AmericanOrnithology.org Volume 123, 2021, pp. 1–14 DOI: 10.1093/ornithapp/duaa064 RESEARCH ARTICLE The Colorado River Delta and California’s Central Valley are critical regions for many migrating North American landbirds Downloaded from https://academic.oup.com/condor/advance-article/doi/10.1093/ornithapp/duaa064/6119082 by guest on 26 January 2021 William V. DeLuca,1,*, Tim Meehan,2 Nat Seavy,3, Andrea Jones,4 Jennifer Pitt,2 Jill L. Deppe,5 and Chad B. Wilsey6, 1 National Audubon Society, Amherst, Massachusetts, USA 2 National Audubon Society, Boulder, Colorado, USA 3 National Audubon Society, Forestville, California, USA 4 National Audubon Society, Sacramento, California, USA 5 National Audubon Society, Washington, District of Columbia, USA 6 National Audubon Society, San Francisco, California, USA * Corresponding author:
[email protected] Submission Date: June 3, 2020; Editorial Acceptance Date: September 24, 2020; Published January 26, 2021 ABSTRACT Migration is an important component of some species full annual cycle. California’s Central Valley and the Colorado River Delta provide important riparian and wetland habitats for migrating waterbirds in the arid west of North America, but little is known about whether these locations are important at the population level to migrating landbirds. We used eBird Status and Trends abundance data to quantify the importance of the Central Valley and Colorado River Delta to landbirds by estimating the proportion of the breeding population of 112 species that use each site during migration. We found that ~17 million landbirds use the Colorado River Delta in the spring and ~14 million in the fall. Across 4 study regions in the Central Valley, up to ~65 million landbirds migrate through in the spring and up to ~48 million in the fall.