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BIRDS Birds are animals that maintain a constant internal body temperature. They have an outer covering of FEATHERS; TWO legs that are covered with SCALES & are used for walking or perching; and front limbs that are modified into WINGS; *NOT ALL Ostrich, Emu, Penguin! BIRDS FLY!! FEATHER Structure made mostly of protein that develops from a pit in the bird’s skin. There are two types of feathers: CONTOUR Feathers (providing lifting force & balance for flight) & DOWN feathers (trap air close to the birds body to keep it warm). Adaptations HIGHLY efficient digestive, respiratory, & circulatory systems; aerodynamic feathers & wings; strong light-weight bones; & strong chest muscles. that allow birds to fly FEEDING Small birds lose heat faster than a larger bird, so small birds must eat more relative to their body size. Birds eat a variety of foods. Bird beaks/bills are adapted to the foods they eat. CROP Birds lack teeth & therefore cannot break food down by chewing. Some birds have a CROP. A crop is a specialized structure that MOISTENS & STORES food before it moves into the GIZZARD or into the stomach. In some birds the crop may (during nesting season) break down cells that produce a protein /fat substance that is regurgitated & fed to young. GIZZARD Birds that eat insects or seeds have a gizzard, which is a muscular organ that helps to mechanically break down food before it reaches the stomach. The gizzard forms part of the stomach. RESPIRATION Birds have a unique & highly efficient respiratory system that allows a ONE WAY flow of air which constantly exposes the lungs to oxygen. This allows birds to maintain a very high metabolic rate. CIRCULATION Birds have a 4-chambered heart & two separate circulatory loops. RESPONSE REPRODUCTION Birds have well-developed sense organs. Their brain can quickly interpret & respond to a lot of incoming signals. They have excellent eyesight. Most species can hear very well. The sense of smell & taste are not well developed in most birds (olfactory bulbs in birds are very small). Both the male and female reproductive tracts open into the cloaca. Bird eggs are amniotic eggs with a hard shell. Most birds incubate their eggs until they hatch. GROUPS OF BIRDS There are 30 different ORDERS of birds. The larges order is the PASERINES (perching birds). Other groups of birds include: Pelicans & their relatives, Parrots; Birds of Prey; Cavity Nesting Birds; Herons & their relatives; Ostriches & their relatives