Raptors and "campo-cerrado" bird mixed flock led by Cypsnagra Hirundinacea (Emberizidae: Thraupinae)

RESUMO

Bird mixed flocks including Cypsnagra hirundinacea and Neothraupis fasciata as species with sentinels were studied in "campo-cerrado" in order to investigate the possible relationship between alertness and the mixed flock leadership. This study was conducted from March to September 1996 and mixed flocks were observed on average for 230h. The time with sentinels were recorded for C. hirundinacea and N. fasciata. The sentinels of Cypsnagra hirundinacea performed most of the vigilance (time with sentinel was on average 42 ± 17 percent, 41 ± 17 percent of which by C. hirundinacea, whereas only 1.2 percent by N. fasciata) and gave all the alarm calls recorded (54 percent of the encounters with raptors stimulated alarm calls). A relationship was verified between time with sentinel and the rate of encounters with raptor (ANOVA, F = 3.0, P < 0.05). The results of this study are an evidence for the anti-predatory function of mixed flocks, in campo-cerrado, and the alertness as a major feature of a leader species, since C. hirundinacea always led those flocks