Linking extreme interannual changes in prey availability to foraging behaviour and breeding investment in a marine predator, the macaroni penguin

Abstract

Understanding the mechanisms that link prey availability to predator behaviour and population change is central to projecting how a species may respond to future environmental pressures. We documented the behavioural responses and breeding investment of macaroni penguins Eudyptes chrysolophus across five breeding seasons where local prey density changed by five-fold; from very low to highly abundant. When prey availability was low, foraging trips were significantly longer and extended overnight. Birds also foraged farther from the colony, potentially in order to reach more distant foraging grounds and allow for increased search times. These extended foraging trips were also linked to a marked decrease in fledgling weights, most likely associated with reduced rates of provisioning. Furthermore, by comparing our results with previous work on this population, it appears that lowered first-year survival rates associated, at least partially, with fledging masses were also evident for this cohort. This study integrates a unique set of prey density, predator behaviour and predator breeding investment data to highlight a possible behavioural mechanism linking perturbations in prey availability to population demography.

Targeted prey fields determine foraging effort thresholds of a marine diver: Important cues for the sustainable management of fisheries

“…Foraging performance of breeding seabirds has been linked to chick condition (Horswill, Trathan, & Ratcliffe, 2017;Pinaud, Cherel, & Weimerskirch, 2005), reproductive success (Dee Boersma & Rebstock, 2009;Piatt et al, 2007) and population growth (Lewis et al, 2006) yet, there are few data linking foraging performance and measures of prey availability concurrently (but see Boyd et al, 2015;Carroll et al, 2017). This study presents a unique account of functional relationships between seabird foraging performance and prey availability facilitated by a comparison between a representative sample of birds simultaneously deployed on survey days that spanned a temporal range of informative variation in prey availability.…”

Important marine areas for the conservation of northern rockhopper penguins within the Tristan da Cunha Exclusive Economic Zone

“…We found temporal and spatial consistency in the areas used during brood-guard trips from the same colonies on Nightingale and Gough across years. Similarly, macaroni penguins at South Georgia were largely consistent in the areas used during broodguard across 5 years, although they ranged more widely in 1 year when food availability was low (Horswill et al 2017). Likewise, trip durations for southern rockhopper penguins on Staten Island, Argen tina, were consistent across 2 years during both broodguard and crèche stages (Raya Rey et al 2007).…”

Changes in prey fields increase the potential for spatial overlap between gentoo penguins and a krill fishery within a marine protected area

“…These lines of evidence show that krill availability in 2001 was sufficient for gentoo penguins to meet their nutritional requirements during short‐range day trips, but low abundance and patchy distribution of krill in 2018 forced them to perform multi‐day trips that extended out to the shelf edge. Similarly, female macaroni penguins at South Georgia extended their foraging ranges and durations in a year of poor krill availability (Horswill et al., 2017) and African penguins Spheniscus demersus in South Africa performed longer duration trips as prey abundance within 40 m of the surface declined (McInnes et al., 2019).…”

“…As residents, gentoo penguins share the South Georgia shelf with the krill fishery during winter, but NTZ1 was believed to prevent their spatial overlap (Handley et al., 2020) based on limited tracking data from a single year that showed birds remain within 17 km of shore (Tanton et al., 2004). However, breeding macaroni penguins Eudyptes chrysolophus at South Georgia extend their foraging ranges when krill is scarce (Horswill et al., 2017). If gentoo penguins respond in a similar way during winter, then low krill availability might elevate the risk of them overlapping with the krill fishery, potentially exacerbating reductions in foraging success in years when food is scarce.…”