AND OTHER SPECIAL SENSES
have panoramic vision of about 300°, and
possible binocular vision of 26°. Sight is an acute sense
and colour vision is important. Preference is probably
for colours that are easiest to see against a green
background, and this ability to
discriminate colour is unlearned.
One-day-old chicks prefer to peck at round rather
than angular objects (Goodwin and Hess, 1969). They
also prefer to peck small (0.3 cm), solid objects, but
would rather approach fairly large ones, especially if
moving or making a rhythmical noise.
of food is based on visual cues and immediate
taste cues. This is important to know when managing
poultry and their food. If the composition of the
food changes due to availability of grains, the hens may
not change easily to eating seeds of a different shape or
is an acute sense in chickens, and communication
within and among flocks of birds takes place
mainly via signals provided by postures, displays and
vocalisations (Mench and Keeling, 2001).
and displays are used to signal threat and
submission (Kruijt, 1964).
varieties of vocalisations are in the categories
of warning and predator alarm calls; contact calls;
territorial calls; laying and nesting
calls; mating calls; threat calls;
submissive calls; distress, alarm or fear calls; contentment
calls; and food calls (Mench and Keeling,
Morphological features associated with the head
and neck are important for both communication and
social recognition (Mench and Keeling, 2001). Comb
size and colour in males and females are influenced by
the levels of sex hormone and are indicators of social
status (Guhl and Ortman, 1953).
known about the sense of smell.
ORGANISATION, DOMINANCE HIERARCHIES AND
three common types of husbandry systems
used for intensively housed chickens:
Chickens are kept in groups of 3–10 birds in
cages with space allowances of 350-600 sq cm per bird
(Mench and Keeling, 2001). Stocking densities vary
around the world, 350 sq cm on average in the United
States, to as high as 700-800 sq cm in Norway and
Switzerland (Savage, 2000).
Meat chicken sheds. These hold from 10,000–70,000
meat birds, housed on litter in either semi-enclosed or
environmentally closed houses. Stocking densities vary
from 30–50 kg live weight per square metre (Mench and
sheds. These house flocks of several thousands
in semi-enclosed or enclosed housing on litter or
wire. The male to female ratio is about 1 to 8–15, with
the space allowance of 0.2–0.3 square metre per bird
(Mench and Keeling, 2001).
social organisation differs in these systems but
peck orders emerge in cages and breeder sheds. This
has not been shown in meat chickens. In cages, there
is a definite hierarchy established by pecking and
threatening when the hens are placed in the cage, usually
a few weeks before laying commences at six
social order in broiler flocks is relatively unimportant
as they are generally processed at an age when
the establishment of social stratification is just beginning
hens have complex interrelationships involving
social rank, aggression, feeding behaviour and egg
production (Mench and Keeling, 2001).
groups kept together for some months, subgroups
form and become restricted to an area. This
means that birds can recognise their own group members
and those of an overlapping territory. It was suggested
that this territorial behaviour is important in large
flocks as it reduces the numbers of conflicts when
strangers meet (McBride and Foenander, 1962). It has
also been shown that individuals are more dominant in
the area where they spend most time. Thus in larger
flocks, hens tend to live in neighbourhoods where they
are well-acquainted (Craig and Guhl, 1969).
hens choose to feed close to each other
when given a choice of feeding locations, which demonstrates
the importance of social attraction (Meunier-
Salaun and Faure, 1984).
are in the same cage and in neighbouring
cages synchronise their feeding.
show socially facilitated feeding, in particular,
they peck more at feed when they have company
than when alone (Keeling and Hurink, 1996).
also been shown (McBride et al.,1963) that
hens do not move randomly in normal intensive housing
conditions—they maintain their heads at regular patterns
of spacing and orientate them to avoid the frontal
aspects of other birds. However, they turn, probably in
defence, to face approaching birds.
that are too low for the chickens to raise
their heads in a threat, aggression is provoked by an
approaching bird rather than by a bird that is in continuous
close proximity (Hughes and Wood-Gush, 1977).
Recognition of each other is based on features of
the head, the comb being the most important cue (Guhl,
distinguish between breeds that are dissimilar
but are unable to distinguish between individuals
of such breeds.
ability of flock mates to recognise and remember
one another becomes very difficult under commercial
poultry husbandry conditions where group sizes are
very large (Mauldin, 1992).
coloured lighting can affect a chicken’s ability
to discriminate between other birds (Mench and
Mortality, production and behavioural problems are
all worse in large groups of hens, which implies the
formation of unstable social groups (Mench
and Keeling, 2001), so this is
particularly a problem in barn/aviary
orders are regarded as highly stable once
established, and in mixed groups, males and females
have their own peck order (Guhl, 1958).
pecking begins to occur within a few weeks
after hatching, stable dominance and subordinate
relationships usually do not become established
until 6–8 weeks of age in cockerels and 8–10 weeks in
pullets (Guhl, 1958).
