Meaning in context

Please look at the underlined in the following context "As the trawler swung in a wide arc toward land, the other congregants crowded Tommy at the railing. The boat nosed up the Waini River, its wake lifting the skirts of the mangroves as parrots flashed in the high canopy. The travelers slipped back in time, passing thatched huts stilted on the riverbanks and Amerindian families, who eyed them warily from dugout canoes". To my understanding the inderlined means- the boat was sailing along the river and in its wake it left torn mangroves, but it is not immediatelty clear what are the skirts of mangroves? And concurrently parrots flashed in the trees above? Thanks a lot.