Rut‐Induced Hypophagia in Male Bighorn Sheep and Mountain Goats: Foraging Under Time Budget Constraints

Abstract

In polygynous ungulates, the rut imposes constraints on male time budgets that generate a trade‐off between maintenance and reproduction, leading to a reduction in time spent foraging. As mating activities can incur substantial somatic costs, males are expected to spend their ‘non‐rutting’ time recovering during the breeding season. If the diminution in time allocated to foraging by males is only a consequence of time budget constraints, males should keep a similar ratio of time spent foraging to lying to that observed in the pre‐rut, leading to an overall reduction of these two activities (the ‘foraging constraint’ hypothesis). Alternatively, if males adopt an energy‐saving strategy, they should limit energy expenditures by reducing foraging but not lying time, as the energy gains of forage intake may not meet the basal energetic requirements, especially in northern and temperate regions (the ‘energy‐saving’ hypothesis). Here, we contrast these two hypotheses by comparing individual daily time budgets of marked adult bighorn sheep rams (Ovis canadensis) and male mountain goats (Oreamnos americanus) during the pre‐rut and the rut. Concordant results for both species support the ‘foraging constraint’ hypothesis, as sexually‐active males reduced time spent foraging and lying from the pre‐rut to the rut because of an increase in time spent in mating‐related activities. Bighorn sheep rams also increased time spent foraging when not engaged in mating tactics, providing further support for a ‘maximisation’ of energy intake in the absence of reproductive opportunities. Because there are also known physiological changes that occur during the rut which may cause appetite suppression, for example to produce metabolic compounds linked with olfactory communication (the ‘scent‐urination’ hypothesis) or to cope with increased burden of parasites (the ‘parasite‐induced anorexia’ hypothesis), further research should aim at simultaneously testing these current hypotheses to better understand rut‐induced hypophagia and its effects on the life histories of male ungulates.

Timing of Reproductive Effort Differs between Young and Old Dominant Male Reindeer

“…However, contrary to Willisch and Ingold (2007) who found that feeding of old male Alpine chamois (Rupicapra rupicapra rupicapra) was higher during the early and late rut than during the peak rut, we observed feeding of old males to be high only during the late rut, but low during the early and peak rut. This result is consistent with our findings that activity level of the old males was high during both the earlyand peak-rut weeks, as there is often a negative relationship between reproductive and maintenance activities, such as feeding (Stearns 1992, Pelletier et al 2009). …”

“…Standing behaviour is associated with female defense because it allows a dominant male to watch members of the group and stay alert to wandering females or intruding males (Clutton-Brock et al 1982, Buschhaus et al 1990, Willisch & Ingold 2007, Mainguy & Côté 2008, while males move during the rut in order to search for receptive females, follow females, and drive them back to the group (Epsmark 1964, Komers et al 1997, Forsyth et al 2005. These activities are both associated with significant energetic costs and reduce time available for foraging (Pelletier et al 2009), which inevitably leads to mass loss or reduced mass gain.…”

Location of rut stands vs. mating opportunities in Przewalski’s gazelle: A field test of the “Resource-based Hypothesis” and “Female Traffic Version of the Hotspot Hypothesis”

“…Some studies suggest that food resources are important for both sexes during rut (Pelletier et al, 1999;Brivio et al, 2010), and essential for dominant males to obtain mating opportunities (Loyau et al, 2007). Our results also show that food resources are important for females because the female group spent of the majority of each day grazing; dominant males ate little during the whole rut season.…”

“…The first category of hypotheses emphasizes the impact of environmental factors such as food resources or special land marks on breeding system evolution in animals. Pelletier et al (1999) and Brivio et al (2010) reported that food resources are important for both sexes during rut and that males and females in alpine ibex Capra ibex and bighorn sheep Ovis canadensis spend more time foraging when they are not engaged in mating. One of the most studied hypothesis for this category is the "Resource-based Hypothesis", which suggests that breeding sites should be formed close to or at resources used by females, for example at feeding sites or nesting sites (Alexander, 1975;Takács et al, 2002;Loyau et al, 2007).…”

Males do not senesce faster in large herbivores with highly seasonal rut

“…Therefore, the absence of costly physiological mechanisms linked to the mating season length on male's actuarial senescence appears as a general pattern in populations of ruminants, whether captive or free-ranging. Actually, although there is evidence for physiological mechanisms that lead to the cessation of food intake during the rut in some seasonally reproducing ruminant species (McMillin et al, 1980;Suttie and Kay, 1985;Miquelle, 1990;Suttie et al, 1992;Newman et al, 1998;Apollonio and Di Vittorio, 2004), investigations performed so far on seasonally reproducing species have reported either a cessation of food intake in relation to the time constraint during the rut (Pelletier et al, 2009;Brivio et al, 2010;Guan et al, 2012;Corlatti and Bassano, 2014;Xia et al, 2014) or no change at all in food intake during the rut (Ding et al, 2012). Thus, the potential absence of a general physiological mechanism across ruminants that regulates food intake during the rut could explain the lack of an effect of the intensity of seasonal reproduction on senescence patterns.…”