Due to the island's diverse plant life, a relatively large number of nesting bird species have been documented. As of March 2006, 92 species were breeding, and of these, approximately 40-50 every year. The barred warbler is one of the regular species with Jomfruland perhaps being the only location in Norway where this bird breeds. Also thrush nightingale, common rosefinch and red-backed shrike are regular breeding species, whereas more irregular finds are of greenish warbler (1992 – only breeding observation in Norway), stock pigeon, northern shoveler and barnacle goose (the latter two on nearby islands). A vast number of birds breed on islets and skerries around Jomfruland, one of these being the black guillemot. Geologically, Jomfruland is part of a large residual moraine from the Ice Age called the Ra step. Jomfruland is the product of the back parts of the moraine (Ra) sticking out of the water. Eastward, the moraine remains underwater from Jomfruland to Mølen in Brunlanes, before it reappears after crossing Tromøy. Where the Ra is connected to the mainland it forms pebble beaches. Between Jomfruland and Tromøy there are shallow waters in places where the moraine almost reaches the water surface.