Birds need to alter their metabolism in order to meet the demands of migration. The storage of energy through the accumulation of fat and the control of sleep in nocturnal migrants require special physiological adaptations. In addition, the feathers of a bird suffer from wear-and-tear and require to be molted. The timing of this molt - usually once a year but sometimes twice - varies with some species molting prior to moving to their winter grounds and others molting prior to returning to their breeding grounds. Apart from physiological adaptations, migration sometimes requires behavioural changes such as flying in flocks to reduce the energy used in migration or the risk of predation.
Why do birds need to molt?
feathers of a bird suffer from wear-and-tear

This technique was very expensive, though, and could not be used for applications such as telemedicine, distance education, and business meetings. Attempts at using normal telephony networks to transmit slow-scan video, such as the first systems developed by AT&T Corporation, first researched in the 1950s, failed mostly due to the poor picture quality and the lack of efficient video compression techniques. The greater 1 MHz bandwidth and 6 Mbit/s bit rate of the Picturephone in the 1970s also did not achieve commercial success, mostly due to its high cost, but also due to a lack of network effect with only a few hundred Picturephones in the world, users had extremely few contacts they could actually call to, and interoperability with other videophone systems would not exist for decades.
What was the bandwidth of AT&T's Picturephone?
1 MHz

Even as animal domestication became relatively widespread and after the development of agriculture, hunting was usually a significant contributor to the human food supply. The supplementary meat and materials from hunting included protein, bone for implements, sinew for cordage, fur, feathers, rawhide and leather used in clothing. Man's earliest hunting weapons would have included rocks, spears, the atlatl, and bows and arrows. Hunting is still vital in marginal climates, especially those unsuited for pastoral uses or agriculture.[citation needed] For example, Inuit people in the Arctic trap and hunt animals for clothing and use the skins of sea mammals to make kayaks, clothing, and footwear.
What was the leather from hunting used for?
clothing