Reference intervals for hematological variables in wild Eastern grey squirrels (Sciurus carolinensis)

The eastern grey squirrel (Sciurus carolinensis) is a North American tree squirrel species which has been introduced to several countries outside its native range. We made use of squirrels culled in Italy within control activities to establish hematological reference intervals for this invasive species, with the aim to broaden the current knowledge about its physiology. Blood from 104 individuals was analysed through a laser analyser. Manual leukocyte differential counts on blood films from a subset of 77 animals were used for validation of the automated counts, resulting in a fairly good agreement between the two methods for all variables excluding monocytes. Reference intervals and the 90% confidence interval of their limits were estimated for 19 hematological variables, partitioning by sex when statistically significant differences were detected. For most variables, our results were comparable with the few data available on the grey squirrel and on related species. An exception was represented by the hematocrit and mean corpuscular volume which were higher than values reported by other authors, and by the mean corpuscular hemoglobin concentration, which was instead lower. This study gathered valuable reference information for studies aimed at disclosing the mechanisms underlying grey squirrels’ invasiveness and for future research on tree squirrels’ physiology.