The McLean's natural history collection is substantial and reflects the considerable importance attached to collecting in this field over the years of the Museum's existence from its inception up until the 1940s. The holding of bird specimens, mainly mounted for display, numbers over 950 and includes significant species such as the extinct Passenger Pigeon and Eskimo Curlew. Other animal groups are represented, including several thousand specimens of insects (mainly Coleoptera and Lepidoptera), and molluscs. The origin of the animal material is world-wide and includes the large mounted big game specimens of R.L. Scott of Scott’s Shipbuilders, Greenock. A number of his specimens are on permanent display and include a Nile crocodile and an Indian Tiger. An Okapi and a Bongo are also on show, both rare animals in museum collections. There are over 1100 herbarium specimens mainly local to Inverclyde.
There are 950 specimens in the fossil collection which includes examples from the animal and plant groups. The specimens mainly come from Scotland, England and Ireland with a few European specimens. There are 637 specimens in the mineral collection. It is a general collection containing a wide range of specimens from around the world and from across the major mineral groups including native elements, carbonates, oxides, sulphides, sulphates and phosphates. Of particular note are the specimens from Canada and Australia.
This are over 3,100 specimens of insects. These comprise 1,587 butterflies, 558 moths and 1,008 coleoptera specimens. Although the collection has large numbers of British specimens there are also holdings of butterflies, moths and beetles from around the world. The specimens date from the mid nineteenth century to the mid twentieth century. Most of the specimens are dried and pinned. The most significant group within the collection are the 67 specimens of mimicry butterflies and moths donated by George Rodgers Macdougall (1843-1917).