Abstract
History
The Phoenix Zoo acquired their first King Vulture (Sarcorampbus papa) on December 29, 1962. This was shortly after our zoo first opened, and it came to us as a wildcaught adult. Thought to be a male, it was housed with various species of raptors and at times alone for 13 years. During this time, it revealed itself to be a female, as it laid an egg in June of 1975 and then two more in April and May of 1976.
In April 1980, we received an adult unsexed bird from the Jacksonville Zoo. The pair was introduced together in a new outdoor aviary built for them. Constructed of telephone poles, steel cable and 1 '' x 2'' welded wire, the aviary measures 20 feet square and 25 feet high with a large, dead tree in the center. Tropical plants and trees were planted in and around all four sides of the exhibit.
The September introduction of the· two birds in this "neutral ground" flight cage went well with little negative interaction. Shortly after, the new bird was sexed and we learned that it, too, was a female. This was a disappointment, however, the two birds remained together until February 1981 when we sent the new bird to the Rio Grande Zoo in Albuquerque.
It wasn't long before we learned of another available, mature King. This one, known to be a male, was acquired from the Bronx Zoo in April 1981. The two were introduced without any problems and by June the male was observed regurgitating to the female, a form of courtship. They were already beginning to form a pair bond. The Bronx bird was a longterm captive of over 20 years like our female and this may have had a lot to do with their compatibility. February 1982 was the beginning of the Phoenix Zoo's continuous, successful King Vulture reproduction.
Behavior and Reproduction
Our pair had a nest platform located eight feet off the ground which they never used. Each season they have consistently chosen to nest in the same northwest corner of the aviary on the ground. Occasionally, a few sticks are collected and dropped in the area of the nest depression. In time, the trees and shrubs planted in and around the exhibit have matured to provide shade and privacy. Additionally, we placed an open fronted plywood box over the nest site to provide more security during incubation, keeping the nest about 90% out of view from the public.
Throughout successive breeding seasons, we learned that although the birds diligently incubate their egg and fiercely guard the nest, we are unable to trust them with their own newly hatched young or pipping chicks. Chicks have been inadvertently killed or deliberately so, and then eaten. Through manipulation and intervention, we have tried to learn if one or both birds were responsible for this behavior and have concluded that either one, if given the opportunity, will grab the chick, whether together or separate. This surely seems odd, when one considers that the male defends the nest and helps the female incubate the egg through the 54-day incubation, only to kill the chick at the climax. In an effort to end this behavior, we have roped off the entire exhibit, denying public access or viewing. We have increased and supplemented their diet to include whole animals such as rodents or chickens in addition to their commercially prepared "Bird of Prey'' diet. None of our attempts to solve the problem made a difference.
We wanted our pair to raise their own chick, but each season their behavior has forced us to pull chicks or incubate the eggs in the incubator. By pulling the egg, we have learned that they will always double clutch; on two occasions they have triple clutched. This has made their nesting season in Phoenix last from December through June. As in the wild, each clutch has but one egg.