Most birds are thought to have severely reduced sense of smell comparated to other vertebrates.  Recent experiments, however, suggest that both Humboldt Penguins and Zebra Finches can distinguish the odors of their relatives from those of non-relatives. In the penguin experiment (Coffin et al. 2011), birds preferred the scent of familiar non-relatives such as nest mates.  Young finches, on the other hand, prefer the scent of their genetic parents even when raised in foster nests (Krause et al. 2012).