Foraging behaviors of White-tailed deer (Odocoileus virginianus) consuming acorns
Odocoileus virginianus readily consume acorns. Acorns are large (1 – 5 g), high in lipids, and dietary lipid content affects deer survival and fecundity. Deer might also ingest acorns because of a high short-term food intake. Leaves of dicotyledous plants (browse) is the forage type commonly consumed by O. virginianus and models of browse food intake reveal that larger bite sizes increase food intake. Deer consuming browse appear to have a maximum bite size and food intake of 1.2 g/bite and 9.8 g/min, respectively. My first objective was to determine whether food intake of acorns exceeded 9.8 g/min. Interestingly, limited data indicated that food intake might decline with increasing acorn (Quercus sp.) mass. I also investigated whether larger acorns reduced food intake because of increased chews per gram of ingested material (chewing investment) and lower bite rates. I measured foraging behaviors of free-ranging deer consuming Q. virginianus (Live oak) or Q. buckleyi (Texas oak) acorns in San Marcos, Texas. I set out 200 acorns in a 1-m 2 area at four feeding locations and recorded the time deer spent feeding on acorns and the number of bites and chews taken. Food intake was the product of acorn mass and bite rate. Five observers collected 92 foraging observations that ranged in length from 1 to 24 minutes from September to December 2020 – 2022. Acorn mass was measured in 57 of those observations. Observation length, time of day, and observer influenced bite and chew rates, and these variables were included in subsequent analyses. The mean acorn mass of Q. virginianus was 1.5 gm (s = 0.7) and 2.8 gm (s = 1.5) for Q. buckleyi. Using linear mixed effects models I estimated a mean food intake on Q. virginianus acorns of 27.22 g/min (SE = 5.1) and 24.55 (4.9) for Q. buckleyi. Deer can ingest acorns faster than the maximum ingestion rate of browse. Analyses of mixed-effects models indicated that bite rate was higher on Q. virginianus acorns but chewing rate was higher on Q. buckleyi corns. Food intake was also lower for Texas than Q. virginianus acorns. An inverse relationship, however, between chewing rate and food intake meant that chewing investment declined with food intake. Elevated chewing rate when deer consumed Q. buckleyi acorns appeared to reduce food intake. In addition to acorn mass, species specific characteristics of acorns such as pliability, texture, and chemical composition might impact deer ingestive behavior. Deer behavior dictating acorn ingestion is complex and requires further investigation.
food intake, white-tailed deer, acorns, bite size, Biology
Smith, J. (2023). Foraging behaviors of white-tailed deer (Odocoileus virginianus) consuming acorns. (Unpublished thesis). Texas State University, San Marcos, Texas.