Deposited on top of the bedrock are a series of drumlins - rounded, elongated hills formed by glacial activity. The drumlins support a mixed forest of spruce, fir, red maple, yellow birch and beech. The low areas between the drumlins tend to be imperfectly drained and support a forest of balsam fir, black spruce, alders and red maple. The islands possess numerous distinct coastal, unforested and forested habitats, each supporting a particular flora and fauna of interest. These habitats include salt marsh, eroding coastal headlands, regenerating open fields and climax hardwood stands.
Birds are excellent indicators of the variety and conditions of habitats.
Over 150 species have been identified on and around the islands. Most notable of the islands' bird life is the nesting of great blue herons and ospreys, the latter believed to be one of the highest concentrations in eastern North America. The islands' natural history resources provide an important opportunity to understand the geologic and coastal geomorphic processes which have combined to shape both the islands and Halifax Harbour. As well, the islands' provide an opportunity to observe and appreciate a diversity of flora and fauna in a near urban setting. Historic Resources McNabs and Lawlor islands are rich in historic resources, and offer excellent opportunities to understand the province's cultural heritage.