Calypte Anna Research Articles

Flight costs of long, sexually selected tails in hummingbirds

The elongated tails adorning many male birds have traditionally been thought to degrade flight performance by increasing body drag. However, aerodynamic interactions between the body and tail can be substantial in some contexts, and a short tail may actually reduce rather than increase overall drag. To test how tail length affects flight performance, we manipulated the tails of Anna's hummingbirds (Calypte anna) by increasing their length with the greatly elongated tail streamers of the red-billed streamertail (Trochilus polytmus) and reducing their length by removing first the rectrices and then the entire tail (i.e. all rectrices and tail covert feathers). Flight performance was measured in a wind tunnel by measuring (i) the maximum forward speed at which the birds could fly and (ii) the metabolic cost of flight while flying at airspeeds from 0 to 14 m s(-1). We found a significant interaction effect between tail treatment and airspeed: an elongated tail increased the metabolic cost of flight by up to 11 per cent, and this effect was strongest at higher flight speeds. Maximum flight speed was concomitantly reduced by 3.4 per cent. Also, removing the entire tail decreased maximum flight speed by 2 per cent, suggesting beneficial aerodynamic effects for tails of normal length. The effects of elongation are thus subtle and airspeed-specific, suggesting that diversity in avian tail morphology is associated with only modest flight costs.

Fiber type homogeneity of the flight musculature in small birds

Studies of medium- and large-bodied avian species have suggested that variation in flight muscle composition is related to differences in flight behavior. For example, slow-twitch or tonic fibers are generally found only in the flight muscles of non-volant or soaring/gliding birds. However, we know comparatively little about fiber composition of the muscles of the smallest birds. Here we describe the fiber composition of muscles from the wings, shoulders, and legs of two small avian species, which also display very high wingbeat frequencies: Anna's hummingbirds (Calypte anna) and zebra finches (Taeniopygia guttata). All flight muscles examined in both species contained exclusively fast oxidative glycolytic (FOG) fibers. These unique results suggest that fast oxidative fibers are both necessary and sufficient for the full range of flight behaviors in these small-bodied birds. Like all other studied birds, the zebra finch gastrocnemius, a tarsometatarsal extensor, contained a mixture of FOG (27.1%), slow oxidative (SO, 12.7%), and fast glycolytic (FG, 60.2%) fibers. By contrast, the hummingbird gastrocnemius lacked FG fibers (85.5% FOG, 14.5% SO), which may reflect the reduced role of the hindlimb during take-off. We further hypothesize that thermogenic requirements constrain fiber type heterogeneity in these small endothermic vertebrates.

Wake patterns of the wings and tail of hovering hummingbirds

The flow fields of slowly flying bats and faster-flying birds differ in that bats produce two vortex loops during each stroke, one per wing, and birds produce a single vortex loop per stroke. In addition, the circulation at stroke transition approaches zero in bats but remains strong in birds. It is unknown if these difference derive from fundamental differences in wing morphology or are a consequence of flight speed. Here, we present an analysis of the horizontal flow field underneath hovering Anna’s hummingbirds (Calypte anna) to describe the wake of a bird flying at zero forward velocity. We also consider how the hummingbird tail interacts with the wake generated by the wings. High-speed image recording and analysis from three orthogonal perspectives revealed that the wing tips reach peak velocities in the middle of each stroke and approach zero velocity at stroke transition. Hummingbirds use complex tail kinematic patterns ranging from in phase to antiphase cycling with respect to the wings, covering several phase shifted patterns. We employed particle image velocimetry to attain detailed horizontal flow measurements at three levels with respect to the tail: in the tail, at the tail tip, and just below the tail. The velocity patterns underneath the wings indicate that flow oscillates along the ventral–dorsal axis in response to the down- and up-strokes and that the sideways flows with respect to the bird are consistently from the lateral to medial. The region around the tail is dominated by axial flows in dorsal to ventral direction. We propose that these flows are generated by interaction between the wakes of the two wings at the end of the upstroke, and that the tail actively defects flows to generate moments that contribute to pitch stability. The flow fields images also revealed distinct vortex loops underneath each wing, which were generated during each stroke. From these data, we propose a model for the primary flow structures of hummingbirds that more strongly resembles the bat model. Thus, pairs of unconnected vortex loops may be shared features of different animals during hovering and slow forward flight.

