The Wilson Journal of Ornithology 121(3):635–637, 2009 Description of the Nest and Eggs of the Black-cheeked Ant Tanager (Habia atrimaxillaris) Luis Sandoval 1,3 and Abraham Gallo 2 ABSTRACT.—The Black-cheeked Ant Tanager (Habia atrimaxillaris) is endemic to the Osa Peninsula on the south Pacific coast of Costa Rica. There is little knowledge of the natural history and especially the reproductive habits of this species. We describe the nest and eggs of the Black-cheeked Ant Tanager based on observations of three nests near Puerto Jime ´nez, Puntarenas, Costa Rica. The nests and eggs were similar to other species of Habia supporting previous work suggesting relationships within Habia. Received 8 October 2008. Accepted 3 February 2009. The five species of ant tanagers (Habia spp.) inhabit rainforests (0–1,800 m above sea level), throughout much of the Neotropics. The Black- cheeked Ant Tanager (H. atrimaxillaris) has the smallest distribution of the two widespread and three range-restricted species (Isler and Isler 1987, Stotz et al. 1996). It is restricted to forest edges and understory of primary and secondary forest in the Osa Peninsula on the south Pacific coast of Costa Rica (Isler and Isler 1987, Stiles and Skutch 1989). This narrow distribution has led to its classification as an endangered species by Bird- Life International (2007), as it is threatened by deforestation and urban development in the Golfo Dulce area. The last 20 years have witnessed a reduction in habitat availability for this species (Roxero-Bixby et al. 2002, Barrantes and Lobo 2005), likely with negative impacts on population size. Knowledge about the natural history of this ant tanager is poor, and nothing is known about its reproductive habits (Isler and Isler 1987, Stiles and Skutch 1989). This lack of information may hinder effective management and conservation. We describe the nest and eggs of the Black- cheeked Ant Tanager based on observations of three nests near Puerto Jime ´nez, Puntarenas, Costa Rica. METHODS Our study area was mature secondary forest at Bosque del Rı ´o Tigre Lodge (BRTL) and Rı ´o Pizote (08u 319 N, 83u 249 W), Puerto Jime ´nez, Puntarenas, at an elevation of 130 m. The habitat in the area is tropical wet forest, characterized by a canopy 30–40 m in height, where common tree species include Pterygota excelsa (Sterculiaceae), Schyzolobium parahyba (Caesalpinaceae), Brossi- mum utile (Moraceae), Ochroma lagopus (Bom- bacaceae), Goethalsia meiantha, and Trichosper- mum meiantha (Tiliaceae). The open understory includes abundant Heliconia spp. (Heliconaceae), Psycotria spp. (Rubiaceae), Calathea spp. (Mar- antaceae), and several species of palms (Cyclan- taceae and Arecaceae). We made daily observations from January to April 2007 at BRTL and once a week at Rı ´o Pizote from January to March 2007. Our nest descriptions are based on three nests, two of which were collected. We measured the inner diameter and depth at each nest collected with callipers. Two eggs were measured at one nest and the eggshells were collected after depreda- tion. All collected samples were deposited at Museo de Zoologı ´a, Escuela de Biologı ´a, Uni- versidad de Costa Rica. RESULTS Nesting Season.—We observed two adult Black-cheeked Ant Tanagers carrying vegetation fibers into a nest on 28 January 2007. The nest appeared nearly complete and was 68 cm above ground level in a Melastomataceae shrub in an area of open understory at the edge of secondary forest at BRTL. The nest contained two eggs on 4 February. A second, completely finished nest was found by E. Vargas, G. Flores, and P. Elizondo on 1 Escuela de Biologı ´a, Universidad de Costa Rica, San Pedro de Montes de Oca, Costa Rica. 2 Bosque del Rı ´o Tigre Lodge, Puerto Jime ´nez, Puntare- nas, Costa Rica. 3 Corresponding author; e-mail: biosandoval@hotmail.com SHORT COMMUNICATIONS 635