Abstract Hummingbirds are known for sustained hovering powered by rapid and continuous wingbeats. Here, we describe and quantify a novel flight behavior—intermittent hovering—in which hovering hummingbirds momentarily pause their wing motion mid-air but maintain their vertical position in space, keeping their wings fully extended at the end of the upstroke. We present the first systematic account of flap-pauses and wing coloration across hummingbirds, and evaluate potential morphological and ecological correlates, as well as evolutionary patterns in the expression of this behavior. Slow-motion footage from 86 species spanning all nine major hummingbird clades shows that at least 45 species exhibited flap-pauses during sustained hovering. Phylogenetic comparative analyses revealed that hovering pauses are evolutionarily conserved and significantly associated with both greater body mass and longer wings. Furthermore, we found that the 16 species in our study with colored underwings also exhibit significantly longer wings. The convergence of intermittent hovering, wing elongation, and chromatic traits leads us to hypothesize that this flight behavior plays a role in visual and/or auditory communication.

Hummingbirds hover, enabling them to serve as exclusive pollinators for many plant groups with which they have coevolved. They combine bird muscle power with insect flight skills to hover and maneuver in any direction. This study investigates an under-explored aspect of their hovering flight: many species exhibit an alternative gait, in which they flap their wings discontinuously, including momentary pauses sporadically interspersed between short series of wingbeats, which collectively generate a pattern we denote as 'intermittent hovering'. These brief pauses have not been characterized in hummingbirds but may play aerodynamic, energetic, and/or signaling roles. To detect and measure intermittent hovering, we present a high-throughput method to quantify these irregular wingbeat pauses using computer vision and signal analysis. High-speed videos of 11 species collected by recording free-living hummingbirds allowed us to track and analyze the pauses during hovering. The proposed algorithm has a precision of 74%, accurately detecting flapping pauses and thus intermittent hovering. Most of the misclassification errors were false positives: when very still hovering hummingbirds were continuously moving their wings, but some of the consecutive frames were similar enough that the algorithm classified them as a brief pause. These false positives, however, are easily discarded upon quick visual inspection, and the algorithm had only 19 false negatives across all videos, actually detecting intermittent hovering if it was present. This method is a step forward in creating tools that help researchers analyze complex behavioral patterns. Our study confirms the feasibility of reliably detecting intermittent hovering, contributing to our understanding of hummingbird flight dynamics.

Birds use song to communicate in multiple contexts, including territoriality and courtship. Of particular interest is the phenomenon of song sharing, in which direct neighbors’ songs are more similar to one another than those of non-direct neighbors. Song sharing has been studied extensively in oscine songbirds. However, despite the high diversity of hummingbird vocalizations, less attention has been given to this lineage. Anna’s Hummingbird (Calypte anna) has a spectrally complex, three-phrase multisyllabic song that varies on both macrogeographic and microgeographic scales. In this study we tested for song sharing between neighbors and for an effect of physical distance on song distance within a single population. In January and February of 2021, we audio recorded 29 Anna’s Hummingbirds in Golden Gate Park, San Francisco, CA. We characterized syllable types, and measured spectral and temporal features of songs in Raven Pro 1.6. We evaluated how Anna’s Hummingbird song form may change over time by comparing our results to those of a study conducted at the same site in 1999 and recordings from the 1980s. In our recordings from 2021, we identified 25 syllable types and eleven song types, and found evidence for both syllable and song type sharing between males with adjacent territories. We found high turnover of syllable types between the 1980’s and 2021, demonstrating the potential for rapid cultural evolution in hummingbird song.

