In common with several of the wader species we get on the shores of Dorset the grey plover is an Arctic breeder coming south to spend the winter here. That said grey plover can be seen all year round with a small number of non-breeding birds choosing to stay here throughout the summer. Less like other waders they tend to be more solitary, even a little territorial, and are rarely seen in any numbers together although they are not uncommon in favoured sandy or muddy sites along the Dorset coast.
The presence all year round is reflected in the weekly reports chart with records for virtually every week of the year but bizarrely, at the time of writing in February 2019, there have been no records for weeks 7 and 8 during the time the Nature of Dorset database has been operating. This may just be coincidental or it may show that wintering birds here decide to move further south in the depth of winter to warmer climes. There is a peak of reports in the spring from week 17 to 19 in May which would indicate passage of migrant birds from Europe and Africa heading back north and stopping off here for rest and food.
The distribution map shows that many of the Poole Harbour sites have grey plover as, too, does Christchurch Harbour and various points along the Fleet. This reflects their habitat preference feeding on mudflats at low tide and moving to nearby higher but wet ground when forced off during high tides.
To make grey plover a Dorset tick I would suggest an autumn visit to Brownsea where they can be seen close up from the hides overlooking the lagoon.