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 species-number, dropping down from 900 birds in 1990 to only one-third of that at the mark of 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 a 700 in 2010.
Meanwhile, despite starting at a 0.75 in 1990, parrots quickly rose to reach the 900 mark after only five years, making this the greatest population increase among the five birds species. This rise, however, did not last long as parrot numbers started plummeting again after the year 1995, with no further escalations. Likewise, whip birds numbers showed a slight increase in 2000, but then went downhill in later years. While all the other bird species were dwindling after the year 2005, swallow numbers expanded by almost 100 birds in the five-year time from 2005 to 2010.