Determination of population age structure from the survivorship of individuals of unknown ages in unicorns and platypuses

Population age structure is an important parameter for wildlife population modelling. However, for many species it is not possible to accurately assess the age of adult individuals. We present a hypothetical example to illustrate a previously described method of determining population age structure from the survivorship of individuals of unknown ages that to our knowledge is unused in the fields of zoology and ecology. We then apply this method to data collected over 10 years for a population of wild platypuses (Ornithorhynchus anatinus), a species whose adult individuals cannot be accurately aged and for which only limited data on life history characteristics are available. Our results show a lower mortality rate over the first years of life of platypuses than the one previous study available for comparison, and suggested a Type I or Type III survivorship curve.