Brownsea is owned by the National Trust and offers a very diverse and interesting range of habitats for flora and fauna, all within easy walking distance of each other. Seeing native wildlife in its natural state is not always easy, but with patience and careful observation, you should always be able to see a variety of wildlife during a visit to Brownsea. The island is famous for being the venue for Baden-Powell's first scout camp.

In the 19th century, a sea wall was built around the part of Poole Harbour known as St Andrew's Bay to create suitable grazing land for livestock on Brownsea. Neglect of the sea wall and the wind pumps that were used to control the water levels led to the creation of the present day non-tidal saline lagoon.

It is a habitat of national and international importance for a variety of birds which use the site for nesting, feeding and roosting throughout the year. The number and types of birds using the lagoon depend on the time of year and the state of the tide in Poole Harbour

In the winter it attracts large numbers of waders including: Avocet, Black- and Bar-tailed Godwit, Grey Plover, Dunlin, Redshank and Greenshank. Sparrowhawk and Peregrine hunt across the lagoon, and Pied Wagtails, Meadow and Rock Pipits, and Kingfishers are seen regularly.

In April the over-wintering birds depart and the summer visitors begin to arrive. Common and Sandwich Terns, migrants from Africa, breed on artificial islands specially built for them by The Dorset Wildlife Trust. From May to July, close views of the parents feeding their young on small fish can be seen from the nature reserve hides. Black-headed Gulls and oystercatchers also nest on the islands and around the edge of the lagoon.

Resident birds include Cormorants, oystercatchers, black backed and black headed gulls, shelducks, mallard and Canada geese can be seen on the lagoon all year round. Grey herons and Little Egrets from the Brownsea heronry regularly roost and feed on the lagoon.