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¹ Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, St. Paul, Minnesota 55108, USA
² Forest Wildlife Populations and Research Group, Minnesota Department of Natural Resources, 1201 E. Hwy. 2, Grand Rapids, Minnesota 55744, USA
³ Corresponding author (email: michelle.powell{at}dnr.state.mn.us)

Winter severity is a primary factor influencing deer survival and reproduction in northern climates. Prolonged, harsh winters can adversely affect body condition of does, resulting in depressed morphologic development of neonates. In this study, we captured 59 white-tailed deer (Odocoileus virginianus) neonates (28 in 2001 and 31 in 2002), following two distinctly different winters, one severe and the other historically mild. Vaginal implant transmitters allowed exact age to be determined for 73% of the neonates; new hoof growth was used to estimate age (days) of the other 27%. Birthdate and morphologic measurements of neonates (i.e., birth mass, new hoof growth, hoof length) were compared by sex and capture year. For known-age neonates (n=43), there was a year-by-sex interaction effect (P=0.01) on birthdate, being later for females during spring 2001 compared with 2002, which was consistent with a significant (P=0.03) year-by-sex interaction for total hoof length (22.3 mm [SE=0.9] and 20.3 [SE=0.8] for females and males in 2001; 19.9 [SE=1.0] and 22.1 [SE=1.0] for females and males in 2002). Interestingly, there was no effect of year on birth mass or birthdate of known-age neonates. A year-by-sex interaction (P=0.04) was determined for birthdates of estimated age (7 days) neonates (n=16), with females born earlier than males in 2001 and later than males in 2002. Dam age had an apparent effect on birthdates of known-age neonates, as fawns born to dams >5 yr old were born later (P<0.01) than fawns born to dams 5 yr old (2 June and 26 May, respectively). Capture year had little effect on 20 hematologic and serum characteristics examined; however, there were significant (P<0.05) sex effects on red blood cell (RBC) counts, serum cholesterol, and cortisol concentrations, and a year-by-sex effect (P=0.04) on triglycerides. Mean corpuscular volume (MCV) was the only blood characteristic that differed (P<0.01) between years, with higher values occurring in spring 2001. We report a range of reference values for blood constituents that have not been previously documented for free-ranging neonates. Overall, winter severity appeared to have little effect on birth, morphologic, or blood characteristics of neonates. Documenting reference values for free-ranging, known-age neonates is of particular importance to enhancing our understanding of their rapid physiologic development, the concomitant changes in mean values of their blood constituents, and the natural variability that appears to be associated with those values. Our findings suggest caution should be exercised when applying physiologic models derived in captivity to free-ranging deer populations.

  Key words:  Blood characteristics, deer neonates, morphologic development, Odocoileus virginianus, reproduction, white-tailed deer, winter severity.