The Spot-flanked Gallinule (Porphyriops melanops) is an endangered wetland-dwelling bird in Colombia. A field experiment was conducted to experimentally quantify the gallinule's food consumption and the nutritional relationships among the food resources it consumes, i.e., whether the abundance of one resource changed the consumption of another. Three wetland plant species were used for the experiments (Limnobium laevigatum, Hydrocotile ranunculoides, Azolla filiculoides), along with sesame seeds (Sesamum indicum) as a surrogate for a seed food source. Pairwise comparisons were made to determine food consumption when resources were equally available (first experiment), and after augmenting the most consumed resource in the previous experiment (second experiment). The gallinules behaved selectively during both experiments, and the value of the foods based on consumption was: L. laevigatum > S. indicum > H. ranunculoides > A. filiculoides. However, in the second experiment, L. laevigatum and S. indicum were equally consumed. Food preferences of the least consumed food in the first experiment indicated that in two pairwise comparisons the resources were perfect substitutes. In three pairwise comparisons the resources were treated as complementary, whereas two resources had an antagonistic relation. In conclusion, the gallinules' preferences depended on the context, and keeping mixtures of the preferred and complementary food resources available for the gallinules may improve the quality of wetlands.