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Variation in Mass and Lactation Among Cohorts of White-Tailed Deer
Bronson K. Strickland, Stephen Demarais & Patrick D. Gerard
Age-specific body mass and % lactation are indices commonly used to monitor status of cervid populations relative to carrying capacity. However, prior-year body condition and reproductive status may influence these indices and alter their interpretation. We examined variation in body mass and % lactation among cohorts of female white-tailed deer (Odocoileus virginianus) to determine: 1) patterns of variation among age classes, 2) if cohorts compensated in subsequent years for restricted somatic development, and 3) the relationship between body mass and % lactation within cohorts. Body mass and % lactation of young deer were more variable than for older deer, potentially making them a more sensitive indicator of population status relative to carrying capacity. The lack of correlation in body mass of cohorts across years implies that cohorts can compensate for restricted somatic development during subsequent years in the environments we studied. Body mass and % lactation were positively correlated in 1.5-year cohorts, suggesting that age of primiparity was affected by body condition. However, mean cohort body mass did not influence % lactation in older cohorts. Our data support that older cohorts (≥3-years-old) have greater resiliency to changes in density or to environmental events as these cohorts demonstrated less annual variation in body mass and % lactation compared to younger cohorts. Annual changes in morphometrics and fecundity of younger-aged cohorts may be the best indicator of animal density relative to carrying capacity, or of environmental events that influence carrying capacity.
Key words: body mass, cohort correlation, cohort variation, lactation, Mississippi, Odocoileus virginianus, white-tailed deer