Cerulean Warbler – first migrant warblers arrive

Cerulean Warbler (Setophaga cerulea): Reinita cerúlea; Pappelwaldsänger; Paruline azurée

The Cerulean Warbler is usually among the first warbler migrants to arrive in Costa Rica from the north on its way to its chief wintering quarters in the northern Andes. Its German name, Pappelwaldsänger (literally, poplar forest-singer), is helpful because it refers to its preference for ‘poplar’ trees. Here, ‘poplar’ really means cottonwoods or aspens, commonly found in North America, but in Costa Rica and in its wintering grounds in South America the species is said to favour coffee plantations with shade trees, where they prefer to forage fairly high in the canopy.

This immature or female bird below was found by John and Milena at Aquiares and was initially difficult to identify:

Early migrant: Cerulean Warbler in the Aquiares coffee fields; photo by John Beer

Warblers just won’t sit still for the photographer!

If only an adult male had been present! Cerulean Warbler near the Aquiares laguna; photo by John Beer

Here’s a good look at a file photo of an adult male:

Male Cerulean Warbler; courtesy of Guillermo Saborío

The light-blue plumage of the male is quite distinctive but most migrants are either immatures or females and, as already noted, you have to be very careful with identifying these. I think that often in the past I must have either misidentified or overlooked them because they are regularly found in small numbers in the Turrialba area. They have very little of the blue tones of the handsome male, whose often quite bright blue plumage caused the bird at first to be called the ‘Azure Warbler’. Here’s a clearer look at a female or immature bird, which, unlike John and Milena’s recent find, shows considerable streaking below:

Female Cerulean Warbler; courtesy of Guillermo Saborío

The wing bars, variable amount of breast streaking and generally greenish-grey/yellowish look can suggest a female or immature male Blackburnian Warbler (Setophaga fusca), another migrant species commonly found in our area. Here’s one of those for comparison:

Female or immature male Blackburnian Warbler at Guayabo National Monument; photo by John Beer

At home in San Antonio my first migrating warbler of the season is usually the Black-and-white Warbler (Mniotilta varia). True to form, it too has now arrived in the Turrialba area.The behaviour of this common migrant from North America is unlike that of other warblers in that it creeps along tree branches rather in the manner of a nuthatch. The female is less brightly marked than the male, with a whitish throat and buffy wash on the underparts:

Female Black-and-white Warbler at La Pastora; photo by John Beer

We’re still in August, so migration has barely begun. September will see further, scattered arrivals from the north joining our resident species. before things really start buzzing in October. Well before then the annual Cerulean Warbler Count, usually led by local expert Ernesto Carman, will be held at the Las Brisas Reserve near La Alegría de Siquirres.

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