The effect of salt content on nectar intake of a New World generalist avian nectarivore (Cyanerpes cyaneus: Thraupidae)

Abstract

Generalist avian nectarivores visit flowers that produce copious sugar-dilute nectar, and some species can not compensate energy intake when fed solutions with low sugar content (≥5% w/w). Intake of dilute sugar diets by specialist avian nectarivores is limited by salt content, but the potential role of salt on nectar intake of generalist nectarivores has not been tested. We examined intake rate and digestion of solutions with varying sucrose concentrations (2.5-30% w/w) by Red-legged Honeycreeper (Cyanerpes cyaneus) and the effect of salt content (20 and 40 mM L-1 NaCl) on the intake rate and digestion of dilute sucrose solutions (2.5% w/w) of this generalist nectarivore. We tested the hypothesis that Red-legged Honeycreepers do not show compensatory feeding when fed dilute sugar diets, and that salt limits the intake rate and digestion of these solutions. We found that this generalist nectarivore showed compensatory feeding when fed sucrose diets ≥5%, but they did not compensate sugar intake when fed a 2.5% sucrose diet. Sucrose intake, sucrose apparent assimilation, and body mass increased when birds were fed dilute sugar diets to which NaCl was added. Addition of salt facilitated feeding on dilute sugar diets, probably by reducing Na+ losses, and increasing Na-dependent glucose transport. Further work on the renal and digestive physiology of generalist avian nectarivores would clarify the role of salt on the intake of dilute sugar solutions.