Many flowers produce nectar in order to attract pollinators such as hummingbirds. Floral nectar is used as the main source of energy for hummingbird and is primarily composed of various concentrations of the disaccharide sucrose and the monosaccharides fructose and glucose (Stiles and Freeman 2003) as well as small amounts of amino acids and electrolytes (Martinez del Rio 1990; Chalcoff et al. 2008).
Since hummingbirds prefer this blend of plant sugars we decided to start our hummingbird nectar research by exploring the specifications of the white table sugar that is offered at the feeders by so many hummer aficionados.
The ecologically accepted "ornithocentric explanation" provides that over time, plants develop different sugar concentrations in their nectars based on the digestive preferences of specific birds in order to increase its chance of pollination (Fleming et al., 2004; Chalcoff, 2008). The explanation contradicts Martinez del Rio's hypothesis and the results that Fleming et al. (2004) found. The contrast to the "ornithocentric explanation" is the "plant-centered explanation" (Chalcoff, 2008) that suggests that plant physiology and floral morphology are the key factors that affect sugar concentrations in nectar, thus causing birds species to adapt (Fleming et aI., 2004; Chalcoff, 2008). None have been proven.
Perhaps many hummers are being "food imprinted," and acquire the taste of the nectar given to it early in its life by its mother and later in life, and plays a dominate role in hummingbird nectar choices. Thus, hummingbirds may have develop a preference for white table sugar.
Evolution of sweet taste perception in hummingbirds by transformation of the ancestral umami receptor
Maude W. Baldwin, Yasuka Toda, Tomoya Nakagita, Mary J. O'Connell, Kirk C. Klasing, Takumi Misaka, Scott V. Edwards, Stephen D. Liberles
Abstract: Sensory systems define an animal's capacity for perception and can evolve to promote survival in new environmental niches. We have uncovered a noncanonical mechanism for sweet taste perception that evolved in hummingbirds since their divergence from insectivorous swifts, their closest relatives. We observed the widespread absence in birds of an essential subunit (T1R2) of the only known vertebrate sweet receptor, raising questions about how specialized nectar feeders such as hummingbirds sense sugars. Receptor expression studies revealed that the ancestral umami receptor (the T1R1-T1R3 heterodimer) was repurposed in hummingbirds to function as a carbohydrate receptor. Furthermore, the molecular recognition properties of T1R1-T1R3 guided taste behavior in captive and wild hummingbirds. We propose that changing taste receptor function enabled hummingbirds to perceive and use nectar, facilitating the massive radiation of hummingbird species.
Sugar Content of Hummingbird Plants in Louisiana Gardens
Page seven (7) of http://losbird.org/news/0326_201_news.pdf
Hummingbirds can fuel expensive hovering flight completely
with either exogenous glucose or fructose
Chris Chin Wah Chen & Kenneth Collins Welch Jr
“Hummingbirds have an optimal fuel-use strategy that powers their high-energy lifestyle, maximizes fat storage, and minimizes unnecessary weight gain all at the same time,” says Kenneth Welch, assistant professor of biological sciences at UTSC and an expert on hummingbirds.
Welch and his graduate student Chris Chen, who is co-author on the research, fed hummingbirds separate enriched solutions of glucose and fructose while collecting exhaled breath samples. They found the birds were able to switch from burning glucose to fructose equally as well.
“What’s very surprising is that unlike mammals such as humans, who can’t rely on fructose to power much of their exercise metabolism, hummingbirds use it very well. In fact, they are very happy using it and can use it just as well as glucose,” says Welch.
Hummingbirds require an incredible amount of energy to flap their wings 50 times or more per second in order to maintain hovering flight. In fact, if a hummingbird were the size of a human, it would consume energy at a rate more than 10 times that of an Olympic marathon runner. They are able to accomplish this by burning only the most recently ingested sugar in their muscles while avoiding the energetic tax of first converting sugar into fat.
From an evolutionary perspective the findings make perfect sense, says Welch. Whereas humans evolved over time on a complex diet, hummingbirds evolved on a diet rich in sugar.
“Hummingbirds are able to move sugar from their blood to their muscles at very fast rates, but we don’t yet fully understand how they are able to do this,” he says.
Humans are not good at burning fructose because once ingested much of it gets taken into the liver where it’s turned into fat. The prevalence of high fructose corn syrup found in products like soda pop is also strongly linked to a rise in obesity rates.
On the other hand because hummingbirds burn sugar so fast that if they were the size of an average person they would need to drink more than one can of soda every minute even though it’s mostly made of high-fructose corn syrup.
“If we can gain insights on how hummingbirds cope with an extreme diet then maybe it can shed some light on what goes wrong in us when we have too much fructose in our diet,” says Welch.
Food for thought---OK for hummers (?) but some links regarding humans and sugar: