. 1999 groups of hens. Whether this effect is due only to their social dominance over the
females or whether it can also be attributable to enhanced formation of subgroups or both, has so far not been clarified. For a cock, it is natural to gather hens and guard them
Ž .
against predators as well as other males McBride et al., 1969 . Therefore, it is likely that the presence of males in a flock would facilitate formation of subgroups. Widowski
Ž .
and Duncan 1995 reported clustering of female hens around the males in a flock of 50 females and 10 males. However, they could not identify any territorial subgroups.
The aim of this study was to investigate whether hens in large intensively housed flocks have home range areas, including a constant roosting site, that they tend to use
more than other areas and whether roosting partners recognize each other as indicated by a lower incidence of aggressiveness than among birds that roost far apart. Based on the
behaviour of free living hens, recognition of roosting partners and existence of home ranges are two important prerequisites for subgroup formation. Since males of feral fowl
are very active in defending their territory, a further aim was to study whether or not
Ž . males had any influence on these parameters. The hypotheses to test were: 1 that birds
would not move over the available area at random but rather tend to stay more within Ž .
certain parts of it than within others; 2 that they would constantly use a specific Ž .
roosting site at night; and 3 that birds using the same roosting site would be less aggressive towards each other as compared with birds roosting far away from each other
in the pen. A fourth hypothesis was that hens from mixed flocks would show the above three behavioural indications to a higher degree than hens from single-sexed flocks.
2. Materials and methods
2.1. Animals and housing Eight groups of ISA Brown laying hybrids were studied in two replicates of four,
with each replicate having two all female and two mixed groups. The birds were housed in large pens in a tiered aviary system. Group sizes ranged from 505 to 634 birds per
pen and density was 16 1 birdsrm
2
of floor area. The mixed groups contained 1 male per 24 2 females. The study was carried out over 2 years, with a replicate per year.
During the second year, the groups, due to a decision by the owner, also consisted of 50 Shaver 288 white females. To be comparable to the first year, only data from ISA
Brown birds were collected. All animals came from the same breeder and were brought up together each year. All groups were kept in the same house on the production farm.
Ž .
There were four pens, each surrounded by wire-mesh walls Fig. 1 . The pens had either four or five sections, each measuring 5.6 = 1.5 m. The limits of each section were
indicated by four wooden posts which were clearly visible and could be used to indicate the position of a bird in the pen. There were five tiers containing perches, feed and water
going through the sections. This provided each section with four ad libitum feeding-pans providing mashed pellets for brown layers, eight nipple drinkers and 20–25 astroturfed
roll-away nests and two separate floor-areas with wood-shavings. Perch length per hen
Ž Fig. 1. Cross section and plan of the system. T0–T5 indicate the different tiers with feeding pans, nipple
. drinkers and perches , Ns nests, L s littered floor, DSsdung scrapers. A–D are the four pens used with the
sections numbered.
was 16.5 cm. The temperature was 23 68C and the photoperiod was 14 L:10 D, with a light intensity ranging from 7 to 20 lx.
2.2. ObserÕations in the home pens At 70 weeks of age in both years, three groups of 10 females sitting closely together
Ž .
shoulder by shoulder during their night roost, about 2 h after the beginning of the dark period, were dyed with either green or blue or both colours, using crayons for sheep
Ž .
marking. In each pen, one group on the tiers T1 or T0 Fig. 1 near each end and one in the middle of the pen were coloured. The birds were observed during the 2 following
days and nights. Number of coloured birds per section was recorded once per hour for 9 Ž
. h, starting 1.5 h after light was turned on. Roosting sites section and tier were recorded
an hour after light was turned off.
2.3. Studies of small sample groups Between week 36 and 53, which is at the peak of egg production, during year 2,
Ž .
about 10 ISA Brown females per pen roosting closely together shoulder by shoulder at night were marked with coloured leg-rings. Four of these marked birds still roosting
together after 10–14 days were randomly picked out at night, individually marked by Ž
. adding leg-rings and put together the ‘‘close’’ group in a littered pen of 1 = 1 = 1 m.
Ž At the same time, four birds that were roosting far apart from each other i.e., 2 tiers
. Ž
and 1 section away, one from each of the fourrfive sections were picked out the .
‘‘apart’’ group , marked with leg-rings and put in another pen. The pens contained four individual nests, 1-m perch space, two food cups, two water cups and wood-shavings as
litter. They were placed next to each other in a room adjacent to the one that housed the larger pens. This anteroom was lighter, but the test pens were shielded off so that they
Ž .
had the same light intensity 7–20 lx as in the large pens. The groups in the two pens could hear, but not see each other.
This procedure with one ‘‘close’’ group and one ‘‘apart’’ group was repeated every fortnight with either birds from mixed flocks or with birds from single-sexed flocks
Ž .
balanced . When all four large pens were done, a new round was started, with new birds, resulting in a total of 16 small sample groups; eight from pens with all-female
flocks and eight from pens with mixed flocks. Ž
All agonistic behaviour in the group aggressive pecks — severe pecks at the anterior part of the body, threats — including stretching the neck, ruffling neck feathers and
displaying the side, and avoidances — including turning away the head, withdrawing, Ž
.. freezing, squatting, crouching and fleeing Oden et al., 1999
as well as gentle and
´
Ž .
severe feather pecks Vestergaard, 1994 were recorded. The performer and recipient of Ž
. each behaviour were identified. Each observation lasted for 2 days 2 = 9 h starting half
an hour after the onset of the light period each day. Each group was watched for 20 min, then there was a 10-min break before the other group was studied and so on, resulting in
eighteen 20-min observations periods per group. For ethical reasons, as high levels of aggression could be expected to occur, the animals in the small groups were supervised
constantly during the light period and also when they were put back into the large flocks to ensure their well-being.
