I'm doing a research paper about the morphological, and behavioral differences of urban and rural populations of Bolbopsittacus lunulatus and I want to know the ideal number of individuals to sample.
It would be better if you refer already published work, sample size could vary according to the species. It is usually more than or at least 20% of the population size.
There is no perfect sample size. I would suggest that you start with simple and robust stats to explore your data. If there is too much variation, then you need to increase your sample size. In other words, sample size will depend on your statistical tests and how variable your measures are.