Unraveling antler progression in desert mule deer: implications for common management practices

Antler characteristics are commonly used in the management of cervid species to achieve a variety of management goals. Such characteristics are commonly the basis for culling criteria to increase mean antler size. However, the efficacy of culling programs is questionable, and there are few robust evaluations of criteria reliability. Without understanding how bucks' antler sizes change through time, which we term antler progression, there is little basis for establishing or testing culling criteria. Interest in mule deer management is increasing, but there is little information on mule deer antler progression available to managers. Antler progression is widely studied in closely related white‐tailed deer, but there is considerable discord on the nature and predictability of it in the literature. Much debate is centered on study design and interpretation, with most studies neglecting the temporally dynamic nature of antler progression. We explicitly compared antler progression dynamics of 54 known‐aged mule deer bucks on the Apache Ranch, near Van Horn Texas. On average, mule deer bucks reached a peak Boone and Crockett score of 387.1 cm at 5.5 years old, but individuals varied in two distinct ways. Of our samples, 71.1% of the variation was attributable to differences in overall antler size throughout the buck's life, which we took as a measure of Lifetime potential. An additional 21.4% was related to the age at which bucks reached their peak score, which varied from 4.5 to 7.5 years old. Variation in Lifetime potential serves as an objective basis for comparing culling criteria, relative to a management objective. We found that the number of tines at age 1.5 predicted whether bucks were in the top 50% of Lifetime potential values only 46% of the time. The absence of G4 tines in 4.5 year old bucks may reliably distinguish below‐average bucks, but few bucks met this criteria and it should be considered with caution. Overall the criteria we evaluated were intrinsically unreliable and difficult to apply reliably when considering uncertainty of aging in the field, undermining the efficacy of culling programs. We hypothesize that supplemental feeding may reduce variability in Age‐at‐peak score, but continued research is required before drawing conclusions.