title: Foraging decisions in a capital breeder: trade-offs between mass gain and lactation.
abstract: The high energetic costs of lactation can lead to fundamental trade-offs in life-history traits, particularly in young females that reproduce before completing body growth. We assessed whether lactating female mountain goats (Oreamnos americanus) used behavioural tactics at fine spatio-temporal scales to increase energy intake to compensate for the costs of lactation. Lactating females increased bite rate and chewing rate compared with non-lactating females, but selected similar foraging sites in terms of plant quality and abundance. At peak lactation, forage intake of lactating females was >40% greater than that of non-lactating females. For females that had reached asymptotic body mass (i.e. > or =6 years old), summer mass gain of lactating females was similar to that of non-lactating females. At 4 and 5 years of age, however, daily mass gain of lactating females was about 20% lower than that of non-lactating females. We conclude that increased foraging may allow fully-grown lactating females to compensate for the energetic costs of lactation, but that there is a major trade-off between mass gain and lactation for younger females.
authors.affiliation: Département de Biologie and Centre d'études nordiques, Université Laval, 1045 avenue de la Médecine, Quebec, Canada. sandra.hamel@uit.no
authors.forename: Sandra
authors.initials: S
authors.lastname: Hamel
authors.forename: Steeve D
authors.initials: SD
authors.lastname: Côté
mesh_terms: D000416:Alberta; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001837:Body Weights and Measures; D004734:Energy Metabolism / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D006041:Goats / Q000502:physiology*; D007774:Lactation / Q000502:physiology*; D016014:Linear Models; D019370:Observation