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100
80
STI
60
40
LT I
20
0
0
1
2
3
4
5
Capture class
FIGURE 8.14
Proportion of birds of each line in five 100-animal capture classes of quails
selected for long or short duration of tonic immobility over 16 generations at three ages: 1, two
weeks old; 2, four weeks old; 3, six weeks old. LTI: (
'
) Age 1, (
K
) Age 2, (
&
) Age 3; STI:
(
K
) Age 1, (
'
) Age 2, (
&
) Age 3.
may reduce detectability. At closer distances, flight reaction predominates.
If flight is unsuccessful, fighting and tonic immobility may follow. The
least-studied behavior in this chain of reactions is the fight reaction. To study
this reaction we placed quail in a crush (squeeze) cage similar to that
described by
Satterlee and Johnson (1988)
. In this apparatus the animal's
movement is restricted but bouts of fight reactions occur when the bird strug-
gles to escape from the rush. The average number of struggles was six in the
long TI line and 56 in the short TI line. Hence the reactions described by
Ratner (1967)
as antipredator responses were more difficult to induce in the
short TI line. Differences in the threshold for the release of fear-related
behavior may explain these line differences.
In the open field, where environmental novelty induces low to moderate
levels of fear (see also
Turro-Vincent et al., 1995
, for a discussion of novelty
and fear responses), short TI line chicks initially showed less freezing but
the difference between the short TI and long TI lines disappears toward the
end of the 30-minute test when the habituation took place. In a capture
experiment where man had the quasi-role of predator short TI line birds
showed fewer flight reactions and were captured first (Mills and Faure,
1995). In situations which stimulate capture (crush cage and inductions
of TI), short TI line birds show strong flight reactions and do not readily
show the TI reaction. Furthermore, if the short TI line birds do show tonic
immobility, its duration is short.
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