title: From video recordings to whisker stable isotopes: a critical evaluation of timescale in assessing individual foraging specialisation in Australian fur seals.
abstract: Estimating the degree of individual specialisation is likely to be sensitive to the methods used, as they record individuals' resource use over different time-periods. We combined animal-borne video cameras, GPS/TDR loggers and stable isotope values of plasma, red cells and sub-sampled whiskers to investigate individual foraging specialisation in female Australian fur seals (Arctocephalus pusillus doriferus) over various timescales. Combining these methods enabled us to (1) provide quantitative information on individuals' diet, allowing the identification of prey, (2) infer the temporal consistency of individual specialisation, and (3) assess how different methods and timescales affect our estimation of the degree of specialisation. Short-term inter-individual variation in diet was observed in the video data (mean pairwise overlap = 0.60), with the sampled population being composed of both generalist and specialist individuals (nested network). However, the brevity of the temporal window is likely to artificially increase the level of specialisation by not recording the entire diet of seals. Indeed, the correlation in isotopic values was tighter between the red cells and whiskers (mid- to long-term foraging ecology) than between plasma and red cells (short- to mid-term) (R(2) = 0.93-0.73 vs. 0.55-0.41). δ(13)C and δ(15)N values of whiskers confirmed the temporal consistency of individual specialisation. Variation in isotopic niche was consistent across seasons and years, indicating long-term habitat (WIC/TNW = 0.28) and dietary (WIC/TNW = 0.39) specialisation. The results also highlight time-averaging issues (under-estimation of the degree of specialisation) when calculating individual specialisation indices over long time-periods, so that no single timescale may provide a complete and accurate picture, emphasising the benefits of using complementary methods.
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia. lkernale@deakin.edu.au.
authors.forename: Laëtitia
authors.initials: L
authors.lastname: Kernaléguen
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
authors.forename: Nicole
authors.initials: N
authors.lastname: Dorville
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
authors.forename: Daniel
authors.initials: D
authors.lastname: Ierodiaconou
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Hoskins
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.|South Atlantic Environmental Research Institute, Stanley, FIQQ1ZZ, Falkland Islands.
authors.forename: Alastair M M
authors.initials: AM
authors.lastname: Baylis
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Sandy Bay, TAS, Australia.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hindell
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Sandy Bay, TAS, Australia.
authors.forename: Jayson
authors.initials: J
authors.lastname: Semmens
authors.affiliation: National Geographic, Remote Imaging Department, Washington, DC, 20036, USA.
authors.forename: Kyler
authors.initials: K
authors.lastname: Abernathy
authors.affiliation: National Geographic, Remote Imaging Department, Washington, DC, 20036, USA.
authors.forename: Greg J
authors.initials: GJ
authors.lastname: Marshall
authors.affiliation: Centre d'Etudes Biologiques de Chizé, UMR 7372 du CNRS-Université de La Rochelle, 79360, Villiers-En-Bois, France.
authors.forename: Yves
authors.initials: Y
authors.lastname: Cherel
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC, 3125, Australia.
authors.forename: John P Y
authors.initials: JP
authors.lastname: Arnould
mesh_terms: D000818:Animals; D001315:Australia; D002247:Carbon Isotopes / Q000032:analysis*; D004032:Diet; D017753:Ecosystem; D004912:Erythrocytes / Q000737:chemistry; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D046069:Fur Seals / Q000502:physiology*; D009587:Nitrogen Isotopes / Q000032:analysis*; D012621:Seasons; D013997:Time Factors; D014738:Vibrissae / Q000737:chemistry*; D014741:Video Recording
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes
keywords: Arctocephalus pusillus; Diet; Nested network; Time aggregating; Vibrissae