Tuesday, December 22, 2015


Despite Costa Rica having a relatively well-studied bird fauna, our five years of field work on the eastern Nicoya Peninsula have yielded many surprising discoveries.  Among the most interesting are our encounters with bird species which, according to the literature, are not expected to occur on the Nicoya Peninsula at all, or at least during the period we visit each year.  Our most recent three-day banding session at the Reserva Natural Absoluta Cabo Blanco provided several examples of how even our basic knowledge of bird distributions needs quite a bit more work.

One species whose capture this morning represented our fourth encounter is the Ruddy Quail-Dove (Geotrygon montana).   The species' Costa Rica distribution as described by The Birds of Costa Rica (by Richard Garrigues and Robert Dean) and BirdLife International (http://www.birdlife.org/datazone/species/factsheet/22690966) extends northward along the Pacific coast only to the Rio Tárcoles.  The Tárcoles lies directly east of the Nicoya Peninsula on the mainland.  A literal (albeit small) gulf separates our encounters of this species with its described distribution.
Female Ruddy Quail-Dove (Geotrygon montata) banded on December 22
Male Ruddy Quail-Dove spotted in January 13, 2014
Another bird encountered this morning that is much more familiar to us North American bird banders is the Wood Thrush (Hylocichla mustelina).  The literature describing the winter range of this species in Costa Rica is incongruous; the most recent edition of The Birds of Costa Rica, depicts the species as being absent from the Nicoya Peninsula, while several reputable sources have published that the species is absent from the Pacific Slope of Costa Rica altogether.  A few other sources (including BirdLife International) correctly include the Nicoya Peninsula in their maps of this species' distribution.  To date we had captured 18 Wood Thrushes at our three banding sites on the Nicoya Peninsula, and today Cabo Blanco produced an additional three. 
Two Wood Thrushes banded on December 22 at Cabo Blanco
Finally, instead of a spacial discrepancy, we have a temporal one; the Swainson's Thrush, according to the most recent edition of The Birds of Costa Rica (Garrigues and Dean, 2014) and the original A Guide to the Birds of Costa Rica (Styles and Skutch, 1989), does occur throughout most of Costa Rica, but only as a passage migrant.  They are said to pass through Costa Rica on their southbound migration in September-November and again on their northbound migration in March-May, but are supposedly absent in December, January, and February.  Apparently the Swainson's Thrush we captured this morning at Cabo Blanco had not read those books, nor had the 17 others we've captured since the project began in 2011.
NPARS's first Swainson's Thrush, banded in 2011
These three species captured this morning are on a list with several other out-of-range or otherwise unexpected bird species that we have encountered since the start of this project.  We find it amazing that even in a country so well-studied (speaking relatively and from a biological perspective), there is still so much to learn about the basic biology of its bird fauna.  We are truly privileged to work in a place with so much to discover.

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