Moult location and diet of auks in the North Sea inferred from coupled light-based and isotopebased geolocation

Abstract

Many pelagic seabirds moult their feathers while at sea, which is an energetically costly behaviour. Mortality rates during moult can be high, so spatial and trophic ecology during this critical period is important for understanding demographic patterns. Unfortunately, individual foraging behaviours specifically linked to at-sea moulting are commonly unclear. This paper combines 2 different approaches to geolocation: data from bird-borne geolocation loggers and stableisotope assignment using carbon and nitrogen isotope maps (isoscapes). Coupling 2 geolocation processes allows some uncertainties associated with isotope-based assignment to be constrained. We applied this approach to quantify species-specific foraging locations and individual trophic variability during feather regrowth in 3 sympatric auk populations breeding on the Isle of May, Scotland (common guillemot Uria aalge, razorbill Alca torda and Atlantic puffin Fratercula arctica). Inferred foraging areas during moult differed between species and feather types. Guillemots likely underwent moult within the southern North Sea, razorbills along the east coast of England and into the southern North Sea and puffins off the east coast of Scotland. Estimates of individual trophic position varied considerably within feather types (up to 1 trophic level difference between individuals), among feather types grown during different time periods and across the 3 species, with guillemots consistently foraging at higher trophic positions than razorbills and puffins. Used in combination, these methods better constrain foraging areas during moulting, and provide a technique to explore individual differences and flexibility in foraging strategy, which is valuable information for both seabird conservation and marine spatial planning.

An environmental (pre)history of European fishing: past and future archaeological contributions to sustainable fisheries

“…In methodological terms, archaeological research demonstrating the trade of a widely distributed species such as G. morhua depends on recent advances in aDNA analysis (Boessenkool et al, ; Star et al, ) and the creation of baseline isoscapes to which stable‐isotope data from archaeological specimens can be compared (Barrett et al, ; Barrett et al, ; Hutchinson et al, ). Early developments in the isotopic provenancing of fishes emerged from within archaeology but are now being augmented greatly by isotope ecologists to trace predator migration and to source marketed fish products (St. John Glew et al, ; Trueman et al, ). The resulting methodological advances are likely, in turn, to enhance archaeological studies of fish trade and of long‐term anthropogenic and environmental effectss on the aquatic environment (Section 4).…”

Effects of body size, sex, parental care and moult strategies on auk diving behaviour outside the breeding season

“…Most species of seabird are seasonal breeders and typically experience varying extrinsic conditions throughout their annual cycle. During the breeding season, individual seabird foraging strategies vary intrinsically depending on sex (Kato et al , Bearhop et al , Welcker et al ), age (Grecian et al ), parental role (Weimerskirch et al ) and social dominance (González‐Solís et al ). The effect of sex on foraging strategy is often associated with size dimorphism, as size differences give rise to competitive exclusion and cause sex‐specific niche specialization via trophic segregation or spatial partitioning (González‐Solís et al , Phillips et al ).…”

“…The scheduling of moult in puffins seems much more variable but typically occurs later than in guillemots and razorbills, with peaks in October and March (Harris et al ). Due to the energetic constraints of moult, coupled with flightlessness (Bridge ), moulting auks are thought to favour productive, sheltered areas with predicable prey (Peery et al , Linnebjerg et al ). However, while it is known that auks continue to dive during their primary wing moult, how their diving capabilities are affected is currently equivocal (Elliott and Gaston ).…”

“…These interspecific differences in body size, post‐fledging parental strategies and moult schedules are superimposed on seasonally changing environmental conditions during the autumn and first half of the winter (Fort et al , Daunt et al ). Guillemots, razorbills and puffins from the Isle of May are predominantly located within shelf areas in the North Sea and northeast Atlantic during the post‐breeding period and throughout the early winter months (Harris et al , 2013, 2015a, St John Glew et al ). Auk post‐parental care and primary moult both occur before the autumnal equinox when days are comparatively long and the weather in the region is relatively benign.…”

“…Therefore, as light availability limits foraging opportunities (Regular et al ), the majority of their diving occurs during daylight hours (Dall'Antonia et al 2001) and may become constrained (both temporally and in depth) during the post‐breeding period. Seabirds are prone to winter wrecks and high mortality rates during this period (Harris and Wanless , 1996, Fort et al , 2013, McFarlane Tranquilla et al ), as well as increased energetic requirements (Elliott and Gaston , Burke and Montevecchi ). Throughout these seasonal changes in extrinsic conditions, auks must forage sufficiently to acquire enough energy to successfully thermoregulate whilst also building up fat reserves (Fort et al , Fayet et al , Anker‐Nilssen et al ).…”