For anyone whose watched the series Planet Earth and sat in awe as the great migrations of Earth traverse environmental extremes, this book gives the story behind the image. Mammals, birds, fish and even insects take on vast journies and have developed complex rituals in doing so. The author brings to life his own experiences with a few of the grandest migrations and also explains why these migrations are declining rapidly. This book is an intellectual look at the complexity and fragility that is the great migrations. This is a must read for those interested in biology, conservation, animal behavior and perhaps, sheds a bit more light at how even the smallest fence designed by man can be devistating to systems that have adapted and depend on perfect numbers to exist.