For the birder set, late summer on the Cape and Islands is synonymous with an assortment of sought-after shorebirds and seabirds. This week was case-in-point, with the rarity parade including a continuing American Avocet at Seagull Beach in Yarmouth, a hyper-rare Common Ringed Plover in Truro, a Franklin’s Gull in Sandwich, and snazziest of all, a Pacific Golden-Plover picked out by unheralded good-birder Lee Dunn over on Nantucket, and representing just the 4 th state record.