I recommend contacting prospective advisers very early. Both the student and the adviser can use early correspondences to assess compatibility of research interests, to refine the applicant’s admission materials, and to assess the ease of social interactions between students and their could-be advisers. PhDs are a long commitment (4-7 years…sometimes even longer…). Given this nature, it is important to choose your major professor carefully. For a sobering comparison, the median duration of a first marriage is around 6.8 years.
Regarding research projects, students are welcome to work on any taxon that they wish. Furthermore, although most of my work has focused on evolutionary behavioral ecology (e.g., social behavior, territoriality, sexual behavior), students should not feel limited to projects directly subsumed within my present research lines. I want my students to feel comfortable initiating their own research questions and, as an adviser, it's my role to help students design studies to address their interests and to help them get the most out of their data.
Finally, I make it a point to have a relatively small laboratory. I take on comparatively few students because I like to work closely with them in the lab and field. Ensuring that students are happy, funded and productive is a major social and professional commitment that I don’t take lightly. It isn’t possible for me to honor this commitment and maintain a very large laboratory. Think hard about what kind of lab you’d like to be a part of. It’s a powerful and exciting decision you’re making.