In 2006 Ernesto Carman first encountered large numbers of CERWs at Las Brisas Nature Reserve while watching a mixed species flock and participating in the flock were 13 Cerulean Warblers!
After consulting literature and ornithologists, this event was considered a possible anomaly; CERWs were known to arrive in large waves some years.
The following year however, Ernesto returned to Las Brisas in late August and early September and once again found CERWs to be the most common migrant, observing anywhere between 1 and 5 individuals in each mixed species flock he encountered.
The pattern was repeating itself, but oddly enough CERWs were not being seen in the same numbers away from Las Brisas and this led to the initiative of an organized, country-wide survey in early September of 2008 to have a larger scale image of where CERWs were in Costa Rica.
Once again Las Brisas was the epicenter for CERWs and all the evidence was suggesting this tiny area on the northeast slopes of Turrialba Volcano was possibly an important stopover site for CERWs. It was then Proyecto Cerúlea was born.
In the following years the “Cerulean Warbler Watch” became a yearly activity in which participants had a good chance of seeing and photographing this enigmatic warbler, but at the same time it served as a platform to educate the public about the importance of stopover habitat for migrants.
Along with the annual survey we also organized workshops and the Costa Rica Birding and Nature Festival to expand our public outreach and impact.
The project has been developing field work focussing on studying the natural history of the CERW during stopover, gathering important data on behavior and diet.
In 2018, Proyecto Cerúlea received a major boost by joining efforts with SELVA and their Neotropical Flyways Project, conducting surveys at different sites within Costa Rica to determine occupancy rates of migratory species such as the Cerulean Warbler to predict where other important stopover sites might be located.
We also did a short period of banding in late August and early September during which we caught and banded 13 CERWs. More importantly we were able to resight and recapture several individuals, providing important data about fat deposition rates and the length of stopovers at Las Brisas.
A nice immature male Cerulean Warbler.
Male of American Redstart (Setophaga ruticilla).
A Cerulean Warbler banded with color band in order to identify it in the field.
A nice immature male Cerulean Warbler.
Kathy Bonilla, Ernesto Carman, Nick Bayly & David Segura.
An adult and immature female Cerulean Warbler.
Comparing a Bay-breasted Warbler with a Chestnut-sided Warbler.
Kathy Bonilla, Ernesto Carman, Nick Bayly & David Segura.
During a full banding season in 2019, covering the busiest months of fall migration from mid-August to late October, we banded 3739 individuals of 135 species. Of those 22 were CERWs!
