Sexual selection for both diversity and repetition in birdsong

Abstract

From fiddler crabs to humans, animals perform repetitive displays showing neuromotor skill and vigour. Consistent repetition of identical notes (vocal consistency) facilitates the assessment of neuromotor skills and is important in communication in birds. Most birdsong research has focused on song diversity as a signal of individual quality, which seems contradictory as repetition is extremely common in most species. Here we show that consistent repetition within songs is positively correlated with reproductive success in male blue tits (Cyanistes caeruleus). A playback experiment shows that females are sexually aroused by male songs with high levels of vocal consistency, which also peaks seasonally during the fertile period of the female, supporting the role of vocal consistency in mate choice. Male vocal consistency also increases with subsequent repetitions of the same song type (a warm-up effect) which conflicts with the fact that females habituate to repeated song, showing decreased arousal. Importantly, we find that switching song types elicits significant dishabituation within the playback, supporting the habituation hypothesis as an evolutionary mechanism driving song diversity in birds. An optimal balance between repetition and diversity may explain the singing style of many bird species and displays of other animals.

A genomic basis of vocal rhythm in birds

“…Intermediately paced or mixed rhythm songs might be unattractive to the opposite-sex 23 and, if hybrids then have lower fitness, drive reinforcement against hybridization 53 . We explored this possibility by testing for evidence of character displacement in IOI and its stability between 87 pure extoni and 94 pusillus individuals (respective ancestry >99%, based on fastSTRUCTURE ancestry values from double-digest restriction-site associated DNA (ddRAD) sequencing).…”

“…Also, instability in hybrid song may affect mate choice as well if females prefer males with more stable songs. A preference for fast, stable song in pusillus invokes the concept of female choice based on male motor performance 69 , an indicator of male quality 70 that has been shown to drive mate choice in passerines 23 , and might therefore underpin asymmetric assortative mating in the tinkerbird hybrid zone. This hypothesis is supported by a pattern of divergent character displacement in rhythmic stability between pusillus and extoni in sympatry compared to allopatry.…”

“…Indeed, most genetic studies on bird song have so far focused on the genes implicated in song learning 13 – 16 , thus leaving the molecular mechanisms underlying the temporal or spectral patterning of bird songs unexplored. In particular, rhythm, which entails song elements regularly distributed in time 17 , 18 , constitutes an essential component of animal communication that mediates key social behaviors 18 , 19 , such as individual recognition 20 and mate selection 21 – 23 . Although comparative approaches have contributed towards a better understanding of the functions of rhythm processing 17 , 24 , it is less clear how rhythmic differences arise and how these are maintained over time.…”

Zebra finch song parameters are affected by the breeding status of the male and the ambient temperature conditions

“…In blue tits (Cyanistes caeruleus), males also adapt their song performance to the breeding stage of the females to increase their breeding chances (Sierro, de Kort, and Hartley 2023).…”