Responses in Bird Communities to Wildland Fires in Southern California

There is a growing body of literature covering the responses of bird species to wildland fire events. Our study was unique among these because we investigated the effects of large-scale wildland fires on entire bird communities across multiple vegetation types. We conducted avian point counts during the breeding seasons for two years before and two years after the Cedar and Otay Fires in 2003 in southern California. Our balanced sampling effort took place at two sites, one low-elevation and one high-elevation, each containing replicate stations (burned and unburned) within five vegetation types: chaparral, coastal sage scrub, grassland, oak woodland, and riparian. Although fire caused some degree of change in the vegetation structure at all of our impacted survey points, we found that the post-fire shrub and tree cover was significantly lower in only two of the vegetation types within the low-elevation site, coastal sage scrub and chaparral. We found no significant changes in cover at the high-elevation site. Using univariate and multivariate analyses, we tested whether the fires were associated with a change in bird species diversity, community structure, and the relative abundance of individuals within a species. We found that species diversity changed in only one circumstance: it increased in coastal sage scrub at the low-elevation site. Multivariate analyses revealed significant differences in the post-fire bird community structure in the low-elevation chaparral, low-elevation coastal sage scrub, and the high-elevation grassland communities. Vegetation characteristics altered by fire, such as decreases in shrub and tree cover, influenced the changes we observed in the bird communities. The relative abundance of some species (lazuli bunting [Passerina amoena] and horned lark [Eremophila alpestris]) significantly increased after the fires, while other species declined significantly (Anna’s hummingbird [Calypte anna], wrentit [Chamaea fasciata], and bushtit [Psaltriparus minimus]). We detected mixed results for the spotted towhee (Pipilo maculatus), which increased in burned chaparral and declined in burned coastal sage scrub within the low-elevation site. We suggest that the observed responses of birds to these fires may be attributed to: (1) the availability of nearby unburned refugia, (2) the continued suitability of post-fire vegetation at the study sites, and (3) the generally high mobility of this taxon.

Dietary sugar as a direct fuel for flight in the nectarivorous bat Glossophaga soricina

It is thought that the capacity of mammals to directly supply the energetic needs of exercising muscles using recently ingested fuels is limited. Humans, for example, can only fuel about 30%, at most, of exercise metabolism with dietary sugar. Using indirect calorimetry, i.e. measurement of rates of O(2) consumption and CO(2) production, in combination with carbon stable isotope techniques, we found that nectarivorous bats Glossophaga soricina use recently ingested sugars to provide approximately 78% of the fuel required for oxidative metabolism during their energetically expensive hovering flight. Among vertebrate animals, only hummingbirds exceed the capacity of these nectarivorous bats to fuel exercise with dietary sucrose. Similar experiments performed on Anna's (Calypte anna) and rufous (Selasphorus rufus) hummingbirds show that they use recently ingested sugars to support approximately 95% of hovering metabolism. These results support the suggestion that convergent evolution of physiological and biochemical traits has occurred among hovering nectarivorous animals, rendering them capable of a process analogous to aerial refueling in aircraft.

The Anna's hummingbird chirps with its tail: a new mechanism of sonation in birds

A diverse array of birds apparently make mechanical sounds (called sonations) with their feathers. Few studies have established that these sounds are non-vocal, and the mechanics of how these sounds are produced remains poorly studied. The loud, high-frequency chirp emitted by a male Anna's hummingbird (Calypte anna) during his display dive is a debated example. Production of the sound was originally attributed to the tail, but a more recent study argued that the sound is vocal. Here, we use high-speed video of diving birds, experimental manipulations on wild birds and laboratory experiments on individual feathers to show that the dive sound is made by tail feathers. High-speed video shows that fluttering of the trailing vane of the outermost tail feathers produces the sound. The mechanism is not a whistle, and we propose a flag model to explain the feather's fluttering and accompanying sound. The flag hypothesis predicts that subtle changes in feather shape will tune the frequency of sound produced by feathers. Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds.

