When it comes to boisterous animals, the siamangs at the Jerusalem Biblical Zoo steal the show. Housed on a small island near the entrance to the park, these primates of the baboon family keep up a constant chorus of calls throughout the morning and evening. And siamangs seem to have only one kind of call - loud. The knack for giving such an impressive shout stems from the siamang's unique throat, which balloons up to the size of its head, giving extra volume to their calls. This ability is put to good use in their native jungles of Malaysia and Thailand, where they can communicate across many kilometers, broadcasting their position to mark their territories. Siamangs live in a state of monogamy, with couples pairing off and raising families as dedicated parents. Each baby receives care and attention from both parents until it is old enough to strike out on its own. The parents are keen to see them leave because tensions between young and old can flare as the parents despair at their offsprings' monkey activities. The zoo's elder pair - Elliot, 22, and Malka, 23, quite old for baboons - have parented several offspring that have since been moved to other wildlife parks in Israel and around the world. Their current adolescent is Richard, aged 8, who will soon move on to another location, leaving his parents to a quiet retirement. Siamangs are very territorial and will attack anything or anyone who wanders into their realm. This sometimes results in savage scenes played out between species at the zoo. The lake around their island is teeming with birdlife; but should a fowl fall foul by straying onto the island in search of food, the siamangs will slay the intruder and then eat the kill. While visitors are sometimes alarmed to see nature at its most brutal, zoo officials do not interfere; it is, after all, just natural. Due to the hot-headed temperament of the siamangs, keepers never venture into the enclosure. They approach the island with a boat that docks at a fenced-off corridor leading to the siamangs' hutch. The fence carries a mild electric current to deter the island's denizens. The fence brought about one of the more dramatic rescue efforts at the zoo. Several years ago, an infant siamang fell from a tree onto the fence and the shock of the fall, combined with the current, threw the baby into a fit. Although physically unharmed, the small animal stopped breathing. In a desperate rescue attempt, one of the zoo keepers performed artificial respiration to revive the infant, which made a full recovery. The siamangs are active most of the day but enjoy a leisurely afternoon nap. Visitors interested in experiencing the siamangs' most animated bellowing should arrive in the morning when the simians are in full voice to greet the new day.