Carrier pigeons fly an average of 76.5 kilometers per hour, which is 55% slower than Swift, the fastest bird flying long distances.

You can get from this sentence:

The average flying speed of homing pigeons per hour is 76.5km = Swift speed ×( 1-55%).

Therefore, the average flying speed of swift per hour is 76.5 \ ~155% ~ = 76.5 ÷ 45% = 170 km.