Oxygen consumption rates in hovering hummingbirds reflect substrate-dependent differences in P/O ratios: carbohydrate as a `premium fuel'

The stoichiometric relationship of ATP production to oxygen consumption, i.e. the P/O ratio, varies depending on the nature of the metabolic substrate used. The latest estimates reveal a P/O ratio approximately 15% higher when glucose is oxidized compared with fatty acid oxidation. Because the energy required to produce aerodynamic lift for hovering is independent of the metabolic fuel oxidized, we hypothesized that the rate of oxygen consumption, VO2, should decline as the respiratory quotient, RQ (VCO2/VO2), increases from 0.71 to 1.0 as hummingbirds transition from a fasted to a fed state. Here, we show that hovering VO2 values in rufous (Selasphorus rufus) and Anna's hummingbirds (Calypte anna) are significantly greater when fats are metabolized (RQ=0.71) than when carbohydrates are used (RQ=1.0). Because hummingbirds gained mass during our experiments, making mass a confounding variable, we estimated VO2 per unit mechanical power output. Expressed in this way, the difference in VO2 when hummingbirds display an RQ=0.71 (fasted) and an RQ=1.0 (fed) is between 16 and 18%, depending on whether zero or perfect elastic energy storage is assumed. These values closely match theoretical expectations, indicating that a combination of mechanical power estimates and ;indirect calorimetry', i.e. the measurement of rates of gas exchange, enables precise estimates of ATP turnover and metabolic flux rates in vivo. The requirement for less oxygen when oxidizing carbohydrate suggests that carbohydrate oxidation may facilitate hovering flight in hummingbirds at high altitude.

Oxidation rate and turnover of ingested sugar in hovering Anna's(Calypte anna) and rufous (Selasphorus rufus)hummingbirds

Hummingbirds obtain most of their dietary calories from floral nectar ingested during hovering flight. Despite the importance of dietary sugar to hummingbird metabolism, the turnover of newly ingested carbon in the pool of actively metabolized substrates has not been adequately characterized in hovering hummingbirds. By combining respirometry with stable carbon isotope analysis of respired breath, we show that in rufous (Selasphorus rufus) and Anna's (Calypte anna) hummingbirds at high foraging frequencies, utilization of newly ingested sugars increased over a period of 30-45 min until it accounted for virtually 100% of the fuel oxidized. This newly ingested sugar disappears from the actively metabolized pool of substrates over a similar time course. These results demonstrate that turnover of carbon in the pool of actively metabolized substrates is rapid; carbon from ingested sucrose is available for oxidation for 30-45 min before being cleared. By monitoring expired CO2 for the appearance and disappearance of the signature characteristic of newly ingested sugar and then calculating energy budgets using video recordings of hummingbird activity, we estimated the proportion of recently ingested sugar used to fuel ongoing metabolism as well as the proportion devoted to energy storage. Consistent differences between species in the percentage of ingested cane sugar oxidized during the 2 h experimental periods suggest that individuals of each species adopted energy intake patterns appropriate to their needs. This approach provides a means by which to examine the partitioning of dietary carbon intake between energy expenditure and storage using non-invasive, field-compatible techniques.

Diagnoses of hybrid hummingbirds (Aves: Trochilidae). 16. Characterization of a striking intergeneric hybrid (Lampornis clemenciae × Calypte anna) from Ramsey Canyon, Huachuca Mountains, southeastern Arizona

A hummingbird specimen from Ramsey Canyon, Huachuca Mountains, southeastern Arizona, represents a hybrid of Lampornis clemenciae (Blue-throated Hummingbird) × Calypte anna (Anna's Hummingbird). The specimen, which constitutes the only verified instance of hybridization between a species in the “mountain gem” group of hummingbirds and a species in the “bee” group, exhibits a blended mosaic of plumage characters of the parental species.

