Enrichment Pulley System

ARBOREAL FEEDERS FOR ORANGUTANS
Michael Stern, Assistant Curator of Primates, Denver Zoo
Courtney Eparvier, Curator of Primates and Sea Lions, Audubon Zoo
Amy Robbins, Team Leader of Primates, Auckland Zoo
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Even when given ample opportunities for climbing, it can be difficult to encourage captive
orangutans to be as arboreal as they are in nature. In Denver, the orangutans enjoy a 16,633
square foot (~ 1/3 acre) outside yard with several mature trees, some reaching over 100 feet
tall. Though they utilize the great climbing opportunities periodically, we were interested in
encouraging them to climb more often. Pulley feeders have been discussed on ape list-servs
at various times, but often are expensive and need to be custom fabricated in a metal shop.
Denver Zoo has experimented with easy to obtain and affordable materials and has been
continually evolving an easy to use, affordable arboreal feeder. Auckland Zoo, in New
Zealand, has also had great success with home-made arboreal feeders. Three designs are
presented here, each with its own set of challenges and benefits. Feeders like those used in
Auckland are highly recommended, but if your zoo does not have the resources or political
will to create something so permanent, don’t be discouraged – many other possibilities
exist for creating arboreal feeding opportunities for orangutans.
DESIGNS
1) Denver Zoo’s initial arboreal feeder, consisting of a rock climbing rope modified to have a stainless steel cable core,
stainless steel cable pulley points and lacrosse balls to help keep the cable in place.
• Pros: Extremely affordable and easily replicable by unskilled craftspeople.
• Con: After extended use, the climbing rope bunched up around the cable, making it very difficult to raise and lower.
2) Denver Zoo’s current feeder, a simple rock climbing rope with lacrosse balls and eye-bolt pulley points. Eye bolts
are 3/8” x 6” long, secured in the tree with wood glue & loctite.
• Pros: Very easy to install and use.
Original Design, Denver Zoo, cable pulley point
3) Auckland Zoo’s design, utilizing stainless steel cables, pulley wheels, swivel connections, welded steel feeding basket
and metal conduit.
ORANGUTAN PROOF?
• Pros: Relatively ape proof and durable over the long term.
While in the planning phase, curators, keepers
and vets in Denver agreed a design with minimal
moving parts would be ideal. While the initial
design worked wonderfully in the short-term and
was reasonably “orangutan proof,” it created
problems in the long-term: bare cables sawed
through the pulley points and cables wrapped in
rope eventually bunched up and made raising
and lowering the feeder impossible.
Since a fully orangutan proof feeder (like those
used at Auckland Zoo) may be mutually exclusive
to one that is also affordable and simple to build
and operate, we started taking the personalities
of our individual animals into account. Only the
first prototype of our arboreal feeder was
“tested” in any way by the apes; subsequent
models, even with clips and other pieces that
could conceivably be removed by the orangutans, were left very much intact. With this in
mind, and with the past history of the apes trading unusual objects rather than using them to
make trouble, curators and keepers felt comfortable using a simpler system.
• Con: Not 100% orangutan proof.
• Con: Requires welding by skilled craftspeople and larger initial investment of time and funding, more effort needed
to raise and lower.
Current design, Denver Zoo, eye-bolt pulley point
Original Design, Denver Zoo, base of tree,
anchoring the cable
Auckland Zoo's orangutan feeders
(New Zealand)
Crank for raising & lowering the metal basket at Auckland Zoo
Swivel mechanism at
Auckland Zoo