Hummingbirds are specialized nectarivores that feed on dilute solutions of sugars with trace amounts of amino acids and electrolytes. Their diets contain excess water that, if absorbed, must be eliminated. It has been hypothesized that in hummingbirds only a small fraction of this dietary water may be absorbed in the intestine. Here, we report the results of experiments designed to examine the relationship between nectar intake and water turnover in hummingbirds. Our results also allow the estimation of water absorption across the intestine and therefore test the hypothesis that ingested water in hummingbirds passes largely unabsorbed through the gastrointestinal tract. We found that fractional and total water turnover increased linearly with water ingestion. At low sucrose concentrations, food intake rates between four and five times body mass per 12 h were not unusual. A simple mass-balance model suggested that 78 % of ingested water was absorbed in the gastrointestinal tract and hence must be processed by the kidneys. However, fractional water absorption was variable and did not appear to be correlated with food or water intake parameters. Our results do not lend support to the hypothesis that the bulk of dietary water passes through the intestine unabsorbed. Although hummingbird kidneys appear well suited to excrete large volumes of dilute urine, rates of energy assimilation in hummingbirds may be constrained by excess water elimination when these birds are feeding on nectars with a low sugar concentration. | T.J. McWhorter and C. Martinez del Rio

PURPOSE Body composition is strongly associated with cardiometabolic risk factors, and accurate measurement of body composition is vital for the management of chronic diseases. In this study, we assessed whether major factors such as urination, aerobic exercise, food, and water consumption had significant effects on body composition by segmental bioelectrical impedance analysis (BIA). METHODS To achieve the goal of this study, research was conducted on 32 healthy young males (n=18) and females (n=14). All participants underwent body composition analysis in four different conditions (both pre- and post-urination, moderate-intensity aerobic exercise for 30 minutes, immediately after food and water consumption, 30, 60, and 120 minutes after each treatment), and segmental BIA was performed using Inbody720. RESULTS We found that after urination, body weight, skeletal muscle mass, and basal metabolic rate (BMR) significantly decreased. However, water intake significantly increased body weight, body fat mass, and body fat percentage. Furthermore, an acute 30-minutes aerobic exercise significantly decreased body weight, fat mass, and fat percentage, and increased skeletal muscle mass and BMR. In addition, impedance decreased immediately and increased 120 minutes after the acute aerobic exercise. Finally, food ingestion significantly increased the body weight, skeletal muscle mass, and BMR. CONCLUSIONS Our study suggests that variables such as urination, exercise, food consumption, and water intake should be considered to accurately assess body composition.