# A Collection of Best Practices for the Collection and Analysis of Bioacoustic Data
## 5 Signal Structure and Evolution: Cultural Effects  
Bioacoustic analyses can also provide insights into questions about signal evolution, that is, the patterns and processes that drive changes in signal structure over time. Studies of acoustic signal evolution have examined a variety of factors. These include the role of morphology, environmental pressures, conspecific interactions, and neutral processes in shaping acoustic communication and have been conducted across a wide variety of taxa including birds, marine and terrestrial mammals, insects, and fishes (e.g., [114; 115; 116; 117; 118]). Disentangling the factors that drive acoustic signal evolution can be difficult but is important for understanding the drivers of cultural and ecological change within and among species (e.g., [119; 120]). One approach to studying the evolution of acoustic signals, in species that learn their vocalizations via imitation, focuses on cultural evolution: that is the interplay among use, learning, and transmission of signals over multiple generations (e.g., [121; 122; 123; 124; 125]). A major challenge in studying cultural evolution is to try to isolate its impact from other potential drivers of acoustic signal evolution (e.g., morphology, sexual selection, environmental factors, or random drift) [117; 118; 126; 127; 128; 129]. To isolate the effect of any given driver, a researcher must either control for all other potential factors or gather a sample that is sufficiently robust to capture all of the variability in other potential factors. In particular, it can be difficult to account for pre-existing variability in the input signal (e.g., songs of tutors), and the effect of that variability on the output signal (e.g., songs of tutes). For experimental studies of song learning and cultural evolution, as in other fields, artifacts of experimental methodology can affect how results are interpreted, so one must ensure that the recording and signal processing parameters employed are appropriate to the question being asked and consistent across all experimental groups in the study. In a set of experimental studies on song learning and cultural evolution conducted with zebra finches, [PERSON] et al. [52; 130] ran laboratory experiments where all parameters were held constant except the song learning conditions. One advantage of this approach was the ability to control which input the first generation of learners received, thus allowing the researchers to systematically map the input signal to the end-product signal. In the 2009 study [130], first-generation birds were isolated and did not have a song tutor. As expected, these birds ended up producing aberrant songs. Aberrant-singing birds were then used as tutors for newly hatched, unrelated finches, and the procedure was repeated over several experimental generations. The authors found that juveniles imitated their tutor but changed some characteristics of their songs so that over three to four generations songs evolved towards the wild-type. Matching unrelated birds as tutors and tutes in this way enabled [PERSON] et al. [130] to isolate song learning from genetic inheritance, so that the resulting patterns of signal evolution could be attributed with confidence to the cultural transmission of signals across generations. Following this, [PERSON] et al. [52] developed a set of experiments to quantify the effect of conspecific tutoring on song learning. In this study, vocal production was compared among three groups of zebra finches, all housed and recorded individually. Birds in an isolate group lacked a song tutor, and as described above for the 2009 study [130], developed songs that were atypical in structure. Birds in a wild-type group were tutored with recordings of wild-type adult songs. Finally, birds in a self-tutored group were not provided with tutors or external models (like the isolate birds) but were provided the opportunity to hear their own recently produced songs, played through speakers.