Abstract
Balancing time allocation among competing behaviours is an essential part of energy management for all animals. However, trade-offs in time allocation may vary according to the sex of the individual, their age, and even underlying physiology. During reproduction, higher energetic demands and constrained internal resources place greater demand on optimizing these trade-offs insofar that small adjustments in time-activity may lead to substantial effects on an individual’s limited energy budget. The most extreme case is found in animals that undergo capital breeding, where individuals fast for the duration of each reproductive episode. We investigated potential underlying drivers of time-activity and describe aspects of trade-offs in time-activity in a wild, capital breeding pinniped, the grey seal Halichoerus grypus, during the lactation period. For the first time, we were able to access full 24-h activity budgets across the core duration of lactation as well as characterize how aspects of stress-coping styles influence time allocation through the use of animal-borne accelerometers and heart rate monitors in situ. We found that there was a distinct trade-off in time activity between time spent Resting and Alert (vigilance). This trade-off varied with the pup’s development, date, and maternal stress-coping style as indicated by a measure of heart rate variability, rMSSD. In contrast, time spent Presenting/Nursing did not vary across the duration of lactation given the variables tested. We suggest that while mothers balance time spent conserving resources (Resting) against time expending energy (Alert), they are also influenced by the inherent physiological drivers of stress-coping styles.Significance statementHow animals apportion their time among different behaviours is key to their success. These trade-offs should be finely balanced to avoid unnecessary energy expenditure. Here, we examine how grey seal mothers balance their activity patterns during the short, but energetically demanding, period of pup-rearing. Animal-borne accelerometers provided a uniquely detailed and continuous record of activity during pup-rearing for 38 mothers. We also used heart rate monitors to provide measures of each individual’s stress-coping style. We found that mothers balance time Resting against remaining Alert while time Presenting/Nursing was largely independent of all factors measured. Stress-coping styles were found to drive the balancing and variation of all behaviours. This novel indication that differences in personality-like traits may drive whole activity budgets should be considered when assessing trade-offs in time allocation across a much wider variety of species.
Highlights
Monitoring changes in fine-scale behaviour is critical to examining trade-offs associated with time allocation
We focus on three behavioural states (Resting, Alert and Presenting/Nursing) where trade-offs in timeactivity likely exist in lactating grey seals as they make up most of a mother’s daily activity budget
For the purposes of this study, we focus on three of these behaviours that make up the greater part (> 90%) of a female’s activity budget during lactation and are more likely to exhibit trade-offs in time-activity allocation; Resting, Alert, and Presenting/Nursing (Table 1)
Summary
Monitoring changes in fine-scale behaviour is critical to examining trade-offs associated with time allocation. Conspecific density plays an important role in driving a wide variety of behavioural trade-offs and can be key in determining reproductive success in a variety of species (Festa-Bianchet et al 1998; Horning and Mellish 2012; Maniscalco 2014). Environmental factors, such as thermal regimes, are already known drivers of population-level behavioural trade-offs in a variety of taxa, and have been shown to be strong drivers of individuals balancing thermoregulatory needs with that of other behaviours (Liwanag et al 2009; Turbill et al 2011; Paterson et al 2012; Heerah et al 2013; Udyawer et al 2017; Pagano et al 2018). Life history requirements may dictate that certain elements of time-activity budgets are less plastic than others
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