Using n-alkane markers to estimate forage intake of mule deer

Dry matter intake (DMI) of free-ranging mule deer (Odocoileus hemionus (Rafinesque, 1817)) in the aspen parkland of east-central Alberta was estimated using the double n-alkane ratio and bite count methods. Eleven female mule deer were given an intraruminal capsule containing synthetic n-alkanes and released into 4-8 ha paddocks. Known concentration of even-chained carbon (C-32) was released from the capsules and recovered 7-10 days later from freshly voided faeces. Odd carbon chains of adjacent length (C-31:C-33) were extracted from vegetation samples gathered during behavioural observations of four tame deer. Calculations from the pairings (C31:C32; C33:C32) provided estimates of DMI that ranged from 1.29 to 2.73 kg/day. DMI was highest during autumn, possibly to prepare for increased energy demands for the upcoming winter. No differences were found in seasonal or annual comparisons of bite rates, but bite sizes differed in all comparisons, suggesting bite size was a critical factor affecting consumption rates for mule deer on northern ranges. Maximum bite sizes rose from 49 +/- 5 mg/bite in July to 213 +/- 58 mg/bite in October. Maximum consumption rates were in October of both years (3.6-4.4 g/min) and occasionally approached theoretical maxima (14.3-15.6 g/min).