The energetic cost of predator avoidance in neonatal ungulates: hiding versus following

Growth rates, milk intake, and activity patterns of neonatal mule deer (Odocoileus hemionus) and mountain goats (Oreamnos americanus) were compared, along with weight changes and activity patterns of their mothers, to determine (i) the energetic costs and trade-offs of following and hiding as strategies to reduce predation and (ii) whether any additional energy cost due to following is borne by the neonate, the mother, or both. Body weights of neonates at 1 and 9 weeks of age did not differ between species, but growth rates differed and changed with time. For the first 4 weeks postpartum, the deer fawns were less active and had a higher growth rate than the goat kids. Growth rates of fawns decreased after the 4th week while growth rates of the kids increased near the 7th week. Throughout the study, individual milk intakes were generally higher for singleton fawns than for twin fawns and single kids. Deer nursing single or twin fawns produced more milk (measured in grams or kilocalories) than did goats. Fawns nursed less frequently but in longer bouts, consuming more milk per bout than the goats. The lactating deer lost weight during early lactation while lactating goats maintained their weight. The energetic cost to goats of following was borne primarily by the neonate, with the additional costs directly associated with following being quite small.