Central-place foraging in large seabird colonies leads to high levels of intra-specific competition for food resources, often resulting in between-colony spatial segregation. However, little is known about within-colony variation in foraging behaviour that may arise from breeding locations. Using little penguins Eudyptula minor from a large colony (ca. 32 000 individuals) on Phillip Island (Australia), we present a novel approach combining GPS, diving, acceleration and bathymetry data. We investigated within-colony variation in 3-dimensional distribution of prey encounters and its consequences for foraging behaviour and breeding success. Over 1 breeding season, we simultaneously tracked 63 little penguins from 2 breeding sites located ~2 km apart and monitored their breeding success. We recorded 58 452 dives, of which 11 992 had prey encounter events associated. Results revealed strong spatial foraging segregation between sites throughout the breeding season and differences between sites in prey encounter depth during chick-rearing (mean ± SE, 11.8 ± 0.2 m vs. 17.3 ± 0.3 m). Birds from one site foraged in deeper waters and apparently experienced higher levels of competition, resulting in lower prey encounter rates and lower foraging efficiency (i.e. body mass gain after foraging trips), hence these birds seemed less successful. However, breeding success was high (>1.5 chicks fledged per pair) at both sites, indicating that food was not a limiting factor that year. Nonetheless, breeding success records over the last 12 yr showed that the site where birds foraged at deeper depths produced fewer chicks. Our findings highlight the importance of understanding small-scale spatial segregation to capture foraging behaviour variation within large seabird colonies.

High precision, high coverage DNA-based diet analysis tools allow great insight into the food web interactions of cryptic taxa. We used DNA fecal-metabarcoding to look for unrecorded taxa within the diet of a generalist central-placed predator, the little penguin Eudyptula minor. We examined 208 scats from 106 breeding pairs throughout August-February in a large colony at Phillip Island, Australia. While we confirmed a largely piscivorous diet, we also recovered DNA sequences from gelatinous and crustaceous plankton groups that have not previously been detected in the little penguin diet using other diet analysis methods. Gelatinous plankton, including salps, appendicularians, scyphozoans, and hydrozoans were present in 76% of samples and represented 25% of all sequences. DNA recovered from minute copepods and appendicularians may indicate links between trophic levels through secondary predation. Percentage frequency of occurrence (%FOO) demonstrated that little penguin diet composition changed over months and stages (incubation, guard, and post-guard) of the breeding season (month: χ 2 = 201.91, df = NA, p < 0.01; stage: χ 2 = 33.221, df = NA, p = 0.015). Relative read abundance (RRA) uncovered variations in the relative abundance of taxa in the diet over months and stages (month: F = 53.18, df = 59, p < 0.001; stage: F = 66.56, df = 29, p < 0.001). The diet became progressively fish-focused over months of the season and stages, while salps were only present in 4 out of 6 months, with a peak in September. Based on their prevalence in this dataset, in this year of very high breeding success (2.15 chicks per pair), salps may constitute a food source for this largely piscivorous generalist. Our work highlights how DNA metabarcoding can improve our understanding of the trophic role of gelatinous plankton and other cryptic taxa.

Summary1. Ectotherms are taxa considered highly sensitive to rapid climate warming. This is because body temperature profoundly governs their performance, fitness and life history. Yet, while several modelling approaches currently predict thermal effects on some aspects of life history and demography, they do not consider how temperature simultaneously affects developmental success and offspring phenotypic performance, two additional key attributes that are needed to comprehensively understand species responses to climate warming. 2. Here, we developed a stepwise, individual-level modelling approach linking biophysical and developmental models with empirically derived performance functions to predict the effects of temperature-induced changes to offspring viability, phenotype and performance, using green sea turtle hatchlings as an ectotherm model. Climate warming is expected to particularly threaten sea turtles, as their life-history traits may preclude them from rapid adaptation. 3. Under conservative and extreme warming, our model predicted large effects on performance attributes key to dispersal, as well as a reduction in offspring viability. Forecast sand temperatures produced smaller, weaker hatchlings, which were up to 40% slower than at present, albeit with increased energy stores. Conversely, increases in sea surface temperatures aided swimming performance. 4. Our exploratory study points to the need for further development of integrative individualbased modelling frameworks to better understand the complex outcomes of climate change for ectotherm species. Such advances could better serve ecologists to highlight the most vulnerable species and populations, encouraging prioritization of conservation effort to the most threatened systems.

1. Detecting changes in marine food webs is challenging, but top predators can provide information on lower trophic levels. However, many commonly measured predator responses can be decoupled from prey availability by plasticity in predator foraging effort. This can be overcome by directly measuring foraging effort and success and integrating these into a measure of foraging efficiency analogous to the catch per unit effort (CPUE) index employed by fisheries.2. We extended existing CPUE methods so that they would be applicable to the study of generalist foragers, which introduce another layer of complexity through dietary plasticity. Using this method, we inferred species-specific patterns in prey availability and estimated taxon-specific biomass consumption.3. We recorded foraging trip duration and body mass change of breeding little penguins Eudyptula minor and combined these with diet composition identified via noninvasive faecal DNA metabarcoding to derive CPUE indices for individual prey taxa. 4. We captured weekly patterns of availability of key fish prey in the penguins' diet and identified a major prey shift from sardine Sardinops sagax to red cod Pseudophycis bachus between years. In each year, predation on a dominant fish species (~150 g/ day) was replaced by greater diversity of fish in the diet as the breeding season progressed. We estimated that the colony extracted ~1,300 tonnes of biomass from their coastal ecosystem over two breeding seasons, including 219 tonnes of the commercially important sardine and 215 tonnes of red cod. 5. This enhanced pCPUE is applicable to most central-placed foragers and offers a valuable alternative to existing metrics. Informed prey-species biomass estimates extracted by apex and meso predators will be a useful input for mass-balance ecosystem models and for informing ecosystem-based management.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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