others on Red-winged Blackbirds showed that territorial males can discriminate between neighbours, strangers and self songs and react differently to each and “stranger song elicited significantly more intense Song Spread displays than did self song”.[16]
(Tape-luring depends heavily on playback of 'stranger' songs/calls – Ed.)

♪ Studies conducted by Dr. Shallin D. Busch of the University of Washington, Seattle on the reproductive endocrinology of the song wren (Cyphorhinus phaeocephalus) using conspecific playback to simulate a territorial intrusion showed that such use resulted in an increase in Luteinizing hormone and testosterone in the territorial male.[20]

♪ Playback of colony sound tests in Zebra Finch (Taeniopygia guttata) colonies conducted by Dr. Joseph R. Waas of the Department of Biology, Queen’s University, Ontario and others to test the hypothesis that “social stimulation, derived from the presence and activities of conspecifics, can hasten and synchronize breeding in colonies of birds” [24] found that such stimulation influenced the breeding schedule and clutch sizes positively.

♪ Speaker-replacement studies by Krebs (1977) showed that song playback affected space use in free-living birds. [We have been unable to access this paper - Ed].

Comments by Scientists: Many scientists and ornithologists have made personal comments on various forums. There are also comments attributed to those who study birds. Many of these comments were contributed to an enlightening discussion on the subject entitled “Audio playback: impact on Neotropical birds?”[6] initiated by Stephen M Smith of the Department of Biology, University of Waterloo, Canada on the NEOORN[26] discussion board. Another meaningful discussion took place on the Birding Aus mailing list which was a source of additional inputs.
Appended are a selective extract of comments/remarks:

♦ Paul G. McDonald, Lecturer and Macquarie University Research Fellow (Birds AUS post,16 Sep 2008)[27] : According to Dr. McDonald playback affects bird behaviour subtly, though energy wastage “as a direct result of playback is probably not very important....”. It is the possibility of long-lasting negative effects of limited playback that are more a cause for concern. These effects may include loss of clutch paternity for resident males and energy expenditure to defend territory even after the playback ceases. He is “not aware of any papers that test this directly, and this is unlikely to lead to any conservation issues. However, it does raise ethical concerns, as the results from the playback may continue well beyond the point birders have left the area”.

♦ Bruce W. Miller, Associate Conservation Zoologist, Wildlife Conservation Society, Gallon, Belize (NEOORN post[6], 22 March 2005): Dr. Miller states that “.... many bird species formerly common are no longer to be found in the same locations where some guides ...... play tapes for 15–20 min without stop”. The birds, however, continue to be found in similar undisturbed habitats. His observations are based on records kept over a period of 14+ years.

♦ Alvaro Jaramillo, Senior Biologist, San Francisco Bay Bird Observatory and professional tour guide leader (NEOORN post[6], 22 March 2005): Mr. Jaramillo has used playback on tours as well as in scientific contexts. He believes that “tape playback is harmless” and the territory holding male emerges the victor in the duel There is an impact on behaviour, “but then it is much better than people trampling vegetation or trying to sneak up on birds...”.

♦ Bridget Stutchbury, Professor and Canada Research Chair, York University, Toronto. Author of 'Silence of the Songbirds' (NEOORN post[6], 28 March 2005): Dr. Stutchbury agrees that playback is to be generally discouraged unless it is used specifically for formal data collection and/or research. According to her, “Recreational playbacks for birding can be harmful if done repeatedly to the same pairs of birds; and it’s unnecessary”.

♦ Bruce Falls, Ornithologist and Professor of Zoology, University of Toronto (NEOORN post[6] , 31 March 2005): According to Dr. Falls, playback is a valuable tool for both research and counting and its use in moderation is justified with the gains outweighing any downsides. His field experiences with White-throated Sparrows and Meadowlarks showed that effect of playback was 'negligible' and the birds "habituated”. Dr. Falls goes on to add that “However, I do have concern for rare birds that are repeatedly assaulted by playback from a succession of groups at the same site. Habituation may limit the damage but I would prefer to err on the side of caution”.

♦ Phil Taylor, Professor, Acadia Biology Department Chair, ACWERN, Nova Scotia (NEOORN post[6], 24 March 2005): Dr. Taylor does not consider careful use of playback to be a “big issue”. He is, however, concerned about the “disruptive” or possible “detrimental” impact of excessive playback or repeated playback aimed at individuals or pairs.

♦ Kathryn E. Sieving, Professor, Wildlife Ecology and Conservation, University of Florida (NEOORN post[6], 25 March 2005): According to Dr. Sieving, audio playback has an impact on (neotropical?) birds. The impact she is aware of is the “increased risk of predation on individuals responding to playbacks”. She gives an example of playback-research studies in Chile, where predatory birds attacked birds responding to conspecific territorial calls. Dr. Sieving goes on to add that “More and more people will be using this technology, and we have to moderate it at some point.”

♦ Jeffrey R. Lucas, Professor, Dept of Biological Sciences, Purdue University (NEOORN post[6], 25 March 2005): Dr. Lucas's comments on the potentially disruption of bird social systems by the use of playback has been described above. He also goes on to say that “The point is that there are lots of ways to disrupt a social system through playbacks, and to do this in order to let some people see a rare bird seems a bit much.”