The Tanzania Bird Atlas project has been documenting the distribution of birds in Tanzania at a half-degree resolution since 1960. Although spatial and temporal coverage during this time is variable, the project maintains a record of observer effort. We study the data set with a Bayesian spatial hierarchical model which accounts for observer effort and includes covariates on habitat and climate via smooth functions. The results for a range of savannah birds show relationships with climate variables and highlight the importance of protected area status in Tanzania.