title: Fat, weather, and date affect migratory songbirds' departure decisions, routes, and time it takes to cross the Gulf of Mexico.
abstract: Approximately two thirds of migratory songbirds in eastern North America negotiate the Gulf of Mexico (GOM), where inclement weather coupled with no refueling or resting opportunities can be lethal. However, decisions made when navigating such features and their consequences remain largely unknown due to technological limitations of tracking small animals over large areas. We used automated radio telemetry to track three songbird species (Red-eyed Vireo, Swainson's Thrush, Wood Thrush) from coastal Alabama to the northern Yucatan Peninsula (YP) during fall migration. Detecting songbirds after crossing ∼1,000 km of open water allowed us to examine intrinsic (age, wing length, fat) and extrinsic (weather, date) variables shaping departure decisions, arrival at the YP, and crossing times. Large fat reserves and low humidity, indicative of beneficial synoptic weather patterns, favored southward departure across the Gulf. Individuals detected in the YP departed with large fat reserves and later in the fall with profitable winds, and flight durations (mean = 22.4 h) were positively related to wind profit. Age was not related to departure behavior, arrival, or travel time. However, vireos negotiated the GOM differently than thrushes, including different departure decisions, lower probability of detection in the YP, and longer crossing times. Defense of winter territories by thrushes but not vireos and species-specific foraging habits may explain the divergent migratory behaviors. Fat reserves appear extremely important to departure decisions and arrival in the YP. As habitat along the GOM is degraded, birds may be limited in their ability to acquire fat to cross the Gulf.
authors.affiliation: Department of Biological Sciences, Eastern Illinois University, Charleston, IL 61920; jldeppe@eiu.edu.
authors.forename: Jill L
authors.initials: JL
authors.lastname: Deppe
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801;
authors.forename: Michael P
authors.initials: MP
authors.lastname: Ward
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801; US Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT 59715;
authors.forename: Rachel T
authors.initials: RT
authors.lastname: Bolus
authors.affiliation: US Geological Survey, Northern Rocky Mountain Science Center, Bozeman, MT 59715;
authors.forename: Robert H
authors.initials: RH
authors.lastname: Diehl
authors.affiliation: Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801;
authors.forename: Antonio
authors.initials: A
authors.lastname: Celis-Murillo
authors.affiliation: Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, MS 39406;
authors.forename: Theodore J
authors.initials: TJ
authors.lastname: Zenzal
authors.affiliation: Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, MS 39406;
authors.forename: Frank R
authors.initials: FR
authors.lastname: Moore
authors.affiliation: Illinois Natural History Survey, University of Illinois, Champaign, IL 61820;
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Benson
authors.affiliation: Department of Entomology and Wildlife Ecology, University of Delaware, Newark, DE 19716;
authors.forename: Jaclyn A
authors.initials: JA
authors.lastname: Smolinsky
authors.affiliation: Department of Biological Sciences, Eastern Illinois University, Charleston, IL 61920;
authors.forename: Lynn N
authors.initials: LN
authors.lastname: Schofield
authors.affiliation: Illinois Natural History Survey, University of Illinois, Champaign, IL 61820;
authors.forename: David A
authors.initials: DA
authors.lastname: Enstrom
authors.affiliation: US Geological Survey, Pacific Island Ecosystems Research Center, Hawaii National Park, HI 96718;
authors.forename: Eben H
authors.initials: EH
authors.lastname: Paxton
authors.affiliation: Department of Civil, Environmental and Geodetic Engineering, Ohio State University, Columbus, OH 43210;
authors.forename: Gil
authors.initials: G
authors.lastname: Bohrer
authors.affiliation: Illinois Natural History Survey, University of Illinois, Champaign, IL 61820;
authors.forename: Tara A
authors.initials: TA
authors.lastname: Beveroth
authors.affiliation: Illinois Natural History Survey, University of Illinois, Champaign, IL 61820;
authors.forename: Arlo
authors.initials: A
authors.lastname: Raim
authors.affiliation: Department of Civil, Environmental and Geodetic Engineering, Ohio State University, Columbus, OH 43210;
authors.forename: Renee L
authors.initials: RL
authors.lastname: Obringer
authors.affiliation: Construction Engineering Research Laboratory, United States Army Corps of Engineers, Champaign, IL 61822.
authors.forename: David
authors.initials: D
authors.lastname: Delaney
authors.affiliation: Illinois Natural History Survey, University of Illinois, Champaign, IL 61820;
authors.forename: William W
authors.initials: WW
authors.lastname: Cochran
mesh_terms: D000273:Adipose Tissue; D025041:Animal Migration / Q000502:physiology*; D000818:Animals; D060851:Gulf of America; D020308:Songbirds / Q000502:physiology*; D014887:Weather
keywords: Gulf of Mexico; ecological barrier; migration; songbirds; weather