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Date: 27 Jun 2010 23:38:00
Title: Hummingbirds




We saw so many White-necked Jacobins at Cuffie it made us want to know more about these fascinating little birds. For some unknown reason this blogs layout has gone weird - tried seven times adjusting and trying to make it right, but given up to get on with my life. Word processor doing it's own thing, nothing to do with me, it looks perfect when it it sent ???

Hummingbirds are birds comprising the family Trochilidae. They are among the smallest birds and include the smallest extant bird species, the Bee Hummingbird. They can hover in mid-air by rapidly flapping their wings twelve to ninety times per second (depending on the species). They can fly backwards, the only group of birds able to do so. Their English name derives from the characteristic hum made by their rapid wing beats. They can fly at speeds exceeding thirty four miles per hour.




Hummingbirds drink nectar, the sweet liquid inside flowers. Like bees, they are able to assess the amount of sugar in the nectar they eat; they reject flower types that produce nectar that is less than 10% sugar and prefer those whose sugar content is stronger. Nectar is a poor source of nutrients, so hummingbirds meet their needs for protein, amino acids, vitamins, minerals, etc. by preying on insects and spiders, especially when feeding young. Most hummingbirds have bills that are long and straight or nearly so, but in some species the bill shape is adapted for specialized feeding. Thornbills have short, sharp bills adapted for feeding from flowers with short corollas and piercing the bases of longer ones. The Sicklebills' extremely decurved bills are adapted to extracting nectar from the curved corollas 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 hummingbirds feed on nectar, the bill is usually only opened slightly, allowing the tongue to dart out and into the interior of flowers. Like the similar nectar-feeding sunbirds and unlike other birds, hummingbirds drink by using protrusible grooved or trough-like tongues. 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 feed in many small meals, consuming many small invertebrates and up to five times their own body weight in nectar each day. They spend an average of 10–15% of their time feeding and 75–80% sitting and digesting.



A huge thrill to get a shot of this little chap 'licking his lips'


Co-evolution with ornithophilous flowers:

Hummingbirds are specialized nectarivores and are tied to the ornithophilous flowers they feed upon. Some species, especially those with unusual bill shapes such as the Sword-billed Hummingbird and the sicklebills, are co-evolved with a small number of flower species. Many plants pollinated by hummingbirds produce flowers in shades of red, orange and bright pink, though the birds will take nectar from flowers of many colours. Hummingbirds can see wavelengths into the near-ultraviolet, but their flowers do not reflect these wavelengths as many insect-pollinated flowers do. This narrow colour spectrum may render hummingbird-pollinated flowers relatively inconspicuous to most insects, thereby reducing nectar robbing. Hummingbird-pollinated flowers also produce relatively weak nectar (averaging 25% sugars w/w) containing high concentrations of sucrose, whereas insect-pollinated flowers typically produce more concentrated nectars dominated by fructose and glucose.




Awake and catchin' forty winks


Aerodynamics of flight:

Hummingbird flight has been studied intensively from an aerodynamic perspective using wind tunnels and high-speed video cameras. Writing in Nature, the biomechanist Douglas Warrick and coworkers studied the Rufous Hummingbird, Selasphorus rufus, in a wind tunnel using particle image velocimetry techniques and investigated the lift generated on the bird's upstroke and downstroke. They concluded that their subjects produced 75% of their weight support during the downstroke and 25% during the upstroke. Many earlier studies had assumed (implicitly or explicitly) that lift was generated equally during the two phases of the wingbeat cycle, as is the case of insects of a similar size. This finding shows that hummingbirds' hovering is similar to, but distinct from, that of hovering insects such as the hawk moths. The Giant Hummingbird's wings beat at eight to ten beats per second, the wings of medium-sized hummingbirds beat about twenty to twenty five beats per second and the smallest can reach one hundred beats per second during courtship displays.




With the exception of insects, hummingbirds while in flight have the highest metabolism of all animals, a necessity in order to support the rapid beating of their wings. Their heart rate can reach as high as 1,260 beats per minute, a rate once measured in a Blue-throated Hummingbird. They also consume more than their own weight in nectar each day, and to do so they must visit hundreds of flowers daily. Hummingbirds are continuously hours away from starving to death, and are able to store just enough energy to survive overnight. Hummingbirds are capable of slowing down their metabolism at night, or any other time food is not readily available. They enter a hibernation-like state known as torpor. Something Bear is getting more expert at by the day. During torpor, the heart rate and rate of breathing are both slowed dramatically (the heart rate to roughly fifty to one hundred and eighty beats per minute), reducing the need for food - oh, Bear hasn't got to that part of the manual yet then. The dynamic range of metabolic rates in hummingbirds requires a corresponding dynamic range in kidney function. The glomerulus is a cluster of capillaries in the nephrons of the kidney that removes certain substances from the blood, like a filtration mechanism. The rate at which blood is processed is called the glomerular filtration rate (GFR). Most often these fluids are reabsorbed by the kidneys. During torpor, to prevent dehydration, the GFR slows, preserving necessities for the body such as glucose, water and salts. GFR also slows when a bird is undergoing water deprivation. The interruption of GFR is a survival and physiological mechanism unique to hummingbirds. Studies of hummingbirds' metabolisms are highly relevant to the question of how a migrating Ruby-throated Hummingbird can cross five hundred miles of the Gulf of Mexico on a nonstop flight, as field observations suggest it does. This hummingbird, like other birds preparing to migrate, stores up fat to serve as fuel, thereby augmenting its weight by as much as 100% and hence increasing the bird's potential flying time.




