Endocrinology in field studies: problems and solutions for the experimental design.

The increasing interest in hormones among field biologists can be frustrating because of the difficulties of applying classical endocrinological methods to natural settings. A few thoroughly tested methods have become popular because of their simplicity of use. This does not mean that such methods are the best or the appropriate ones for all studies. In this brief review I will examine some common problems encountered by field biologists who want to study the relationships between a morphological, behavioral, or physiological trait and a hormone. First, I will discuss why questions asked in the field often differ substantially from those asked in the laboratory, and how to adapt the design of the experiment accordingly. Second, I will review alternative methods to study hormone-trait relationships and how to combine them to strengthen the conclusions that can be drawn from the study. Then, I will discuss how to find the right control for a hormonal manipulation. Finally, I will examine the pitfalls associated with long-term hormonal treatment and the available methods for such types of studies.