Water management in nectar-feeding birds

nectarivory is widespread in birds, but best known in three unrelated families on different continents: the American hummingbirds, Australasian honeyeaters, and the sunbirds of Africa and Asia. Bird pollinators require substantial nectar rewards and their flowers produce copious nectar, which is,

Hummingbirds rely on both paracellular and carrier-mediated intestinal glucose absorption to fuel high metabolism

Twenty years ago, the highest active glucose transport rate and lowest passive glucose permeability in vertebrates were reported in Rufous and Anna's hummingbirds (Selasphorus rufus, Calypte anna). These first measurements of intestinal nutrient absorption in nectarivores provided an unprecedented physiological foundation for understanding their foraging ecology. They showed that physiological processes are determinants of feeding behaviour. The conclusion that active, mediated transport accounts for essentially all glucose absorption in hummingbirds influenced two decades of subsequent research on the digestive physiology and nutritional ecology of nectarivores. Here, we report new findings demonstrating that the passive permeability of hummingbird intestines to glucose is much higher than previously reported, suggesting that not all sugar uptake is mediated. Even while possessing the highest active glucose transport rates measured in vertebrates, hummingbirds must rely partially on passive non-mediated intestinal nutrient absorption to meet their high mass-specific metabolic demands.

Decomposition of Nitrogenous Compounds by Intestinal Bacteria in Hummingbirds

Abstract Degradation of urinary nitrogen-containing compounds by bacteria in the ceca of birds occurs in a number of herbivorous and omnivorous species, and cecal absorption of the products of that degradation has been reported in chickens. This recycling of nitrogen may play an important role in nitrogen balance, especially in those species with low dietary nitrogen intake. We report, for the first time, degradation of nitrogenous compounds by intestinal bacteria in a bird that is nectarivorous and lacks ceca, Anna's Hummingbird (Calypte anna). Hummingbirds subsist year-round on a liquid diet with an exceptionally low-nitrogen content. Ureteral urine containing ammonia, urea, and uric acid has been observed in the lower intestinal tract of Anna's Hummingbird. Bacteria obtained from intestinal contents and homogenates of the anterior and posterior intestine of this species were able to break down uric acid, urea, and potassium urate, but not sodium urate. This degradation is the necessary first step in the recycling of nitrogen. Assessing its significance will involve determining whether the products of microbial breakdown are subsequently absorbed across the intestinal walls of these unique animals.

THE SEASONAL DISTRIBUTION AND ABUNDANCE OF HUMMINGBIRDS IN OAK WOODLAND AND RIPARIAN COMMUNITIES IN SOUTHEASTERN ARIZONA

Abstract We examined the distribution and abundance of hummingbirds at two study sites in southeastern Arizona, where we banded over 8000 individuals and 11 species in a 6-year period. We trapped approximately once a week from April to October at each site, from 1988–1992 at Sonoita, in oak woodlands, and 1991–1993 at Harshaw Creek, in a riparian area. Anna's (Calypte anna), Black-chinned (Archilochus alexandri), and Rufous (Selasphorus rufus) Hummingbirds were the most abundant species. At Harshaw Creek, Broad-billed (Cynanthus latirostris) and Costa's (Calypte costae) Hummingbirds occurred in significant numbers. A massive fall migration occurred at both sites, but few hummingbirds moved northward in spring. The large numbers of migrants were spaced over time within seasons, and the timing of peak migration for a species varied among years. Fall-migrant Black-chinned Hummingbirds peaked earliest with adult males preceding adult females and juveniles, followed by Rufous Hummingbirds (predominantly juveni...

