A common spring migrant and perhaps the most common diving duck that is a passage migrant. This species can be found regularly during May and June while birds likely begin appearing during April in most years and birds linger into the summer season regularly as well. Overall numbers typically peak in mid-late May, though substantial numbers can be found throughout the spring season. There have been a few nesting records on St. Paul Island in recent years (2014, 2017, and 2018). This species can often be found in late June and early July with occasional summer wanderers also arriving from the end of June into early August. Since 1995, there have been summer season sightings on a nearly annual basis but nesting evidence has only been recorded in those three years. Fall migrants usually do not arrive until September, though arrivals could occur any time after August 25th, with numbers peaking in late September and substantial numbers of birds still present through mid-October most years and likely remaining in the islands until there is no more open water in late fall or early winter. This species has been recorded once in winter though it likely does occur more regularly during that season as an early migrant in the spring and a late fall lingerer.
Greater Scaup is circumpolar with different subspecies breeding in Eurasia and North America. The Eurasian subspecies, marila, has been documented once in the Pribilofs, 29 June 1966. These subspecies cannot be identified from each other in the field and both likely occur with some regularity.
