In 2005, Rasmussen was part of a large multi-institutional collaboration investigating biodiversity hotspots, which have a prominent role in conservation. The study assessed locations quantitatively for three criteria of bird diversity – species richness, the level of threat, and the number of endemic species. The results demonstrated that hotspots did not show the same geographical distribution for each factor. Only 2.5% of hotspot areas are common to all three aspects of diversity, with over 80% of hotspots registering on only one criterion. Each criterion explained less than 24% of the variation in the other factors, suggesting that even within a single taxonomic class, different mechanisms are responsible for the origin and maintenance of various aspects of diversity. Consequently, the different types of hotspots also vary greatly in their utility as conservation tools.