potential problem in the industry, depending on
spacing and the strain of poultry, is the frequency and
severity of agonistic acts. Al-Rawi and Craig (1975) did
an interesting experiment, beginning with relatively generous
space allowances per hen and then decreasing
the space. They found that social interaction rate
increased as space decreased then suddenly fell off as
space decreased further. It has been shown that individuals
behave less aggressively towards subordinates
in the near presence of dominant flockmates. This ‘third-party-effect’
(Ylander and Craig, 1980) is associated
with a reduction in agonistic behaviouror it may be due
to the lack of space for threat displays.
results of this experiment on spacing indicate
that interpretation of the results is important. Another
point to be aware of is that selection for productivity
traits may cause behavioural changes. Increased
aggressiveness and social dominance, prior to full
maturity (Bhagwat and Craig, 1977) has accompanied
the selection for early onset of egg production in several
genetic stocks studied.
Higher-ranking hens may have better egg production
than the lowest ranked bird in a cage, possibly
because the higher ranked birds have greater access to
feed (Cunningham and van Tienhoven, 1983).
aggression is seen at the feed trough, where
there is some competition among the chickens (Mench
and Keeling, 2001). Aggression in cages is relatively
low, as the small group size in the cages allows the
hens to establish a stable dominance hierarchy (Mench
and Keeling, 2001). Once a social group becomes
organised, the incidence of agonistic interactions
decreases (Mauldin, 1992).
of displays occurs before mating, based on a
stimulus-response sequence (Fischer, 1975) initiated by
the male (see diagram).
(Modified from Fischer, 1975).
courtship displays are generally elaborate,
involving vocalisations and noises, postures, spreading
of the feathers to increase apparent size and emphasise
plumage characteristics (Kovach, 1975).
behaviour and dominance relationships are
important in the management of mating. Because the
female must crouch to elicit courting behaviour in the
male and this is also a submissive behaviour, high-status
females are often difficult to mate. Although it is
never done commercially, research suggests that to
overcome this, chickens may be sub-flocked and this
reduces the number of individuals each may dominate
or be submissive towards. When high-ranking hens are
isolated from hens lower in the peck order, they crouch
more often than when in the larger flock, and hens in the
middle and lower thirds of the peck order crouched less
often (Guhl, 1950).
behaviour or broodiness has been selected
out of commercial laying strains so it is not important in
intensive poultry husbandry systems.
broody hen with chicks, a bond is formed and
the chicks learn to respond to the maternal feeding call,
distress call and to the hen’s ‘purring’ sound as she settles
down. Repeated exposure to her, accompanied by
food, guidance and protection, strengthen the filial
bond. Exposure to maternal calls during embryonic
development may be important for the development of
post-hatch species-specific maternal call recognition
precocial, birds are self-sufficient after hatching,
but parents serve an important protective function
while also teaching the chicks about edible and inedible
foods (Nicol and Pope, 1996).
chicks imprint on their parents in the first
few days of life (Rodgers, 1995). Imprinted chicks
remain close to the imprinted object, which is normally
a parent, but under laboratory conditions may be a variety
of different objects (Mench and Keeling, 2001).
Sometimes males will hound other males, which can
be a problem.
Caged birds may exhibit some abnormal behaviour
such as head flicks and feather pecking, i.e., pecking
and pulling the feathers of other birds (Mench and
Keeling, 2001). Feather-pecking may be a form of redirected
ground pecking (Blokhuis, 1989). Experience in
early life with ground pecking may influence pecking
behaviour in later life (Blokhuis, 1991). The motivation
for the redirection of ground-pecking happens when the
incentive value of the ground is low, compared with the
incentive value of pecking substrates (Bindara, 1969).
In high-density situations, the birds and feathers make
up a higher proportion of stimuli relative to the litter
area. It is possible that the birds may perceive the
feathers as dust and that may
cause a redirection of groundpecking to
feather-pecking (Hansen and Braastad,
some housing systems, cannibalism can be a
Pseudo-mating occurs most frequently between highranking
males and low-ranking males, who are pursued
and trodden (Guhl, 1949) and indicates that dominance
relationships are important. The same situation may
occur in flocks of hens.
ALTERNATIVE HUSBANDRY SYSTEMS
ongoing research into alternative husbandry
systems, which may in the future replace the cage.