DECOMPOSITION OF NITROGENOUS COMPOUNDS BY INTESTINAL BACTERIA IN HUMMINGBIRDS

Abstract Degradation of urinary nitrogen-containing compounds by bacteria in the ceca of birds occurs in a number of herbivorous and omnivorous species, and cecal absorption of the products of that degradation has been reported in chickens. This recycling of nitrogen may play an important role in nitrogen balance, especially in those species with low dietary nitrogen intake. We report, for the first time, degradation of nitrogenous compounds by intestinal bacteria in a bird that is nectarivorous and lacks ceca, Anna's Hummingbird (Calypte anna). Hummingbirds subsist year-round on a liquid diet with an exceptionally low-nitrogen content. Ureteral urine containing ammonia, urea, and uric acid has been observed in the lower intestinal tract of Anna's Hummingbird. Bacteria obtained from intestinal contents and homogenates of the anterior and posterior intestine of this species were able to break down uric acid, urea, and potassium urate, but not sodium urate. This degradation is the necessary first step in th...

Changes in the composition of the urine of yellow-vented bulbuls (Pycnonotus xanthopygos): the effects of ambient temperature, nitrogen, and water intake.

Uricotely (uric acid >50% of urinary nitrogen) in birds was once considered ubiquitous. However, Anna's hummingbirds (Calypte anna) have been shown to be an exception to this rule; under conditions of low ambient temperature (T(a)) and on a nitrogen-free diet, they increased their water intake and often became ammonotelic (ammonia >50% of urinary nitrogen). Our aim was to identify the effects of nitrogen intake, water intake, and T(a) on the ammonia excretion of yellow-vented bulbuls (Pycnonotus xanthopygos). We chose this predominantly frugivorous species because many of the characteristics of nectarivores that were used to explain increased ammonia excretion by C. anna are also characteristics of frugivorous birds. We assayed ureteral urine composition in eight yellow-vented bulbuls (P. xanthopygos), each randomly allocated a diet of 20% (0.6 M) sucrose solution supplemented by either 1.03 g/L or 7.23 g/L soy protein and held at a T(a) of either 28 degrees C or 10 degrees C. Food, and therefore water, intake rates varied with nitrogen intake but not with T(a). Food intake increased significantly with decreased nitrogen intake, while concentrations of all the excretory compounds in the urine (P<0.05) decreased; yet their proportions in the urine did not change significantly. The lower T(a) had no significant effect on food intake or on the concentration of uric acid. However, at 10 degrees C, the ammonia and urea concentrations increased (P<0.05), and this led to a significant increase in the proportion of ammonia in the urine. Our results demonstrate that, when bulbuls are exposed to low T(a), they are able to save energy by increasing the proportion of the ammonia in their urine.

Morphological and molecular characterization of Encephalitozoon hellem in hummingbirds

Microsporidiosis was identified as a cause of enteritis in wild, migratory hummingbirds (Calypte anna). Electron microscopic examinations of parasites showed microsporidian spores with a double spore coat and a polar filament containing four to six coils, compatible with the genus Encephalitozoon. Molecular analysis of ribosomal RNA genes further identified the parasites from droppings and small intestinal segments as Encephalitozoon hellem, genotype I. Microsporidial spores were identified in 19% of droppings from C. anna, Archilochus alexandri and Selasporus sasin using Gram or modified trichrome staining methods. Since E. hellem is an opportunistic pathogen in immunocompromised humans, the pathogenic potential in avian hosts, the zoonotic potential of this parasite, and the role of birds as reservoirs needs to be further explored.

Neural song control system of hummingbirds: Comparison to swifts, vocal learning (Songbirds) and nonlearning (Suboscines) passerines, and vocal learning (Budgerigars) and nonlearning (Dove, owl, gull, quail, chicken) nonpasserines

