This is not normal behavior as the male will stay with the pen and the nest to protect them. However, should something have occurred to the male, this would be the reason for his not returning. You might check with the RSPCA or Swan Support in Datchet (since we do not know where you are located) and see if there was an injured swan picked up from the area. If so, once it is rehabilitated, it will be returned to its habitat and mate. By asking, you will also alert the officials to check the area to see if the swan is in distress and will also provide them with information so that if the swan is being cared for, it will be returned to the habitat quickly since it has a nesting mate. The Regal Swan