Inma Estevez

Group size and perching behaviour in young domestic fowl.

To test the hypothesis that young domestic fowl perform less perch-related antipredator behaviour with increasing group size, White Leghorn pullets were reared in four replicate groups of 15, 30, 60 and 120 at a constant density of 5 birds/m(2). Each pen contained perches 20, 40 and 60cm above the ground. Perch space per bird per perch level was the same for all groups. It was predicted that, with increasing group size, domestic fowl would (1) spend less time on perches (i.e. more time down on the floor); (2) be less vigilant while perching; (3) spend relatively more time preening down on the floor. As predicted, the proportion of 3- to 18-week-old birds roosting on perches during scans throughout the photoperiod decreased with increasing group size, from 41+/-1.7% in groups of 15 birds to 33+/-1.6% in groups of 120 birds. This effect was due to reduced use of the lower perches; use of the highest perches was high at all group sizes. The proportion of birds vigilant on the highest perches of those present on that perch level decreased with increasing group size. The proportion of birds engaged in the vulnerable activity of preening down on the floor increased with group size. The frequency of transitions between floor and perches was not affected by group size but birds received more disturbances from other birds when on the top perch level in the larger groups. Thus, the decline in vigilance on the top perch level with increasing group size was not due to reduced disturbance from other birds. In conclusion, despite domestication and protection from non-human predators, changes in the use of perches by young domestic fowl with increasing group size were consistent with the antipredator hypothesis.

Dynamics of aggression in the domestic fowl

Abstract We conducted three experiments designed to investigate the effect of group size (GS) on the frequencies of different types of aggressive acts performed by 11–21-week-old White Leghorn pullets. In these experiments, we systematically controlled for bird density, pen size, and previous social experience in groups of different sizes. Aggression was measured in the context of competition for a limited supply of highly attractive food provided in two patches (central and peripheral) in addition to the regular (ad libitum) food supply. The birds were observed in their original groups of 15, 30, 60 and 120 birds (3–4 replicate groups per GS), reared together since hatch, or in temporary sub-groups of the original groups. In the first experiment (space per bird constant, pen size and GS history varying), the number of aggressive pecks delivered per food patch declined as GS increased from 15 to 120 birds. In the second experiment, utilising birds from the groups of 120 only (space per bird varying, pen size and GS history constant), the number of aggressive pecks delivered per patch increased as temporary GS increased from 15 to 60 birds. In the third experiment (space per bird and pen size constant, GS history varying), the number of aggressive pecks delivered per patch was constant among groups of 15 birds obtained from the groups of 15, 30, 60 and 120 birds. In all experiments, the central food patch was exploited sooner than the peripheral one. The actual number of birds at a food patch at a given time was more important in determining the frequency of aggression at the food patch than the number of birds present in an enclosure or previous GS experience. When a high number of individuals was present at a food patch, aggression at that patch was relatively infrequent. The results support the hypothesis that aggression in the domestic fowl is a dynamic process, with decisions about aggressive behaviour being made facultatively according to the relative costs and benefits of different behavioural strategies at a given time and place rather than being fixed obligatorily at a constant level according to the number of birds present in an enclosure and their ability to form dominance relationships.

Influence of vertical panels on use of space by domestic fowl

In the wild, cover is used by animals to seek shelter from the elements, protection from predators and aggressive conspecifics and as a way to reduce inter-animal communication. Rearing environments for captive raised fowl often contain open areas that are lacking in complexity and that are greatly underused. As a result, use of space within pen-type enclosures is often not uniform. This paper investigates the effect of increased environmental complexity on the use of space by broilers. The experiment consisted of three cover treatments (mesh panels, frame panels and no cover) and three group sizes (80, 110 and 140). The vertical panels, constructed of PVC piping, were positioned in pen centers, while the pen centers in the no cover treatment were left empty. It was hypothesized that the provision of vertical panels to pen centers would attract birds into the central space and would lead to a more uniform distribution of birds. Using a grid-coordinate system set up in each pen, scan samples were taken on the use of space in each pen four times per day, 3 days per week from 5 to 44 days of age. Use of space in the central region for the two cover treatments was significantly higher than for the no cover treatment (P<0.0001). The effect of cover treatment on the mean percentage of birds using the central space was influenced by age (P<0.0001) and by group size (P<0.05). Differences in the use of space between the frame and mesh treatment were only found during week 1. In the side, end and middle regions surrounding the panels, use of space was influenced by cover treatment and age (P<0.0001). Over 80% of the use of pen center occurred at the ends and sides of the panels. These results support the hypothesis that the presence of vertical panels results in a more uniform distribution of birds within the pen by increasing the number of birds using the center.

