1 –––––––––––––––––––––––––––––––––––––––– © 2020 Nordic Society Oikos. Published by John Wiley & Sons Ltd Subject Editor: Ronald C. Ydenberg Editor-in-Chief: Tomas Alerstam Accepted 17 November 2020 00: 1–12, 2020 doi: 10.1111/jav.02629 JOURNAL OF AVIAN BIOLOGY www.avianbiology.org Journal of Avian Biology 2021: e02629 Migrant shorebirds operate within a series of landscapes and must adjust their daily activities to achieve seasonal time and energy objectives. Night roosts are essential landscape elements that provide safety from predators for many shorebird species. What costs migrants incur to use night roosts and how these costs vary across stag- ing sites are poorly understood. We tracked 42 adult whimbrels Numenius phaeopus with satellite transmitters and used night locations to delineate 39 night roosts during spring and fall migration. We used daytime locations to measure round-trip commut- ing distances between night roosts and foraging areas and estimated daily commuting costs including distance, time and metabolic energy expenditure. We identifed night roosts on ofshore islands (n = 20) and onshore locations including along habitat edges (n = 13) and on topographic highs within extensive marshes (n = 6). Mean daily com- muting costs varied between roosts. Whimbrels took 3.9–52.1 min (median = 15.2) to fy 3.1–42.2 km (median = 12.3) which costs 6.1–82.4 kj (median = 22.3) in lean mass energy expenditure and 8.1–109.2 kj (median = 31.5) in leaving mass energy. Birds using ofshore roosts had twice the commuting distance and associated costs compared to those using onshore roosts. Te contribution of commuting costs to the premigratory energy budget ranged from 1.5 to 18.8% with costs for nearly 30% of roosts exceeding 10%. Commuting costs to and from night roosts appear to be biologically relevant within some staging sites and should be considered among other constraints faced by migrants during stopover periods when food or time is limiting. Keywords: fight costs, migration, night roosts, Numenius phaeopus, satellite tracking, Western Atlantic Flyway, whimbrel Communal roosts are essential landscape features for most shorebirds within migra- tory staging sites (Rogers 2003, Colwell 2010). Te daily, alternating pattern of individuals congregating within communal areas to rest and then dispersing through- out the surrounding landscape to forage is common across a wide range of species The costs of using night roosts for migrating whimbrels Bryan D. Watts, Fletcher M. Smith, Chance Hines, Laura Duval, Diana J. Hamilton, Tim Keyes, Julie Paquet, Lisa Pirie-Dominix, Jennie Rausch, Barry Truitt, Brad Winn and Paul Woodard B. D. Watts (https://orcid.org/0000-0001-8244-6951) ✉ (bdwatt@wm.edu), F. M. Smith, C. Hines and L. Duval, Center for Conservation Biology, College of William & Mary, Williamsburg, Virginia, USA. – D. J. Hamilton, Mount Allison Univ., Sackville, New Brunswick, Canada. – FMS and T. Keyes, Georgia Dept of Natural Resources, Wildlife Resources Division, Non-game Conservation Section, Brunswick, Georgia, USA. – J. Paquet, Canadian Wildlife Service, Environment and Climate Change Canada, Sackville, New Brunswick, Canada. – L. Pirie-Dominix, Canadian Wildlife Service, Environment and Climate Change Canada, Iqaluit, Nunavut, Canada. – J. Rausch and P. Woodard, Canadian Wildlife Service, Environment and Climate Change Canada, Yellowknife, Northwest Territories, Canada. – B. Truitt, Te Nature Conservancy’s Virginia Coast Reserve, Nassawadox, Virginia, USA. – B. Winn, Manoment Inc., Manomet, Massachusetts, USA. Article