title: Human-Induced Long-Term Shifts in Gull Diet from Marine to Terrestrial Sources in North America's Coastal Pacific: More Evidence from More Isotopes (δ2H, δ34S).
abstract: Measurements of naturally occurring stable isotopes in tissues of seabirds and their prey are a powerful tool for investigating long-term changes in marine foodwebs. Recent isotopic (δ(15)N, δ(13)C) evidence from feathers of Glaucous-winged Gulls (Larus glaucescens) has shown that over the last 150 years, this species shifted from a midtrophic marine diet to one including lower trophic marine prey and/or more terrestrial or freshwater foods. However, long-term isotopic patterns of δ(15)N and δ(13)C cannot distinguish between the relative importance of lower trophic-level marine foods and terrestrial sources. We examined 48 feather stable-hydrogen (δ(2)H) and -sulfur (δ(34)S) isotope values from this same 150-year feather set and found additional isotopic evidence supporting the hypothesis that gulls shifted to terrestrial and/or freshwater prey. Mean feather δ(2)H and δ(34)S values (± SD) declined from the earliest period (1860-1915; n = 12) from -2.5 ± 21.4 ‰ and 18.9 ± 2.7 ‰, respectively, to -35.5 ± 15.5 ‰ and 14.8 ± 2.4 ‰, respectively, for the period 1980-2009 (n = 12). We estimated a shift of ∼ 30% increase in dependence on terrestrial/freshwater sources. These results are consistent with the hypothesis that gulls increased terrestrial food inputs in response to declining forage fish availability.
authors: Environment Canada , 11 Innovation Boulevard, Saskatoon, Saskatchewan S7N 3H5, Canada.
authors: Keith A
authors: KA
authors: Hobson
authors: Department of Forest and Conservation Sciences, University of British Columbia , Vancouver, British Columbia V6T 1Z4, Canada.|Procellaria Research & Consulting , 944 Dunsmuir Road, Victoria, British Columbia V9A 5C3, Canada.
authors: Louise K
authors: LK
authors: Blight
authors: Department of Forest and Conservation Sciences, University of British Columbia , Vancouver, British Columbia V6T 1Z4, Canada.
authors: Peter
authors: P
authors: Arcese
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D059001:Aquatic Organisms; D002247:Carbon Isotopes / Q000032:analysis; D046091:Charadriiformes / Q000502:physiology*; D004032:Diet; D005241:Feathers / Q000737:chemistry; D005399:Fishes; D020387:Food Chain; D005618:Fresh Water; D006801:Humans; D006859:Hydrogen / Q000032:analysis; D009587:Nitrogen Isotopes / Q000032:analysis; D009656:North America; D010140:Pacific Ocean; D011235:Predatory Behavior; D013460:Sulfur Isotopes / Q000032:analysis
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes; D013460:Sulfur Isotopes; D006859:Hydrogen