Locomotion is important for both naturally and sexually-selected behaviors. Maximal locomotor performance is physiologically challenging, and hence has been a focus of many studies that attempt to link morphology, performance and fitness. In particular, locomotor performance of males during courtship behaviors has become an interesting area of study because variation in performance can reveal individual differences in males which may be of interest to choosy females. Thus, sexual selection can result in extreme male locomotor performances which can lead to sexual dimorphism and sexual differences in locomotor performance. Hummingbirds are an ideal study organism to address these questions because males perform aerial courtship displays that seem to push the limits of their locomotor capabilities. Specifically, the focus of this dissertation is the shuttle display, a short-ranged low-speed side-to-side lateral flight display males perform for females. A hallmark of this display is a drastic increase in wingbeat frequency relative to hovering which must be challenging perform. This dissertation shows that flight performance is sexually selected in hummingbirds, most likely via female choice for male aerial displays. In black-chinned hummingbirds (Archilochus alexandri), sexual differences in flight performance exist, and variation in shuttle-display performance suggests the display is an index signal of male acceleration. Extreme male locomotor performance during courtship is seen in a wide diversity of species. These results further our understanding of how extreme male locomotor performances evolve, and the consequences of sexual selection on male locomotor performance.

This dissertation introduces and makes use of the Particle-into-Liquid-Sampler coupled to a Time-of-Flight mass spectrometer (PILS-ToF), a new instrumental method used here to provide new chemical characterization information on secondary organic aerosol (SOA). The PILS-ToF instrument improves upon drawbacks found in current state-of-the-art mass spectral chemical characterization methods to include lack of time resolution and ion fragmentation by electron impact ionization in the Aerodyne Aerosol Mass Spectrometer (AMS). The functionality of the PILS-ToF for collection and response to SOA particle formation is validated against a scanning mobility particle sizer (SMPS), a widely accepted and standardized physical chemical characterization instrument, for a well characterized SOA formation experiment, dark ozonolysis of á-pinene. The PILS-ToF is also used to lend insight into oligomer growth during the NO photo-oxidation of isoprene. It is of atmospheric importance to study SOA formation from isoprene as it is globally the most abundant non-methane hydrocarbon in the

ambient. SOA from isoprene is further studied using the PILS-ToF as part of the suite instrumentation at the University of California, Riverside, College of Engineering, Center for Environmental Research and Technology (CE-CERT) atmospheric chamber providing a complete chemical and physical characterization of SOA formed by isoprene with various oxidants under a myriad of oxidant concentration conditions. In addition, the PILS-ToF is used, again in tandem with other chemical and physical characterization methods at CE-CERT, to probe temperature effects on SOA formation from isoprene under many different oxidizing conditions. Finally, the PILS-ToF is used to provide new mechanistic information on SOA formation from trimethylamine and tributylamine, two tertiary amines emitted from anthropogenic and animal husbandry processes. For these two teriary amines the PILS-ToF provides evidence of oligomerization giving a potential explanation to the high SOA yields from these parent compounds.

All locomotion produces sound and flight is no exception. In owls, flight sounds are quieted by three wing and feather features: the leading-edge comb, a modified barb structure that projects dorsally from the front edge of the outermost primary feather (P10), the velvety dorsal surface of flight feathers, and the fringed vane of flight and tail feathers. There are two hypotheses for the evolution of quieting features: stealth and self-masking. Under the stealth hypothesis, we predict quiet flight evolved to aid owls in sneaking up on prey. Under the self-masking hypothesis, we predict quiet flight evolved to aid acoustic hunters in locating prey. To test these hypotheses, we investigated the relationship between leading-edge comb morphology and ecology (Chapter 1), tested the function of the dorsal velvet in Barn Owls (Chapter 2), and investigated the function of quieting features in Lesser Nighthawks, another nocturnal bird (Chapter 3). In Chapter 1, We used phylogenetic generalized least squares (pgls) to test the correlation between comb morphology and the stealth or self-masking scores. We found comb morphology to be correlated with both stealth and self-masking (pgls; DF = 66 test-statistic = -3.92; P-value = 0.0002). In Chapter 2, impairing the dorsal velvet of 10 feathers on 13 barn owls increased broadband sound production and the upstroke increased more than the downstroke, such that the upstroke of manipulated birds was louder than the downstroke, supporting the frictional noise hypothesis. Finally, In Chapter 3, we found Lesser Nighthawks initiated pursuit of prey at a greater distance than the audible detection distance of insects (0.5 m) both when hunting on the ground (1.1 ± 0.2 m; P-value = 0.02) and on the wing (2.5 ± 0.4 m; P-value <0.0001), suggesting they use visual cues to initiate pursuit of prey under these conditions. This dissertation contributes to a research area which has received little consideration: the role of sound and hearing in predation.

Here I examine vocal learning in the Costa’s hummingbird. I used the standard isolation experiment technique utilized for decades to study vocal learning in songbirds. Young male Costa’s hummingbirds were raised in isolation, with playback of adult song, and with playback in the presence of an adult model. All bird vocalizations were recorded to examine song ontogeny. I found that the necessary conditions required for vocal learning of a tutor song to take place in a lab setting included the presence of an adult model during tutoring and the tutor song must be Costa’s like. I developed a timeline of song ontogeny events including information about the onset of singing, and the stages of song development. Another experiment examined the timing of the sensitive phase by tutoring Costa’s for 20 hours in one of three different 30-day tutoring periods: Early (35-65 days post hatch (dph)), Mid (75-105 dph), and Late (115-145 dph). Results indicated that Costa’s can learn some vocal information across all three tutoring periods but that the amount of tutoring during one tutoring period was insufficient for production of normal Costa’s song. Finally, I examined open-ended vocal learning by exposing previously isolated birds to other Costa’s hummingbirds and found that songs change after exposure, even after two years of isolation.

Background

Objective

Design

Subjects

Measures

Results

Conclusions