Effects of density on perching behavior of broiler chickens

Exercise through perching has been suggested as a way to reduce the impact of leg problems in broiler chickens. It is possible that higher stocking densities may motivate birds to perch more, and perhaps reduce some of the detrimental effects to broiler health seen with high stocking densities. The goal of this research was to investigate the effects of density (10, 15, and 20birds/m(2)) and perch design on the frequency of perch utilization. Mixed sex broilers were assigned to 36 pens in a four perch treatmentxthree density factorial with three replications for each treatment/density combination in a randomized complete block design. Pens were assigned to one of four perch treatments: control (no perches), horizontal (three horizontal perches), angled (three 10 degrees angled perches), or mixed angle (one horizontal, one 10 degrees angled, and one 20 degrees angled perch), at each of the three densities. The results show that although the frequency of perch use was low, (2.6%+/-0.15), significant preferences were clear. Perching frequency was significantly higher when birds were raised at stocking densities of 15 (2.88+/-0.303) or 20birds/m(2) (2.76+/-0.211), as opposed to 10birds/m(2) (2.10+/-0.209) as indicated by a marginally significant main effect (p<0.0597), and a significant linear effect (P<0.0427). The birds used the horizontal perches the most, followed by 10 degrees angled and mixed angle perch treatments with decreasing frequency. An effect of age was found, in that perching increased during the first 4 weeks, and dropped off significantly at the end of the rearing period for all perch treatments. In general, perches closest to the hallway or outside of the house were used more than perches in the middle of the pen. Preferential use of the highest section of the 10 degrees angled perches was also found. The applied perch treatments or densities did not significantly affect final body weight or feed conversion. Percent mortality due to heat stress showed a significant increase with density, while mortality not caused by heat stress did not change with perch treatment or density.

Use of space in the domestic fowl: separating the effects of enclosure size, group size and density

An understanding of how confined animals move within the space available to them is essential in the design of effective captive environments that maximize animal welfare. In addition to the obvious effect of enclosure size, other factors such as the number of individuals in the group and their density per unit of area are likely to affect movement patterns. Yet determining the specific contribution of each (enclosure size, group size and density) is a challenge because confounding between two or more of these factors is experimentally difficult to avoid. The aim of our study was to isolate their unique effects by using multiple contrasts with an efficient experimental design that included combinations of groups of 10, 20 and 30 domestic fowl (Gallus gallus domesticus) housed in 1.5, 3.0 and 4.5 m2 enclosures. This treatment structure enabled us to make comparisons across increasing enclosure size at both constant group size and constant density. In this study we show that enclosure size and density are the primary factors affecting patterns of movement and use of space for groups of domestic fowl. Animals in larger enclosures maintained larger nearest-neighbour distances, travelled greater distances and had bigger home ranges as measured by minimum convex polygons. These results suggest that larger enclosures encourage more exploratory movement in groups of domestic fowl. However, the positive effects of large enclosures may be limited by the effects of density. In this study, we found that group size had few effects.

Using artificial cover to reduce aggression and disturbances in domestic fowl

Abstract Differential use of space by domestic fowl may contribute to unnecessary aggressive interactions and disturbances among birds. Greater use of space near pen walls results in aggregations of birds around peripheral regions, leaving central areas unoccupied. These open areas provide opportunities for aggressive interactions between birds, while high levels of disturbances occur along the periphery as birds enter and leave the wall region to rest. This paper investigates the effects of increased environmental complexity on the occurrence of aggression and disturbances among broiler chickens. It was hypothesized that the provision of vertical panels to pen centers would reduce unnecessary interactions between birds by increasing the number of quality resting places and decreasing the amount of open areas. The experiment consisted of three cover treatments (mesh panels, frame panels and no cover) and two group sizes (80 and 110). Vertical panels, constructed of PVC piping, were positioned in pen centers, while pen centers in no cover treatments were left empty. Disturbances and aggressive interactions were recorded during 5min continuous focal samples of 180 focal individuals from 1 to 6 weeks of age. The presence of cover did not significantly influence the appearance of aggressive interactions ( P >0.05). The percentage of pens with observed aggression was significantly affected by age ( P P P >0.05). Disturbance frequency was influenced by the presence of cover ( P

