In determining a potential site for a wind farm requires many considerations. Besides the required wind density (average wind speed of an area), the possible siting of a wind farm requires many considerations. There are physical restrictions such as buildings, trees, and other obstructions to the winds flow (Gipe 270). These obstructions create turbulent wind flow which is not as effective for turbines. Next we have restrictions from different levels of government, such as building permits, zoning laws, and town approval (273). This has been the most difficult of restrictions as it has caused controversy in recent years. Furthermore, avian migration routes and the wellbeing of other wildlife must be respected. There has been significant issue with sites like the Altamont pass in California where a large number of old turbines were erected in an area used by various raptor for hunting and nesting grounds (Gipe 462). There were many birds deaths, and since many turbines have been replaced with larger, slower, and thus less hazardous upgrades. These steps are meant to reduce the impact of a wind farm as well as create a sustainable power source.