I found 3 Purple Sandpipers amidst a flock of 500+ Dunlin and 100 Sanderlings actively feeding at the waters edge between the Boathole and Crescent Beach about 2 hours after high tide. Also in the flock were 3 Black-bellied Plovers and a late Ruddy Turnstone though the Purples were not with them. The flock often broke into sub-flocks of 100-200 birds; two purples stuck toggether with one group and the third was always in a different sub-group.
I seldom see Purples on Duxbury Beach though they are regular at Manomet - probably because there isn't as much rocky territory for them - almost none for an hour on either side of high tide. Thus I've not had a good opportunity to photograph them before today. These 4 photos are of 2 of the 3 individuals that were intermingled in one of the sub-flocks.