For nutrition, hummingbirds eat a variety of insects, including mosquitoes, fruit flies, and gnats in flight or aphids on leaves and spiders in their webs. The lower beak of hummingbirds is flexible and can bend as much as 25 degrees when it widens at the base, making a larger surface for catching insects. Hummingbirds hover within insect swarms in a method called "hover-hawking" to facilitate feeding.
To supply energy needs, hummingbirds drink nectar, a sweet liquid inside certain flowers. Like bees, they are able to assess the amount of sugar in the nectar they eat; they normally reject flower types that produce nectar that is less than 10% sugar and prefer those whose sugar content is higher. Nectar is a mixture of glucose, fructose, and sucrose, and is a poor source of nutrients, requiring hummingbirds to meet their nutritional needs by consuming insects.
Hummingbirds do not spend all day flying, as the energy cost would be prohibitive; the majority of their activity consists simply of sitting or perching. Hummingbirds eat many small meals and consume around half their weight in nectar (twice their weight in nectar, if the nectar is 25% sugar) each day.[100]Hummingbirds digest their food rapidly due to their small size and high metabolism; a mean retention time less than an hour has been reported. Hummingbirds spend an average of 10–15% of their time feeding and 75–80% sitting and digesting.
Because their high metabolism makes them vulnerable to starvation, hummingbirds are highly attuned to food sources. Some species, including many found in North America, are territorial and will try to guard food sources (such as a feeder) against other hummingbirds, attempting to ensure a future food supply for itself. Additionally, hummingbirds have an enlarged hippocampus, a brain region facilitating spatial memory used to map flowers previously visited during nectar foraging.
Hummingbird beaks are flexible[98] and their shapes vary dramatically as an adaptation for specialized feeding. Some species, such as hermits (Phaethornis spp.) have long bills that allow them to probe deep into flowers with long corollae. Thornbills have short, sharp bills adapted for feeding from flowers with short corollae and piercing the bases of longer ones. The sicklebills' extremely decurved bills are adapted to extracting nectar from the curved corollae of flowers in the family Gesneriaceae. The bill of the fiery-tailed awlbill has an upturned tip, as in the avocets. The male tooth-billed hummingbird has barracuda-like spikes at the tip of its long, straight bill.
The two halves of a hummingbird's bill have a pronounced overlap, with the lower half (mandible) fitting tightly inside the upper half (maxilla). When a hummingbird feeds on nectar, the bill is usually opened only slightly, allowing the tongue to dart out and into the interior of flowers. Hummingbird bill sizes range from about 5 mm to as long as 100 mm (about 4 in). When catching insects in flight, a hummingbird's jaw flexes downward to widen the gape for successful capture.
Perception of sweet nectar
Perception of sweetness in nectar evolved in hummingbirds during their genetic divergence from insectivorous swifts, their closest bird relatives. Although the only known sweet sensory receptor, called T1R2, is absent in birds, receptor expression studies showed that hummingbirds adapted a carbohydrate receptor from the T1R1-T1R3 receptor, identical to the one perceived as umami in humans, essentially repurposing it to function as a nectar sweetness receptor. This adaptation for taste enabled hummingbirds to detect and exploit sweet nectar as an energy source, facilitating their distribution across geographical regions where nectar-bearing flowers are available.
Tongue as a micropump[edit]
Hummingbirds drink with their tongues by rapidly lapping nectar. Their tongues have tubes which run down their lengths and help the hummingbirds drink the nectar. While capillary action was believed to be what drew nectar into these tubes, high-speed photography has revealed that the tubes open down their sides as the tongue goes into the nectar, and then close around the nectar, trapping it so it can be pulled back into the beak. The tongue, which is forked, is compressed until it reaches nectar, then the tongue springs open, the rapid action traps the nectar and the nectar moves up the grooves, like a pump action, with capillary action not involved. Consequently, tongue flexibility enables accessing, transporting and unloading nectar.
Feeders and artificial nectar
In the wild, hummingbirds visit flowers for food, extracting nectar, which is 55% sucrose, 24% glucose and 21% fructose on a dry-matter basis.[112] Hummingbirds also take sugar-water from bird feeders. Such feeders allow people to observe and enjoy hummingbirds up close while providing the birds with a reliable source of energy, especially when flower blossoms are less abundant. A negative aspect of artificial feeders, however, is that the birds may seek less flower nectar for food, so reduce the amount of pollination their feeding naturally provides.[113]
White granulated sugar is the best sweetener to use in hummingbird feeders. A ratio of 1 part sugar to 4 parts water, or 25% concentration, is a common recipe,[114] although hummingbirds will defend feeders more aggressively when sugar content is at 35%, indicating preference for nectar with higher sweetnessand sugar content. it to the nectar. Some people speculate red dye could be bad for the birds, although this claim has not received scientific attention. Commercial products sold as "instant nectar" or "hummingbird food" may also contain preservatives and/or artificial flavors as well as dyes, and are not necessary, although the long-term effects of these additives on hummingbirds have not been systematically studied. Although some commercial products contain small amounts of nutritional additives, hummingbirds obtain all necessary nutrients from the insects they eat, rendering added nutrients unnecessary.
Other animals also visit hummingbird feeders. Bees, wasps, and ants are attracted to the sugar-water and may crawl into the feeder, where they may become trapped and drown. Orioles, woodpeckers, bananaquits, raccoons and other larger animals are known to drink from hummingbird feeders, sometimes tipping them and draining the liquid. In the southwestern United States, two species of nectar-drinking bats (Leptonycteris yerbabuenae and Choeronycteris mexicana) visit hummingbird feeders to supplement their natural diet of nectar and pollen from saguaro cacti and agaves.
Visual cues of foraging
Hummingbirds have exceptional visual acuity providing them with discrimination of food sources while foraging. Although it is commonly believed that hummingbirds are attracted to color while seeking food, such as red flowers or artificial feeders, experiments indicate that location and flower nectar quality are the most important "beacons" for foraging. Hummingbirds depended little on visual cues of flower color to beacon to nectar-rich locations, but rather they used surrounding landmarks to find the nectar reward.
In at least one hummingbird species – the green-backed firecrown (Sephanoides sephaniodes) – flower colors preferred are in the red-green wavelength for the bird's visual system, providing a higher contrast than for other flower colors. Further, the crown plumage of firecrown males is highly iridescent in the red wavelength range (peak at 650 nanometers), possibly providing a competitive advantage of dominance when foraging among other hummingbird species with less-colorful plumage. The ability to discriminate colors of flowers and plumage is enabled by a visual system having four single cone cells and a double cone screened by photoreceptor oil dropletswhich enhance color discrimination.
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