Last month my first paper got published a year after the first submission. In this paper we assess how diet affects the macroevolutionary dynamics of all bird species, and found that omnivores - species that feed on multiple food items - have lower (even negative) net diversification. This pattern arises from either smaller speciation and/or greater extinction when compared to all other dietary guilds.
Associated with that, there is a prevalence of transitions from all guilds into omnivory. Based on these two patterns, we decided to call omnivores a “macroevolutionary sink”.
The link for the PDF is this.