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Subjects and Housing
The Northern bald ibis is restricted to few colonies in Morocco, Syria and Turkey (Pegoraro
1996), but was present in central Europe until the 1600s. Starting in 1997, a group of semi-
tame, free-flying Northern Bald Ibises was established in the Alm valley, Upper Austria.
From 1997-2000 zoo-bred chicks were hand-raised at the KLF in coordination with the
European Breeding Programme EEP (Böhm 1999; Tintner and Kotrschal 2002). Since then,
the group is self-sustaining. In 2006, the group consisted of 32 individuals and was housed in
an aviary in the local Cumberland game park, Grünau. The aviary consists of one large
compartment and an adjacent wooden tower (7m in height). In this tower construction, birds
are protected against rain as well as predators. Additionally, wooden shelves provide space for
breeding. The aviary is open year round, allowing birds to fly freely during day. They forage
in groups on meadows several kilometres around the aviary and return at night for roosting.
Supplemental food is provided during winter. All birds are marked individually with coloured
leg bands.

       In the aviary, one closed room allows individual testing of birds. This room is
separated from the other parts of the aviary by solid wooden walls; two large windows ensure
natural light conditions. The hand-raised birds of the group are accustomed to enter this room
and to be separated from the group while in close contact with human experimenters.
We used the daily winter feedings for our experiment as birds stay in the aviary until the
morning feeding. Therefore, tests were conducted before feeding, when birds were willing to
enter the testing room.

Experimental Procedure
Tests were carried out in February 2006 (Experiment 1) and 2007 (Experiment 2),
respectively. Most of the subjects (9 out of 12, four males, five females) participated in both
experiments. One bird (female) had died between the experiments; two birds (one male, one
female) could be used only in 2006 because they were already engaged in courtship displays
and nest building in February 2007. They were replaced by another male and female that did
not accept physical separation in 2006 but did so without any problem in 2007.

       In both years, experiments were conducted within a week. Test-subjects (observers)
received one session per day, consisting either of test trials or control trials (e.g. day 1: test
trials, day 2: control 1, day 3: control 2). Most birds were used as model and observer, but
they could play just one of the two roles on a given day. Generally, those birds that were
tested as observers in the first days were used as models in the following days and vice versa.

       In experiment 1, we used a laser pointer to elicit look-ups of model birds. Since some
habituation of the models to the projections of the laser pointer became apparent at the end of
the experiment 1, we refrained from using it in Experiment 2. We used an opaque tube
instead, mounted vertically to the wall behind the barrier (opposite to the test subject’s
position). The experimenter pulled a piece of food in and out of the tube via a thin nylon
thread, inducing the model to look in the given direction.

       Attentiveness of observers towards the model, in the sense that it was clearly in their
visual field, was achieved simply by the (small) size of test room. The response interval was
set to 10 s because previous studies have confirmed that this is an appropriate measure for
medium-sized birds (e.g. Schloegl et al 2007) and comparable to primates (e.g. Tomasello et
al 1999). Indeed, the ibises’ average time to respond was 3 s in Experiment 1 and 5 s in
Experiment 2. As the corvids, the ibises did not maintain oriented in the indicated direction
for the rest of the time interval but turned away after 1-3s (see supplementary videos). The
rapid habituation to the model’s looks (after just two trials) may indicate that the ibises can
inhibit their gaze following response. However, the rapid habituation may also reflect just an
artefact of our set-up, since birds never got any feedback to their responses. It is conceivable
that under more naturalistic situations, the stimulus attracting the model birds’ attention (e.g. a
bird of prey) might be visible for the gaze following bird as well.

Böhm C (1999) Ten years of Northern bald ibis EEP: a review. In: Böhm C, editor. 2nd Int EEP
       Studbook. Insbruck: Alpenzoo. pp. 73-88.
Pegoraro K (1996) Der Waldrapp. Vom Ibis, den man für einen Raben hielt. Wiesbaden: AULA.
Schloegl, C., Kotrschal, K. & Bugnyar, T. 2007 Gaze following in Common Ravens (Corvus corax):
       Ontogeny and Habituation. Anim. Behav., 74, 769-778.
Tomasello, M., Hare, B. & Agnetta, B. 1999 Chimpanzees, Pan troglodytes, follow gaze direction
       geometrically. Anim. Behav., 58, 769-777.
Tintner A, Kotrschal K (2002) Early Social Influence on Nestling Development in Waldrapp ibis
       (Geronticus eremita). Zoo Biology 21: 467-480.