birding...

Superb Parrot Polytelis swansonii ©Ian Montgomery http://birdway.com.au

Apart from Antarctica, Australia is the world`s driest continent and climate is the major factor affecting, directly and indirectly, the distribution of Australian birds. Eastern Australia is especially well known for its seemingly unpredictable extremes in weather. Floods or droughts are a regular feature. For example, eastern Australia has experienced a severe drought during the past two years. Drought conditions have eased recently along the eastern seaboard of New South Wales but inland dry conditions remain. In contrast, large areas of the central New South Wales coastal region were severely affected by floods in early 2001.

New South Wales covers a land area of about 800,000 square kilometres, extending over 12 degrees of longitude and 6 degrees of latitude. In broad climatic terms, New South Wales is within a temperate zone, i.e. a mild, equable climate that is mostly free from extremes of heat and cold. However, very high temperatures occur in the northwest of NSW and very cold temperatures on the Southern Highlands. The climate changes markedly east to west and this is evidenced by significant differences in vegetation. In part, the climatic variation occurs because of the presence of the Great Dividing Range, which runs the full length of NSW from north to south never being more than 150kms from the coast; it rises abruptly from the coastal plain and much of the rain borne by the onshore winds is lost before the wind passes over. The coastal strip has good rainfall and relatively mild temperatures being influenced by the warm waters of the adjacent Tasman Sea. The annual median rainfall along the east coast ranges from 2,000mm in the far north coast to around 750mm on the far south coast. Winter snow falls, mostly in the Southern Alps (the far southern section of the Great Divide) and severe frosts can occur anywhere in this high country of the Great Divide. As one travels west, beyond the Great Divide, the rainfall decreases and extremes in temperature occur.

The Southern Oscillation and its impact on the region`s climate - Australian weather patterns occur because of a phenomenon known as the Southern Oscillation (SO). The SO is a major air pressure shift occurring between the eastern Pacific and the western Pacific/Asian regions as a result of large-scale interactions between the ocean and the atmosphere and has a profound effect on climate variability, season to season and year to year. A sustained positive variation in the SO Index are known as a La Nina and a sustained strongly negative variation is called an El Nino. Each can appear to occur randomly. When negative variations occur there are widespread drought conditions.

Ocean Waters - Regular boat trips now travel to the Continental Shelf and into the adjacent waters from Swansea (a suburb of Newcastle); Sydney, Wollongong and Eden (far south coast). An outcome of this activity is that most recent new vagrants to NSW have been seabirds. Two groups of seabirds can be distinguished, those that mainly frequent Ocean Waters and those that are primarily found in Inshore Waters. Ocean waters encompasses all areas of deep water east of the Australian Continental Shelf, being waters greater than 200 metres. The sea from the NSW coastline to the edge of the Continental Shelf and any large bays and estuaries opening into the ocean form the Inshore Waters. The NSW coastline, coastal islands, the volcanic island of Lord Howe and its associated rock outcrops and reefs, and seamounts (undersea mountains) modify oceanic waters so they contain high concentrations of food and larger numbers of seabird are often associated with these places.

Landform - The Great Dividing Range is both a climatic barrier and a distribution barrier for birds by separating the narrow and wetter coastal plain from the drier inland. A number of westward range offshoots of the Great Dividing Range (notably the Liverpool, Warrumbungle and Nandewar Ranges) extend the range of some coastal rainforest and forest dwelling species. The lowest section of the Great Dividing Range occurs in the Upper Hunter and, here, woodlands similar to those of the inland enable typically inland birds to move towards coastal areas.

Throughout the Divide, upland areas from 300 metres to over 2,150 metres are known as Tablelands, are the treed plateaux of New England, the Blue Mountains to Bathurst and Orange, Goulburn, Yass and the Monaro and the high plateaux of Kosciusko and Kiandra. Far from being level, their surface consists of a series of very broad, undulating valleys. They experience obvious altitudinal changes in climate, particularly cold winters and mild summers. Interspersed on the tablelands are open grass or heath lands. Previously, extensive temperate woodlands largely covered much of the tableland area as well as extending onto the riverine plains and the far western rangelands. Today, these woodlands have been extensively cleared and modified for agricultural pursuits, primarily sheep-wool production and cereal cropping. As one progresses west of the Divide, the land flattens to dry plains and, here, the major rivers are important in determining bird distribution.

The far western plains country may appear largely featureless to some travellers but there are numerous outcrops in the northern two thirds of the State and faulted and warped peneplains raise their heads abruptly near Broken Hill. These are the Barrier Ranges that at 390 - 480 metres practically tower above the surrounding plains. Further north the Grey Range, rising to between 260m and 330m, also stands above the plains landscape. These ranges and other outcrops introduce added diversity to the surrounding landscape.