Author ORCID Identifier

0000-0002-1446-8929

Date of Award

Summer 8-10-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Neuroscience Institute

First Advisor

Laura Carruth

Second Advisor

Aras Petrulis

Third Advisor

Elliott Albers

Fourth Advisor

Megan Gall

Fifth Advisor

Harold Zakon

Abstract

While most birds sing and hear between 2–6 kHz, four Andean hummingbirds vocalize between 9–16 kHz. This phenomenon provides an opportunity to investigate the evolution of vocal signals, the factors that selected for these traits, and the adaptations that enable their use. I hypothesized that some hummingbirds have evolved high-frequency (HF) vocalizations to adapt to their habitat acoustics, facilitating communication.

I conducted behavioral observations to elucidate the function of HF signals and found that hummingbirds use these vocalizations in territorial contexts. In one species, males also use HF song to court females, and there are dialects across populations. These findings suggest that HF vocalizations are used in conspecific communication and that, in some cases, sexual selection exerted pressure for the evolution and diversification of HF signals. Then, I evaluated ecological factors driving the evolution of HF vocalizations in hummingbirds. I found that these vocalizations are broadcast at a noise-free frequency range in the acoustic environment, likely avoiding masking by ambient noise. Moreover, HF vocalizations attenuate and degrade at short distances, suggesting that they are likely short-range communication signals. These results support the hypothesis that hummingbirds adapted to vocalize at high frequencies to prevent signal masking during conspecific communication. Finally, I investigated neural responses to HF vocalizations in hummingbirds. I studied behavioral and brain responses to the playback of the HF song in the Ecuadorian Hillstar, showing that these hummingbirds hear conspecific HF songs. This is the first evidence that birds can hear HF sounds and suggest that other hummingbirds producing HF calls likely hear these sounds. Finally, I investigated sex differences in the activation of the brain’s Social Behavior Network in response to the HF song, a territorial signal for males and a courtship song for females.

Altogether, my research shows that some hummingbirds evolved extraordinary vocal and hearing capabilities to avoid signal masking in their habitats when communicating with conspecifics. Studying HF vocalizations in hummingbirds unveiled the presence of auditory adaptations for communication amid challenging environmental conditions. It also opens new avenues to study adaptations for vocal production and sensory processing of an evolutionary novel signal.

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