Sex-specific calls are used in male-male agonistic encounters and male-female courtship in many animal species. The ring-tailed lemur (Lemur catta) is a gregarious Malagasy strepsirhine with twenty-two distinct vocalizations for adults, including two male-specific vocalizations and an additional vocalization with male-specific functions: the howl, the squeal, and the purr. Proposed intra-sexual agonistic functions for these three vocalizations have never been empirically tested. This study’s purpose was to investigate the functions of howling, squealing, and purring in the ring-tailed lemur, and to assess the relationships between the rates of these vocalizations and male dominance. From March to July 2010, I collected 600 hours of total data and 480 hours of focal data on male ring-tailed lemurs aged three and older at Beza Mahafaly Special Reserve, Madagascar. I observed each male continuously for 30 minutes at a time and noted behaviours including all vocalizations and all agonism using one–zero sampling at 2.5-min intervals. I calculated male dominance rank and vocalization rates from these data. My results indicated that male dominance rank is correlated with male purring rate and with squealing rate, but not with howling rate. Male purring rate increased during intra-sexual agonism and was associated with aggression in agonistic encounters. Squealing rate increased during male-male agonism and indicated both aggression and submission in male-male encounters. Howling rate increased during inter-group encounters and a greater number of males participated in multi-male howling choruses when non-group members were present. Purring and squealing are agonistic vocalizations and used in male-male agonism in the ring-tailed lemur, while howling is used in inter-group encounters.

Sex-specific calls are used in male-male agonistic encounters and male-female courtship in many animal species. The ring-tailed lemur (Lemur catta) is a gregarious Malagasy strepsirhine with twenty-two distinct vocalizations for adults, including two male-specific vocalizations and an additional vocalization with male-specific functions: the howl, the squeal, and the purr. Proposed intra-sexual agonistic functions for these three vocalizations have never been empirically tested. This study’s purpose was to investigate the functions of howling, squealing, and purring in the ring-tailed lemur, and to assess the relationships between the rates of these vocalizations and male dominance. From March to July 2010, I collected 600 hours of total data and 480 hours of focal data on male ring-tailed lemurs aged three and older at Beza Mahafaly Special Reserve, Madagascar. I observed each male continuously for 30 minutes at a time and noted behaviours including all vocalizations and all agonism using one–zero sampling at 2.5-min intervals. I calculated male dominance rank and vocalization rates from these data. My results indicated that male dominance rank is correlated with male purring rate and with squealing rate, but not with howling rate. Male purring rate increased during intra-sexual agonism and was associated with aggression in agonistic encounters. Squealing rate increased during male-male agonism and indicated both aggression and submission in male-male encounters. Howling rate increased during inter-group encounters and a greater number of males participated in multi-male howling choruses when non-group members were present. Purring and squealing are agonistic vocalizations and used in male-male agonism in the ring-tailed lemur, while howling is used in inter-group encounters.

Speech development in autism spectrum disorder (ASD) has rarely been studied, yet residual speech sound errors are over 30 times more common in children with ASD than in the general population. Two main theories could explain this. The Social Feedback Loop proposes that toddlers with ASD vocalize less often and so have fewer opportunities to benefit from adult feedback. Thus, fewer vocalizations and perceptible differences in those vocalizations should be found in toddlers with ASD. The Speech Attunement Framework proposes that while toddlers with ASD “tune in” to their native languages well enough to acquire language normally, they lack the ability to “tune up” their articulation to the same level of precision as typically-developing children. Thus, differences in the vocalizations of toddlers with ASD may be perceptible or not, and should exist irrespective of differences in vocalization rate. This study longitudinally examines vocalization rate, consonant inventory size, and voice-onset time (VOT) in syllable-initial bilabial stops using 30-minute speech samples from toddlers in three groups: those at low risk for ASD (LRC), those at high risk for ASD with ASD themselves (HRA+), and those at high risk for ASD without ASD (HRA ) . Transient delays in consonant development were found in both HRA- and HRA+, but only HRA+ toddlers vocalized less often. Further, the relationship between vocalization rate and consonant inventory was significantly different from LRC only for HRA-. VOT development was similar across groups, except that fewer HRA+ 36-month-olds produced distinct /b/ and /p/ populations, as measured by t-test and by Cohen’s d ≥ 0.8 between mean VOTs in the two populations of stops. Results support the Speech Attunement Framework. Consonant acquisition delays are not related to differences in vocalization rate and are not found only in toddlers who develop ASD. The finding of sub-perceptual acoustic differences in stop production in toddlers who develop ASD, with no accompanying differences in production rate, also supports the Speech Attunement Framework. This suggests that the Social Feedback Loop is not diminished in ASD by lower vocalization rate, but that toddlers with ASD may have diminished ability to monitor their own speech.