Behavior

 

Cerulean Warblers are very active and spend most of their time looking for their food in the foliage on the outer part of the branches. They search for their prey on the underside of the leaves, oftentimes sallying out from another branch to pick the invertebrate from the leaf. This sallying behavior is actually a good clue to the presence of a CERW. 

The data shared on this site focuses on the Cerulean Warbler's behavior during its stopover in Costa Rica.  Although this species has been studied more extensively on its breeding and wintering grounds, its natural history during stopover is poorly known.

 

Many of the videos and photographs here are for documentation purposes and their quality is based on scientific value!

CERW typical foraging behavior

They are almost always foraging along with mixed species flocks with many migratory and resident species, especially Lesser Greenlet (Pachysylvia decurtata).  During their time in Costa Rica they are almost completely silent. They are most often heard doing their buzzy flight call which is easily missed and rarely do they give a short chip note. 

On a couple of occasions we have spotted CERWs bathing in small creeks and run-off, retreating afterwards to a small tree to preen for a few minutes. We have also observed them settling in on the tip of a branch to sleep for the night, between 8 - 12 meters above the ground.  They arrived at their roost ca. 17:35 when there was still plenty of daylight and did not leave the perch until 05:25.

CERW preening after bathing

Diet

During their stopover in Costa Rica their diet consists mainly of small caterpillars, katydids, spiders and moths.  They also consume  the small fruits of three different Melastomes, Hyeronima alchorneoides and the orange aril covering the seeds of Casearia arborea.

First documentation of a CERW eating fruit (2008).
First documentation of CERW eating fruit (2008)
CERW eating a caterpillar

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