Neighbourhood analysis as an indicator of spatial requirements of broiler chickens

The appropriate stocking density for broiler chickens is a much discussed topic in animal welfare. To determine at which stocking density the level of crowding becomes aversive to 4–6-week-old broiler chickens, spatial distribution and behaviour of groups stocked at 8, 19, 29, 40, 45, 51, 61 or 72 birds per 3.3 m² were analysed. Spatial distribution was evaluated using three different indices: inter-individual distances, nearest neighbour distances and Dirichlet polygon areas. The assumption was that broilers would increase the distance to their pen mates if high densities (i.e., close proximity to pen mates) were experienced as aversive, whereas they would decrease this distance if close proximity was experienced positively. Increased distances to pen mates would lead to increased nearest neighbour distances and a more homogeneous distribution (i.e., lower variation of inter-individual distances and of Dirichlet-polygon size) than expected by chance. The distribution expected by chance was determined from both a random distribution and a ‘resource-corrected’ random distribution (which incorporated environmental influences on spatial distribution but excluded social ones).Behavioural observations showed that at higher stocking densities more sitting bouts (P = 0.003) and adjustments of the sitting and lying posture (P < 0.001) occurred. It was also found that nearest neighbour distance varied according to behaviour (P = 0.001). Birds that were eating/drinking were further apart from their nearest neighbour than birds that were foraging, preening, adjusting their sitting or lying posture or showing “other” behaviour.The results from all three methods of spatial analysis suggested that broilers in groups ≥19 birds per 3.3 m² (ultimately equivalent to 15 kg/m²) started to experience the proximity of conspecifics as aversive at some point during the last 3 weeks of rearing. However, nearest neighbour distance analysis showed evidence of aversiveness earlier in life than the other methods of analyzing spatial distribution (variation in inter-individual distance and polygon size), suggesting that nearest neighbour distance is the more sensitive indicator of space requirements.When uneven use of the different areas within the pen was reflected in the expected distribution (i.e., for comparisons to the resource-corrected random distribution) different results were obtained than when such measures were omitted (i.e., for comparisons to the random distribution). As such, this study emphasises the importance of accounting for environmental influences on distribution within a pen.     

Space Availability in Confined Sheep during Pregnancy,Effects in Movement Patterns and Use of Space

Space availability is essential to grant the welfare of animals. To determine the effect of space availability on movement and space use in pregnant ewes (Ovis aries), 54 individuals were studied during the last 11 weeks of gestation. Three treatments were tested (1, 2, and 3 m²/ewe; 6 ewes/group). Ewes'' positions were collected for 15 minutes using continuous scan samplings two days/week. Total and net distance, net/total distance ratio, maximum and minimum step length, movement activity, angular dispersion, nearest, furthest and mean neighbour distance, peripheral location ratio, and corrected peripheral location ratio were calculated. Restriction in space availability resulted in smaller total travelled distance, net to total distance ratio, maximum step length, and angular dispersion but higher movement activity at 1 m²/ewe as compared to 2 and 3 m²/ewe (P<0.01). On the other hand, nearest and furthest neighbour distances increased from 1 to 3 m²/ewe (P<0.001). Largest total distance, maximum and minimum step length, and movement activity, as well as lowest net/total distance ratio and angular dispersion were observed during the first weeks (P<0.05) while inter-individual distances increased through gestation. Results indicate that movement patterns and space use in ewes were clearly restricted by limitations of space availability to 1 m²/ewe. This reflected in shorter, more sinuous trajectories composed of shorter steps, lower inter-individual distances and higher movement activity potentially linked with higher restlessness levels. On the contrary, differences between 2 and 3 m²/ewe, for most variables indicate that increasing space availability from 2 to 3 m²/ewe would appear to have limited benefits, reflected mostly in a further increment in the inter-individual distances among group members. No major variations in spatial requirements were detected through gestation, except for slight increments in inter-individual distances and an initial adaptation period, with ewes being restless and highly motivated to explore their new environment.     

Inter-male Spacing and Aggression in African Painted Reed Frogs,Hyperolius marmoratus

Inter-male spacing and the role of aggression in the maintenance of spatial organization was examined in choruses of Hyperolius marmoratus males housed in a semi-natural enclosure. The effects of chorus size on spacing patterns, nearest neighbour distances and male aggressive behaviour were examined. Males were found to reduce nearest neighbour distances as chorus size increased. This was accompanied by a shift in spacing pattern from even in small choruses (5–9 males) to random in choruses of 10 to 13 males. In choruses of 14, spacing patterns were once again even. The reason for these shifts is unclear but may reflect a sudden, rather than gradual increased tolerance by individuals to high neighbour call intensity as space to call from becomes more limited. The level of male aggression was influenced by chorus size and the time of night. In general, more aggressive interactions occurred in high density choruses. However, this did not translate into higher levels of individual male aggression as density increased. Individual male aggression was high in early evening choruses and declined to a minimum at peak chorusing time. High levels of aggression during early evening may reflect the establishment of calling sites by males, while the drop in aggression at peak chorusing time may occur in response to the presence of females in the chorus at this time or as a consequence of masking of neighbours calls.     

