Abstract
Across an individual's life, foraging decisions will be affected by multiple intrinsic and extrinsic drivers that act at differing timescales. This study aimed to assess how female Australian fur seals allocated foraging effort and the behavioural changes used to achieve this at three temporal scales: within a day, across a foraging trip and across the final six months of the lactation period. Foraging effort peaked during daylight hours (57% of time diving) with lulls in activity just prior to and after daylight. Dive duration reduced across the day (196 s to 168 s) but this was compensated for by an increase in the vertical travel rate (1500–1600 m·h−1) and a reduction in postdive duration (111–90 s). This suggests physiological constraints (digestive costs) or prey availability may be limiting mean dive durations as a day progresses. During short trips (<2.9 d), effort remained steady at 55% of time diving, whereas, on long trips (>2.9 d) effort increased up to 2–3 d and then decreased. Dive duration decreased at the same rate in short and long trips, respectively, before stabilising (long trips) between 4–5 d. Suggesting that the same processes (digestive costs or prey availability) working at the daily scale may also be present across a trip. Across the lactation period, foraging effort, dive duration and vertical travel rate increased until August, before beginning to decrease. This suggests that as the nutritional demands of the suckling pup and developing foetus increase, female effort increases to accommodate this, providing insight into the potential constraints of maternal investment in this species.
Highlights
In order to maximise reproductive success, individuals must efficiently accumulate resources to invest in reproductive endeavours
Foraging effort in April was lowest for the study period with the general tread of foraging effort increasing throughout the study period (Figure 5). These results suggest that overall foraging effort increases throughout the study period, it is not a result of increasing foraging trip durations; rather AUFS achieve this by increasing their diving effort within a foraging trip
The current study found that foraging effort and diving behaviour in female AUFS provisioning pups varied at multiple temporal scales
Summary
In order to maximise reproductive success, individuals must efficiently accumulate resources to invest in reproductive endeavours. Efficient foraging (behaviours that minimise cost while maximising gain) will improve lifetime fitness and be selected for over time [1,2]. In the little brown bat (Myotis lucifugus) foraging duration is inversely linked to prey density with individuals spending more time resting on nights when prey densities are low [5]. At the ecological level (i.e. an individual’s lifetime), foraging decisions will be shaped and/or constrained by multiple intrinsic and extrinsic drivers. These include the type of resource being gathered, such as, a predator being limited in foraging time by the behaviour of their prey [6]. Animals adopting a central place foraging strategy during offspring provisioning are constrained in foraging range by the duration they can leave their offspring alone [9]
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