Whilst the black-necked grebe is primarily a northern European breeding species from Denmark eastwards it does breed in Britain, mainly in Scotland and in northern areas of England. Being from the northern regions it is another bird species forced south by the severe winter weather and the southern coast of England suits some of them and they can be seen in suitably sheltered locations around Dorset.
The first arrivals seem to come in around week 40 in late September and reports then increase over time with peak numbers being reported in December and January. Numbers seem to start to decline during February and by week 15 in mid-April they are all gone for another winter. It could be that numbers vary from year to year depending on weather conditions and bad weather in February might also drive some of our winter population further south in to France and Spain.
They like open but sheltered sea water locations and so the records mainly come from Poole Harbour, Studland Bay and Portland Harbour with occasional reports from Weymouth Bay and from along the Fleet. Some off shore movement is sometimes seen from Portland Bill, along Chesil Beach and also from Mudeford.
The black-necked grebe is, to my mind, a species that is likely to be overlooked unless you are specifically seeking it out. Any of the sites mentioned above will be good places to look for them in mid-winter but you need to brush up the differences between this species and great-crested grebe and also between this and the very similar but less frequent Slavonian grebe.