Breeding Dispersal of Eastern Bluebirds Depends on Nesting Success but Not on Removal of Old Nests: An Experimental Study (La Dispersión Reproductiva de Sialia sialis Depende en el Éxito del Anidamiento Pero no en la Remoción de Nidos Viejos: Un Estudio Experimental)

• Published in: Journal of field ornithology 1997, Vol.68 (3), p.323-330
• Main Authors: Gowaty, Patricia Adair, Plissner, Jonathan H.
• Format: Article
• Language: English
• Subjects: Animal nesting; Aviculture; Bird nesting; Breeding; Breeding seasons; Breeding sites; Female animals; Male animals; Nesting sites; Parasites; Sialia sialis
• ISSN: 0273-8570; 1557-9263

One hypothesis to explain both within- and between-season breeding dispersal is that individuals move in response to degradation in the suitability and/or quality of their nesting sites. This hypothesis was experimentally examined by manipulating the suitability and/or quality of nesting boxes used by Eastern Bluebirds (Sialia sialis) on one study site in upstate South Carolina. From 12 randomly assigned boxes, old nests, parasites, dead nestlings, old food or feces were not removed, as they were from 12 other randomly assigned boxes. There were 24 nesting attempts in cleaned boxes; 26 in not-cleaned boxes. Third brood nesting attempts occurred in only one of the cleaned boxes but in five of the not-cleaned boxes. Only 59% of individuals stayed to breed again within the season in not-cleaned boxes, whereas 72% stayed in cleaned boxes. Equal numbers of both males and females returned to breed in cleaned and not-cleaned boxes during the next breeding season, however. Both within- and between-season breeding dispersal is significantly more likely after unsuccessful nesting attempts than successful nesting attempts. There was no significant effect of cleaning or not cleaning nesting boxes on the chance of nesting attempts or the numbers of nestlings fledged from nesting boxes. /// Una hipótesis para explicar tanto la dispersión dentro de- como entre- temporadas reproductivas es que los individuos se mueven como respuesta a la degradación en la adecuación y/o calidad de sus lugares de anidaje. Se examinó esta hipótesis experimentalmente al manipular la adecuación y/o la calidad de cajas de anidaje usadas por Sialia sialis en un lugar de estudios en el norte de Carolina del Sur. No se removieron nidos viejos, parásitos, crías muertas, alimento viejo o heces fecales de 12 cajas aleatoriamente seleccionadas, mientras que estos elementos fueron removidos de otras 12 cajas aleatoriamente seleccionadas. Se dieron 24 intentos de anidar en cajas limpiadas; 26 en cajas no limpiadas. Solo se obtuvo un intento de anidar por tercera vez en una caja limpiada, pero en cajas no limpiadas ocurrió cinco veces. Tan solo un 59% de los individos se quedaron para volver a reproducirse en la temporada en las cajas no limpiadas, mientras que 72% se quedaron en cajas limpiadas. Sin embargo, números iguales de machos y de hembras volvieron a anidar en cajas iimpiadas y no limpiadas en la próxima temporada reproductiva. Tanto la dispersión reproductiva dentro de y entre temporadas es si