Behavior And Reproduction
Bulbuls that are found in forests tend to be secretive. By contrast, those found in garden settings or parks can be bold and gregarious, social. Bulbuls can be very social and are found in groups with their own species and with other species. The spotted greenbul, for instance, is extremely gregarious and travels in a group with other greenbuls in flocks that might have from five to fifty birds. This group never stays too long in one place, even when food is plentiful. Other species that are social, the striated bulbul and the yellow-streaked bulbul, also live in active flocks. Many bulbuls show aggressive behavior toward members of their own species in addition to those of other species.
Most bulbuls have distinctive singing voices—from chattering to whistles. The chance of hearing a bulbul in a tropical forest is high, and they are usually heard before they are seen. Though few are musical, some bulbuls have beautiful and melodious songs, including the yellow-spotted nicator in West Africa, and the yellow-crowned bulbul, found in Borneo. The greenbul is noted for its constant singing throughout the day, all year long.
Bulbuls as a whole are not migratory, moving to other places seasonally, though some species that are adapted to the cooler climates and temperate zones would be considered partly migratory. The black bulbul, for instance, migrates in flocks of several hundred birds at a time to southern China in the winter months. Brown-eared bulbuls that have been banded and recaptured have been shown to migrate within the Japanese islands. Other bulbuls are sedentary, stay in one place, and might move only a few hundred yards (meters) over a period of several years. Most bulbuls live and travel in pairs, or in family groups, complete with its juvenile members.
Bulbul reproduction can vary. It depends on the climate and region. Breeding can be connected to rainfall, with some species breeding before and after the monsoon, rainy, season. Some species breed year-round, even through the rainy seasons. Most are monogamous (muh-NAH-guh-mus; having only one mating partner) and territorial. Mating rituals vary as well, with some species chasing each other while calling out in a soft tone. In most species, both parents usually work on the nest, though in some species it is only the female. Bulbuls generally have a clutch size (number of eggs in the nest) of two, with three for the yellow-whiskered bulbul and one for the West African nicator. Some of the Asian species can have clutches of four or five. The incubation period, time spent sitting on the nest before hatching, varies for the different species but can last from eleven to fourteen days.