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.     

Effects of temperature acclimation on body mass and energy budget in the Chinese bulbul Pycnonotus sinensis

Chinese bulbuls(Pycnonotus sinensis) are small passerine birds that inhabit areas of central, southern and eastern China. Previous observations suggest that free–living individuals of this species may change their food intake in response to seasonal changes in ambient temperature. In the present study, we randomly assigned Chinese bulbuls to either a 30 °C or 10 °C group, and measured their body mass(BM), body temperature, gross energy intake(GEI), digestible energy intake(DEI), and the length and mass of their digestive tracts over 28 days of acclimation at these temperatures. As predicted, birds in the 30 °C group had lower body mass, GEI and DEI relative to those in the 10 °C group. The length and mass of the digestive tract was also lower in the 30 °C group and trends in these parameters were positively correlated with BM, GEI and DEI. These results suggest that Chinese bulbuls reduced their absolute energy demands at relatively high temperatures by decreasing their body mass, GEI and DEI, and digestive tract size.     

乙醇浓度对圈养长舌果蝠摄食糖水量的影响

正在自然生境中,果蝠主要以果实或者花蜜为食,成熟果实或花蜜由于微生物发酵而含一定量的乙醇。乙醇在生态系统中是一种常见物质,它是生物厌氧代谢的终端产物之一(Van Waarde,1991)。一旦果实成熟,它们中的糖分就会被微生物或者自身发酵代谢成乙醇(Battcock and Azam-Ali,1998;Dudley,2000,2004)。果实中的乙醇浓度主要是由这些以糖分为能源的发酵微生物的扩增状态来决定     

Physiological and biochemical thermoregulatory responses of Chinese bulbuls Pycnonotus sinensis to warm temperature: Phenotypic flexibility in a small passerine

Temperature is an important environmental cue for the regulation of thermogenesis in small birds. We tested the hypothesis that a small passerine, the Chinese bulbul Pycnonotus sinensis can decrease thermogenesis in response to warmer temperatures by decreasing body mass, the organ mass and changing physiological and biochemical processes in the liver and muscle. Captive Chinese bulbuls decreased in body mass and basal metabolic rate (BMR) during 4 weeks of acclimation to 30±1 °C. They also showed a decrease in liver, kidney and small intestine mass and reduced mitochondrial state-4 respiration and cytochrome C oxidase (COX) activity in the liver and muscle compared to 10±1 °C. Furthermore, BMR was positively correlated with body mass, organ mass (liver, kidney, small intestine and entire digestive tract), and mitochondrial state-4 respiration and cytochrome C oxidase (COX) activity in the liver and muscle. These results indicate that changes in body mass, organ mass and respiratory enzyme activity are mechanisms by which Chinese bulbuls adapt to warmer temperatures. The data support the hypothesis that such physiological flexibility is ubiquitous in birds.     

Ingestion patterns and daily energy intake on a sugary diet: the Red Lory Eos bornea and the Malachite Sunbird Nectarinia famosa

This study examines whether nectarivorous birds regulate daily energy intake as proposed by Lloyd in 1991. Two Old World nectarivorous species, a large non-passerine, the Red Lory Eos bornea, and a small passerine, the Malachite Sunbird Nectarinia famosa, were fed 0.25 mol/1 sucrose (9%), 0.73 mol/1 sucrose [24%] or 0.73 mol/1 glucose in separate laboratory trials to determine hourly and overall daily rate of sugar intake and consumption. Overall daily energy intake rates of the Malachite Sunbird and the Red Lory support the hypothesis of regulated energy intake for nectarivorous Old World birds. However, the species differ in their ingestion patterns through the day. The Red Lory ingests large volumes initially, regardless of sugar type. This is possibly a consequence of their large size and having a crop in which food can be stored. The Malachite Sunbird showed more regular hourly consumption through the day, and no change in mass during the day. Intake rates of both species were greater on lower sugar concentrations.     

浙江温州地区4种雀形目鸟类消化道形态特征比较

食性是影响鸟类消化系统形态结构的重要因子之一.本文对丝光椋鸟Sturnus sericeus、白头鹎Pycnonotus sinensis、小鹀Emberiza pusilla及红头长尾山雀Aegithalos concinnus 4种雀形目鸟类的消化道形态结构进行了比较研究.结果发现,4种雀形目鸟类总消化道及各消化器...     

Food choice by Blue-gray Tanagers in relation to protein content

We tested discriminatory ability and food choice in relation to protein content of the diet in wild-caught Blue-gray Tanagers (Thraupis episcopus), a generalist tropical frugivorous bird. In two sets of experiments we offered to five individual birds in pair-wise choice trials two nearly iso-caloric experimental diets differing in their protein content only. Protein contents of the experimental diets were 4.6 vs. 1.4% in the first experiment and 3.2 and 1.5% (dry matter basis) in the second experiment. Response varied among individual tanagers, but 6 of the 10 birds showed a clear preference for the food highest in protein. Two individuals displayed a strong positional preference. When testing each treatment group, birds ate daily significantly more of the food that had higher protein content. We conclude that Blue-gray Tanagers prefer richer nitrogen foods. Our results also demonstrate that Blue-gray Tanagers have remarkable discriminatory abilities, they reacted to differences in protein content as small as 0.09% fresh matter. We show for the first time discriminatory ability and preference of wild frugivorous birds for foods richer in protein under controlled conditions. Our findings support the hypothesis that frugivorous birds can act as selective agents for fruit pulp composition.     

