Long‐term individual foraging site fidelity—why some gannets don't change their spots

Abstract

Long-term individual foraging site fidelitywhy some gannets don't change their spots. Ecology, 96(11), There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.http://eprints.gla.ac.uk/113930/ shown that individual foraging site fidelity (IFSF -when individuals consistently forage in only a 19 small part of their population's home range) occurs in some colonial breeders. Short-term IFSF 20 could result from animals using a win-stay, lose-shift (WSLS) foraging strategy. Alternatively, it 21 may be a consequence of other forms of individual specialisation. Pelagic seabirds are colonial 22 central-place foragers, classically assumed to use flexible foraging strategies to target widely 23 2 dispersed, spatiotemporally patchy prey. However, tracking has shown that IFSF occurs in many 24 seabirds, although it is not known whether this persists across years. To test for long-term IFSF 25 and to examine alternative hypotheses concerning its cause, we repeatedly tracked 55 northern 26 gannets from a large colony in the North Sea within and across three successive breeding 27 seasons. Gannets foraged in neritic waters, predictably structured by tidal mixing and thermal 28 stratification but subject to stochastic wind-induced overturning. Both within and across years, 29 coarse to mesoscale (10s km) IFSF was significant but not absolute and foraging birds departed 30 the colony in individually consistent directions. Carbon stable isotope ratios in gannet blood 31 tissues were repeatable within years and nitrogen ratios were also repeatable across years, 32 suggesting long-term individual dietary specialisation. Individuals were also consistent across 33 years in habitat use with respect to relative sea surface temperature and in some dive metrics yet 34 none of these factors accounted for IFSF. Moreover, at the scale of weeks, IFSF did not decay 35 over time and the magnitude of IFSF across years was similar to that within years, suggesting 36 that IFSF is not primarily the result of WSLS foraging. Rather, we hypothesise that site 37 familiarity, accrued early in life, causes IFSF by canalising subsequent foraging decisions. 38Evidence from this and other studies suggests that IFSF may be common in colonial central-39 place foragers, with far-reaching consequences for our attempts to understand and conserve these 40 animals in a rapidly changing environment. 41 42

Methods for detecting and quantifying individual specialisation in movement and foraging strategies of marine predators

“…Ecologists have often treated conspecific individuals as broadly equivalent, after accounting for age, sex and other group effects (Bolnick et al 2003, Yama moto et al 2014, Wakefield et al 2015. However, there is increasing realisation that individuals in many animal populations differ substantially in resource use ('niche variation'), and the term 'individual specialisation' has been used to describe heterogeneity in resource use , Patrick et al 2014.…”

“…Moreover, if a wide range of habitats and resources are used, a particular species or population may be better buffered against anthropogenic impacts, as individuals are likely to respond in different ways to changes in the environment (Tinker et al 2008, Dias et al 2011, Masello et al 2013. Hence, the characterisation of divergent behaviour or strategies may provide important in sights into the ecology, evolution, conservation and management of the species (Thiemann et al 2011, Wakefield et al 2015, Ramírez et al 2016.…”

“…Individual specialisation and behavioural consistency are known to be widespread across a range of taxa and behaviours; they have been demonstrated for a number of species of marine predators in foraging behaviour, migratory routes, dive characteristics, diet, timing of events, activity patterns and habitat choice, and foraging site fidelity during breeding and non-breeding periods (Hoelzel et al 1989, Staniland et al 2004, Sargeant et al 2005, Guilford et al 2011, Thiebot et al 2011, Patrick et al 2014, Yamamoto et al 2014, Wakefield et al 2015. Because marine predators forage on highly patchy and more or less predictable food resources at the coarse-to meso-scale (tens to hundreds of kilometres) and over days and weeks, the incidence of specialisation is unsurprising (Weimerskirch 2007, Wakefield et al 2015.…”

“…Because marine predators forage on highly patchy and more or less predictable food resources at the coarse-to meso-scale (tens to hundreds of kilometres) and over days and weeks, the incidence of specialisation is unsurprising (Weimerskirch 2007, Wakefield et al 2015. The recurrent use of similar areas may increase familiarity with feeding conditions, including fine-scale resource availability and distribution (Hamer et al 2007, Ramírez et al 2016.…”

“…The recurrent use of similar areas may increase familiarity with feeding conditions, including fine-scale resource availability and distribution (Hamer et al 2007, Ramírez et al 2016. Marine predators will often target regions characterised by local physical features or processes, including eddies, frontal systems, upwelling zones and shelf breaks, that increase primary production or serve to aggregate various types of prey (Kappes et al 2010, Louzao et al 2011, Pinet et al 2011, Baylis et al 2012, Arthur et al 2015, Wakefield et al 2015. Foraging behaviour and diet specialisations may therefore emerge as a result of the spatial and temporal availability and predictability of prey (Woo et al 2008, Navarro & González-Solís 2009, Patrick et al 2015, Sommerfeld et al 2015.…”