A siege of egrets?

I admit I had to go online to find a collective term for egrets. I found that a group of herons are referred to as a scattering, a sedge or a siege- so I assume these apply to egrets too? My ship has been working mid way between Dakar, Senegal and the Cape Verde archipelago- for the past 10 days or so we have been circa 150+ nm from the nearest land and remarkably I have seen over a 100 egrets flying over the ocean. The birds have usually been in small flocks of 2 to 4 birds with a single flock of 8 being the largest group. All the birds have come up from the south and south west and been observed battling their way into the NE F5/6 winds that have been prevalent during my time here. Many of the birds have landed on the ship and taken advantage of the many wind-blown insects that have accumulated on the decks. I can't work out where these birds have come from or where they are trying to get to- I assume they have rounded the 'bulge' of west Africa to the SE having been displaced over the ocean and are desperately trying to get back to the coast of Mauritania or thereabouts. I have identified cattle egrets, a couple of great white egrets and what I think are probably intermediate egrets on account of their greenish lores and dark-tipped bills. All other species observed on migration here from blackcaps, redstarts, kestrels and swifts have all been heading south- as expected at this time of year- so a bit of a migration/displacement mystery to add to the many that I have encountered over the years, but a spectacle to be enjoyed anyhow. 

a chart showing my recent position

probable intermediate egret

probable GWE (left) and intermediate (right)