For the endangered Saltmarsh Sparrow, nesting is a pick-your-battles endeavour. Nest too far below the high tide line, and you could lose your babies to flooding. Nest too far above the high tide line, and parasites may invade the nest, spreading disease and robbing parents and juveniles of valuable body mass. What's a bird to do?! This month we're talking about evolutionary trade-offs and the article, "Tidal flooding is associated with lower ectoparasite intensity in nests of the Saltmarsh Sparrow" (Nightingale & Elphick, 2017).