An analysis of factors influencing spatial distribution in flocks of grazing sheep

The spatial distribution of small groups of sheep (5–40) when grazing at a range of densities (4–29 sheep ha^?1) was investigated experimentally. Under these conditions, where the sheep groups rarely split into distinct sub-groups, the angular distributions of the sheep were usually random, but the radial distributions were not. A “concentration curve” representing the density of the sheep as a function of their distance from the centroid of the flock exhibited a peak at a distance varying with breed, flock size and density. Dorset Horn sheep were distributed more widely than Merino, Polwarth, Corriedale or Southdown sheep. Distribution, also measured as area “occupied” per sheep, ranged from 15 to 67 m² among these breeds.Two breeds were studied in detail. Both Merino and Corriedale sheep spread further apart as flock size increased. As density decreased, Merinos but not Corriedales came closer together. There was little correlation in these studies between area occupied per sheep and distance to first nearest neighbour, because distance to nearest neighbour varied relatively little compared with that of average area occupied. Thus, spatial dispersion seems to have two components: (a) a relationship to a neighbour by each individual; (b) spatial cohesion of the group as a whole which is influenced by group size and density.     

Behaviour of Bachelor Males of the Przewalski Horse (Equus ferus przewalskii) at the Reserve Askania Nova

The aim of this study was to investigate social relationships between Przewalski horses at a high density in a bachelor group housed in a 3.5-ha enclosure. The group consisted of 16 males aged 5 to 16. Behavioural data were collected during 18 days, total 216 h. Fifteen minute focal animal sampling was used; each horse was observed three times a day for a total of 45 min. The occurrence of 25 behaviours was recorded, and group spacing behaviour was studied using nearest neighbour recordings. The group divided into four subgroups; this supports earlier findings of bachelor groups (n≥10) dividing into two or more subgroups if they included several males aged >5 years. The total frequency of social interactions was 14.6±1.1 h^?1. Although the density of the group in this study was higher than in other zoos, the males interacted agonistically only 3.6 h^?1. The most frequently observed social behaviour categories were friendly interactions. This study shows possibilities to use some investigative behaviours (marking, flehmen, olfactory investigation, etc.) as indicators of social status of animals in a group.     

Ecological and Social Determinants of Group Cohesiveness and Within‐Group Spatial Position in Wild Assamese Macaques

Individual spatial positioning plays an important role in mediating the costs and benefits of group living and, as such, shapes different aspects of animal social systems including group structure and cohesiveness. Here, we aim to quantify variation in individual spacing behaviour and its correlates in a group of wild Assamese macaques (Macaca assamensis) in north‐eastern Thailand, which experiences both predation pressure and within‐group feeding competition. Data on individual spatial positions were collected during group scans using GPS devices and results suggest that both group cohesiveness and individual spatial positions within a group can be adjusted to mediate the costs and benefits of group living. Individuals had greater nearest neighbour distances and lower numbers of close neighbours when the group was feeding, compared to when the main group activity was resting/social or moving. This is likely due to the high costs of proximity associated with feeding competition. Immature individuals and females with young infants which are more vulnerable to predation were located closer to the centre of the group than both adult males and females without infants. This indicates the importance of predation risk in driving individual spatial position. Among adults, higher ranking individuals occupied more central positions within the group while lower ranking individuals were more peripheral. It appears that low ranking individuals trade reduced feeding interference and improved feeding success for increased predation risk. This could help explain why females in the study population do not display a rank related skew in energy intake.     

The effect of zooplankton abundance on feeding behaviour and prey size selection in Atlantic salmon,Salmo salar,alevins1

In an experiment on the effect of zooplankton density on feeding behaviour and prey size selection in Atlantic salmon (Salmo salar) alevins, total behavioural activity (feeding, social, ambiguous) was positively related to prey abundance up to a density of 350 items 1^?1, after which activity peaked. Feeding error (missed attacks and/or rejected ingestions) increased with prey density. The likelihood that an alevin would attack an item upon which it had binocularly fixed (no. bites/no. visual fixes) peaked at densities of 270 items 1^?1 and then declined. Feeding success (no. ingestions per bite or per fixation) also peaked and then declined. Changes in success were reflected in total number of items found in the gut. At high prey abundance (608 items 1^?1) only 0.5 – 0.9 mm copepods were preferred components of alevin diets. Over all prey densities, preferred sizes of cladocerans and copepods did not overlap. These results may reflect a perceptual constraint (at high zooplankton densities) on alevin feeding behaviour.     

