Eight Multistate Models C A R L J . S C H WA R Z 8.1 Introduction The original modeling framework for capture­recapture studies assumed homogeneous behavior among animals and was concerned with estimat- ing parameters, such as survival or abundance, for a single uniform popu- lation. In many situations, this is unrealistic because animals within a population are not homogeneous with respect to survival and catchabil- ity, and heterogeneity in these parameters can lead to biases in estimates. In their key paper, Lebreton et al. (1992) developed a modeling frame- work based on partitioning populations into homogeneous subpopula- tions (groups) based on fixed, unchanging attributes, such as sex. These models and the AIC model selection framework (chapter 1) start with