Use of free water by nesting lesser prairie-chickens

The lesser prairie-chicken (Tympanuchus pallidicinctus) is a grassland grouse of semiarid regions. Use of free water has been hypothesized as necessary for egg formation during drought. We assessed the use of hydrogen isotopes (deuterium, δ²H) to determine if female lesser prairie-chickens use and incorporate free water during egg formation by testing the relationship between isotope ratios in available free water and eggshells. We collected eggshells from 124 nests and 282 free water samples from three sites in Kansas in 2013 and 2014. Eggshells had δ²H values similar to free water in the year of severe drought but were dissimilar the year with lessened drought severity. With an established link between lesser prairie-chicken eggshells and free water during severe drought, we have identified a mechanism behind observations of lesser prairie-chicken water use. We have demonstrated that hydrogen isotopes can be used to test research questions related to use of free water.