Can't see the “hood” for the trees: Can avian cooperative breeding currently be understood using the phylogenetic comparative method?

Cooperative breeding in birds has traditionally been studied via long-term investigations of single populations. In the last two decades the phylogenetic comparative method has been applied to draw generalizations and make predictions about the global distribution of cooperative breeding. These studies generally test single causative factors and have attributed importance to slow life histories, the role of enemies, the way that lifetime fidelity facilitates kin selection, the benefits of help and helping when the climate fluctuates, and the advantages of continuing to live as families after young become nutritionally independent. Surprisingly, no analysis has focused explicitly on the role of the prohibition of dispersal by habitat saturation, the most frequently hypothesized explanation for cooperative breeding when these studies began. In this contribution I critically review this literature, and argue that it has failed to explain obvious phylogenetic and biogeographic patterns in the distribution of cooperation breeding. I identify several common flaws in the way that these studies have been conducted, and suggest that progress may depend on restructuring the question into several components. However, application of appropriate models is likely to fall foul of biases and deficiencies in the data available to populate the analyses, and I argue that a more collaborative, targeted and systematic approach to data collection may be necessary.