The processing of blood samples can be delayed during health assessments of wildlife populations in distant locations. The use of whole blood preservatives may be useful in these situations. However, there is scant information regarding their use in nonmammalian species. This study tested the efficacy of two cell preservatives on whole blood collected from 12 Attwater's prairie chickens (Tympanuchus cupido attwateri). The preservatives used were Streck Cell Preservative© (SCP), a proprietary proteinaceous stabilizer developed for human flow cytology and validated in other mammalian species, and formalin, which is commonplace in histopathology, but its use in whole blood has been limited to fish. Grouped blood samples were treated with heparin, SCP, or formalin and analyzed at 0, 1, 4, and 7 days after collection for packed cell volume (PCV), complete blood count (CBC), and cellular morphology. SCP effectively preserved most cell types in Attwater's prairie chicken blood samples over a period of 7 days, with the exception of monocyte cell counts, which were significantly reduced from day 0. Formalin maintained total white blood cell counts at baseline levels measured by hemocytometer, but irregular staining characteristics prevented accurate analysis of differential counts or cellular morphology. Both preservatives altered PCV compared with the heparin control, but these values remained constant over time, highlighting the need for method-specific reference intervals. The validation of SCP in Attwater's prairie chickens supports its potential for use in other avian species for the collection of accurate hematologic data when the processing of blood samples may be delayed.