The graph illustrates the numbers of five kinds of birds dwelling in Wollai Park during the period from 1990 to 2010.
From a quick glance, all five bird species had a tendency to decrease in number over the twenty-year period, albeit at significantly different rates.
It is clear that kookaburras experienced the greatest decline in numbers, dropping from 900 birds in 1990 to only one-third of that number by 2010. Crows also started at about 900 birds in 1990, though the drop was not as steep as that of kookaburras, since the crow population remained quite high at 700 in 2010.
Meanwhile, despite starting at 750 birds in 1990, parrots quickly rose to reach the 900 mark after only five years, making this the greatest population increase among the five bird species. This rise, however, did not last long as parrot numbers started plummeting again after 1995, with no further escalations. Likewise, whipbirds numbers showed a slight increase in 2000, but then went downhill in later years. While all the other bird species were dwindling after 2005, swallow numbers expanded by almost 100 birds in the five years from 2005 to 2010.