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Importance of tropical mixed‐species flocks for migratory birds in shade‐grown coffee: implications of foraging together

2021; Association of Field Ornithologists; Volume: 92; Issue: 3 Linguagem: Inglês

10.1111/jofo.12379

1557-9263

Jenny Muñoz, Gabriel J. Colorado Z.,

Plant and animal studies

Group living is a widespread social strategy that allows animals to optimize foraging with dynamic trade-offs between reduced predation risk, enhanced foraging, and increased competition. Birds across terrestrial habitats form mixed-species flocks, where dozens of resident and migratory species forage together throughout the day. The effect of flock participation and group size on the foraging behavior of migratory and resident species is poorly known, particularly in the tropics. Using foraging observations, we examined the effects of flock participation on the foraging ecology of four species of Neotropical migrants and three resident species in shade-grown coffee plantations in the Colombian Andes in 2011. We showed that resident and migrant birds in mixed-species flocks largely increased the number of foraging attempts, expanded their foraging repertoire, and exhibited greater overlap in use of foraging maneuvers compared with solitary individuals. We found an effect of group size on foraging rate, with feeding attempts increasing monotonically or showing a hump-shaped pattern, and also found that movement rates increased with increasing flock diversity. These results support the idea that flock participation enhances foraging success and reduces perceived predation risk, but also show niche convergence among flocking species, along with higher movement rates and more agonistic interactions as group size increases. Finally, our results provide insight into the importance of mixed-species flocks for birds of conservation concern, including Cerulean Warblers (Setophaga cerulea), a Neotropical migrant shown to be highly restricted to foraging in flocks in their wintering areas. Importancia de bandadas mixtas tropicales para aves migratorias en café de sombra: implicaciones de la búsqueda de alimento conjunta Vivir en grupo es una estrategia social común que permite a los animales optimizar la búsqueda de alimento con un equilibrio dinámico entre un reducido riesgo de depredación, mejoramiento en la búsqueda de alimento y un incremento en competencia. Las aves en hábitats terrestres conforman bandadas mixtas de especies, en las cuales docenas de especies residentes y migratorias buscan alimento juntas a lo largo del día. El efecto de la participación en bandadas y el tamaño de grupo en el comportamiento de búsqueda de alimento en especies migratorias y residentes es poco conocido, particularmente en los trópicos. Usando observaciones de búsqueda de alimento, examinamos los efectos de la participación en bandadas en la ecología de la búsqueda de alimento de cuatro especies de aves migratorias Neotropicales y tres especies de aves residentes en plantaciones de sombrío de café en los Andes de Colombia en 2011. Mostramos que las aves residentes y migratorias en bandadas mixtas de especies incrementaron ampliamente el número de intentos de búsqueda de alimento, expandieron su repertorio de búsqueda de alimento y exhibieron un mayor traslape en el uso de maniobras de búsqueda de alimento comparado con individuos solitarios. Encontramos un efecto del tamaño del grupo en las tasas de búsqueda de alimento, con intentos de alimentación incrementándose monotónicamente o mostrando un patrón en forma de joroba, y que las tasas de movimiento incrementaron con el aumento en la diversidad de la bandada. Estos resultados apoyan la idea que la participación en bandadas mejora el éxito en la búsqueda de alimento y reduce el riesgo de depredación percibido, pero también muestran la convergencia de nicho entre especies que buscan alimento, junto con tasas de movimiento más altas y más interacciones agonísticas a medida que el tamaño de grupo incrementa. Finalmente, nuestros resultados proveen evidencia sobre la importancia de las bandadas mixtas para especies de aves de preocupación en conservación, incluyendo la Reinita Cerúlea (Setophaga cerulea), un ave migratoria Neotropical que ha mostrado ser altamente restringida a bandadas cuando busca alimento en sus sitios no reproductivos. Fig. S1. Locations of studied coffee farms in southwestern Antioquia included Finca Cultivares (A), Finca Gualanday (B), and Finca la Cumbre (C). Fig. S2. Effect of seasonality on the attack rates of bird species in shade-grown coffee plantations in the Colombian Andes. The solid line is the predicted value of attack rate as a function of day of the season. Fig. S3. Effect of group size on the attack rates of bird species in shade-grown coffee plantations in the Colombian Andes. For the resident (a) Hemithraupis guira, (b) Setophaga pitiayumi, (c) Zimmerius chrysops, and the migratory species (d) Cardellina canadensis, (e) Setophaga cerulea, (f) Setophaga fusca, (g) Oreothlypis peregrina and resident Circles indicate individual birds. The solid line is the predicted value of attack rate as a function of flock size (number of individuals). The grey shading shows the confidence intervals based on the standard errors of the estimates. Fig. S4. Relationships between attack rate and movement rate of bird species in shade-grown coffee plantations in the Colombian Andes. A generalized linear mixed model was fitted to the data. Black represents individuals foraging in flocks, grey represent individuals foraging solitary. Table S1. Model summaries of attack rate for each species with the predictors social context and day of season. Glm including time of the observation as an offset. Table S2. Model summaries of movement rate for each species with the predictors social context and day of season. Glm including time of the observation as an offset. Note: the parameter estimates were back transformed for easier interpretation. Appendix S1. Diversity and composition of mixed-species flocks in shade-grown coffee plantations in the Colombian Andes. Date indicates ordinal date, site indicate locality (L1Finca cultivares, Jerico; L2 Finca Gualanday, Fredonia; L3 Finca La cumbre, Tamesis). Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.