Most bulbuls are found in pairs, or in small groups that tend to be family parties and often include juveniles. Mostly monogamous and territorial, except for the yellow-whiskered greenbul (Pycnonotus latirostris), a lekking species, some bul-buls will form groups that defend a large home range together. Both the leaf-love and the swamp greenbul will gather and chorus to defend communal territory. In the case of the swamp greenbul, the loud vocalizations are accompanied by displays of spread wings and tail.
The timing of bulbul reproduction varies greatly, depending on the climate and region. In some areas breeding appears to be tied to rainfall, and many species have two broods per year, usually before and after the monsoon sea son. Breeding is common year-round in other species, and some African species may breed throughout the rainy season, or after the rains. Most bulbuls are monogamous and territorial, often the pair-bond is maintained year after year. One species, the yellow-whiskered greenbul, has a quite flexible social system, and in high density areas uses leks, but is monogamous and territorial in lower-density areas. There is evidence of cooperative breeding in a handful of species including, the spotted greenbul, the yellow-throated leaf-love, and Ixonotus. Groups of four to six birds will feed the young, usually both in the nest and after leaving it.
Pre-copulatory displays have been observed in some bul-buls, in which the birds chase each other while softly calling. Little is known about the selection of the nest. It is usually built by both parents, although in some cases just the female. Nests tend to be an untidy cup nestled in the fork of a tree. The construction materials vary, but usually include a variety of twigs, rootlets, plant stems, grasses, cobwebs, and hairs. Some species "decorate" the outside of the nest with fern fronds or bark strips. There are usually two eggs per clutch, although there may be as many as five, and there is great variation in the egg color and markings, even within a single species. Some eggs are elongated ovals, others truncated ovate, they may be glossy white, pinkish, lilac, gray, brown, and mauve with scratchy markings, blotches, or spots, sometimes concentrated at one end so the egg appears to be "capped." In some species both parents incubate the eggs, in others the female only, usually for 10-14 days. Young are born naked and are usually cared for by both parents. They are often just given insects at first, even among the species that primarily eat fruit. They generally fledge at 14 days, but as early as seven days in some species.
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