Living in a complex social world—one with shifting alliances and competitors—is often cited as the key reason humans, dolphins, and spotted hyenas evolved large brains. Now, researchers say that social complexity also underlies the braininess of parrots, which have big brains relative to their body size. To understand the social lives of these birds, the scientists observed wild populations of monk parakeets (Myiopsitta monachus), a small parrot, in Argentina and captive ones in Florida. They recorded how often the birds (pictured) were seen with other individuals and how they interacted—and then analyzed the parakeets’ social networks. The birds, the researchers report online today in The Auk: Ornithological Advances, prefer to spend time with one specific individual, usually their mate. In the captive populations, the birds also had strong associations with one or two other individuals, numerous more moderate relationships, and only a few that were weak. The scientists also recorded aggressive interactions among the captive birds, revealing that monk parakeets have a dominance hierarchy based on which birds won or lost confrontations. Thus, the parakeets’ society has layers of relationships, similar to those documented in other big-brained animals. Living in such a society requires that the birds recognize and remember others, and whether they are friend or foe—mental tasks that are thought to be linked to the evolution of significant cognitive skills.