title: Large herbivores surf waves of green-up during spring.
abstract: The green wave hypothesis (GWH) states that migrating animals should track or 'surf' high-quality forage at the leading edge of spring green-up. To index such high-quality forage, recent work proposed the instantaneous rate of green-up (IRG), i.e. rate of change in the normalized difference vegetation index over time. Despite this important advancement, no study has tested the assumption that herbivores select habitat patches at peak IRG. We evaluated this assumption using step selection functions parametrized with movement data during the green-up period from two populations each of bighorn sheep, mule deer, elk, moose and bison, totalling 463 individuals monitored 1-3 years from 2004 to 2014. Accounting for variables that typically influence habitat selection for each species, we found seven of 10 populations selected patches exhibiting high IRG-supporting the GWH. Nonetheless, large herbivores selected for the leading edge, trailing edge and crest of the IRG wave, indicating that other mechanisms (e.g. ruminant physiology) or measurement error inherent with satellite data affect selection for IRG. Our evaluation indicates that IRG is a useful tool for linking herbivore movement with plant phenology, paving the way for significant advancements in understanding how animals track resource quality that varies both spatially and temporally.
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA jmerkle@uwyo.edu.
authors.forename: Jerod A
authors.identifier: 0000-0003-0100-1833
authors.initials: JA
authors.lastname: Merkle
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA Haub School of Environment and Natural Resources, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Kevin L
authors.initials: KL
authors.lastname: Monteith
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Ellen O
authors.initials: EO
authors.lastname: Aikens
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Matthew M
authors.initials: MM
authors.lastname: Hayes
authors.affiliation: Utah Division of Wildlife Resources, Salt Lake City, UT 84114, USA.
authors.forename: Kent R
authors.initials: KR
authors.lastname: Hersey
authors.affiliation: Yale School of Forestry and Environmental Studies, New Haven, CT 06511, USA.
authors.forename: Arthur D
authors.initials: AD
authors.lastname: Middleton
authors.affiliation: Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Brendan A
authors.initials: BA
authors.lastname: Oates
authors.affiliation: Western Ecosystems Technology, Inc., Laramie, WY 82001, USA.
authors.forename: Hall
authors.initials: H
authors.lastname: Sawyer
authors.affiliation: Wyoming Game and Fish Department, Pinedale, WY 82941, USA.
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Scurlock
authors.affiliation: U.S. Geological Survey, Wyoming Cooperative Fish and Wildlife Research Unit, Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Kauffman
mesh_terms: D025041:Animal Migration; D000818:Animals; D016164:Bison; D003670:Deer; D017753:Ecosystem; D060434:Herbivory; D010944:Plants; D012621:Seasons; D012756:Sheep; D062211:Spatio-Temporal Analysis
keywords: forage maturation hypothesis; green wave hypothesis; habitat selection; large herbivores; migration; normalized difference vegetation index