4. Discussion
As expected, group members delivered more aggressive pecks and threats to the
introduced bird when in the small pen compared with the large experimental pen. The
number of these aggressive pecks are most important in respect to the problems in
commercial fattening of turkeys as they cause serious injuries which may lead to death.
T. Buchwalder, B. Huber-Eicher / Applied Animal Behaviour Science 89 (2004) 207–214 211
Fig. 1. Mean number of fights, chases, aggressive pecks and threats, and mean ratio of distance between the
introduced bird and test-group members compared with the distance between test-group members, per test in the
small and large experimental pen. Probability levels are indicated by *P < 0.05.
The introduced bird also kept a larger distance from the group members in the larger of the
two experimental pens, confirming our hypotheses, that in the small pen it would be more
difficult for the introduced bird to retreat far enough to avoid the attacks of its opponents.
However, the introduced bird did not make use of all of the available space in the large pen.
A distance of 50 cm more was apparently enough to provoke significantly less pecks to the
head and neck, indicating a critical distance to avoid such injurious pecking, as well as a
tendency to join the group. In fact, it seemed that the introduced bird was trying to become
integrated into the group and just took the opportunity of retreating in risky situations when
being the target of aggressive behaviour. From our results it is not clear exactly how much
space turkeys need to be able to retreat to the observed 151 cm, but it must be between 1
bird/m2 (small pen) and 0.08 (large pen) i.e. much lower than the usual 3 birds/m2 in
commercial fattening of turkeys. The observed distance may represent an upper limit
where turkeys are able to recognise conspecifics individually. Individuals further away
would then no longer be recognized as unfamiliar and therefore not be antagonised. Gigas
(1987) reports that turkeys can recognise a grain of maize from a maximal distance of
150 cm. Dawkins (1995) found that laying hens discriminate conspecifics only up to 50 cm
distance away. The questions as to the maximum distance at which turkeys are able to
recognise conspecifics individually and at which maximal density they are still able to
retreat far enough to avoid risky aggressive interactions will be rewarding objectives for
further research.
In contrast to aggressive pecking and threats, we did not find significant differences
in the number of fights and chases between the small and large pens. For both actions,
we expected higher number of incidences in the small pen, but instead we observed that
the introduced bird frequently did not respond to the challenge of its opponents, when in
the smaller pen so that fighting did not occur. Chases only occurred following a fight and
consequently there were also less chases observed. We may only speculate on the
reasons for these low numbers of incidences, but possibly the birds simply did not have
enough space to perform the action or were aware of a risk of injury. This is supported
by the low number of leaps observed. Turkeys use their wings to jump at the
opponent when leaping, and in a restricted space, the wings are at a high risk of getting
broken.
To summarise, the present study shows that in small groups of turkeys, an increase in
floor space reduces the number of aggressive pecks and threats aimed at an introduced
unfamiliar conspecific. Additionally, we found evidence that there might be a critical
distance at which this aggressive behaviour is avoided.
We conclude that one of the reasons for high injury rates in fattening turkey toms reared
under commercial breeding conditions might be the restricted space due to high stocking
density which prevents the birds from moving far enough away from attacking conspecifics
to avoid injuries.