Spatio-temporal patterns of colony distribution in monodomous and polydomous species of North African desert ants,genus <Emphasis Type="Italic">Cataglyphis</Emphasis>

Summary Two monogynous species of North African desert ants belonging to the formicine genus Cataglyphis exhibit extremely different habitat preferences, population densities, and population structures. C. fortis is the only Cataglyphis species within the salt-pan flats of the Algerian and Tunisian chotts and sebkhas, whereas C. bicolor, alongside C. albicans and C. ruber, inhabits the nutritionally richer low-shrub semi-deserts surrounding the salt pans. We present a comparative study of the spatio-temporal patterns of colony distribution of the two monogynous species over periods of at least 5 (maximally 15) years. In C. fortis low population densities (0.5 kg body mass per km²) and, correspondingly, large inter-nest distances (40.6 m mean nearest neighbour nest distance) are correlated with absolute intra-annual and high inter-annual nest-site stability (more than 75% inter-annual survival rate) and a monodomous colony structure. In C. bicolor the population density is one hundred times higher (42 kg body mass per km², 9.1 m mean nearest neighbour nest distance), nest-site stability is extremely low in both intra-annual and inter-annual terms (67% intra-annual survival rate for 13-day periods; less than 5% inter-annual survival rate), and polydomy prevails. These marked differences in population structure are discussed with respect to adapted traits such as foraging range, running speed, and relative lengths of the legs.Received 8 August 2003; revised 27 November 2003; accepted 2 December 2003.     

Die analyse des dispersionsmusters und seine bedeutung für eine population räuberischer wasserwanzen (Notonecta glauca L.)

Zusammenfassung Aus Serienfilmaufnahmen wurde das Verteilungsmuster der Individuen des Rückenschwimmers Notonecta glauca in natürlichen und künstlichen Populationen verschiedener Dichte und Geschlechterzusammensetzung analysiert. Die Abstände zwischen jedem Tier und seinem nächsten Nachbarn wurden gemessen und mit den errechneten Werten aus Populations-Modellen bekannten Verteilungstyps verglichen. Es zeigte sich, daß jede Rückenschwimmer-Population mit einer höheren Dichte als 6 Tieren pro m² einer Zufallsverteilung folgt. Änderungen im Zahlenverhältnis der Männchen gegenüber den Weibchen bzw. in der Altersstruktur der Population (3. Larvenstadium bis Imago) hatten keinen Einflß auf den Dispersionstyp. Für Populationen mit geringeren Dichten als 7 Tieren pro m² ist der Unterschied in der Größe des mittleren interindividuellen Abstands einer simulierten Zufallsverteilung gegenüber einem Gleichverteilungs-Modell nicht bei allen Abundanzen signifikant. Deshalb kann nicht entschieden werden, ob Notonecta-Populationen dieser geringen Dichte zufällig oder gleichmäßig verteilt sind. Die Übereinstimmung des Verteilungsmusters der Rückenschwimmer-Populationen mit einer Zufallsverteilung weist darauf hin, daß diese räuberischen Wasserwanzen kein das Verteilungsmuster bestimmendes Verhalten besitzen.

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Summary From photographic recordings the distribution of individuals of the back swimmer Notonecta glauca in natural and artificial populations of various densities and sex ratios were analysed. The distances between each animal and its nearest neighbour were measured and compared with calculated data from population models with known dispersion patterns. It was shown that each back swimmer population with a higher density than 6 animals per m² follows a random distribution. Varying the ratio of males to females in the population has no influence on the type of dispersion nor has age from 3. instar to imago. In populations with smaller densities than 7 animals per m² the difference in average interindividual distance between a random dispersion model and a uniform dispersion model is not significant for each density. Therefore it is impossible to decide whether Notonecta-populations with these low densities are randomly or uniformly distributed. The agreement of the dispersion pattern of the back swimmer populations with a random distribution indicates the absence of any behaviour affecting dispersion of this predatory water bug.

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Mit Förderung der Deutschen Forschungsgemeinschaft (Bewilligungen an Prof. Dr. H. Markl, Az. Ma. 374/4; 741, 29-3).     

