all_birds is the maximum clade credibility tree of 9982 avian species (and 3301 sister pairs) from Pulido-Santacruz and Weir (2016). Branch lengths are time-calibrated in millions of years.
References
Pulido-Santacruz, P. and J. T. Weir. 2016. Extinctioin as a driver of avian latitudinal diversity gradients. Evolution 70: 860-872.