Claudia Mettke-Hofmann and Eberhard Gwinner of the Max Planck Research Center for Ornithology in Germany studied 131 birds from two similar species that had been raised by hand. The garden warbler (top image) is a migratory bird, whereas the Sardinian warbler (bottom image) remains close to home. The researchers left the animals in a pair of attached rooms in which only one room had food for a period of eight and a half hours. After delays ranging from four days to a year, the birds were reintroduced to the two rooms, although this time neither chamber contained food. The scientists observed that up to a year later, garden warblers spent significantly more time investigating the room that had previously supplied a food source than Sardinian warblers did. In fact, the nonmigratory birds only preferred the room that had once provided food for about two weeks.
Previous studies of migration patterns had revealed that many migratory birds return to the same breeding and stopover sites year after year. The new findings suggest that these long trips have influenced the learning and memory capabilities of migratory birds. The authors note that "the long-lasting memory of garden warblers is exceptional and, to our knowledge, provides the first evidence that memory duration may be related to migration."