Quantity over quality? Prey-field characteristics influence the foraging decisions of little penguins ( Eudyptula minor )

Abstract

Quantifying prey characteristics is important for understanding the foraging behaviour of predators, which ultimately influence the structure and function of entire ecosystems. However, information available on prey is often at magnitudes which cannot be used to infer the fine-scale behaviour of predators, especially so in marine environments where direct observation of predator–prey interactions is rarely possible. In the present study, animal-borne video data loggers were used to determine the influence of prey type and patch density on the foraging behaviour of the little penguin ( Eudyptula minor ), an important predator in southeastern Australia. We found that numerical density positively influenced time spent foraging at a patch. However, when accounting for calorific value in density estimates, individuals spent longer at dense patches of low-quality prey. This may reflect a trade-off between capture effort and calorific gain as lower quality prey were captured at higher rates. During the breeding season, foraging trip distance and duration is constrained by the need to return to the colony each day to feed offspring. The results of the study suggest that, under these spatio-temporal constraints, little penguins maximize foraging performance by concentrating efforts at larger quantities of prey, irrespective of their calorific quality.

Beneath the Antarctic sea‐ice: Fine‐scale analysis of Weddell seal (Leptonychotes weddellii) behavior and predator–prey interactions, using micro‐sonar data in Terre Adélie

“…The foraging distances observed in our study are consistent with former studies on the fine‐scale spatial use of lactating females demonstrating very restricted foraging area (Larue et al., 2019 ). Presence of pups may limit females' foraging trip distance, as observed in other marine species such as little penguin (Sutton & Arnould, 2022 ).…”

Energetic consequences of prey type in little penguins ( Eudyptula minor )

“…The swimming speed of a juvenile baitfish is approximately one tenth that of an adult fish [ 13 ] and, thus, it is possible that little penguins prefer targeting juvenile fish, finding them easier to capture. Indeed, a recent study demonstrated that little penguins spent longer periods at patches of juvenile prey [ 35 ]. While this prey type may be of lower energetic value, it may make for an efficient meal as it occurs in large schools and has shorter handling times in comparison to other prey.…”

“…However, its short chase and handling duration, and schooling nature, would mean its capture rate could be comparatively high, allowing individuals to rapidly exploit prey patches. Indeed, the prominence of bellowsfish in the present study would suggest that little penguins may rely on these fish as an important prey item, given their high capture rate and abundance [ 35 ]. By contrast, while the estimated gross energy gain from jellyfish was also relatively low, their longer handling time (possibly due to their larger size) contributed to their low energetic profitability.…”

“…[30][31][32][33][34]), some aspects of their foraging strategies are not well understood [20]. In particular, little is known of the factors which influence the time spent foraging and interacting with prey items and the possible reasons for their foraging decisions [35]. Furthermore, there is little information on prey chase and handling times and the factors influencing these behaviours.…”

Decoding Ten Years of Little Penguin Foraging: Bio-Logging Reveals Foraging Patterns with Implications for Climate Change Mitigation and Marine Spatial Planning

“…Our analysis showed that hunting time decreased with warmer waters, especially during the Guard and Post Guard stages (min-max SST 12-18.4 ºC). During the breeding season, little penguins can switch foraging strategy, requiring different hunting time, and targeting different types of prey and prey aggregations with varying energetic content (Cavallo et al 2020;Sutton & Arnould 2022). More dispersed and/or less abundant prey in colder and less-stratified waters, or increased prey availability in warmer and stratified waters (Meyer et al 2020) can lead to changes in effort allocated to hunting activities.…”