Individual vocal signatures show reduced complexity following invasion

Abstract

The manner in which vocal learning is used for social recognition may be sensitive to the social environment. Biological invaders capable of vocal learning are useful for testing this possibility, as invasion alters population size. If vocal learning is used for individual recognition, then individual identity should be encoded in frequency modulation patterns of acoustic signals. Furthermore, frequency modulation patterns should be more complex in larger social groups, reflecting greater selection for individual distinctiveness. We compared social group sizes and used supervised machine learning and frequency contours to compare contact call structure between native range monk parakeets (Myiopsitta monachus) in Uruguay and invasive range populations in the U.S. Invasive range sites exhibited fewer nests and simpler frequency modulation patterns. Beecher’s statistic revealed reduced individual identity content and fewer possible unique individual signatures in invasive range calls. Lower estimated social densities and simpler individual signatures are consistent with relaxed selection on the complexity of calls learned for individual recognition in smaller social groups. These findings run counter to the traditional view that vocal learning is used for imitation, and suggest that vocal learning can be employed to produce individual vocal signatures in a manner sensitive to local population size.

Temporary behavioral responses to playbacks by a pest parrot and implications for management

“…Parakeets may also respond based on the locality of the call, which has been observed in rufous-collared sparrows (Zonotrichia capensis) (Danner et al, 2011), yellow-naped Amazons (Amazona auropalliata) (Wright & Dorin, 2001), and stonechats (Saxicola torquata) (Mortega, Flinks, & Helm, 2014). Moreover, monk parakeets exhibit unique vocal signatures in contact calls tied to individual identities, and these individual signatures are simpler in smaller nonnative range populations, which suggests that monk parakeets use contact calls to recognize distinct individuals (Smith-Vidaurre, Araya-Salas, & Wright, 2020;Smith-Vidaurre, Perez-Marrufo, & Wright, 2021). Therefore, it may be useful for researchers to explore behavioral responses to familiar or unfamiliar individuals to determine which calls may be best for management purposes.…”

“…For conspecific vocalizations, we randomly selected non-native (n = 3) and native (n = 3) range monk parakeet contact calls collected in previous studies (Smith-Vidaurre, Araya-Salas, & Wright, 2020;Smith-Vidaurre, Perez-Marrufo, & Wright, 2021). We used contact calls as our stimuli because parrots often use these vocalizations to maintain auditory contact within pairs and flocks (Bradbury & Balsby, 2016).…”

Evidence for vocal signatures and voice-prints in a wild parrot

“…Monk parakeets are popular pets with good vocal imitative abilities and like all parrots, are life-long vocal learners. Their contact calls have been extensively studied (Martella and Bucher 1990;Buhrman-Deever, Rappaport, and Bradbury 2007;Smith-Vidaurre, Araya-Salas, and Wright 2020;Smith-Vidaurre, Perez-Marrufo, and Wright 2021;Smeele et al 2022), with these studies suggesting that monk parakeet contact calls contain an individual signal (Smith-Vidaurre, Araya-Salas, and Wright 2020). In their invasive range, they also appear to exhibit geographically distinct dialects in contact calls (Buhrman-Deever, Rappaport, and Bradbury 2007;Smeele et al 2022), although this is much less pronounced in their native range (Smith-Vidaurre, Araya-Salas, and Wright 2020).…”