The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar-feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar-feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte-free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte-free food they produced excreta containing less than 0.5 mM l⁻¹ each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l⁻¹ sucrose) contained more than 35 mM l⁻¹ of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar‐feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar‐feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte‐free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte‐free food they produced excreta containing less than 0.5 mM l^?1 each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l^?1 sucrose) contained more than 35 mM l^?1 of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

Time-dependent thresholds for torpor initiation in the rufous hummingbird (Selasphorus rufus)

Summary Three models for torpor initiation were tested in rufous hummingbirds (Selasphorus rufus) during moult, when these birds appear to avoid the use of torpor. In model 1, the level of energy reserves at which torpor is initiated (the threshold) remains constant throughout the night. In model 2, the threshold declines throughout the night, at a constant rate equivalent to the rate at which energy reserves are depleted during torpor. In model 3, the threshold declines at a rate equivalent to the rate of energy reserve depletion during torpor for most of the night, but at a higher rate (corresponding to the rate of energy expenditure during normothermia) during the final 2 h of the night, when these birds are usually normothermic. Model 1 predicts the most frequent and longest bouts of torpor, whereas model 3 predicts the fewest and shortest bouts. To determine the thresholds for each of 12 birds, food supply was manipulated to induce entry into torpor at different times on successive nights. Threshold slopes matched the predictions of model 3 most closely. Calculations comparing observed incidence of torpor with the predictions of model 1 show that the actual, time-dependent threshold for torpor initiation resulted in a 72% reduction in the number of torpor bouts compared with the number of torpor bouts that should have been initiated by a constant threshold. The advantage of a time-dependent threshold is that, although torpor is initiated when needed to prevent energy reserves from falling below a critical level, the amount of time spent in torpor can be minimized. This may be especially important to rufous hummingbirds during the spring moult, because lowered metabolic rates during torpor probably result in decreased rates of feather replacement during the moult and may thus have consequences for thermoregulation, territorial defence, and timing of the spring migration.     

Context-dependent foraging decisions in rufous hummingbirds

A core assumption implicit in economic models of animal choice is that subjects assign absolute utilities to options that are independent of the type and number of alternatives available. Humans sometimes appear to violate this assumption and employ relative, as opposed to absolute, currencies when making choices. Recent evidence suggests that animals too might sometimes employ relative choice mechanisms. We tested this idea by measuring the foraging preferences of rufous hummingbirds (Selasphorus rufus) faced with choices analogous to those in which human use of relative currencies is evident. The birds experienced three treatments: a binary choice between two artificial flower types designated concentration (20 microl, 40% sucrose solution) and volume (40 microl, 20%), and two trinary treatments in which a third decoy option (either concentration decoy: 10 microl, 30% or volume decoy: 30 microl, 10%) was added to the set. The birds' preferences differed significantly across the three treatments. In the trinary treatments, the effect of the decoy options was to increase the preference for the option that dominated the decoy. These results are similar to those reported in the human choice literature, and are compatible with the hummingbirds using a relative evaluation mechanism in decision making.     

Resource use,energetic profitability,and behavioral decisions in migrant rufous hummingbirds

Summary Migrant Rufous Hummingbirds (Selasphorus rufus) defend nectar resources at stopover sites while replenishing fat reserves needed for migratory flights. During late summer in the Sandia Mountains, central New Mexico, they defend the wasp- and bee-pollinated Scrophularia montana from other hummingbirds. Both hummingbirds and hymenopterans exploit Scrophularia nectar during the early part of its flowering period. As summer colony growth increases the densities of the eusocial hymenopterans by 100–150%, their exploitation of Scrophularia nectar lowers its mean standing crop in flowers by 200–300%. Sometime during the summer, Rufous Hummingbirds abandon and do not further use this resource for the remaining 3–4 weeks of its flowering period. The abandonment always occurs when the mean standing crop of nectar is approximately 0.2–0.3 L/ flower. This paper describes a model of Rufous Hummingbird energetics, that shows abandonment occurred 1–3 days after they passed the threshold at which the resource could have provided their minimum daily energy requirements. I suggest that constraints imposed by a highly competitive social environment severely reduced the options available to the hummingbirds, and caused them to continue to defend a resource that could no longer meet their energetic requirements.     

