Evolution of the syrinx of Apodiformes, including the vocal-learning Trochilidae (Aves: Strisores).

The vocal organ of birds, the syrinx, represents a key innovation in the evolutionary history of vertebrate communication. Three major avian clades: passerines, parrots, and hummingbirds, independently acquired both specialized syringeal structures and vocal-production learning, between which a functional relationship has been proposed but remains poorly understood. In hummingbirds, the syrinx has never been studied comparatively alongside non-learning relatives in the parent clade Strisores.

Ostrich (Struthio camelus) syrinx morphology and vocal repertoire across postnatal ontogeny and sex: Implications for understanding vocal evolution in birds.

Vocal production in birds has been the target of considerable research that mostly has focused on phylogenetically well-nested songbirds. Anatomical descriptions and recordings of many non-songbirds have often only focused on a single ontogenetic stage or sex. While basic morphology of the vocal organ (syrinx) of ostrich (Palaeognathae, Struthio camelus) has been known since the 1800s, descriptions of its vocal repertoire and syrinx anatomy since then have been incomplete or inconsistent.

Oxytocin receptor antagonism during early vocal learning reduces song preference and imitation in zebra finches.

In species with vocal learning, acquiring species-typical vocalizations relies on early social orienting. In songbirds, for example, learning song requires dynamic social interactions with a "tutor" during an early sensitive period. Here, we hypothesized that the attentional and motivational processes that support song learning recruit the oxytocin system, which is well-understood to play a role in social orienting in other species.

Song preferences predict the quality of vocal learning in zebra finches.

In songbirds, learning to sing is a highly social process that likely involves social reward. Here, we tested the hypothesis that during song learning, the reward value of hearing a particular song predicts the degree to which that song will ultimately be learned. We measured the early song preferences of young male zebra finches (Taeniopygia guttata) in an operant key-pressing assay; each of two keys was associated with a higher likelihood of playing the song of the father or that of another familiar adult ("neighbor").

High-frequency vocalizations in Andean hummingbirds.

Hummingbirds possess a number of unique features. A recent report in Current Biology[1] showed that the Black Jacobin (Florisuga fusca), a Brazilian hummingbird in the Topazes clade, produces high-frequency vocalizations outside the known hearing range of birds. Here, we report that four hummingbird species in the Andean clade [2,3] also exhibit high-frequency vocalizations: the Ecuadorian Hillstar (Oreotrochilus chimborazo), with the highest fundamental frequency (mean F0 = 13.

Sound-induced monoaminergic turnover in the auditory forebrain depends on endocrine state in a seasonally-breeding songbird.

Sensory responses to courtship signals can be altered by reproductive hormones. In seasonally-breeding female songbirds, for example, sound-induced immediate early gene expression in the auditory pathway is selective for male song over behaviourally irrelevant sounds only when plasma estradiol reaches breeding-like levels. This selectivity has been hypothesized to be mediated by release of monoaminergic neuromodulators in the auditory pathway.

To Become Senders, Songbirds Must be Receivers First.

Courtship signals are attractive; in other words, receivers are motivated to approach courtship signals. Though the concept of a receiver is commonly associated in the literature with that of a mate seeker, young songbirds that are learning to sing by imitating conspecifics are also receivers. Juvenile songbirds are attracted to conspecific songs, which has been shown by juveniles working to hear song in operant chambers.

Testosterone and Haemosporidian Parasites Along a Tropical Elevational Gradient in Rufous-Collared Sparrows (Zonotrichia capensis).

Elevation has been proposed as a dominant ecological variable shaping life history traits and subsequently their underlying hormonal mechanisms. In an earlier meta-analysis of tropical birds, elevation was positively related to testosterone levels. Furthermore, parasitism by avian haemosporidians should vary with elevation as environmental conditions affect vector abundance, and while testosterone is needed for breeding, it is hypothesized to be immunosuppressive and thus could exacerbate haemosporidian infection.