Trophic niches of a seabird assemblage in Bass Strait, south-eastern Australia

Abstract

The foraging niches of seabirds are driven by a variety of factors, including competition for prey that promotes divergence in trophic niches. Bass Strait, south-eastern Australia, is a key region for seabirds, with little penguins Eudyptula minor, short-tailed shearwaters Ardenna tenuirostris, fairy prions Pachyptila turtur and common diving-petrels Pelecanoides urinatrix being particularly abundant in the region. The trophic niches of these species were investigated using isotopic values in whole blood and by identifying prey remains in stomach contents. The four species occupied different isotopic niches that varied among years, seasons and regions. Little penguins consumed mainly fish whereas the three procellariforms primarily consumed coastal krill Nyctiphanes australis. The dietary similarities between the procellariforms suggest that food resources are segregated in other ways, with interspecific differences in isotope niches possibly reflecting differential consumption of key prey, divergent foraging locations and depth, and differences in breeding phenology. Because oceanographic changes predicted to occur due to climate change may result in reduced coastal krill availability, adversely affecting these seabird predators, further information on foraging zones and feeding behaviour of small procellariform species is needed to elucidate more fully the segregation of foraging niches, the capacity of seabirds to adapt to climate change and the potential for interspecific competition in the region.

Temporal and spatial differences in the post-breeding behaviour of a ubiquitous Southern Hemisphere seabird, the common diving petrel

“…Conversely, this difference could be linked to the predictability of food resources in the vicinity of the breeding areas [ 83 ]. In southeastern Australia and New Zealand, the locally abundant coastal krill Nyctiphanes australis [ 82 ] is a key food source for CDP [ 34 ] (C. M. Miskelly 2019, personal observation). However, this euphausiid undergoes extreme inter-annual variations in biomass and distribution, considerably affecting the reproductive success of various fish [ 82 ] and seabird species [ 84 , 85 ].…”

“…While some studies have recently investigated the distribution of multiple populations of small petrels during this period, most have focused on a small proportion of populations and/or limited spatial range of the species [28,31]. The common diving petrel (CDP, Pelecanoides urinatrix) is a small procellariiform seabird (110-160 g) feeding on macrozooplankton [32][33][34]. This species breeds on numerous islands along a wide latitudinal gradient (35°-55°S) throughout the Atlantic, Indian and Pacific oceans, with an estimated 8-10 million breeding pairs (figure 1; [5]), though substantial differences in breeding phenology are evident among populations (figure 1).…”

Contrasting impacts of environmental variability on the breeding biology of two sympatric small procellariiform seabirds in south-eastern Australia

“…The present study documented inter-annual variations in the breeding phenology, chick growth and breeding success of FP and CDP breeding in northern Bass Strait, south-eastern Australia. Interestingly, these variations, which are likely to be related to shifts in food availability [55], differed between the species despite their consumption of similar prey [44].…”

“…To investigate the influence of environmental factors on breeding biology, monthly averages in sea surface temperature (SST) was obtained for areas considered important to the study species (Fig 1). The summer period plays a key role in the growth and reproduction of Australian krill (Nyctiphanes australis) in Bass Strait [52], the main prey of both FP and CDP [44]. Additionally, CDP have been observed to migrate during the post-breeding period to subantarctic regions [37] which may provide resources necessary for winter survival and preparation for subsequent breeding.…”

“…Considering 60% of Australian seabirds breed in Bass Strait [42], FP and CDP are especially at risk of interspecific competition for food in a changing ecosystem [33]. Relatively little is known of the ecology of these predominantly subantarctic species in south-eastern Australia [43,44]. Such information is crucial for understanding how they may respond to the rapidly changing conditions in the area.…”