The influence of testosterone on territorial defence and parental behavior in male free-living rufous whistlers, Pachycephala rufiventris

We studied a population of rufous whistlers, Pachycephala rufiventris, throughout a single breeding season in central New South Wales, Australia. We evaluated the relation between plasma testosterone (T) and reproductive behaviors using both simulated territorial intrusions (STIs) and subcutaneous T implants. We compared circulating T values to aggression levels of males (using STI) during pair bond and territory establishment and again during incubation. Although plasma T levels were significantly lower in the latter period, male responsiveness to STI, in terms of proximity to decoy, call rate, and number of attacks on the decoy, was indistinguishable between the two breeding stages. T levels of males exposed to STI were not different from the levels of unexposed free-living males at the same breeding stage. The effect of exogenous T on parental behavior was examined by comparing duration of incubation bouts of males and their mates prior to and after T treatment. T males significantly reduced the amount of time they incubated following implantation, whereas Control males maintained their incubation effort. After cessation of breeding activities, T males displayed significantly higher call rates due to increased use of the primary intersexual advertisement call in this species. The reduction of incubation behavior following T implantation emphasises the functional significance of the rapid decline in T in free-living males during incubation. The results from both experiments suggest that intersexual advertisement, rather than territorial aggression, may be dependent on high T levels in this species.     

Lice and ticks of the eastern rufous mouse lemur, Microcebus rufus, with descriptions of the male and third instar nymph of Lemurpediculus verruculosus (Phthiraptera: Anoplura)

Sucking lice and ticks were collected from live-trapped eastern rufous mouse lemurs, Microcebus rufus Geoffroy, in and around the periphery of Ranomafana National Park, southeastern Madagascar, from 2007 to 2009. Samples of 53 sucking lice (Insecta: Phthiraptera: Anoplura) and 28 hard ticks (Acari: Ixodidae) were collected from 36 lemur captures representing 26 different host individuals. All of the lice were Lemurpediculus verruculosus (Ward) (6 males, 46 females, 1 third instar nymph). Only the holotype female was known previously for this louse and the host was stated to be a "mouse lemur." Therefore, we describe the male and third instar nymph of L. verruculosus and confirm M. rufus as a host (possibly the only host) of this louse. All of the ticks were nymphs and consisted of 16 Haemaphysalis lemuris Hoogstraal, 11 Haemaphysalis sp., and 1 Ixodes sp. The last 2 ticks listed did not morphologically match any of the Madagascar Haemaphysalis or Ixodes ticks for which nymphal stages have been described.     

Spermophagy in semen in the red wolf,Canis rufus

The red wolf (Canis rufus) is an endangered species with 194 individuals remaining in the wild and in various captive facilities. Breeding efforts at the Graham, WA site (Point Defiance Zoo and Aquarium) have involved artificial insemination with fresh or frozen semen in an effort to increase population and maximize the genetic potential of the stock. Electron microscopic observations were made in semen specimens obtained by electroejaculation from mature males prior to their use in an effort to determine semen parameters that might be useful in guiding breeding procedures. Sperm samples were either fixed immediately or treated with capacitating media and fixed after 4 to 7 hr of incubation. Many of the specimens examined were pyospermic (white cell in semen) and showed evidence of spermophagy, primarily by neutrophils. Of the six animals surveyed, only one showed little evidence of spermophagy, and three had extensive pyospermia and spermophagy but this finding was not correlated with fertility. Samples fixed immediately as well as those incubated for several hours showed evidence of spermophagy, indicating that the phagocytosis was not the result of culture. Gene pool restriction and/or captive stress may be contributing factors of reduced semen quality. © 1994 Wiley-Liss, Inc.     

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.     

Cost of territory establishment in hummingbirds

Summary Time spent in territorial defense was measured during territory establishment for non-breeding Black-chinned (Archilochus alexandri) and Anna's (Calypte anna) hummingbirds. Newly established territory holders spent more time chasing intruders than neighboring established owners, which served as controls. This higher investment in defense by the new owners was due to 1) a longer time spent per each chase and 2) in some cases, a higher frequency of chases at the onset of territory ownership.     