Commercial egg layers are housed mostly in cages in
groups of 3–10, with much restriction on the bird’s
movement. Meat chickens are housed on litter in either
semi-enclosed or environmentally closed houses, often
in groups up to 70,000 birds.
birds are maintained in free-range conditions
as it is uneconomical in terms of labour, food
requirements and wastage in egg handling, problems of
predators and disease control, and lack of egg hygiene
(Sainsbury, 1980). Free-range eggs have a 15–20%
rate of dirty eggs that are classed as second-rate eggs,
whereas the rate in conventional caging is 2% (Slack-
problem of deciding what is best for a hen is difficult
and some researchers have devised experiments
in which they provided birds with a choice of flooring
(Hughes and Black, 1973; Hughes, 1976) and a choice
of environments (Dawkins, 1980; Wegner, 1980).
chose fine hexagonal mesh over coarse
rectangular mesh and over perforated steel sheet. It
seemed that the hexagonal mesh supported the bird’s
foot at more points than the other two floors. In comparing
wire and litter floors, it was found that previous
experience with either wire or litter floors affected the
choice: birds reared on litter spent more time on litter
than those raised on wire.
environmental preference studies (Dawkins,
1980), hens were given a choice of cage or an outside
run. Hens used to living outside in the garden all chose
the run. Hens previously used to living in cages tended
to choose the cage on first trial, although subsequently
they came to choose the run. So choice is strongly
influenced by previous experience. The fact that the
hens prefer an outside run to a cage is not indicative of
suffering in a cage. Preference in itself is no indication
egg laying, hens will work to gain access to
nest sites. The demand for this resource is inelastic.
Hens in cages without nests often show abnormal activities
during prelaying, such as increased pacing,
reduced sitting and displacement behaviours (Sherwin
and Nicol, 1993). So, if cages contain a nesting box,
there is an opportunity for more normal behaviour.
Different systems have been tested for performance
and behaviour traits of laying hens since 1977 in Celle,
Germany (Wegner, 1980).
Comparison of different maintenance systems.
Free-range system with deep litter, deep litter without
range and battery cages. Egg production has been
found to be more economical in cages (i.e., less feed
Comparison of different cage types with different
numbers of hens per cage. There is reason to suppose
that some differences exist in behaviour between
battery and deep-litter systems, so cage types other
than the conventional battery cages are being compared.
two types of ‘get-away’ cages developed in
England and The Netherlands.
(i) 80 cm x 100 cm x 65 cm (l x w x
d) cage with three perches and two feed
troughs at equal levels on both sides of
the cage, with 16 and 20 hens, respectively,
with four nests per cage. The cages are either filled with
wood shavings or the sloping floor that forms the roof of
the cage below allows the eggs roll into a collecting tray.
Fibre mats are put into the nests to make them more
attractive. It is a two-tiered system. This design had
problems as the hens used the nests to scratch, sand
bath and rest in, so 25–30 per cent of eggs were dirty,
destroyed or eaten. Too much labour was required to
supply litter daily and collect the eggs.
(ii) 1 m x 1 m x 55–80 cm (w x d x
h) Celle cage with four nests, each with a
sloping fibre floor, two feed troughs on
both sides and one sand bath. The whole
cage floor has a 5° slope from the side of the sand bath
to the side of the nests. It is also a two-tiered system.
production in these get-away cages with 15–30
hens per cage of 1 sq m floor area is similar to that in a
conventional cage with three or four hens per cage.
Some disadvantages of this system were cracked eggs
at the floor, which was not elastic enough; and the sand
bath, which was opened eight weeks after the start of
laying, was immediately used for laying and was forced
to be shut. Monitoring of hens was also difficult in this
cages (e.g., the Edinburgh modified cage).
These cages are similar to battery cages but provide
more features for the chickens, which allows a wider
variety of behavioural characteristics. The cage houses
four hens and provides them with a perch, a nesting box
and a dust bath (Wathes and Charles, 1994).
aviary and perchery systems. The main idea is to
make better use of the space between floor and ceiling
in the poultry house by installing several horizontal levels
and so increase the number of hens per square
metre of floor area. The aviary system used was made
of plastic foil and measured 8.50 m wide x 12 m long (10
hens per square metre of floor area).
use of height is achieved by having two rows
of perches along the house. One feed trough is on the
floor and the other is on the perches. There is a ‘farmer
automatic nest’ in two parallel rows and in two tiers,
which can be moved out of the aviary into a special
room where the eggs are automatically removed from
the litter. Nipple drinkers provide water. Good results for
laying performance and number of losses compared
with hens in cages, have been achieved.
analysis of results was completed in April
1981, and a report referred to the West German government.
Murphy (1982) gives an outline of the final
conclusions in her comprehensive report. She states
that if all aspects studied are considered, then none of
the systems may be described as totally adequate for
the overall welfare of the birds.
showed overall advantages in economy and
hygiene; there was significantly less social conflict
among the birds with a lesser number and intensity of
threats, agonistic pecks and associated vocalisations,
and fewer deaths from cannibalism than in the floor systems.
However, when compared to floor-housed birds,
those in cages showed more behaviour indicative of
conflict and frustration during nest selection and egglaying
behaviour. It has been recommended that further
research into completely new husbandry systems or
modifications of existing systems be carried out to provide
optimal conditions in all aspects of egg production.
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