 In 2006, under aegis of "National Geographic", Buettner collaborated with Poulain and Costa Rican demographer Dr. Luis Rosero-Bixby to identify a fourth longevity hotspot in the Nicoya Peninsula.In 2008, again working with Poulain, he found a fifth longevity hotspot on the Greek Island of Ikaria.In April 2008, Buettner released a book on his findings, "The Blue Zones