Free-ranging red-tailed hawks (Buteo jamaicensis) commonly present to wildlife facilities and veterinary clinics for injury or illness, and bloodwork is often an essential tool in their diagnostic workup. However, the type of anticoagulant used and the sample storage time prior to processing may potentially impact hematological values. This study evaluated differences between EDTA and lithium heparin (HEP) preserved blood samples in packed cell volume (PCV), total solids (TS), estimated WBC counts by smear, and WBC differential counts. Additionally, differences in estimated WBC counts and WBC differential counts between anticoagulant-free (AF) and anticoagulant preserved blood smears were evaluated. Values were compared at time of blood collection and again after refrigeration for two, six, and 24 hours. Packed cell volume and TS were not significantly different between type of anticoagulant or time stored. Statistically significant differences in estimated WBC counts between AF samples and ETDA samples were found at all time points after time of collection (p = 0.025, 0.021, 0.010 for t = 2, 6, 24, respectively), while no differences were noted between AF samples and HEP samples. White blood cell differential count was impacted with variable significance by both time and anticoagulant. Clinically, HEP should be considered the anticoagulant of choice in this species and consideration should be taken to evaluate samples as close to collection time as possible.