Energy,predators and the behavior of feeding hummingbirds

Summary Current evidence suggests that many animals trade off energy gain against the risk of predation while feeding. In contrast, energetic considerations alone have proven successful in explaining and predicting the behaviour of feeding hummingbirds. This success may reflect the relative lack of natural predation on hummingbirds, but this study suggests that it may additionally reflect the lack of studies taking a predation perspective. In particular, when Anna's hummingbirds (Calypte anna) are faced with an obstructed view of their surroundings, they engage in behaviour suggestive of anti-predatory vigilance. In doing so, they voluntarily reduce their rate of energy intake. These birds also forgo better feeding opportunities that occur close to the ground, where observations suggest they are wary of opportunistic predators such as roadrunners (Geococcys californianus). While energy-based concepts will remain useful in the study of hummingbird feeding behaviour, the lack of predation on these birds should not be equated with an insensitivity to the risk of predation. This realization may lead to further insights into hummingbird-plant interactions, and hummingbird biology in general.     

Cell wall-less, free-living spirochetes in Antarctica

The phylogeny of an Antarctic, cell wall-less, bacterial strain was determined by sequencing PCR amplified 16S rDNA, and comparison of the sequence with other bacterial 16S rRNA sequences available in databanks. Although the strain was phenotypically very similar to members of the genus Anaeroplasma, phylogenetic analyses showed it was a member of the order Spirochaetales. Until now, the order was one of the few bacterial orders in which phylogeny was reflected in a uniform morphology of its members. The viability of wall-less cells in cultures of spirochetes and spirochetal infective material warrants reinvestigation.     

Respiration rates in heterotrophic,free-living protozoa

Published estimates of protozoan respiratory rates are reviewed with the object of clarifying their value in ecological studies. The data show a surprisingly large variance when similarly sized cells or individual species are compared. This is attributed to the range of physiological states in the cells concerned. The concept of basal metabolism has little meaning in protozoa. During balanced growth, energy metabolism is nearly linearly proportional to the growth rate constant; at the initiation of starvation, metabolic rate rapidly declines. Motility requires an insignificant fraction of the energy budget of protozoans. For growing cells, metabolic rate is approximately proportional to weight^0.75 and the data fall nearly exactly on a curve extrapolated from that describing the respiration rates of poikilotherm metazoans as a function of body weight. It is conceivable that protozoan species exist with lower maximum potential growth and metabolic rates than those predicted from cell volume and the equations derived from the available data. However, the lack of information concerning the state of the cells studied prevents verification of this idea. Laboratory measurements of protozoan respiratory rates have no predictive value for protozoa in nature other than delimiting a potential range. For small protozoans, this range may, on an individual basis, represent a factor of 50.     

Asymmetrical expression of transsexual phenotypes in hummingbirds

I present evidence for asymmetry in the expression of transsexual traits in adult hummingbirds. Among females, individuals with male-like plumage are common and define a continuous range of variation. Among males, individuals with female-like plumage are rare and define discontinuous plumage morphs. Quantitative characters also distinguish transsexuals from other members of their sex, but the characters involved differ for male-like females (bill length) and female-like males (bill, wing and tail length). Gonadal development is correlated with transsexuality only in males; female-like males have significantly smaller testes than male-like males. Both sexes demonstrate a significant negative association between plumage brightness and bill length. This association suggests an ecological basis for transsexuality because differences in plumage and bill morphology are associated with differences in foraging behaviour within and between hummingbird species. Morphological differences between transsexuals and non-transsexuals imply that plumage sexual dimorphism is more likely to evolve through changes in the frequency of female, rather than male, transsexual variants.     

Diversification in Adelomyia hummingbirds follows Andean uplift

The Andes are known to have influenced speciation patterns in many taxa, yet whether species diversification occurred simultaneously with their uplift or only after uplift was complete remains unknown. We examined both the phylogenetic pattern and dates of branching in Adelomyia hummingbirds in relation to Andean uplift to determine whether diversification coincides with the chronological phases of the uplift or with recent climatic fluctuations after Andean formation. Results suggest that the genus Adelomyia originated in the central Andes in the Miocene and was found to be comprised of six deeply divergent phylogroups dating between 3.5 and 6 Ma. The most basal splits in the tree, corresponding to the most southerly distributed of the six phylogroups, diverged in the late Miocene, whereas the northern phylogroups originated during the early-to-mid-Pliocene, when the northern Andes reached heights sufficient to support Adelomyia populations. Although we provide evidence for a southern origin for the group, the subsequent diversification of the northern phylogroups did not strictly follow the hypothesized south-to-north orogeny of the Andes. Further genetic structure within phylogroups may have resulted from Pleistocene climate fluctuations after the onset of the six lineages during the Mio-Pliocene. We explore the processes that promoted diversification in the Andes and suggest that in at least some groups, divergence was coupled to Andean orogeny.