2. General methods
2.1. Animals and husbandry Ž
Female ISA Brown chicks a medium hybrid laying strain originally derived from .
Rhode Island Red = Rhode Island White cross were obtained from a commercial Ž
. supplier at 1 day of age. They were randomly allocated to groups of 10 Experiment 1
Ž .
or 6 chicks Experiment 2 and housed in wooden boxes measuring 110 = 38 = 48 cm Ž
. length = width = height . These rested on shelving raised 1 m off the floor and all the
boxes faced in the same direction. The 1-cm wire-mesh floor of each box was raised 2 cm off the shelving to allow the passage of excreta. Chick starter mash and water were
provided ad libitum in plastic hoppers attached to wire grids suspended from the rear walls of each box. For maintenance purposes, the wire grids could be removed and
replaced remotely, thus minimizing the chicks’ visual contact with the experimenter. Ambient temperature was maintained at approximately 308C, by placing a dull emitter
heater above each cage. The photoperiod ran from 0500 to 1900 h.
The 38 = 48-cm wall at one end of the box was fixed in place only by hinges and was thus easily removable. This allowed easy presentation of a television monitor at the
end of the home cage. A wire-mesh grid situated directly behind the removable wall prevented the chicks escaping at this time while allowing them a clear view of the
monitor screen.
2.2. The open field The open field was situated in a separate room, to ensure auditory isolation, and the
ambient temperature was maintained at a similar level to that of the home environment. Ž
The apparatus consisted of a wooden box, measuring 75 = 75 = 60 cm length = width .
Ž =
height . One of the walls contained a ‘window’ measuring 40 = 40 cm length = .
width and covered with 2-cm wire-mesh. Thus, when a television monitor was placed behind this window, the screen was clearly visible to the chick under test. The walls of
the open field were painted matte black and, when the monitor was not being presented, the window was covered with a sheet of black card to ensure uniform wall colour. The
floor was painted light grey and it was delineated with black ink to form a grid of 16
Ž .
2
squares 4 = 4 , each measuring 18.75 cm . This grid pattern facilitated recording of the chick’s position and locomotor activity. Each row of four squares was labelled as a
zone, ‘Zone 4’ being nearest to and ‘Zone 1’ farthest from the window. The chicks’ responses were recorded on videotape using an overhead camera. The open field was
rotated between trials, to minimize any confounding effects of positional cues.
3. Experiment 1
3.1. Treatments and testing Eighty 1-day-old female ISA Brown chicks were housed in groups of 10 and assigned
at random to one of two treatments. Half the groups were exposed to the video image of
Ž .
an Apple Macintosh SS programme for 20 min, twice a day morning and afternoon , from 2 to 8 days of age. The SS video was filmed from a computer monitor using a
camcorder. The chosen SS was ‘Fish’, where a number of small, multi-coloured fish Ž
swim across a dark background. This image is known to be attractive to chicks Jones et .
al., 1996, 1998 and it is thought to be biologically neutral, i.e., unlike previous studies Že.g., Evans and Marler, 1991, 1992; Keeling and Hurnik, 1993; McQuoid and Galef,
. 1993 , it bears no connotations of predation, feeding or social attraction. During video
presentation, the end wall of the home box was removed and the television monitor was moved into place. Gaps between the sides of the box and the monitor were covered with
black cardboard in order to minimize visual contact with the experimenter or any other extraneous stimuli. Because removal of the wall during video presentation tended to
disturb the chicks slightly, the end walls of the remaining cages containing the control Ž .
N chicks were also removed twice a day. A wooden board painted the same colour as the home box was immediately moved into place during this procedure.
At test, each chick was placed individually in the open field at either 9, 10 or 11 days of age. Each chick was captured individually, carried in a cardboard box to the test room
and placed in the centre of the open field facing the ‘window’ behind which one of two stimuli was already in place. These consisted of either the familiar ‘Fish’ SS video or
Ž .
Ž . just a matte black cardboard sheet BC . Thus, the four test groups consisted of: 1
Ž . Ž .
reared and tested with the screensaver SSrSS ; 2 reared with SS, but tested with the Ž
. Ž . Ž
. Ž .
black card SSrBC ; 3 reared without SS but tested with it NrSS , and 4 no Ž
. exposure to SS during rearing and tested with the black card NrBC .
The latency to vocalize and the number of vocalizations were recorded directly. Other behaviours were recorded on videotape for later analysis using a micro camera sus-
pended directly over the open field. At the end of the 4-min observation period, the chick was removed and its head was marked with black ink before its return to the home
box. This facilitated identification of untested chicks. The floor of the open field was wiped clean with a dry tissue after each test.
