Adaptations for High Altitude Birds

Adaptations for High Altitude Birds Birds have developed the ability to maintain flight at various altitudes. The focus of this essay was placed specifically on flight at high altitudes. The characteristics of birds which maintain flight at high altitudes were found to be enhanced gaseous exchange efficiency, higher O2 affinity haemoglobin, and increase O2 diffusion to muscle fibers as a result of an increase in capillary-fiber ratio in a high-altitude hypoxic environment. It has also been seen that birds found at high altitudes have larger wingspans thereby reducing the energetic costs of flight in low-density air. Key words: Altitude, hemoglobin, hypoxic, wingspan Introduction Though not all birds are capable of flight, most birds are commonly recognized by flight. Birds are found all over the surface of the Earth (Bicudo et al, 2010) in a variety of environments which they are adapted to. Here we will explore the physiology of high altitude bird flight. The main focus will be placed on migrating birds due to the l arge amount of research performed on the species and migrating birds are found at a huge range of altitudes. As stated by Bicudo et al (2010), â€Å"High altitude experienced by birds that reside or breed in high mountains or by migrating birds that must cross such ranges† are considered to be high elevation specialist’s. Factors associated with high altitude causes this environment to be especially challenging for avian flight, these factors includes â€Å"high ambient wind speeds, low air temperatures, low oxygen availability and low air density† (Altshuler and Dudley, 2006). These factors may be detrimental in a birds’ flight performance specifically on bird biomechanics (lift and drag) of avian flight (Altshuler and Dudley, 2006). A consequence of the factors may result in energetics cost being higher in the severely hypoxic and cold environment (Butler and Bishop, 2000). The objective of this essay is to discuss the many features of birds which appea r to be important for high altitude flight (Scott, 2011). Environmental factors at high altitude As stated by Altshuler and Dudley (2006), a gradient in altitude indicates a change in numerous environmental parameters. As altitudes increase, temperature and humidity decrease, however, day length or solar angle of incidence remains the same (Altshuler and Dudley, 2006). An altitude increase, there is a systematic decrease O2 partial pressure (Bicudo et al., 2010). This is one of the most importance changes taking place with regards to respiratory and metabolism due to the reduced availability of oxygen. As partial pressure reduces, there is an inversely increase in the gaseous diffusion coefficient. Furthermore, wind speed increases with altitude, studies propose that birds can minimize their energy costs of flights through the use of wind assistance (Bicudo et al., 2010). As altitude increases, there is also a noticeable decrease with in water content. This decrease in water content in cool air at high elevations may result in desiccation (Bicudo et al., 2010). Thus high oxygen demands for flight are at odds with a decreased O2 availability, air density and lift (Altshuler and Dudley, 2006). Physiology of flight at high altitude Muscles Flight requires a high endurance capacity, for this reason, it relies on oxidative metabolism for energy (Bicudo et al. 2010). The pectoralis muscles of a bird is considered the â€Å"flight motor† of a bird and constitute up to 35% of the total body mass (Bicudo et al. 2010). Long distance migrants â€Å"flight motor† muscles possess rapidly oxidative glycolytic muscle fibers and short distance migrants â€Å"flight motor† muscles possess muscle fibers with a much lower oxidative capacity as well as fast-acting glycolytic fibers (Bicudo et al. 2010). It should be noted that muscle capillary-per-fiber number is higher in highly aerobic pectoral muscles and less aerobic leg muscles for high altitude birds (B icudo et al. 2010).