Hummingbirds have long lifespans for organisms with such rapid metabolisms. Though many die during their first year of life, especially in the vulnerable period between hatching and leaving the nest, those that survive may live a decade or more. Among the better-known North American species, the average lifespan is three to five years. By comparison, the smaller shrews, among the smallest of all mammals, seldom live more than two years. The longest recorded lifespan in the wild is that of a female Broad-tailed Hummingbird that was ringed as an adult at least one year old then recaptured eleven years later.



A rare glimpse for us of the Rufous-tailed Hummingbird, the Jacobin waits patiently in line



Hummingbirds are restricted to the Americas, from southern Alaska to Tierra del Fuego, including the Caribbean. The majority of species occur in tropical and subtropical Central and South America, but several species also breed in temperate climates and some hillstars even occur in alpine Andean highlands at altitudes of up to seventeen thousand, one hundred feet. The greatest species richness is in humid tropical and subtropical forests of the northern Andes and adjacent foothills, but the number of species found in the Atlantic Forest, Central America or southern Mexico also far exceeds the number found in southern South America, the Caribbean islands, the US and Canada. About twenty five different species of hummingbirds have been recorded in the US, less than ten from Canada and the same number for Chile. Colombia alone has more than one hundred and sixty and the comparably tiny Ecuador has about one hundred and thirty species. The Rufous Hummingbird is one of several species that breed in western North America and are wintering in increasing numbers in the southeastern US, rather than in tropical Mexico. Thanks in part to artificial feeders and winter-blooming gardens, hummingbirds formerly considered doomed by faulty navigational instincts are surviving northern winters and even returning to the same gardens year after year. Individuals that survive winters in the north, however, may have altered internal navigation instincts that could be passed on to their offspring. The Rufous Hummingbird nests farther north than any other species and must tolerate temperatures below freezing on its breeding grounds. This cold hardiness enables it to survive temperatures well below freezing, provided that adequate shelter and feeders are available.



Hummingbird canvas. A colour plate illustration from Ernst Haeckel's Kunformen der Natur 1899



As far as is known, male hummingbirds do not take part in nesting. Most species build a cup-shaped nest on the branch of a tree or shrub, though a few tropical species normally attach their nests to leaves. The nest varies in size relative to species, from smaller than half of a walnut shell to several centimeters in diameter. In many hummingbird species, spider silk is used to bind the nest material together and secure the structure to its support. The unique properties of silk allow the nest to expand with the growing young. Two white eggs are laid, which, despite being the smallest of all bird eggs, are in fact large relative to the hummingbird's adult size. Incubation lasts fifteen to nineteen days, depending on species, ambient temperature, and female attentiveness to the nest. Their mother feeds the nestlings on small arthropods and nectar by inserting her bill into the open mouth of a nestling and regurgitating the food into its crop.


There are between three hundred and twenty five to three hundred and forty species of hummingbird, depending on taxonomic viewpoint, historically divided into two subfamilies, the hermits (subfamily Phaethornithinae, thirty four species in six genera), and the typical hummingbirds (subfamily Trochilinae, all the others).



                                                                                          One of the Nazca Lines in Peru, depicts a hummingbird. We hope to see this in September


Feeders and artificial nectar:

Hummingbirds will either hover or perch to feed; red feeders are preferred, but coloured liquid is not necessary and may be hazardous to their health. Hummingbirds will 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. Only white granulated sugar is proven safe to use in hummingbird feeders. A ratio of one cup sugar to four cups water is a common recipe. Boiling and then cooling this mixture before use has been recommended to help deter the growth of bacteria and yeasts. Powdered sugars contain corn starch as an anti-caking agent; this additive can contribute to premature fermentation of the solution. Brown, turbinado, and "raw" sugars contain iron, which can be deadly to hummingbirds if consumed over long periods. Honey is made by bees from the nectar of flowers, but it contains sugars that are less palatable to hummingbirds and promotes the growth of microorganisms that may be dangerous to their health. Red food dye is often added to homemade solutions. Commercial products sold as "instant nectar" or "hummingbird food" may also contain preservatives and/or artificial flavors as well as dyes. The long-term effects of these additives on hummingbirds have not been studied, but studies on laboratory animals indicate the potential to cause disease and premature mortality at high consumption rates. Although some commercial products contain small amounts of nutritional additives, hummingbirds obtain all necessary nutrients from the insects they eat. This renders the 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, 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. 



In myth and culture:

Aztecs wore hummingbird talismans, the talismans being representations as well as actual hummingbird fetishes formed from parts of real hummingbirds: emblematic for their vigor, energy, and propensity to do work along with their sharp beaks that mimic instruments of weaponry, bloodletting, penetration and intimacy. Hummingbird talismans were prized as drawing sexual potency, energy, vigor and skill at arms and warfare to the wearer. The Aztec god Huitzilopochtli is often depicted as a hummingbird. The Nahuatl word huitzil (hummingbird) is an onomatopoeic word derived from the sounds of the hummingbird's wing-beats and zooming flight. The Ohlone tells the story of how Hummingbird brought fire to the world. Trinidad and Tobago is known as "The land of the hummingbird," and a hummingbird can be seen on that nation's coat of arms and 1-cent coin as well as its national airline, Caribbean Airlines.








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