preferred to more complex ones, or at least to those used here. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Chicken welfare; Environmental enrichment; Pecking devices; Preferences
1. Introduction
Ž .
Chickens will actively seek stimulation Mench, 1994; Jones, 1996 and the opportu- nity to engage in foraging and exploratory behaviours is considered particularly impor-
Ž tant to them Blokhuis, 1986; Appleby et al., 1992; Rogers, 1995; Huber-Eicher and
. Wechsler, 1998; Newberry, 1999 . For example, both chicks and adult hens readily
Ž investigated and manipulated non-food as well as food-related items Gvaryahu et al.,
. 1994; Huber-Eicher and Wechsler, 1998; Jones and Carmichael, 1998, 1999a , broiler
chickens readily moved from their home pens through a gate into a nearby area when Ž
. this contained novel objects that were changed daily
Newberry, 1999 , and the introduction of conspicuous and manipulable objects into the previously least preferred
halves of chicks’ home cages resulted in a numerical trend towards increased usage of Ž
. those areas Jones and Carmichael, 1999b . Despite this, intensively housed birds are
often reared in barren, invariant environments that minimise the opportunities for exploration. Such environmental impoverishment can compromise the birds’ welfare by
increasing fearfulness, depression, feather pecking and cognitive impairment as well as
Ž leading to reduced productivity Appleby et al., 1992; Mench, 1992; Jones, 1996, 1997;
. Wemesfelder and Birke, 1997 .
Encouragingly, environmental enrichment can reduce many of the harmful states identified above as well as increasing the chickens’ behavioural repertoire and improv-
Ž ing their health and performance Jones, 1982; Yasutomi and Adachi, 1987; Vestergaard
. et al., 1993; Braastad, 1990; Nicol, 1992; Gvaryahu et al., 1994; Jones, 1996 . Putative
enrichment stimuli have included a wide variety of manipulable andror novel objects, foods, pictures or sounds, as well as intuitively desirable resources, such as nest boxes,
Ž perches, straw and pecking devices Jones, 1986; Braastad, 1990; Reed et al., 1993; Gao
et al., 1994; Gvaryahu et al., 1994; Jones and Carmichael, 1999a; Jones and Rayner, .
1999 . Although most studies reported beneficial effects of enrichment, an occasional cautionary note has been sounded. For example, the provision of operant feeders, shoe
Ž .
laces, plastic rods and a commercially available enrichment item Agri-Toy elicited alarm and actually increased social pecking in groups of floor-housed laying hens
Ž .
Lindberg and Nicol, 1994 . Furthermore, some stimuli, e.g., baubles, motorised devices, Ž
Agri-toys, elicited much less interest than others and were ignored in time Braastad, .
1990; Sherwin, 1993; Gao et al., 1994; Jones et al., 1996; Jones and Carmichael, 1999a . Inconsistencies across studies may reflect the choice of enrichment stimuli according to
their availability, cost and human preconceptions of what constitutes enrichment rather than a critical consideration of the chickens’ preferences and predispositions.
Surprisingly, though pecking behaviour has received considerable attention; the available information on pecking preferences is limited, sometimes contradictory and,
Ž .
with a few exceptions see below , often of little strategic relevance. For example, it is accepted that young chicks have a strong propensity to peck at small, three-dimensional
Ž .
objects Dawkins, 1968; Hogan, 1973; Rogers, 1995 . However, the range of test stimuli Ž
. has generally been small and a recent report
Huber-Eicher and Wechsler, 1998 suggests that the above propensity might not always translate into a preference. Indeed,
chicks showed more foraging behaviour when they had access to large polystyrene blocks or bundles of long-cut straw rather than to polystyrene beads or a layer of
Ž .
shredded straw, respectively Huber-Eicher and Wechsler, 1998 . Similarly, although Ž
feathers are considered to be particularly attractive stimuli for pecking Appleby et al., .
1992 , their attractiveness may depend on whether or not they are on the bird. Indeed, though gentle pecking at the feathers of other chicks appears as early as 3 days of age
Ž .
Blokhuis, personal communication , we found that young chicks pecked much more readily at string than at bunches of feathers collected from age-matched conspecifics
Ž .
Jones et al., 1997 . Neither is there consensus concerning chicks’ preferences for Ž
pecking at certain colours even when the class of stimulus, e.g., food, is the same see .
Experiment 2 . In view of these apparent inconsistencies we attempted to establish the birds’ pecking
preferences in a systematic manner by presenting pair-housed chicks with a choice of stimuli. Previous studies revealed that string was the most attractive of a number of
Ž stimuli presented to chicks of the ISA Brown laying strain Jones et al., 1997; Jones and
. Carmichael, 1999a . We now asked if this preference would generalize to include chicks
of another commercial laying strain and we assessed the effects of manipulating the component features of that type of stimulus eliciting the greatest interest in order to
identify its most attractive form. Therefore, in Experiment 1 we measured the pecking preferences of pair-housed Lohmann Brown chicks for lengths of string, chains or beads
Ž .
when these were presented consecutively one stimulus per day or simultaneously for 10 min on each of 3 consecutive days. Rationales for our choice of stimuli are given in
the introductions to each experimental section. Preference was defined as the tendency for the chicks to peck sooner and more often at one stimulus than at the others. Having
determined which stimulus elicited most interest we then varied its component features. Colour preferences were examined in Experiment 2; here the chicks were simultane-
Ž .
ously presented with five differently coloured white, yellow, blue, green or red
versions of the preferred stimulus. The effects of combining colours within a stimulus Ž
. thus arguably increasing complexity and of varying the size of the preferred device
were studied in Experiments 3 and 4, respectively. Experiment 5 examined chicks’ responses to bunches of string that either incorporated small silver beads or not.
Ž .
We focused on only one sex in the present study because the duration persistence of attention that chickens pay to specific stimuli is known to be sensitive to sex and to
Ž .
circulating levels of testosterone Andrew, 1972 . We chose females for the present study because the number of laying hens kept in industry far exceeds that of cockerels.
2. General methods
