title: Decadal declines in avian herbivore reproduction: density-dependent nutrition and phenological mismatch in the Arctic.
abstract: A full understanding of population dynamics depends not only on estimation of mechanistic contributions of recruitment and survival, but also knowledge about the ecological processes that drive each of these vital rates. The process of recruitment in particular may be protracted over several years, and can depend on numerous ecological complexities until sexually mature adulthood is attained. We addressed long-term declines (23 breeding seasons, 1992-2014) in the per capita production of young by both Ross's Geese (Chen rossii) and Lesser Snow Geese (Chen caerulescens caerulescens) nesting at Karrak Lake in Canada's central Arctic. During this period, there was a contemporaneous increase from 0.4 to 1.1 million adults nesting at this colony. We evaluated whether (1) density-dependent nutritional deficiencies of pre-breeding females or (2) phenological mismatch between peak gosling hatch and peak forage quality, inferred from NDVI on the brood-rearing areas, may have been behind decadal declines in the per capita production of goslings. We found that, in years when pre-breeding females arrived to the nesting grounds with diminished nutrient reserves, the proportional composition of young during brood-rearing was reduced for both species. Furthermore, increased mismatch between peak gosling hatch and peak forage quality contributed additively to further declines in gosling production, in addition to declines caused by delayed nesting with associated subsequent negative effects on clutch size and nest success. The degree of mismatch increased over the course of our study because of advanced vegetation phenology without a corresponding advance in Goose nesting phenology. Vegetation phenology was significantly earlier in years with warm surface air temperatures measured in spring (i.e., 25 May-30 June). We suggest that both increased phenological mismatch and reduced nutritional condition of arriving females were behind declines in population-level recruitment, leading to the recent attenuation in population growth of Snow Geese.
authors.affiliation: Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada.
authors.forename: Megan V
authors.initials: MV
authors.lastname: Ross
authors.affiliation: Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada.|Environment and Climate Change Canada, 115 Perimeter Road, Saskatoon, Saskatchewan, S7N 0X4, Canada.
authors.forename: Ray T
authors.initials: RT
authors.lastname: Alisauskas
authors.affiliation: U.S. Geological Survey Alaska Science Center, 250 Egan Drive, Juneau, Alaska, 99801, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Douglas
authors.affiliation: Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan, S7N 5E2, Canada.|Environment and Climate Change Canada, 115 Perimeter Road, Saskatoon, Saskatchewan, S7N 0X4, Canada.
authors.forename: Dana K
authors.initials: DK
authors.lastname: Kellett
mesh_terms: D000818:Animals; D001110:Arctic Regions; D002170:Canada; D005260:Female; D005777:Geese / Q000502:physiology*; D060434:Herbivory; D012098:Reproduction; D012621:Seasons
keywords: 
  Chen caerulescens caerulescens
  ; 
  Chen rossii
  ; Arctic; breeding phenology; climate change; density dependence; ecological mismatch; geese; nutrient reserves