Many species of nightjar reportedly produce short, impulsive wing sounds during courtship, but the kinematics and physical mechanisms of sound production remain speculative. Using synchronized infrared high‐speed video and audio recordings we describe the mechanism of sound production of a sonation in the nocturnal family Caprimulgidae; the wing‐snapping of male scissor‐tailed nightjars Hydropsalis torquata. This sound is a short, sharp, loud, ‘tk', produced singly in a jump display (jump snap), in a syncopated series during a flight display (flying snaps), and in a fast series during copulation (copulation snaps). To produce these ‘tk' sounds, males rapidly elevated and supinated the wings to slam opposing wrists together. The videos falsify the hypotheses that sound is produced by intra‐ or inter‐wing colliding feathers or by clapping (i.e. a pulse of air accelerating to escape a constricted space, as in human hand‐clapping), as there was no contact by the surface of opposing wing‐feathers. Instead, the physical acoustic mechanism appears to be impulsive collisions between the wing bones (radii) which then vibrate, like wing‐snapping of Manacus manakins. A low‐frequency mechanical thud, produced by an unknown intra‐wing mechanism during the downstroke is also present in flying snaps and copulation snaps, and occurs independently during fast takeoff. Fluffle was produced by feathers rustling and colliding in preen‐like behavior that has likely a communicative function. An additional male display, the wing rattle, made in flight during chases, has a complex acoustic structure including a similar yet distinct mechanical impulsive sound, the thud, a whoosh, and vocal sounds, indicating a suite of possible sound production mechanisms. The wings seemingly do not touch during the wing‐rattle, suggesting that the second type of impulsive sound is produced by intra‐wing feather collisions. Preliminary comparisons indicate the conservation of homologous sound‐producing mechanisms and sounds in New World nightjars.

Flight speed has important fitness consequences for flying animals, but how the parts of the flight apparatus limit top speed remains unknown. Morphology, kinematics and flight performance are strongly correlated with species and sex class, which complicates attempts to dissect the contribution of each element to flight performance. We performed two experiments to assess how sexual dimorphism within a species and morphological variation between species influence maximum flight speed. Burst capacity is often hypothesized to be representative of generalized flight performance and may be correlated with top speed. In experiment one, we found top speed and burst capacity were negatively correlated in female but not male Archilochus alexandri. In experiment two, we used path analysis to disentangle the relative contributions of muscle size and wingbeat kinematics on maximum flight speed in both sexes of four species: A. alexandri, Calypte anna, Calypte costae and Selasphorus sasin. Considered separately, muscle size was more strongly associated with variation in both flight speed and burst capacity compared with wingtip velocity. In a post hoc model comparing muscle size and wingbeat kinematics, only muscle size remained a significant predictor for both assays, but substantial variance in top speed remains unexplained. There was no significant correlation between flight speed and burst capacity despite sex-specific differences, suggesting flight muscle composition may be an important predictor of performance for a given flight assay. Overall, top speed and burst capacity represent uncorrelated measures of flight 'performance', and significant predictors of flight speed remain unexplored.

ABSTRACT In species that learn their song, cultural transmission of song components can lead to the accumulation of variants that differ among populations, resulting in the formation of dialects. Three avian clades are thought to have independently evolved song learning – parrots, oscine passerines, and hummingbirds. Dialects have mainly been studied in passerines. We extend the study of dialects to the bee hummingbird clade, focusing on Anna’s and Costa’s hummingbirds ( Calypte anna and C. costae ). Both species are vocal learners. Anna’s produces complex, three phrase, multi-syllable songs and Costa’s produces simple, one phrase songs. We recorded 5-24 males per population (5 Costa’s and 6 Anna’s populations) across the species’ ranges in the Western United States and tested for evidence of geographic variation in song. We found minor population differences in frequency measures of Costa’s song, but song form was invariant across populations. Anna’s song was contrastingly variable with population differences in both syllable use and multiple spectral and temporal measures. The most strongly differentiated Anna’s population in our study, Seattle (Washington State), is the product of a recent northward range expansion facilitated by human activities that provide additional food sources for hummingbirds. The loss and modification of syllables in this population is suggestive of a founder effect on song. This study provides insight into song evolution in non-passerine vocal learners and contributes to understanding of how complex signals evolve.

