On cool nights, the body temperature of hummingbirds can drop from a daytime norm of about 40.5 degrees C (105 F) to an overnight low of about 21 degrees C (70 F). The RTHU heart, on average, beats about 250 times per minute while at rest, and about 1,220 per minute while flying. Hummingbirds are unusual in that they all appear to lack the fourth aortic arch, requiring that the right ductus caroticus transport blood to the abdominal aorta. As in mammals, the heart of the RTHU, is four-chambered, with the right side receiving deoxygenated blood and pumping it to the lungs, and the left side receiving oxygenated blood from the lungs and pumping it to the body. Hummingbirds also have the greatest concentration of oxygen-carrying red blood cells ( erythrocytes). The heart if the Ruby-throated Hummingbird (RTHU) and its relatives makes up about 2.5% of the bird's body weight, making relatively the largest heart in the animal kingdom. The liver also stores lipids (fats) that can be released and metabolized quickly lipids can make up 15% of the liver's weight in a Ruby-throated Hummingbird in mid-summer, and the level can rise to 45% just prior to migration. The digestive tract consists of a short esophagus a thin-walled and distensible crop (holding sac) soft proventriculus (where chemical digestion begins) a gizzard, or muscular stomach (mucous-secreting location for mechanical grinding of the hard parts of insects) a duodenum (where liver bile and pancreatic enzymes continue chemical digestion) a 5cm (2") small intestine (where digested nutrients are absorbed into the circulatory system) a large intestine (water re-absorption and temporary storage of wastes) and cloaca (a common area from which solid and liquid wastes and reproductive cells-egg and sperm-are released). The hummingbird digestive tract is a long tube through which food, then waste, passes quickly. The Ruby-throated Hummingbird and its relatives have the most rapid metabolisms found in birds. Hummingbirds do NOT use the tongue and bill as a straw. A hummingbird laps up nectar with its tongue by extending and contracting it up to 13 times per second. The tongue (right) of the Ruby-throated Hummingbird is split (below right) and somewhat broadened and brushy at the tip, allowing capillary action to draw in more fluid. The mouth contains only a few taste buds and salivary glands. The tongue itself splits in the floor of the mouth and the two rear forks wrap under the jaw, behind and over the head, and insert in the front of the bird's skull (see skull photo above and skeleton photo below). The bill protects a long tongue (below) with a brushy tip that is used by the hummingbird to lap up nectar the hummingbird does NOT suck up liquid using its beak as a straw. The hummingbird has considerable control of its bill and can open just the tip. It measures about 15-20mm in length and can open no more than about 1cm wide at the tip. The bill of the Ruby-throated Hummingbird is one of its most distinctive features. The Senses: Sight, Hearing, Taste, Smell & TouchĪll photos & text © Bill Hilton Jr. Likewise, some aspects of hummingbird physiology accommodate its high metabolic needs.Ĭlick on the terms below for descriptions of unusual RTHU anatomy and physiology for broader information about typical avian or vertebrate internal anatomy and processes, please consult a general reference work or an ornithology or zoology text. Some structures are absent or are relatively larger or smaller than in other birds-apparent adaptations for the unusual hummingbird lifestyle that includes hovering flight, feeding on flowers, etc. The Ruby-throated Hummingbird, Archilochus colubris, for the most part, exhibits typical avian internal anatomy. HUMMINGBIRD INTERNAL ANATOMY & PHYSIOLOGY
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