The Osaplace Peninsula is in the South Pacific region of Costa Rica supporting some of the letter largesthere stands of mature tropical forest left on the Pacific coast of Mesoamerica. The Osa is well known for being one of the most biologically intense places on earth holding 2.5% of the world’s biodiversity. It is an extremely important wintering area for Neotropical migratory birds and well over half of Costa Rica’s avifauna including a handful of threatened and endemic species. This checklist includes birds from the Osa Peninsula and the entire Osa Conservation Area (ACOSA) where you will find nearly 500 species spread across 15 parks, reserves and refuges including Costa Rica’s crown jewel Corcovado National Park. These irreplaceable protected areas conserve a wide range of natural habitats that offer visitors the opportunity to enjoy birds in breathtaking settings. The taxonomy and nomenclature follow the American Ornithological Society (AOS) checklist of North and Middle American birds, 7th Edition. The sequence of family order follows "The Birds of Costa Rica: A Field Guide" by Richard Garrigues for easy reference in the field. Key to Residency M = Migratory Neotropical migratory birds PM = Passage Migrant Birds that migrate through the area but don’t stay E = Endemic Birds that are endemic to Costa Rica RE = Regional Endemic Birds that are endemic to Costa Rica and Panama M/Res = Migrant/Resident Birds that have both resident and migrant populations BM = Breeding Migrant Birds that migrate to Costa Rica to breed Key to Abundance C = Common Could be seen daily U = Uncommon Not seen daily or only locally common to specific areas R = Rare Found a few times a year or endangered found in their restricted habitat Ca = Casual Not expected but has happened Acc = Accidental One or two records Unk = Unknown Needs more information * International Union for the Conservation of Nature (IUCN) red list species are listed and highlighted in red. The Front Cover: This image is the Scarlet Macaw, an iconic bird that is abundant on the Osa Peninsula. This beautiful species has lost a considerable amount of habitat across the Central American portion of its range. Fortunately, the Osa is one of the Scarlet Macaws’ remaining strongholds in Central America and can be found just about anywhere! Photo credits pg 2; Black-cheeked Ant-Tanager by Manuel Sanchez, Scarlet Macaw by Alan Dahl—Focused on Nature and the Yellow-billed Cotinga by Karen Leavelle. 19 2 Abundance Residency, Baltimore Oriole Icterus galbula M, C place place Shinyletter Cowbird Molothrus bonariensis C Checklist of Birds: Osa Region letter here here Bronzed Cowbird Molothrus aeneus C Lista de Aves: Area de Conservacion Osa (ACOSA) Giant Cowbird Molothrus oryzivorus U Melodious Blackbird Dives dives C Family Tinamidae (Tinamous) Great-tailed Grackle Quiscalus mexicanus C Great Tinamou (NT: IUCN) Tinamus major C Crested Oropendola Psarocolius decumanus U Little Tinamou Crypturellus soui C Montezuma Oropendola Psarocolius montezuma U Family Cracidea (Curassows, Chachalacas, Guans) Family Fringillidae (Euphonias) Gray-headed Chachalaca Ortalis cinereiceps C Yellow-crowned Euphonia Euphonia luteicapilla C Crested Guan Penelope purpurascens C Thick-billed Euphonia Euphonia laniirostris C Great Curassow (VU: IUCN) Crax rubra U Yellow-throated Euphonia Euphonia hirundinacea C Family Odontophoridae (New World Quail) Elegant Euphonia Euphonia elegantissima U Marbled Wood-Quail Odontophorus gujanensis U Spot-crowned Euphonia Euphonia imitans RE, C Crested Bobwhite Colinus cristatus R White-vented Euphonia Euphonia minuta C Family Heliornithidae (Sungrebe) Sungrebe Heliornis fulica UNK Family Podicipedidae (Grebes) This checklist of North and Middle American birds follows the American Ornithological Least Grebe Tachybaptus dominicus C Society (AOS); the official source for taxonomy and nomenclature of birds found in this Pied-billed Grebe Podilymbus podiceps U region. It incorporates changes through the 61st supplement 7th edition. The Family Anatidae (Ducks) sequence of family order follows "The Birds of Costa Rica: A Field Guide" by Richard Black-bellied Whistling-Duck Dendrocygna autumnalis C Garrigues for easy reference in the field. Muscovy Duck Cairina moschata C The Auk, Volume 137, Issue 3, 1 July 2020, ukaa030, https://doi.org/10.1093/auk/ Blue-winged Teal Spatula discors M, C ukaa030 Cinnamon Teal Spatula cyanoptera M, R Northern Shoveler Spatula clypeata M, U American Wigeon Mareca americana M, R A place for notes….