The possible roles of ethanol in the relationship between plants and frugivores: first experiments with egyptian fruit bats

In this paper we discuss how yeast, fungi ubiquitously presentin sugar-rich fruit, can influence the interaction between frugivoresand fleshy-fruited plants via ethanol. We suggest that plants,the seeds of which are mostly dispersed by vertebrates, exploitthe ethanol from alcoholic fermentation by yeast in their seeddispersal strategy. Moderate consumption of ethanol, i.e., atconcentrations close to those in naturally ripening fruit, byfrugivores may have beneficial short- and long-term effectsfor these potential dispersers, whereas consumption of largerquantities may have negative short- and long-term effects. Ethanolvapor emanating from palatable fruit may act as an odor cue,guiding bats and other frugivores to the fruit, and aiding themto assess its quality. In addition, we suggest that ingestedethanol may be an appetitive stimulant. We also evaluate thepossibility that ethanol within fruit may be used as a sourceof energy by frugivorous vertebrates. Our preliminary data indicatethat Egyptian fruit bats (Rousettus aegyptiacus) can use theodor of ethanol to assess food suitability, but also that itmay not serve as an attractant over short distances (i.e., <1m). Instead, ethanol is avoided at concentrations greater than1%, a value which might typically characterize overripe andotherwise unpalatable fruit. Our initial results further indicatethat Egyptian fruit bats significantly decrease their food consumptionif it contains 1 or 2% ethanol. Overall, ethanol may play diverseroles in the nutritional ecology and behavior of fruit-eatingbats, and in the interaction between frugivores and plants,in general.     

Effects of ethanol on food consumption and skin temperature in the Egyptian fruit bat (Rousettus aegyptiacus)

Since mammalian frugivores generally choose to eat ripe fruit in which ethanol concentration ([EtOH]) increases as the fruit ripens, we asked whether ethanol acts as an appetitive stimulant in the Egyptian fruit bat, Rousettus aegyptiacus, and also studied the effects of ethanol on their skin temperature (T(s)). We hypothesized that the responses of fruit bats to dietary ethanol are concentration dependent and tested the predictions that the bats' response is positive, i.e., they eat more when [EtOH] in the food is in the range found in naturally ripe fruit, while it negatively affects them at higher concentrations. We also tested the prediction that in winter, even when availability of fruit is low and thermoregulatory costs are high, ingestion of ethanol by fruit bats is low because assimilated ethanol reduces shivering thermogenesis and peripheral vasodilation; these, alone or together, are detrimental to the maintenance of body temperature (T(b)). In summer, captive bats offered food containing 0.1% ethanol significantly increased consumption over food with no ethanol; they did not change consumption when food contained 0.01, 0.3, or 0.5% ethanol; but significantly decreased consumption at higher levels of ethanol [EtOH], i.e., 1 and 2%. In winter, captive bats ate significantly less when their food contained 0.1% ethanol than when it contained 0, 0.3, or 0.5%. During summer, freshly caught bats ate significantly more ethanol-containing food than freshly caught bats in winter. Skin temperature (T(s)) in Egyptian fruit bats decreased significantly at an ambient temperature (T(a)) of 12 °C (winter conditions) after gavage with liquid food containing 1% ethanol. The effect was clearly temperature-dependent, since ethanol did not have the same effect on bats gavaged with food containing 1% or no ethanol at a T(a) of 25 °C (summer conditions). In conclusion, ethanol may act as an appetitive stimulant for Egyptian fruit bats at low concentrations, but only in summer. Bats are deterred by food containing [EtOH] corresponding to that in overripe, unpalatable fruit (1 and 2%). Furthermore, during winter, Egyptian fruit bats are deterred by ethanol-rich fruit, possibly due to the potential thermoregulatory consequences of ethanol consumption.     

Comparisons of Dispersal Success between the Species Fruiting Prior to and Those at the Peak of Migrant Frugivore Abundance

I evaluated whether plants gain high dispersal success by synchronizing their fruiting with frugivore abundance. Fruiting phenologies, seasonal fluctuations in the abundance of frugivorous birds, and consumption of fruits by birds and Japanese macaques, Macaca fuscata Blyth, were studied in the montane forest of Yakushima for two years. At the community level, fruiting phenologies and seasonal fluctuations in frugivorous bird abundance were asynchronous because Zosterops japonica Temminck et Schlegel, a resident frugivore, decreased in number during the fruiting season. In addition, Symplocos myrtacea Sieb. et Zucc. fruited in September, before the migration of frugivorous birds (Turdus spp. and brown-eared bulbuls Hypsypetes amaurotis Temminck) in November and December. The phenology of other fruit species (Eurya japonica Thunb. and Cleyera japonica Thunb.p.p.emend. Sieb. et Zucc) were synchronized with migrant frugivorous birds. Fruit species with phenologies that are synchronized with migrant frugivore abundances have higher dispersal success either by birds (C. japonica) or macaques (E. japonica). Macaques predated most of the seeds of S. myrtacea. Dispersal success of S. myrtacea is low both by birds and macaques, thus the early fruiting by S. myrtacea does not seem to be an adaptation to maximize dispersal success by depending on resident dispersers or by avoiding intense competition for dispersers.