Geographic variation in the flight call of the Cuban Parrot (Amazona leucocephala) and its taxonomic relevance
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Abstract: Because bird vocalizations often reflect population differentiation and can create barriers to gene flow, ornithologists frequently rely on vocalizations for defining species limits. Our previous work on morphology and plumage variation within the Cuban Parrot (Amazona leucocephala) suggested greater diversity than previously recognized. Because some island populations are highly endangered, additional characters are needed to help define taxonomic units within this group. Here, we tested two hypotheses: that the flight call (a form of contact call) of parrots from each of the six extant island populations is diagnosably distinct, and that the structure of the call, as assessed by discriminant function analysis, corresponds to variation in molecular, morphological, and plumage characters (i.e., character concordance). To test these hypotheses, we spectrographically examined both qualitative and quantitative characters of the flight call of 23 individuals recorded from the six extant island populations on Abaco and Inagua (the Bahamas), Cuba, Isla de la Juventud, Cayman Brac, and Grand Cayman. As anticipated, we found the flight call of each population to be diagnosably distinct. However, when only quantitative characters were considered, flight call structure was not fully congruent with the molecular, morphological, and plumage differences that exist among island groups. Specifically, the flight calls from Grand Cayman were less distinct structurally than expected, and Cayman Brac calls were more distinct from those of Cuba and Isla de la Juventud than expected. Although diagnosability is important for examining taxonomic limits in birds, applying this principle to vocalizations may be problematic, particularly when a strong cultural component exists. This appears to be the case for psittacids, whose contact calls are subject to strong cultural influences (i.e., learning). Thus, the diagnosable differences we found among populations should not be interpreted as support for species-level differentiation. Although a more complete analysis of the cultural differences (vocal and other learned behaviors) among island populations is needed, we recommend that each population be managed not only as a separate conservation unit, but also as a culturally significant unit.
Keywords: Amazona leucocephala, conservation taxonomy, Cuban Parrot, culturally significant unit, flight call, systematics, vocalization
Resumen: Variación geográfica en la llamada durante el vuelo de la Cotorra Cubana (Amazona leucocephala) y su relevancia taxonómica- Como las vocalizaciones en las aves usualmente reflejan diferencias poblacionales y pueden crear barreras al flujo genético, los ornitólogos con frecuencia se apoyan en las vocalizaciones para definir los límites de las especies. Trabajos previos en morfología y variación del plumaje de la Cotorra Cubana (Amazona leucocephala) sugieren una mayor diversidad de la reconocida previamente. Debido a que las poblaciones en algunas islas estan fuertemente amenazadas, caracteres adicionales son necesarios para ayudar a definir las unidades taxonómicas dentro de este grupo. En este trabajo se someten a prueba dos hipótesis: que la llamada durante el vuelo (una forma de llamada de contacto) de cada una de las seis poblaciones isleñas remanentes son diferenciables con valor diagnóstico y que la estructura de la llamada, evaluada por un análisis de función discriminante, corresponde con las variaciones moleculares, morfológicas y caracteres del plumaje (ej. concordancia de caracteres). Para poner a prueba estas hipótesis, se examinaron desde el punto de vista espectrográfico caracteres cualitativos y cuantitativos de las llamadas de vuelo de 23 individuos grabados de poblaciones en Abaco e Inagua (Bahamas), Cuba, Isla de la Juventud, Cayman Brac y Grand Cayman. Como fue predicho, se encontró que las llamadas fueron diferentes. Sin embargo, cuando se consideraban solo caracteres cuantitativos, la estructura de la llamada de vuelo no fue totalmente congruente con las diferencias moleculares, morfológicas y diferencias de plumaje que existen entre estos grupos en las islas. Específicamente, los cantos durante el vuelo fueron menos diferentes que lo esperado, desde el punto de vista estructural, en Grand Cayman, mientras que en Cayman Brac fueron más diferentes que lo esperado, en relación con Cuba e Isla de la Juventud Aunque el valor diagnóstico es importante para examinar los límites entre especies en las aves, aplicar este principio a las vocalizaciones puede ser problemático, particularmente cuando existe un componente cultural fuerte. Este parece ser el caso de los psitácidos, cuyo canto está sujeto a fuertes influencias culturales (ej. aprendizaje). Por tanto, las diferencias diagnosticables encontradas entre poblaciones no deben interpretarse como apoyo para una diferenciación a nivel de especie. Aunque un análisis más completo de las diferencias culturales (vocales y otras conductas aprendidas) entre islas es necesario, se recomienda que cada población sea manejada no solo como unidades de conservación separadas sino también como unidades culturalmente significativas.
Palabras clave: Amazona leucocephala, Cotorra Cubana, llamadas de vuelo, sistemática, taxonomía para la conservación, unidad culturalmente significativa, vocalización
Résumé: Variation geographique du cri au vol chez l’Amazone de Cuba (Amazona leucocephala) et sa valeur taxonomique- Les ornithologues utilisent les vocalisations des oiseaux pour séparer les espèces car ils reflètent souvent des différences populationnelles et peuvent être ainsi à l’origine de limitations aux échanges génétiques. Nos précédents travaux sur les variations morphologiques et de plumage de l’Amazone de Cuba (Amazona leucocephala) suggèrent une diversité plus forte que précédemment considérée. En raison des fortes menaces pesant sur certaines populations insulaires, il est important de pouvoir disposer de caractères supplémentaires d’identification taxonomique dans ce groupe. Nous avons testé deux hypothèses, d’une part que le cri au vol (une forme de cri de contact) des six populations insulaires pouvait être diagnostique, et d’autre part, que la structure de ce cri, tel que décrit par analyse discriminante correspondait à des variations de caractéristiques moléculaires, morphologiques et du plumage. Pour tester ces hypothèses, nous avons analysé de les spectrogrammes des cris au vol, qualitativement et quantitativement, pour 23 oiseaux issus des six populations de Abaco et Inagua (Bahamas), de Cuba, Isla de la Juventud, Cayman Brac, et Grand Cayman. Comme anticipé, les cris au vol de chaque sous population se sont avérés discriminants. Toutefois, la variabilité de la structure du cri au vol au niveau des seules caractéristiques quantitatives ne s’est pas avérée totalement corrélée avec les différences moléculaires, morphologiques et de plumage. En particulier, les cris au vol des oiseaux de Grand Cayman ont été moins structurellement distincts qu'attendu, alors que ceux de Cayman Brac l'ont été plus qu'attendu par rapport à ceux de Cuba et de l'ïle de la Juventud. L’utilisation de ce type de méthode bien qu’importante pour analyser les frontières taxonomiques chez les oiseaux, peut donc s’avérer problématique lorsqu’elle est appliquée aux vocalisations, en particulier lorsqu’il existe un fort facteur culturel. Cela semble être le cas chez les Psittacidés, pour lesquels existe une forte influence culturelle (comme l’apprentissage) sur les cris de contact. Ces différences diagnostiques trouvées entre les populations ne doivent donc pas être interprétées pour justifier une différence d’espèce. Bien qu’une analyse plus complète des différences culturelles (vocales ou pour d’autres comportements appris) soit nécessaire, nous recommandons que chaque unité de conservation soit gérée non seulement comme une unité de conservation particulière, mais aussi comme une unité culturelle unique.
Mots clés: Amazona leucocephala, Amazone de Cuba, cri au vol, systématique, taxonomie de conservation, unité culturelle particulière, vocalisation
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