Research led by the University of East Anglia (UEA) sheds new light on how mountain birds adapt to changes in climate. Scientists know that species diversity changes as you go up a mountain, but it is not clearly understood why this is the case. One theory is that it is mostly because of long-term evolution, and the climate niches species have adapted to over millions of years. Another—the "energy efficiency" hypothesis—suggests it is about how species today manage their energy budgets and compete for available resources that vary in space and time.