2.4. Statistical analyses Ž
To determine if the location as defined by the section recorded and calculated as .
mean percentage of observations per day of the coloured birds differed from the Ž
random distribution, we used chi-squared tests with 3 and 4 degrees of freedom df ; the .
pens had 4 or 5 sections . Because of the number of tests performed and the risk for mass significance, the comparisons marked with
U
and
UU
cannot be considered strictly significant. However, those comparisons with a P-value less than 0.001 indicate that the
location of the birds differ significantly from a random distribution. The results are shown in Table 1.
Chi-square tests with 1 df were also used to test the null hypothesis that hens from end groups were randomly distributed in the two sections ‘‘same’’ and ‘‘adjacent’’ at
Table 1 Roosting site constancy over 2 nights and the tendency to stay during daytime within the same section as was
Ž .
2
used during the night roost ns16 end groups, 8 middle groups . x -values in brackets Penryear
Composition Night roost constancy
Daytime location end gr I
middle gr end gr II
end gr I middle gr
end gr II
U UU
U UU
Ž .
Ž .
Ž .
Ž .
Ar1 single-sexed
9.22 NS
17.0 7.9
NS 47.5
UU UU
U
Ž .
Ž .
Ž .
Ar2 single-sexed
38.8 NS
22.0 NS
9.4 NS
UU UU
Ž .
Ž .
Br1 single-sexed
NS NS
NS 21.6
NS 24.6
UU UU
U
Ž .
Ž .
Ž .
Br2 mixed
26.8 NS
24.6 NS
NS 10.6
UUU U
UUU
Ž .
Ž .
Ž .
Cr1 mixed
18.1 NS
13.0 NS
NS 18.1
UU UU
UU U
Ž .
Ž .
Ž .
Ž .
Cr2 single-sexed
35.4 NS
31.0 40.8
11.0 NS
UU UUU
U UU
Ž .
Ž .
Ž .
Ž .
Dr1 mixed
17.0 14.1
8.6 NS
NS 50.0
U UU
UU
Ž .
Ž .
Ž .
Dr2 mixed
9.2 NS
21.0 24.3
NS NS
NSs not significant, Chi-square-analysis per group with 3 df for tests in pens A and D, and 4 df for tests in pens B and C. A small P-value indicates that the distribution differs significantly from a random distribution
Ž .
see also Section 2.4 .
U
P - 0.05.
UU
P - 0.001.
UUU
P - 0.01.
the night roost and during the daytime. The values were calculated as mean percentages per night of birds for each section. Results are shown in Figs. 2 and 3.
Differences between the 16 small sample groups in the frequencies of the recorded behaviours were analysed using repeated measures ANOVA. The values for the nine 20
Ž .
Fig. 2. The percentage of birds observed roosting in the same section and tier as they were marked in, Ž
. adjacent section and most distant section, respectively. Values are means SEM for two end groups and one
Ž .
middle-group per flock four single-sexed and four mixed flocks observed at 2 nights. The mean percentage for each group was used in the chi-squared test. The test showed that the number of hens roosting in ‘‘same’’
section was significantly higher than the number of hens roosting in ‘‘adjacent’’ section both for end-groups Ž
2
. Ž
2
from single-sexed flocks x s 34.47, P - 0.001, 1 df
and end-groups from mixed flocks x s 46.98,
. P - 0.001, 1 df .
Fig. 3. The percentage of observations of birds during daytime in the same section as they were marked in, Ž
. adjacent section and most distant section, respectively. Values are means SEM for two end groups and one
Ž .
middle group per flock four single-sexed and four mixed flocks observed for 2 days. The mean percentage for each group was used in the chi-square test. The test showed that the number of hens found in ‘‘same’’
section was significantly higher than the number of hens found in ‘‘adjacent’’ section both for end-groups Ž
2
. Ž
2
from single-sexed flocks x s 5.38, P - 0.05, 1 df
and end-groups from mixed flocks x s 3.93,
. P - 0.05, 1 df .
Ž .
Fig. 4. The frequency of aggressive pecks over a 2-day period nine 20-min observations per day in small Ž
. sample groups from all-female flocks. The values shown are the mean number SEM of aggressive pecks
Ž .
per 20 min for four groups of birds picked out roosting closely together ‘‘close’’ and four groups of birds Ž
. picked out roosting far apart from each other ‘‘apart’’ . The values from day 1 are used in a repeated measure
Ž .
ANOVA. The test showed no effect in groups from single-sexed flocks F s 0.72, df s1 and 6, P s 0.43 .
Ž .
Fig. 5. The frequency of aggressive pecks over a 2-day period nine 20-min observations per day in small Ž
. sample groups from mixed flocks. The values shown are the mean number SEM of aggressive pecks per
Ž .
20 min for four groups of birds picked out roosting closely together ‘‘close’’ and four groups of birds picked Ž
. out roosting far apart from each other ‘‘apart’’ . The values from day 1 are used in a repeated measure
ANOVA. The test showed a significant difference between the ‘‘close’’ and the ‘‘apart’’ groups from mixed Ž
. flocks F s6.13, df s1 and 6, P - 0.05 .
min-periods day 1 in the experiment were used to test the difference between the Ž
. treatments ‘‘close’’ and ‘‘apart’’, using eight groups per treatment Altman, 1994 . The
results are shown in Figs. 4 and 5. Statistics in both experiments were performed using Ž
. Statview for Macintosh, Version 1.0 .
3. Results
