Mercury is a globally-increasing pollutant. At high concentrations it is a potent neurotoxin. However, we know relatively little about exposure to low levels of mercury. Here we will explore the effects of low-level dietary mercury (equivalent to a tuna fish sandwich) on sperm form and function in a common bird, the zebra finch. This will give us crucial insight in to how male fertility is affected by this increasingly common chemical, which has implications for medicine and conservation.