Cross‐Validation of Diet Determination Methods for Seabird Conservation

ABSTRACT Seabirds are recognized as one of the most vulnerable groups of birds, with around a third of species identified as globally threatened. The conservation of seabirds is often linked with their feeding and diet, due to undesirable interactions with human‐related fishing activities and fisheries depletion/climate change impacting food resources. Therefore, understanding the diet of seabirds is often a critical first step towards identifying effective conservation measures. DNA metabarcoding and hard parts analyses provide a foundation for assessing the diet of predatory seabird species, giving insight into predator–prey relationships and ecosystem‐wide food webs. Congruency between these two methods would increase confidence, providing validation that either method provides a reliable representation of the diet. This study on the diet of the endangered New Zealand king shag (Leucocarbo carunculatus) compared the frequency of occurrence of fishes detected from the same regurgitated pellets (n = 191) using both hard parts and DNA metabarcoding methodologies. The number of pellets with overlapping fish families showed a significant positive correlation between methods (r = 0.96; p < 0.001), with 50 out of 191 pellets showing complete alignment and only two pellets without any alignment. Both methods confirmed the predominance of Bothidae (DNA: 71% of pellets, hard parts: 77%, total: 80%) and Rhombosoleidae (DNA: 45%, hard parts: 51%, total: 59%) taxa in the diet of king shags, while also revealing the consumption of a diversity of other fish species. Overall, this study demonstrates that the two methods provide a complementary approach for revealing the dominant fish prey species in the diet, as well as providing an overview of the diversity of prey species (DNA: 14 unique species, hard parts: 8, total: 28). However, the inexact alignment between the two methods for detecting every taxon in every pellet suggests differences in detection, especially for less common taxa and for DNA metabarcoding, where species‐level resolution is dependent on adequate DNA database sequence entries of taxa in the local area. In addition, filtering thresholds for DNA metabarcoding further influenced alignment. Overall, the results indicate that both methods provide consistent detection of major prey items; however, reliably capturing the full diversity of prey species with either method is reliant on a sufficient sample size

Meadowbirds on the horizon of southwest Friesland:Insights of the International Wader Study Group workshop, 28 September 2018

Internationale ecologische kennis die de landbouw in Zuidwest-Friesland met biodiversiteit verbindt / Harvesting international ecological knowledge to connect farming practices in the southwest of Friesland with biodiversit

The nutritional nexus: Linking niche, habitat variability and prey composition in a generalist marine predator

International audienceOur understanding of the niche concept will remain limited while the quantity and range of different food types eaten remain a dominant proxy for niche breadth, as this does not account for the broad ecological context that governs diet. Linking nutrition, physiology and behaviour is critical to predict the extent to which a species adjusts its nutritional niche breadth at the levels of prey (“prey composition niche,” defined as the range of prey compositions eaten) and diet (“realized nutritional niche” is the range of diets composed through feeding on the prey).Here, we studied adult chick‐rearing Australasian gannets Morus serrator to propose an integrative approach using sea surface temperature anomalies (SSTa), geographic location and bathymetry over different years, to explore their relationship with the nutritional composition of prey and diets (i.e. prey composition and nutritional niche breadth), habitat use and foraging behaviour.We found that gannets feed on prey that varied widely in their nutritional composition (have a broad prey composition niche), and composed diets from these prey that likewise varied in composition (have a broad realized nutritional niche), suggesting generalism at two levels of macronutrient selection.Across seasons, we established “nutritional landscapes” (hereafter nutriscapes), linking the nutritional content of prey (wet mass protein‐to‐lipid ratio—P:L) to the most likely geographic area of capture and bathymetry. Nutriscapes varied in their P:L from 6.06 to 15.28, over time, space and bathymetry (0–150 m).During warm water events (strong positive SSTa), gannets expanded their foraging habitat, increased their foraging trip duration and consumed prey and diets with low macronutrient content (wet mass proportions of P and L). They were also constrained to the smallest prey composition and realized nutritional niche breadths.Our findings are consistent with previous suggestions that dietary generalism evolves in heterogeneous environments, and provide a framework for understanding the nutritional goals in wild marine predators and how these goals drive ecological interactions and are, in turn, ultimately shaped by environmental fluctuations

Data on foraging behavior, prey and diet composition in Australasian gannets, Farewell Spit (New Zealand)

The package contains six data sets on foraging behavior, prey and diet composition of Australasian gannets at Farewell Spit (New Zealand)

Table_1_Interacting Roles of Breeding Geography and Early-Life Settlement in Godwit Migration Timing.docx

While avian migration timing is clearly influenced by both breeding and non-breeding geography, it is challenging to identify the relative and interdependent roles of endogenous programs, early-life experience, and carry-over effects in the development of adult annual schedules. Bar-tailed godwits Limosa lapponica baueri migrate northward from New Zealand toward Asian stopover sites during the boreal spring, with differences in timing between individuals known to relate to their eventual breeding-ground geography in Alaska. Here, we studied the timing of northward migration of individual godwits at three sites spanning 1,100 km of New Zealand’s 1,400-km length. A lack of morphological or genetic structure among sites indicates that the Alaskan breeding population mixes freely across all sites, and larger birds (southern breeders) tended to migrate earlier than smaller birds (northern breeders) at all sites. However, we unexpectedly found that migration timing varied between the sites, with birds from southern New Zealand departing on average 9.4–11 days earlier than birds from more northerly sites, a difference consistent across 4 years of monitoring. There is no obvious adaptive reason for migration timing differences of this magnitude, and it is likely that geographic variation in timing within New Zealand represents a direct response to latitudinal variation in photoperiod. Using resightings of marked birds, we show that immature godwits explore widely around New Zealand before embarking on their first northward migration at age 2–4 years. Thus, the process by which individual migration dates are established appears to involve: (1) settlement by sub-adult godwits at non-breeding sites, to which they are highly faithful as adults; (2) a consequent response to environmental cues (i.e., photoperiod) that sets the local population’s migration window; and (3) endogenous mechanisms, driven by breeding geography, that establish and maintain the well-documented consistent differences between individuals. This implies that behavioral decisions by young godwits have long-lasting impacts on adult annual-cycle schedules, but the factors guiding non-breeding settlement are currently unknown.</p