Elaborate male display behaviours that require high locomotor performance have been hypothesized to honestly signal male quality to choosy females. Alternatively, challenging displays of locomotor performance may result from arbitrary female preferences. In several species of hummingbirds, males perform elaborate aerial displays during courtship. Male black-chinned hummingbirds perform a 'highperformance' courtship display to females: a low-speed shuttle display during which wing beat frequency is substantially elevated relative to hovering. We recorded males performing shuttle displays to live caged females to examine which display kinematic variables (such as wing beat frequency) are correlated, and assessed whether there is evidence that the shuttle display is constrained by a flight performance trade-off. We also subjected males to an asymptotic load-lifting assay to test whether shuttle display flight performance was correlated with this general flight performance assay. We found that elevated shuttle display wing beat frequency was positively correlated with acceleration and velocity during the display and that the display was constrained by a trade-off between cycle frequency and amplitude of the flight path. We found no relationship between asymptotic load-lifting performance and any shuttle display performance variable. We suggest this elaborate display behaviour may serve as an index signal of male flight performance that females could use to judge individual males during mate choice decisions. (c) 2025 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

One feather structure associated with an owl's ability to fly quietly is the soft dorsal surface on their flight feathers: the velvet. This velvet is a mat of elongated filamentous pennulums that extend up from feather barbules. The aerodynamic noise hypothesis posits this velvet reduces aerodynamic noise caused by the formation of turbulence, while the structural noise hypothesis posits the velvet acts as a dry lubricant, reducing frictional noise produced by feathers sliding past one another. We investigated the structural noise hypothesis by quantifying the length of the velvet on 24 locations across the wing of the barred owl (Strix varia) and then qualitatively assessing the presence of velvet in 24 bird species. We found that velvet has evolved at least 4 times independently (convergently) in owls, nightbirds, hawks and falcons. Then, we rubbed 96 pairs of feathers together from 17 bird species (including the four clades that have independently evolved velvet) under three experimental treatments: control, hairspray applied (to impair the velvet) and hairspray removed. The sound of feathers rubbing against each other was broadband, similar to the sound of rubbing sandpaper or Velcro. Species with velvet produced rubbing sounds that were 20.9 dB quieter than species without velvet, and velvet-coated feathers became 7.4 dB louder when manipulated with hairspray, while feathers lacking velvet only increased in loudness by 1.7 dB, relative to the control treatments. These results all support the hypothesis that the velvet primarily functions to ameliorate the sounds of feathers rubbing against other feathers.

Wingbeat frequency estimation is an important aspect for the study of avian flight, energetics, and behavioral patterns, among others. Hummingbirds, in particular, are ideal subjects to test a method for this estimation due to their fast wing motions and unique aerodynamics, which result from their ecological diversification, adaptation to high-altitude environments, and sexually selected displays. Traditionally, wingbeat frequency measurements have been done via "manual" image/sound processing. In this study, we present an automated method to detect, track, classify, and monitor hummingbirds in high-speed video footage, accurately estimating their wingbeat frequency using computer vision techniques and signal analysis. Our approach utilizes a zero-shot learning algorithm that eliminates the need for labeling during training. Results demonstrate that our method can produce automated wingbeat frequency estimations with minimal supervision, closely matching those performed by trained human observers. This comparison indicates that our method can, in some scenarios, achieve low or zero error compared to a human, making it a valuable tool for flight analysis. Automating video analysis can assist wingbeat frequency estimation by reducing processing time and, thus, lowering barriers to analyze biological data in fields such as aerodynamics, foraging behavior, and signaling.

The have evolved to produce communication sounds (sonations) with their wings, tail, feet, or beak dozens if not hundreds of times independently.Ongoing work continues to uncover many new examples of sonations and the physical acoustic mechanisms by which these sounds are produced.The repeated (convergent) evolution of a trait permits sophisticated evolutionary tests of how and why it evolves.Here, we outline a series of adaptive questions about the evolution of sonations: Does producing sonations entail tradeoffs with other functions, such as flight?How do sonations co-evolve with production of vocalizations?How do sonations co-evolve with behavior?Compared to vocalizations, do sonations occupy the same functional space as vocalizations?Do sonations occupy the same acoustic space as vocalizations?Each of these questions has already received some attention within individual bird clades, but with so many independent origins across birds, the bigger picture has only begun to appear.