Use of horizontal and angled perches by broiler chickens

Abstract Roosting increases the survival of wild relatives of domestic birds. Thus, we expected chickens to choose to roost on perches. We predicted that birds would use angled perches more than horizontal ones because an angled roost would be more similar to tree branches and thus more attractive to the birds, and also easier for the birds to access. We assigned 768 male broilers to 16 pens in a 4 treatment×4 replication randomized complete block design. Each of the four pens within each block contained one of the following treatments: 0° treatment (three 0° perches); 20° treatment (three 20° perches); mixed angle treatment (one 0°, 10° and 20° perch); and a control (no perches). Angled perches were designed to slope upward from the floor to facilitate access to the perches by broilers at all ages. A combination of differently angled perches within the same pen (mixed angled treatment) provided more roosting choices at all ages, as well as allowed the birds to use different angled perches as their size and strength changed with age. The perch designs differed significantly only in height at one end (slope). Perches were constructed of 1.9 cm inside diameter polyvinyl chloride (PVC) pipes, and were 91 cm in length with 5 equally spaced 28 cm long PVC crossbars. Perch use was recorded every 15 min for three consecutive hours, 4 days each week from day 3 to 42 using instantaneous scan sampling. Mean perch use was low across all treatments (2%), possibly due to heavy body weight and high ambient temperature in later weeks. However, distinct perching patterns were identified. Perch use was highest in the 0° treatment and lowest in the 20° treatment. Within the mixed angle treatment, 0° perch use was highest, followed by 10° and 20° perch use, respectively. Perching generally increased with age but peaked at week 5. A decline in perching occurred at week 6, a period during which the birds had the heaviest body weights and ambient temperatures remained high. We determined that perching increased with age of bird (through week 5), decreased with hotter temperatures, was greater for perches with lower angles (0° and 10°), and followed a daily crepuscular pattern.

Access to barrier perches improves behavior repertoire in broilers

Restriction of behavioral opportunities and uneven use of space are considerable welfare concerns in modern broiler production, particularly when birds are kept at high densities. We hypothesized that increased environmental complexity by provision of barrier perches would help address these issues by encouraging perching and enhancing use of the pen space across a range of stocking densities. 2,088 day-old broiler chicks were randomly assigned to one of the following barrier and density treatment combinations over four replications: simple barrier, complex barrier, or control (no barrier) and low (8 birds/m2), moderate (13 birds/m2), or high (18 birds/m2) density. Data were collected on focal birds via instantaneous scan sampling from 2 to 6 weeks of age. Mean estimates per pen for percent of observations seen performing each behavior, as well as percent of observations in the pen periphery vs. center, were quantified and submitted to an analysis of variance with week as the repeated measure. Barrier perches, density and age affected the behavioral time budget of broilers. Both simple and complex barrier perches effectively stimulated high perching rates. Aggression and disturbances were lower in both barrier treatments compared to controls (P<0.05). Increasing density to 18 birds/m2 compared to the lower densities suppressed activity levels, with lower foraging (P<0.005), decreased perching (P<0.0001) and increased sitting (P = 0.001) earlier in the rearing period. Disturbances also increased at higher densities (P<0.05). Use of the central pen area was higher in simple barrier pens compared to controls (P<0.001), while increasing density above 8 birds/m2 suppressed use of the central space (P<0.05). This work confirms some negative effects of increasing density and suggests that barrier perches have the potential to improve broiler welfare by encouraging activity (notably by providing accessible opportunities to perch), decreasing aggression and disturbances, and promoting more even distribution of birds throughout the pen space.

Appearance Matters: Artificial Marking Alters Aggression and Stress

Artificial marking of animals for identification is frequently employed by researchers in the behavioral, biomedical, agricultural, and environmental sciences. The impact of artificial marking on experimental results is rarely explicitly considered despite evidence demonstrating that changes in phenotypic appearance can modify animal behavior and reproductive success. Here we present evidence that artificial marking of individuals within a social group has frequency-dependent effects on the behavior and physiology of domestic fowl (Gallus gallus domesticus). We demonstrate that when only 20 or 50% of individuals within a group were artificially marked, the marked birds received more aggression and had lesser body mass than the unmarked individuals within the same group. Furthermore, in groups in which only a small proportion of the individuals were marked, we report altered plasma epinephrine and dopamine levels in marked individuals. These effects of marking were imperceptible when all birds in a group were marked. This finding has important implications for animal research because, when only a subset of group members is artificially marked and used for data collection, the results obtained may not be representative of the population.

Effects of crowding and access to perches on aggressive behaviour in broilers

Abstract To test the hypothesis that the frequency of aggression in broiler chickens will be lower in response to increased crowding and perch availability, groups of broiler were observed from 2 to 6 weeks of age. Both the type of aggression and the pen region in which the interaction occurred were recorded. Birds were housed at three crowding levels: least crowded (0.1m 2 per bird), moderately crowded (0.067m 2 per bird) and highly crowded (0.05m 2 per bird). These crowding levels corresponded to group sizes of 45, 67 and 90 birds, respectively. The perch treatments were: horizontal (three 0° perches), 10° angled (three 10° angled perches), mixed angle (one 0° perch, one 10° angled perch and one 20° angled perch) and control (no perches). We found that levels of threats and other types of aggressive interactions per bird were significantly lower in the moderately crowded treatment compared to the least crowded treatment. Aggressive interactions occurred much more frequently in the open regions of the pen, followed by areas containing perches. Contrarily, aggression in the feeder and drinker regions were rare. The main effect of perch treatment tended towards significance for the frequency of threats ( P =0.067) with the angled and horizontal perch treatments having the highest levels of threats. However, the effects of perch treatment on the level of other interactions were more complex as indicated by the significant interaction among location, perch treatment and age ( P