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.

Combined bio-logging and stable isotopes reveal individual specialisations in a benthic coastal seabird, the Kerguelen shag

“…Foragers would be expected to maximize foraging efficiency even more when provisioning young as foraging effort is increased to meet the energy requirements of the offspring [2]. Individual specialisations have been suggested as a way to avoid competition with conspecifics and to increase individual foraging efficiency (including prey finding, handling, and digesting) [3].…”

Environmental and Physiological Influences to Isotopic Ratios of N and Protein Status in a Montane Ungulate in Winter

“…The controls on accruing, maintaining, and mobilizing nutrient stores for reproduction can vary substantially within and among species by body size, food availability, offspring mass, and milk production. Some northern and alpine ungulates, such as muskoxen ( Ovibos moschatus ) [18], mountain goats ( Oreamnos americanus ) [19], [20], and bighorn sheep ( Ovis canadensis ) [17] rely solely on stored capital for production of young. Alternatively, others, such as caribou ( R. tarandus ) use primarily capital and some income to meet nutrient demands throughout a reproductive event [21], [22], whereas roe deer ( Capreolus capreolus ) rely exclusively on income to produce offspring [12].…”

“…Protein demands for reproductive females peak during lactation, which typically occurs within the first few weeks of the growing season [27]. Nutrient requirements for lactation commonly necessitate the use of maternal capital as well as the increased intake of forages [12], [19]. Winters with deep snow affect maternal investment of caribou by reducing birth mass of offspring, which may decrease calf survival and recruitment [7].…”

Female mountain goats, Oreamnos americanus , associate according to kinship and reproductive status

“…Previous studies on the same population have also shown that lactating females spend more time foraging than nonreproductive females, reducing their time spent lying down (Hamel & Côte, 2008); this difference in activity budget could favour the association of lactating females and segregate lactating and nonreproductive females. On the other hand, lactating females forage in the same areas and have a higher biting rate than nonlactating females (Hamel & Côte, 2009), which could allow females of both reproductive status to remain in the same groups. Thus, lactating female mountain goats and nonreproductive ones did not segregate, even if lactating females seemed to prefer to associate with each other.…”