Captive Rearing Experiments Confirm Song Development without Learning in a Tracheophone Suboscine Bird

Abstract

The origin of vocal learning in animals has long been the subject of debate, but progress has been limited by uncertainty regarding the distribution of learning mechanisms across the tree of life, even for model systems such as birdsong. In particular, the importance of learning is well known in oscine songbirds, but disputed in suboscines. Members of this diverse group (∼1150 species) are generally assumed not to learn their songs, but empirical evidence is scarce, with previous studies restricted to the bronchophone (non-tracheophone) clade. Here, we conduct the first experimental study of song development in a tracheophone suboscine bird by rearing spotted antbird (Hylophylax naevioides) chicks in soundproofed aviaries. Individuals were raised either in silence with no tutor or exposed to standardized playback of a heterospecific tutor. All individuals surviving to maturity took a minimum of 79 days to produce a crystallized version of adult song, which in all cases was indistinguishable from wild song types of their own species. These first insights into song development in tracheophone suboscines suggest that adult songs are innate rather than learnt. Given that empirical evidence for song learning in suboscines is restricted to polygamous and lek-mating species, whereas tracheophone suboscines are mainly monogamous with long-term social bonds, our results are consistent with the view that sexual selection promotes song learning in birds.

Global macroevolution and macroecology of passerine song

“…Equally, however, oscines generally learn their songs while suboscines do not (Touchton et al. ), and so it is possible that this pitch change is associated with song learning. Below we also discuss how differing environmental affinities might affect the clades’ song pitch and complexity.…”

“…Songs in oscines are typically learnt, whereas songs in suboscines are more often innate (Kroodsma and Miller ; Beecher and Brenowitz ; Touchton et al. ), potentially making the oscine clade more sensitive to rapidly changing ecological influences on song production (Rios‐Chelen et al. ).…”

Status of the globally threatened forest birds of northeast Brazil

“…Existing populations may become extinct with one or two decades without intervention and are unlikely to persist long-enough to benefit from the effects of any (hypothetical) reforestation plans. However, there are few precedents for the animal husbandry and captive breeding of suboscine passerines (although see Touchton et al, 2014), so appropriate 'practice' species (e.g., Myrmotherula axillaris as a surrogate for M. snowi) should be selected first to assess the viability of such an approach before the lives of individuals of the rarer species are risked.…”

Evolution of Vocal Diversity through Morphological Adaptation without Vocal Learning or Complex Neural Control

“…Avian vocal learning and associated neural adaptations are thought to have played a major role in bird diversification [4–8], whereas functional significance of substantial morphological diversity of the vocal organ remains largely unexplored. Within the most species rich order, Passeriformes, ‘tracheophones’ are a suboscine group that, unlike their oscine sister taxon, does not exhibit vocal learning [9] and is thought to phonate with tracheal membranes [10, 11] instead of the two independent sources found in other passerines [12–14]. Here we show tracheophones possess three sound sources, two oscine-like labial pairs and the unique tracheal membranes, which collectively represent the largest described number of sound sources for a vocal organ.…”