The cuckoo comes to us in April, sings its song in May, lays its eggs in June and then it flies away. That may be a little bit of over simplification but it is not that far from reality. The cuckoo can be heard from late April and it was always considered to be confirmation that spring was truly here and letters were written to the Time newspaper to report the first cuckoo. Now the cuckoo's 'song' is less common than it was even ten years ago and research into why it is declining so rapidly is ongoing. It is only my perception but I think they may have fared better in 2018, there were certainly a lot more reports than in 2017. The cuckoo's main host species are reed warblers, dunnocks and meadow pipits so here in Dorset cuckoos are most common near our substantial reed beds but they can also be found in open heath and countryside.
Apart from a record in week 12 (late March) which must be considered abnormal the weekly reports show cuckoos arriving in week 15 toward the latter end of April. I always reckoned to hear the first cuckoo of spring on, or about, the 21st April each year which would tie in with this. Records are at their peak in weeks 16 to 22 in May through until mid June when they are most vocal and then they tail away through July with odd records coming right through until August and these will be young birds starting their journey south. Incredibly there have been records from as late as October!
Sixty sites have reported cuckoo in 2017 and 2018 combined but most of these have just one record. The distribution map shows they are widely distributed but with a substantial cluster around Poole Harbour where there are a lot of reed beds. The cuckoo does seem to like the Dorset heaths as well and they also frequent the Weymouth area and the Fleet.
Hearing a cuckoo calling in May is your best indicator for getting cuckoo on to your Dorset list. If you want to see one then you need to track down the calling bird at it song perch.