Hummingbirds’ 22-million-year-old history of remarkable change is far from complete

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The first comprehensive map of hummingbirds' 22-million-year-old family tree — reconstructed based on careful analysis of 284 of the world's 338 known species — tells a story of rapid and ongoing diversification. The decade-long study also helps to explain how today's hummingbirds came to live where they do.

The first comprehensive map of hummingbirds' 22-million-year-old family tree — reconstructed based on careful analysis of 284 of the world's 338 known species — tells a story of rapid and ongoing diversification. The decade-long study reported in the Cell Press journalCurrent Biology on April 3 also helps to explain how today's hummingbirds came to live where they do.

Part of the secret to the birds' remarkable success lies in the formation of nine principal groups or clades, hummingbirds' unique relationship to flowering plants, and the birds' continued spread into new geographic areas, the researchers say.

"Hummingbirds have essentially been reinventing themselves throughout their 22-million-year history," says Jim McGuire of the University of California, Berkeley.

While all hummingbirds depend on flower nectar to fuel their high metabolisms and hovering flight, coordinated changes in flower and bill shape have helped to drive the formation of new species of both hummingbirds and plants. Remarkably, as many as 25 hummingbird species are able to coexist in some places.

"One of the really cool features of hummingbird evolution is that they all eat the same thing yet have diversified dramatically," McGuire says. "It really is a big surprise that hummingbirds have divided the nectarivore niche so extensively."

Written By: Science Daily
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2 COMMENTS

  1. BREAKING NEWS….

    EVOLUTION STILL HAPPENING

    …end of breaking news. I know that there is more than that in there but when will people get their heads around evolution and it’s continuing effects on living things that reproduce.

  2. As well as the diversification of beak shapes to co-evolve with specific flowers, there have been other challenging adaptations to the climates in diverse habitats resulting from their high-energy metabolism.

    http://scienceblogs.com/grrlscientist/2006/04/09/hummingbirds-and-torpor/

    There are more than 330 described species of hummingbirds, and occasionally a new species is discovered by ornithologists and added to the list. Even though most people think of them exclusively as tropical birds, hummingbirds are found in diverse habitats, ranging from the wettest to the driest, from sea level to over 14,000 feet (4400 meters).

    The greatest diversity of hummingbird species is the neotropics (New World tropics) but many species live in or migrate to temperate zones in the United States and Canada to breed. Sometimes, for reasons that are not entirely clear, individual birds remain behind for the winter, and sometimes, they survive. Thus, as average seasonal temperatures increase, hummingbirds are increasingly becoming established as year-round residents outside of their traditional ranges. Anna’s Hummingbird is one species whose range has expanded steadily northward as seasonal temperatures have become milder. Thus, this bird is now a common year-round resident along the northwestern coast of the United States and even into some parts of Canada.

    As most people know, hummingbirds feed on flower nectar, which is a tempting “gift” of high-energy sugars provided by flowers in exchange for pollination. In addition to nectar, hummingbirds also consume large quantities of small insects, which are full of higher-energy fats as well as essential proteins. Because of their tremendous metabolic requirements, hummingbirds have voracious appetites. Equivalent to the average human consuming an entire refrigerator full of food, hummingbirds eat roughly twice to thrice their own body weight in flower nectar and tiny insects each day.

    Besides being among the smallest of all warm-blooded animals, hummingbirds also lack the insulating downy feathers that are typical for many other bird species. Due to their combined characteristics of small body size and lack of insulation, hummingbirds rapidly lose body heat to their surroundings. Even sleeping hummingbirds have huge metabolic demands that must be met simply to survive the night when they cannot forage. To meet this energetic challenge, hummingbirds save enough energy to survive cold nights by lowering their internal thermostat at night, becoming hypothermic. This reduced physiological state is an evolutionary adaptation that is referred to as torpor.

    Torpor is a type of deep sleep where an animal lowers its metabolic rate by as much as 95%. By doing so, a torpid hummingbird consumes up to 50 times less energy when torpid than when awake. This lowered metabolic rate also causes a cooled body temperature. A hummingbird’s night time body temperature is maintained at a hypothermic threshold that is barely sufficient to maintain life. This threshold is known as their set point and it is far below the normal daytime body temperature of 104°F or 40°C recorded for other similarly-sized birds.

    Research shows that this set point is actively maintained by the bird’s internal thermostat. “If you try to cool an animal down below this new set point, it will generate enough body heat to maintain that set point,” says Sara Hiebert, hummingbird expert and associate professor of biology at Swarthmore College in Swarthmore, Pennsylvania.

    There are several types of torpor, classified mostly by duration and season. For example, when torpor takes place for long periods of time during the winter, it is known as hibernation. However, unlike hibernation, hummingbird torpor can occur on any night of the year so it is referred to as daily torpor or noctivation. Because tropical hummingbird species also have rigid metabolic budgets, even they rely on daily torpor to conserve energy.

    Torpid hummingbirds exhibit a slumber that is as deep as death. In 1832, Alexander Wilson first described hummingbird torpor in his book, American Ornithology; “No motion of the lungs could be perceived … the eyes were shut, and, when touched by the finger, [the bird] gave no signs of life or motion.”

    Awakening from torpor takes a hummingbird approximately 20 minutes. During arousal, heart and breathing rates increase and hummingbirds vibrate their wing muscles. Heat generated by vibrating muscles, or shivering, warms the blood supply. Shivering is sufficient to warm the hummingbird’s body by several degrees each minute and the bird awakens with enough energy reserves to see him through to his first feeding bouts of the morning. Interestingly, hummingbirds reliably awaken from torpor one or two hours before dawn without any discernible cues from the environment. Thus, it appears that the bird’s internal circadian clock triggers arousal.

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