Black-capped chickadees (Poecile atricapillus) and mountain chickadees (P. gambeli) are ecologically segregated due to differences in habitat preference. However, forestry practices in northwestern Canada have created a mosaic of coniferous (mountain chickadee habitat) and deciduous forest patches (black-capped habitat), which might explain cases of observed regional sympatry between these 2 closely related species. In Poecile species, social hierarchies amongst conspecific individuals influence lifehistory parameters such as mate choice. As a result, interspecific social hierarchies might drive hybridization between these 2 closely related species. By conducting field observations and aviary experiments, we demonstrated that black-capped chickadees are dominant over mountain chickadees. Using a combination of species-specific phenotypes (plumage), mitochondrial DNA (mtDNA) to assess maternal genotype, and microsatellite markers, we confirmed that genetic mixing occurs within our contact zone but that the pattern of parentage appears directional. All but one of the adult hybrids was phenotypically identified as mountain chickadee and had mountain chickadee mtDNA. Furthermore, all nestlings where microsatellites detected mixedspecies ancestry were from mountain chickadee nests with both attending parents having mountain chickadee phenotypes. All mtDNA from these nestlings was mountain chickadee except for one individual, and in all cases, these nestlings showed genetic patterns of having arisen through extrapair copulations between female mountain and male black-capped chickadees. Our results suggest that hybridization may result from males of the mountain chickadees having lower expression of a preferred trait (dominance) than the black-capped chickadees.
In vocal learners, such as songbirds, the ability to maintain an internal acoustic structure between songs during a chorus seems to be positively correlated with the singer’s condition and may, therefore, represent a reliable measure of the singer’s condition. For instance, some internal ratios in the black-capped chickadee ( Poecile atricapillus) fee-beesong are more stable in the song of dominant males than in the song of subordinate males, suggesting that dominant birds are better at maintaining the internal song structure than subordinate males. Habitat quality is also known to affect the behaviour of this species. Birds settling in young forest have a lower song output and lower reproductive success than birds occupying mature forests, and it is suggested that those differences arise from differential food availability across habitats. As recent studies suggest that song performance can be altered by food limitation at the time of song learning, we explore whether habitat quality has a similar effect on the ability to maintain internal song structure as does social rank. We paired males by similar social rank, but who occupied different habitat types, and compared the consistency of male song within his dawn chorus. The ability to maintain an internal song structure of birds occupying young forests was consistently lower than birds occupying mature forests. Our results demonstrate that the same difference that exist in song structure between male differing in social rank also exist between males differing in the habitat in which they sing.
Resumen. El coro del amanecer es un comportamiento colectivo que involucra una red de aves expresándose al mismo tiempo. Dos hipótesis pueden explicar los mecanismos de cantos del amanecer. La "hipótesis dependiente de la condición" propone que el canto coral del amanecer constituye una "red emisora" en la cual la señal es dada en todas las direcciones pero no depende de los coros de los vecinos del cantante. El resultado de la canción depende de la condición, por lo que puede estar limitado por la cantidad de alimento a la cual tiene acceso el emisor en su territorio. Por otro lado, la "hipótesis de dinámica social" propone que durante el coro las aves están interactuando constantemente con sus vecinos. bajo este escenario, el coro del Abstract. The dawn chorus is a collective behavior involving a network of birds signaling at the same time. Two hypotheses can explain the mechanisms of dawn singing. The "conditiondependent hypothesis" states that the dawn chorus consists of a "broadcast network" in which the signal is given in all directions but is not dependent on the singer's neighbors' chorus. The song output is condition dependent and can thus be limited by the amount of food to which a signaler has access to in its territory. On the other hand, the "social-dynamic hypothesis" states that during the chorus the birds are constantly interacting with their neighbors. Under this scenario, the dawn chorus consists of an "interactive network" and the song output is not dependent on the condition of the signaler but on the interaction with the neighbors. To determine which scenario best explains the mechanisms of the dawn chorus in the black-capped Chickadee (Poecile atricapillus), we set up a supplemental-feeding experiment in a dyadic fashion by providing 3.5 g of mealworms to selected birds and compared their song output to that of unfed counterparts by controlling for rank and habitat. We found that fed birds, both dominant and subordinate males, sang more than unfed birds. We thus conclude that body condition is a critical variable contributing to individual differences in song output in the black-capped Chickadee and consequently the functioning of the dawn-chorus network. 3 The Condor 111(3):560-564 The Cooper Ornithological Society 2009amanecer consiste en una "red interactiva" y la canción resultante no depende de la condición del emisor sino de la interacción con los vecinos. Para determinar cuál escenario explica mejor los mecanismos del coro del amanecer en Poecile atricapilla, establecimos un experimento de alimentación suplementaria de un modo dinámico brindando 3.5 g de larvas de tenebrios a aves seleccionadas y comparando sus cantos con aves no alimentadas, controlando por rango social y hábitat. Encontramos que las aves alimentadas, incluyendo tanto machos dominantes como subordinados, cantaron más que las aves no alimentadas. Por lo tanto, concluimos que la condición corporal es una variable crítica que contribuye a las diferencias individuales en la producción de cantos en P. atricapillus y, co...
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