composition in the flocks, birds marked while roosting at the ends of the pens were significantly more often observed within these areas than in other areas of the pen during daytime and came
Ž .
back to the same roosting sites at night P - 0.05–P - 0.001 . This was not the case for birds from the middle of the pens, where the distribution in the pen in most cases did not differ from
random. These results show that laying hens in large groups are rather constant in their use of space, which indicate the presence of home ranges. However, environmental features that facilitate
localisation may be important. In summary, we think that these findings indicate the existence of subgroup formation. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Chickens; Spatial utilization; Agonistic behaviour; Sex composition
1. Introduction
In a natural habitat, feral fowl and red jungle fowl form groups and stay within a Ž
. Ž
certain area, the home range or territory if defended , and a constant roosting site if .
Ž .
undisturbed . In red jungle fowl Collias and Collias, 1967 or feral domestic fowl Ž
. McBride et al., 1969 , the home ranges become territories in the breeding season and
are actively defended by the dominant males, which is also a well-known behaviour in Ž
. fowl that are housed and cared for by humans e.g., McBride and Foenander, 1962 . The
Ž dominance is connected to the ‘‘personal sphere’’ of the male which is a kind of
. portable territory , a behaviour that is also expressed by subordinate males without fixed
Ž .
territories McBride et al., 1969 . However, territorial behaviour or personal spheres are not a uniquely male phenomenon. Broody hens defend the area around their chicks and
Ž .
Craig and Guhl 1969 found territorial behaviour in all-female flocks of domestic fowl Ž
. Rhode Island Reds . They also found that the tendency for individual birds to stay and
be dominant within a certain area seemed to be stronger in flocks of 400 than in flocks of 200 birds.
In a large flock, a hen cannot recognize all other individuals, and some authors have found that hens in this situation tend to keep together in subgroups of well known birds
Ž .
McBride, 1964; Bolter, 1987; Grigor et al., 1995 . However, according to other studies,
¨
Ž hens in large flocks move around without any sign of subgroup formation Hughes et al.,
. 1974; Appleby et al., 1989 , although Appleby et al. mentioned that crowding strongly
restricted the free movements of the hens. Ž
Hens usually prefer the company of familiar birds Bradshaw, 1992; Appleby and .
Ž Jenner, 1993; Dawkins, 1996 and show aggression towards unfamiliar birds Hughes,
. 1977; Zayan, 1987a , which might lead them to form small groups of familiar birds
Ž .
within a large flock. Grigor et al. 1995 found that birds tended to avoid strangers more than both high-ranking and low-ranking familiar birds. They concluded that birds
therefore might try to move within a restricted area to minimize the risk of meeting strangers. It is also very probable that social factors, like rank position, restrict the bird’s
Ž .
Ž .
movements Craig and Guhl, 1969 . Gibson et al. 1986 for example, found that low-ranking individuals moved only over a restricted area as compared to high-ranking
birds. Ž
Female aggressiveness is reduced in the presence of males in small McBride, 1964; .
Ž Craig and Bhagwat, 1974; Bsary and Lamprecht, 1994 as well as in large Oden et al.,
´
. 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
