More than most researchers, Bernd Heinrich’s research is rooted in his background as a naturalist, and his powers of observation. He knew his study species very well, so he was quick to identify anomalous or surprising phenomena. He was particularly attracted to evolutionary puzzles – traits that on the surface appear to be maladaptive. One example of an evolutionary puzzle discussed in this chapter was an observation of caterpillars tossing parts of leaves down from trees (when they could be eating them). A second example was ravens making a ruckus when they find a large carcass, thereby being forced to share the food bonanza with many other birds they attract to the scene. Both studies show how science is an iterative process, which involves testing and rejecting multiple alternative hypotheses. Heinrich brought his research into the laboratory as well, designing ingenious experiments to explore the mechanisms underlying insect thermoregulation. One theme shaping Heinrich’s research is the connection between the natural environment and how natural selection influences behavioral and physiological patterns.

The social intelligence hypothesis states that a complex social life is cognitively challenging and thus a driving force for mental evolution. Support for the hypothesis comes mainly from studies on primates, and more recently also from birds, specifically corvids. In this paper, I review what is known about the socio-cognitive skills of common ravens, a corvid species that has been intensively studied over the past twenty-five years. The findings show that temporary foraging groups are composed of individuals with different degrees of familiarity and structured by different types of social relationships. Familiar ravens show profound knowledge about their own and others’ relationships, and they appear to use this knowledge selectively and strategically in cooperative and competitive settings. The studies on ravens may thus inform our understanding of what constitutes social complexity and which cognitive skills are selected for.