No abstract

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 = 13.4 kHz), the Buff-tailed Coronet (Boissonneaua flavescens), Speckled Hummingbird (Adelomyia melanogenys) and Violet-tailed Sylph (Aglaiocercus coelestis). The presence of high-frequency vocalizations in hummingbirds belonging to different lineages poses the question of whether high-frequency vocalizations in this group of birds have been, so far, overlooked. These Andean species are closely related but live in two different habitats. Our characterization of ambient noise in each habitat suggests that the hummingbirds are exposed to different acoustic challenges, and that the frequency content of the vocalizations of the cloud-forest species is adapted accordingly. The function of these signals and the selection pressures driving their evolution remain unknown.

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”). To minimize the effects of exposure on learning, we implemented a novel reinforcement schedule that allowed us to detect preferences while balancing exposure to each song. On average, the juveniles significantly preferred the father’s song early during song learning, before actual singing occurs in this species. When they reached adulthood, all the birds copied the father’s song. The accuracy with which the father’s song was imitated was positively correlated with the peak strength of the preference for the father’s song during the sensitive period of song learning. Our results show that preference for the song of a chosen tutor, in this case the father, predicted vocal learning during development.

Some hummingbirds produce unique high-frequency vocalizations. It remains unknown whether these hummingbirds can hear these sounds, which are produced at frequencies beyond the range at which most birds can hear. Here, we show behavioral and neural evidence of high-frequency hearing in a hummingbird, the Ecuadorian Hillstar (Oreotrochilus chimborazo). In the field, hummingbirds responded to playback of high-frequency song with changes in body posture and approaching behavior. We assessed neural activation by inducing ZENK expression in the brain auditory areas in response to the high-frequency song. We found higher ZENK expression in the auditory regions of hummingbirds exposed to the high-frequency song compared to controls, while no difference was observed in the hippocampus between groups. The behavioral and neural responses show that this hummingbird can hear sounds at high frequencies. This is the first evidence of the use of high-frequency vocalizations and high-frequency hearing in conspecific communication in a bird.

The remote Nangaritza Valley of southeast Ecuador has high bird diversity, combining Amazonian birds with species typical of eastern Andean slopes and foothills, a small number of taxa endemic to the Cordillera del Cóndor region of southern Ecuador and northern Peru, as well as a few forms from the dry Marañón valley region. Here, we update and review avifaunal records from the Nangaritza Valley, comparing them with the bird fauna of the Cordillera del Kutukú and making a brief assessment of bird conservation in the area. To date, 535 species are known to occur in the Nangaritza Valley, including eight species endemic or near endemic to the outer ridges and adjacent Andean slopes in southeast Ecuador and northeast Peru. Conservation perspectives in the area are not favorable owing to increasing deforestation, expansion of the agricultural frontier and mining concessions, which threaten eight regional endemic species.