Experimental broods were treated as follows: each nest was assigned a number. Each numbered nest was randomly assigned to one of two groups: "odd clipped" or "even clipped." In nests assigned to "odd clipped" the first chick hatched was clipped, the second was just handled, all other odd-numbered hatchlings were clipped and even-numbered ones not. The reverse was true for the "even clipped" broods.
Here it can be seen that there is an advantage to being orange in a nest of both orange and black chicks. Statistical analysis reveals that the differences seen in the experimental broods are significant. In mixed broods of both black and orange chicks, the orange chicks are fed more often, grow faster and survive in greater numbers. The evidence supports the hypothesis that there is a selective advantage to being orange.