Males of certain hummingbird species such as Anna's hummingbirds (Calypte anna) learn their song during postnatal development. Here we report that male Anna's hummingbirds and male Amazilia hummingbirds (Amazilia amazilia), two singing hummingbird species, possess forebrain areas that are similar in morphological appearance, location, and connectivity to the song control areas RA (nucleus robustus archistriatalis), HVC (nucleus hyperstriatalis ventrale, pars caudale, or higher vocal center), and LMAN (lateral part of nucleus mangnocellularis anterioris) of oscine passerines (songbirds). The vocal control areas of songbirds are further defined by the expression of androgen receptors. Similarly, the singing hummingbird species express androgen receptors in the LMAN-like area and in the HVC-like area. The hummingbird RA projects to the medullary syringeal motonucleus nXIIts (nucleus hypoglossus pars tracheosyringealis) and the respiratory premotonucleus RAm (nucleus retroambigualis). The HVC-, RA-, and LMAN-like areas are rudimentary in adult male ruby-throated hummingbirds (Archilochus colubris) and Allen's hummingbirds (Selasphorus sasin) and not distinguishable in female hummingbirds, none of which sing. Vocal-area-like forebrain areas (delineated by the cytoarchitecture or androgen receptor expression) were not found in vocal nonlearning swifts and suboscines, the taxonomic sister groups of hummingbirds and songbirds, respectively. These areas were also missing in owls, ring doves, gulls, and gallinaceous species, nonpasserines that do not learn vocalizations. Budgerigars (vocal learners) are known to have forebrain vocal areas, but these areas do not express sex steroid receptors. These data suggest that hummingbirds and songbirds belong to two groups of birds that have common forebrain circuits. Parts of this circuit are organized as nuclear-like structures (LMAN, HVC, RA) in species that learn to sing.

Glomerular and medullary architecture in the kidney of Anna's Hummingbird

Hummingbirds have rates of water turnover that are among the highest of any bird, consuming up to five times their body mass in nectar each day. To determine if the processing of these extraordinary volumes of water is associated with structural specializations in the kidney, we examined the renal morphology of Anna's hummingbird (Calypte anna) using scanning electron microscopy of vascular and tubular casts. The glomerular tufts are simple, containing a single, unbranched capillary that is spiraled or folded back on itself only one or two times. There is no evidence that nectarivory in this species is associated with a relative increase in the size of the glomeruli. The medullary cones are small, containing only a few loops of Henle and collecting ducts. The vasa recta form a complex network of branching and anastomosing capillaries. In this nectarivore, the structures necessary to produce urine that is hyperosmotic to plasma are poorly developed or absent, which is consistent with urine osmolalities that are uniformly low. J. Morphol. 240:95–100, 1999. © 1999 Wiley-Liss, Inc.

Glomerular and medullary architecture in the kidney of Anna's Hummingbird.

Hummingbirds have rates of water turnover that are among the highest of any bird, consuming up to five times their body mass in nectar each day. To determine if the processing of these extraordinary volumes of water is associated with structural specializations in the kidney, we examined the renal morphology of Anna's hummingbird (Calypte anna) using scanning electron microscopy of vascular and tubular casts. The glomerular tufts are simple, containing a single, unbranched capillary that is spiraled or folded back on itself only one or two times. There is no evidence that nectarivory in this species is associated with a relative increase in the size of the glomeruli. The medullary cones are small, containing only a few loops of Henle and collecting ducts. The vasa recta form a complex network of branching and anastomosing capillaries. In this nectarivore, the structures necessary to produce urine that is hyperosmotic to plasma are poorly developed or absent, which is consistent with urine osmolalities that are uniformly low. J. Morphol. 240:95-100, 1999. © 1999 Wiley-Liss, Inc.

Hyperglycemia in hummingbirds and its consequences for hemoglobin glycation

We measured levels of glucose and glycated hemoglobin in the blood of three of the world's smallest nectarivorous birds, the Anna's ( Calypte anna), Costa's ( Calypte costae), and ruby-throated hummingbirds ( Archilochus colubris). Plasma glucose levels of hummingbirds that were fasted overnight (17 mM) were higher than those in any mammal and are among the highest ever measured in a fasting vertebrate. Glucose levels in hummingbirds just after feeding were extreme, rising as high as 42 mM. The surprisingly high blood glucose concentrations in hummingbirds were accompanied by glycated hemoglobin levels that are the highest ever measured in birds but are lower than those of non-diabetic humans. How hummingbirds tolerate blood glucose levels that cause serious neurological and microvascular pathologies in diabetic humans and animals remains unknown.