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Hummingbirds are native American birds that make up the TRO family. They are the smallest of the birds, most of which are 7.5 – 13 cm (3 – 5 in) long. In fact, the smallest living bird is the hummingbird, which weighs less than 2.0 grams (0.07 ounces) at 5 centimeters (2.0 inches).
They are called hummingbirds because of the hum of their flapping wings. They can be heard by humans because of their high frequency of flapping. They hover in the air at fast wing beat speeds, with the largest species taking about 12 beats per second, while some of the smallest species taking more than 80 beats. Among the species measured in the wind tunnel, the highest speed is more than 15 m / S (54 km / h; 34 mph), and some species can dive at more than 22 m / S (79 km / h; 49 mph).
Hummingbird has the largest specific mass metabolic rate in any homotherm. In order to save energy in the absence of food and in the absence of food at night, they can enter hibernation, similar to hibernation, reducing the metabolic rate to 1 / 15 of the normal speed.
According to lensch's law, hummingbirds exhibit gender size dimorphism. In small species, males are smaller than females, while in strong species, males are larger than females. The degree of this gender difference is different between the evolutionary branches of hummingbirds. For example, the evolutionary branch of mellisugini shows a large biphasic nature, with females larger than males. On the contrary, lophomithini branch shows very small size dimorphism. Males and females are similar in size. There is also sexual dimorphism in the size and shape of bills between male and female hummingbirds. In many evolutionary branches, females have longer and more curved bills, which is conducive to obtaining nectar from tall flowers. For males and females of the same size, females tend to have larger bills.
Due to courtship constraints, gender size and billing differences may evolve as the mating display of male hummingbirds requires complex aerial operations. Males tend to be smaller than females, saving energy for competitive foraging and participating in courtship more frequently. Therefore, sexual selection will benefit the smaller male hummingbirds.
Female hummingbirds tend to be larger, need more energy, have longer beaks, and can more effectively enter the gaps of the nectar's tall flowers. As a result, females are better at foraging, getting nectar and supporting the energy needs of larger bodies. Therefore, directed selection will be beneficial to the larger hummingbirds in obtaining food.
Another evolutionary reason for this sexual act dimorphism is that the competition for nectar between the sexes of each species is the driving factor. Depending on which gender occupies the territory of the species, it is advantageous for the other gender to have a longer bill and be able to eat multiple flowers, thus reducing intraspecific competition. For example, in the longer male hummingbird species of hummingbirds, males have no specific territory and have a leek mating system. In species where males are shorter than females, males defend their resources, so females must have longer females to feed on a larger range of flowers.
In order to meet the needs of courtship and territorial competition, many male hummingbirds' feathers have bright colors, which is caused by pigmentation in feathers and prismatic cells in the top layer of feathers of head, nostril, chest, back and wings. When sunlight hits these cells, it is broken down into different wavelengths of light, which are reflected to the observer with different degrees of intensity, while the feather structure acts as a diffraction grating. The color of the rainbow hummingbird is a combination of refraction and pigmentation, because the diffraction structure itself is made of melanin (a pigment), and may also change color due to carotenoid pigmentation, and depends on the soft black, brown or gray of melanin.
Just by moving the position, the feathered area of the soft bird can immediately turn red or bright green. For example, in a courtship exhibition, the male of Anna's hummingbird, with its colorful body and feathers facing the sun, improves the display value of the iridescent feathers for females interested.
A study of Anna's hummingbirds found that dietary protein was a factor in the color of feathers, because birds that received more protein had much longer colored crown feathers than those that ate a low protein diet. In addition, birds on a high protein diet have a yellower (higher chroma) green tail feather than those on a low protein diet.
