| FLOYD HAYES |
| Hayes, F. E. 2006. Variation and hybridization in the Green Heron (Butorides virescens) and Striated Heron (B. striata) in Trinidad and Tobago, with comments on species limits. Journal of Caribbean Ornithology 19:12-20. Abstract.�The rufous-necked Green Heron (Butorides virescens) of North America and the Caribbean hybridizes with the gray-necked Striated Heron (B. striata) of South America in Panama and southern Caribbean islands. I analyzed historic and current variability of the two taxa in Trinidad and Tobago by comparing museum specimens and live individuals in the field with a color photograph of nine voucher specimens used as a hybrid index. In Trinidad, the population is dominated by B. striata, whereas B. virescens and intermediate individuals are rare. In Tobago, B. virescens is the predominant form, with small numbers of B. striata and intermediate individuals. The increased variability and intermediacy of individuals in Tobago strongly implies hybridization, and the higher proportion of intermediate individuals among museum specimens suggests a shift within the past century toward relatively �pure� phenotypes. Neck color was unrelated to clinal variation, seasonality, or habitat. The distribution of phenotypes differs markedly between populations of Butorides in Trinidad and Tobago, which are separated by only 36 km, suggesting that competitive exclusion may preclude B. virescens from colonizing Trinidad and B. striata from colonizing Tobago. Because the two taxa may often have opportunities to interbreed on Tobago but tend to mate assortatively, they appear to have achieved essential reproductive isolation, thus supporting their current treatment as distinct species. Resumen.�La Garcita Verde (Butorides virescens) con cuello rufo de Norteam�rica y el Caribe se hibridiza con la Garcita Estriada (B. striata) con cuello griz de Suram�rica, en Panam� y las islas caribe�as del sur. Se analiz� la variabilidad hist�rica y actual de ambos taxas a trav�s de la comparaci�n de espec�menes de museo y animales vivos con una fotograf�a a color de nueve de nueve ejemplares utilizados como patrones del h�brido. En Trinidad la poblaci�n est� dominada por B. striata, mientras que B. virescens e individuos intermedios son raros. En Tobago, B. virescens es la forma predominante, con peque�os n�meros de B. striata e individuos intermedios. La variabilidad incrementada incrementada y los caracteres intermedios en los individuos de Tobago sugieren fuertemente hibridizaci�n y la mayor proporci�n de individuos intermedios entre los espec�menes de museo sugiere un cambio en el siglo pasado hacia los fenotipos �puros�. El color del cuello no estuvo relacionado a variaciones clinales, estacionales o de h�bitat. La distribuci�n de los fenotipos difiere marcadamente entre las poblaciones de Butorides en Trinidad y Tobago, que estan separadas tan solo por 36 km, lo que sugiere que la exclusi�n competitiva evita la colonizaci�n de Trinidad por B. virescens y la de Tobago por B. striata. Como ambos taxas tienen frecuentes oportunidades de entrecruzarse en Tobago, pero tienen un apareamiento asociativo, parece ser que han alcanzado un aislamiento reproductivo esencial que apoya su tratamiento actual como especies diferentes. Key words.�Butorides striata, Butorides virescens, Green Heron, hybridization, species limits, Striated Heron, Tobago, Trinidad, variation |
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