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During the Sonoran Desert Summer, saguaro cacti produce an abundant fruit crop whose nutrients and water have distinctive stable isotope compositions. Carbon stable isotope analyses indicated that, at the peak of saguaro fruit production, saguaro fruit represented >90% of White-winged Dove and similar to50% of Mourning Dove carbon incorporation. Over the entire summer, saguaro fruit comprised 50% and 14% of the diet of White-winged and Mourning Doves, respectively. In White-winged Doves, VC of their liver tissue and deltaD (deuterium) of their body water were linearly correlated, indicating that saguaro fruit was an important source of both nutrients and water. In Mourning Doves, in contrast, VC and deltaD were not correlated. Mourning Doves acquired nutrients but not water from saguaro fruit. Stable isotopes revealed that a common food plant sometimes provides a very different suite of resources to the different species that consume it.