Finally, we need to define the current population numbers as a starting point from which population evolve under different scenarios. This is usually taken as c. 1000 individuals (Siegfried 1992, \citep{Simmons2005,Taylor2015}. The proportion of birds out of the total population that fall into the different age categories is given by the steady state proportions considering mean values for all life history parameters. The steady state proportions can be calculated using the right eigenvector of the population transition matrix (see below, and \citealt{Caswell2001}).