The new pairs came from outside the population shown, and the discrepancy in territory size might have to do with either the already-present birds having experience/learned about the habitat, allowing them to take more space. Alternatively, the new birds may come from a population less well adapted to the particular habitat shown in Fig. 54.25.
Work Step by Step
They key here is to imagine what differences, learned or innate, might exist between the removed pairs and those from outside.