Woodstars are a clade of small hummingbirds with poorly known life history. One reason why they are insufficiently characterized is they tend to be little represented in museum collections. The Cornell Lab of Ornithology's Macaulay Library, an online database of user-uploaded photographs, is a complementary source of phenological information. Here, stimulated by our own field observations, we analyzed up to 200 photos per species from the Macaulay Library to investigate whether adult male Slender-tailed Woodstar (Chaetocercus [Microstilbon] burmeisteri), Amethyst Woodstar (Calliphlox amethystina), Chilean Woodstar (Eulidia yarrellii), Peruvian Sheartail (Thaumastura cora), and Purple-collared Woodstar (Thaumastura [Myrtis] fanny) molt into a drab-throated, nonbreeding plumage distinct from the better known iridescent-throated breeding plumage. We investigated these 5 species because adult males have elongated, dimorphic tails, meaning that we could distinguish adult males from immature males by their tail morphology alone. The photos show that, post-breeding, entire populations of Slender-tailed Woodstar and Peruvian Sheartail males replace their iridescent throat feathers with non-iridescent feathers, then molt back into their breeding plumage a few months later. The holotype of Microstilbon insperatusTodd 1913, type species of the genus Microstilbon, is an adult male of Slender-tailed Woodstar in the nonbreeding plumage that we describe here. Our data also suggest that male Amethyst, Chilean, and Purple-collared woodstars have a second distinct nonbreeding plumage. In these 3 species, photos showing the apparent drab-throated male plumage were rare, suggesting these species might have complex breeding phenology with some individuals molting into the nonbreeding plumage at the same time that others were breeding in iridescent-throated plumage. The rapidly growing number of photographs available in the Macaulay Library makes this resource valuable for documenting phenology, including for rare species such as woodstars. Datos de ciencia ciudadana revelan muda a un plumaje no-reproductivo desva & iacute;do en cinco especies de estrellitas (Mellisuginae, Trochilidae)Las estrellitas son un clado de peque & ntilde;os colibr & iacute;es con historias de vida poco conocidas. Una de las razones por las que no est & aacute;n adecuadamente caracterizadas es que tienden a estar poco representadas en colecciones de museo. La Macaulay Library del Laboratorio de Ornitolog & iacute;a de Cornell, una base de datos en l & iacute;nea de fotograf & iacute;as cargadas por usuarios, es una fuente complementaria de informaci & oacute;n fenol & oacute;gica. Aqu & iacute;, estimulados por nuestras propias observaciones de campo, analizamos hasta 200 fotograf & iacute;as por especie de la Macaulay Library para investigar si los machos adultos de picaflor enano (Chaetocercus [Microstilbon] burmeisteri), picaflor amatista (Calliphlox amethystina), picaflor de Arica (Eulidia yarrellii), picaflor de cora (Thaumastura cora) y la estrellita de collar p & uacute;rpura (Thaumastura [Myrtis] fanny) mudan a un plumaje no-reproductivo de garganta desva & iacute;da, distinto del m & aacute;s conocido plumaje reproductivo de garganta iridiscente. Investigamos estas 5 especies porque los machos adultos tienen colas elongadas y dim & oacute;rficas, por lo cu & aacute;l podemos distinguir a los machos adultos de los machos inmaduros por la morfolog & iacute;a de su cola. Las fotograf & iacute;as muestran que, despu & eacute;s de la reproducci & oacute;n, poblaciones enteras de machos de C. burmeisteri y T. cora reemplazan las plumas iridiscentes de su garganta con plumas no iridiscentes y luego mudan nuevamente a su plumaje nupcial unos meses despu & eacute;s. El holotipo de Microstilbon insperatusTodd 1913, especie tipo del g & eacute;nero Microstilbon, es un macho adulto de C. burmeisteri en el plumaje no-reproductivo que aqu & iacute; describimos. Nuestros datos tambi & eacute;n sugieren que los machos de C. amethystina, E. yarrellii y T. fanny tambi & eacute;n tienen este segundo plumaje no-reproductivo distintivo. En estas 3 especies, las fotograf & iacute;as mostrando el aparente plumaje masculino de garganta desva & iacute;da fueron escasas, lo que sugiere que estas especies podr & iacute;an tener una fenolog & iacute;a reproductiva compleja, con algunos individuos mudando al plumaje no-reproductivo al mismo tiempo que otros se reproducen en plumaje de garganta iridiscente. El n & uacute;mero cada vez mayor de fotograf & iacute;as disponibles en la Macaulay Library hace que este recurso sea valioso para documentar la fenolog & iacute;a, incluso para especies raras como las estrellitas.

