The integration of energy and nitrogen balance in the hummingbirdSephanoides sephaniodes

Abstract

SUMMARYFloral nectars are rich in energy but contain only traces of amino acids,and it has been hypothesized that arthropods may be an important source of energy and amino acids for hummingbirds. We studied the nitrogen requirements of hummingbirds as well as how they use small arthropods to satisfy their nitrogen and energy requirements and how organ mass varies with nitrogen intake. Non-reproductive green-backed firecrowns Sephanoides sephaniodes were maintained for 10 days on diets containing 0%, 0.96%,1.82%, 4.11% and 11.1% nitrogen (dry-matter basis). A second group of individuals were fed with varying amounts of nitrogen-free nectar supplemented with fruit flies. Finally, non-reproductive hummingbirds were captured as a control group for analysis of organ mass and size as well as fat content.The maintenance nitrogen requirement of green-backed firecrowns determined by regression was 1.42 mg N day-1, yet they required nearly 10 mg N day-1 to maintain body mass. When arthropods were available, we observed that hummingbirds required approximately 150 fruit flies to maintain body mass, which corresponds to a 5% nitrogen diet. Interestingly, when nectar was restricted (to 4 ml day-1), or was absent, arthropods alone were not able to satisfy the body mass balance requirements of hummingbirds,suggesting that arthropods are not adequate as an energy source. In the group offered an 11.1% nitrogen diet, the size and surface of the small intestine,and liver and kidney mass increased in comparison with the control group(non-reproductive field hummingbirds) or the nitrogen-free group, suggesting a nitrogen overload. Our results are in agreement with other studies showing low nitrogen requirements by nectarivores. An important point to stress is that nitrogen digestibility declined in the 11.1% nitrogen diet, which strongly supports our nitrogen absorption saturation hypothesis.

Testosterone levels in feces predict risk‐sensitive foraging in hummingbirds

“…Therefore, hummingbirds received a 20% sucrose solution (nectar), supplemented with minerals and vitamins, proteins (0.71 g/50 ml of solution; ProMod, Abbott) and 5 g of nitrogen. The diet was offered over a 24‐h period with ad libitum consumption (sensu López‐Calleja et al ).…”

Drinking problems on a ‘simple’ diet: physiological convergence in nectar-feeding birds

“…Furthermore, nectar amino acid composition may not match nitrogen requirements in terms of essential amino acids. Nitrogen levels found in most floral nectars are generally insufficient to meet the nitrogen requirements of nectarivorous vertebrates (López-Calleja et al, 2003). Supplementing their nectar diet with pollen (Fleming and Moore, 2012), insects or spiders is therefore important, especially during seasons when the birds are moulting or breeding.…”

Homeokinetics/Homeodynamics: A Physical Heuristic for Life and Complexity

“…The metabolic demand of a hummingbird in daily flight (it would be greater in migratory flight) has been measured at 43 kJ/day (i.e., 5 W average power output; López-Calleja, Fernández, & Bosinovic, 2003), another colossal figure considering the small size of the bird studied (about 3 gm). At about 1-2 W/gm, the hummingbird's regular metabolism puts our basal state metabolism to shame (about 1 W per kilogram)!…”