Upon analysis of the videotapes we measured the latencies to the first step and to enter Zone 4, i.e., the row of squares closest to the window, as well as the numbers of
steps and squares entered. An ‘approach’ score was also estimated for each chick. Thus, its position was recorded at 5-s intervals during the 4-min test period; it scored 1 when it
was in Zone 1 and this score progressed through 2 and 3 to 4 if it was in the zone nearest the window. If the chick remained in the centre of the open field, i.e., on the line
separating Zones 2 and 3, after the first 5 s it was given a score of 2.5 until it moved fully into one of the zones. Thereafter, if a chick was observed on the border between
zones, it was judged to be in the zone containing the major part of its body. Because position was recorded 48 times, the overall score ranged from a minimum of 48 to a
maximum of 192. Thus, higher scores reflected close approach to the stimulus.
Sample sizes were uneven across treatments and days because mortality reduced the Ž
. number of available chicks to 78. Therefore, the effects of rearing SS or N , test
Ž .
condition SS or BC , day of testing and their interactions on the recorded behaviours were examined using a General Linear Model analysis of variance, which takes
unbalanced designs into account. Because the data did not fit a normal distribution, they were transformed to logarithms to better fit the assumptions of the analysis.
C.H. Clarke,
R.B. Jones
r Applied
Animal Beha
Õ iour
Science 66
2000 107
– 117
111 Table 1
Ž .
Ž .
Ž . Open-field responses back-transformed meansstandard errors of female domestic chicks reared with SS or without N daily exposure to a screensaver video and
Ž .
Ž .
then tested with the video SSrSS, NrSS or a black card SSrBC, NrBC and the results of tests of the effects of rearing, test conditions and their interactions Ž
. df s1
Ž . Behaviour
Treatmentrtest Effect of P
Ž .
Ž .
Ž .
Ž .
Ž .
Ž .
SSrSS ns 20 SSrBC ns 20
NrSS ns 20 NrBC ns18
Rearing SS or N Test SS or BC
Rearing=test Ž .
Lat. vocalize s 10.82.1
7.81.5 15.53.1
8.61.8 NS
- 0.03
NS Ž .
Lat. first step s 39.16.8
32.95.8 42.17.5
47.28.9 NS
NS NS
Ž . Lat. enter Zone 4 s
72.311.1 109.917.2
153.124.3 104.717.6
- 0.03
NS -
0.02 Ž
. Vocalizations no.
385.464.7 433.774.1
363.662.8 333.761.2
NS NS
NS Ž
. Steps no.
67.712.5 57.410.8
42.58.1 40.48.1
- 0.04
NS NS
Ž .
Areas entered no. 18.63.5
15.93.0 11.12.1
11.72.4 -
0.04 NS
NS Approach score
159.67.8 125.96.2
117.25.9 134.37.1
- 0.02
NS -
0.001 Ž .
Ž .
df s Degrees of freedom; Lat.s latency to; s sseconds; no. s number; NSs not significant, P 0.05.
3.2. Results and discussion There were no detectable effects of day of testing on any of the behaviours. On the
other hand, there were significant effects of rearing on the chicks’ latencies to enter zone Ž
. 4 as well as on their approach scores, numbers of steps and of areas entered Table 1 . In
general terms, SS chicks entered zone 4 sooner, spent longer in that area and were more active than the controls. However, there were significant interactions between rearing
and test conditions on two of the variables; SSrSS chicks entered zone 4 sooner and scored higher approach than SSrBC ones whereas the reverse was true for NrSS and
NrBC chicks. These findings probably reflect attraction towards the video image in the open field by SS chicks because of its familiarity whereas the novelty of this stimulus
likely elicited neophobia and avoidance in the naive controls.
Analysis of variance also revealed a significant effect of test condition on the latency to vocalize; the presence of SS in the open field delayed vocalization regardless of
Ž .
rearing condition Table 1 . This effect in the N controls, which had never experienced the video, probably reflected their fear of this novel stimulus whereas the presence of
this familiar stimulus may have dampened the expression of this social reinstatement Ž
. behaviour Faure et al., 1983 in SS ones.
Fear inhibits all other behaviour systems, including exploration and social reinstate- Ž
. ment see Jones, 1996 . Therefore, our findings that SS chicks were significantly more
active in the open field and tended to vocalize sooner and more than N ones, regardless of test condition, suggested that prior video stimulation may have reduced underlying
fearfulness. This suggestion was examined in Experiment 2.
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