Here we examine whether vocal learning in Costa's hummingbird, Calypte costae, is open-ended. Openended learning is the ability of a vocal learning animal to memorize and learn to incorporate new song material into its vocal repertoire after reaching sexual maturity. Open-ended vocal learners are able to learn as adults because they have either a sensitive phase that never closes or a seasonal reopening of the sensitive phase. In prior experiments, we raised 18 individually housed male Costa's hummingbirds in isolation chambers from fledging (day 21 posthatch) until they were approximately 1 year old. During that time, they were tutored and learned song that was individually specific and stable. Here we report what happened when we moved cohorts of eight (in 2017) and six (in 2018) of these similar to 1-year-old birds to communal housing in two outdoor aviaries, placing them in physical, visual and acoustic contact with other adult Costa's hummingbirds that sang songs to which each individual had never previously been exposed. The remaining four 1-year-old birds (in 2018) were instead kept in isolation for their second year as a control, then first exposed to each other at 2 years of age. Within 2 months, all of the 1-year-old birds rapidly changed their songs to produce novel songs that were unique to each aviary. The control birds that remained in isolation for a second year did not change their songs. These second-year birds then changed their songs when they were moved to the aviaries and exposed to novel song for the first time at 2 years of age. Although additional experiments are important (e.g. tutoring adults raised in the wild), our results show that Costa's hummingbirds have open-ended vocal learning through at least their third year.

Male ducks in the genus Oxyura produce bill-drumming displays, sometimes called "bubbling display." We recorded high-speed video and sound of the bill-drumming display in >= 4 captive Ruddy Ducks (Oxyura jamaicensis) to ask: how is the sound produced? Our videos showed that, while fl oating in the water adjacent to a conspecific, the male struck his bill against his upper breast approximately 8.6 times over the course of 1 s. The breast, which had been inflated with air via both tracheal and interclavicular air sacs, visibly recoiled from each impact, producing motion in the water, including bubbles. These bill-to-breast collisions produced an atonal thumping sound; the display then ended with a vocalization as the tracheal air sac deflated. We recorded males performing this display on land and producing the normal sound, thus, the bubbling of the water is not integral to the acoustic qualities of the display. Histology on 4 birds showed that the tracheal air sac became more developed in breeding males, allowing males to inflate it, creating a stretched membrane that is struck with the bill (i.e., a drum). The entire structure in the neck of the Ruddy Duck male during the breeding season may develop to enhance sound production and/or protect the male against this constant beating created by the display.

Hummingbirds are often sexually dimorphic, the males of many species showing an ornamental gorget that females lack. Males use this ornamental plumage to attract mates and establish a territory, while females build nests and care for the young alone. In Los Angeles, California, we observed a nesting Anna’s Hummingbird with male-like plumage on the crown and gorget but the rectrix morphology of a female—and it reared chicks. The extent of gorget development on this individual likely represents one of the most extreme examples of a male-plumaged female hummingbird yet documented.

Gene flow can affect evolutionary inference when species are undersampled. Here, we evaluate the effects of gene flow and geographic sampling on demographic inference of 2 hummingbirds that hybridize, Allen's hummingbird (Selasphorus sasin) and rufous hummingbird (Selasphorus rufus). Using whole-genome data and extensive geographic sampling, we find widespread connectivity, with introgression far beyond the Allen's × rufous hybrid zone, although the Z chromosome resists introgression beyond the hybrid zone. We test alternative hypotheses of speciation history of Allen's, rufous, and Calliope (S. calliope) hummingbird and find that rufous hummingbird is the sister taxon to Allen's hummingbird, and Calliope hummingbird is the outgroup. A model treating the 2 subspecies of Allen's hummingbird as a single panmictic population fit observed genetic data better than models treating the subspecies as distinct populations, in contrast to morphological and behavioral differences and analyses of spatial population structure. With additional sampling, our study builds upon recent studies that came to conflicting conclusions regarding the evolutionary histories of these 2 species. Our results stress the importance of thorough geographic sampling when assessing demographic history in the presence of gene flow.