Pattern analysis in bryozoan and spirorbid communities. II. Distance sampling methods

The spatial pattern of settlements of the bryozoan Alcyonidium polyoum (Hassall) and of Spirorbis spirorbis (L.) on plastic (Perspex) disks has been examined using nearest-neighbour analysis. Cumulative frequency distributions of ω = r², where r is the distance from each individual to its nearest neighbour, have been set up and compared with those expected assuming random settlement on each disk. Deviation above the expected line indicates aggregation and deviation below it indicates regularity or spacing apart. At low densities (< 7.4 cm^?2) Spirorbis settlements were demonstrably aggregated and at high densities (> 18.2 cm^?2) they displayed spacing apart. Alcyonidium ancestrulae showed aggregation at all densities (1.4–45.6 cm^?2) under the null hypothesis that when a larva encounters an ancestrula it moves away and settles randomly elsewhere. Truncating the cumulative distributions to consider only the settlement within aggregations still showed no evidence of spacing apart. Under a different null hypothesis, that a larva encountering an ancestrula settles contiguously to it, spacing apart was demonstrated only at unnaturally high densities (> 13 cm^?2). It is concluded, on the basis of observed larval exploratory behaviour and naturally occurring settlement densities, that settling Alcyonidium larvae do not space apart. The biological significance of this finding is discussed.     

The Effect of Density and Temperature on the Swimming and Aggregating Behaviour of the Backswimmer,Anisops deanei (Heteroptera: Notonectidae) and Subsequent Encounter Rate with a Sit-and-Wait Predator

Four different swimming behaviours of the backswimmer, Anisops deanei, each characterized by a different angular position of the metathoracic legs and speed, are described along with the effect of water temperature and density on (1) the number of each behaviour exhibited and (2) total time spent swimming, per unit time. Generally, as density increased the swimming activity in each behaviour decreased while as temperature increased swimming activity increased. The direction of the effects were the same when total time spent swimming per unit time was examined. Nearest neighbour analysis showed that A. deanei form obvious aggregations in laboratory tanks as density increases, and this effect remains significant at least to the third neighbour. Density had a significant effect on neighbour distances whereas temperature did not. It was hypothesized that the primary function of these aggregations, which are also commonly observed in the field, is an anti-predator behaviour. Laboratory experiments using models of a common sit-and-wait predator of A. deanei, showed that although the encounter rate increased with both water temperature and density the observed encounter rate at the higher densities was significantly less than expected with a random distribution of prey. It is suggested that this defence effect would also exist with more mobile predators like fish.     

Trade-offs between social behaviour and foraging by sheep in heterogeneous pastures

In heterogeneous pastures, groups of sheep may have to alter their social behaviour in order to graze patches of preferred vegetation. In this event, patch size, inter-patch distance and the contrast between patch and background vegetation are likely to affect behaviour. In this experiment, groups of five female Scottish Blackface sheep grazed for 2-h periods in 0.1ha grass plots containing seven 1.5mx1.5m patches of improved vegetation, with inter-patch distances of 1.5, 6 or 11.5m. Background vegetation was of either medium or poor quality. Control plots contained no patches. On average, sheep spent 44% of the time grazing patches, although patches comprised only 1.6% of the total plot area. Inter-patch distance did not affect accumulated time spent grazing patches during the first 30min, but patch residence time and the number of sheep on a patch increased with inter-patch distance. The distribution of nearest neighbour distances was altered when patches were 6 or 11.5m apart, compared to no patches. Accumulated time spent grazing patches and the number of sheep on a patch were greater with poor than medium backgrounds. Sheep visited patches frequently and for short periods and it is suggested that sheep often moved off patches as a result of competition. The results provide evidence that sheep make trade-offs between social and foraging behaviour and demonstrate the importance of interactions between social spacing and the size and spacing of vegetation patches, when sheep forage in heterogeneous pastures.     

The influence of density on frequency-dependent food selection: a comparison of four experiments with wild birds

We compare the results of four experiments, conducted at different times and with different protocols, that explored the relationship between frequency-dependent selection and prey density in wild birds feeding on artificial populations of coloured baits. One (experiment 4) used pastry baits that differed only in the presence or absence of a red stripe, and this experiment provided no evidence for any kind of selective behaviour. The other three experiments used green and brown baits, and they all provided evidence for a trend towards increasing anti-apostatic selection with high densities (>100 baits m^–2). However, one of these (experiment 3) provided no evidence for frequency-dependent selection at low densities (0.5–20 baits m^–2), while the other two experiments concurred in suggesting a trend towards increasing apostatic selection with low densities (down to 2 baits m^–2). Together, these experiments both support and qualify the published findings of experiment 1 that frequency- dependent selection by wild birds on bait populations is modified by density. Experiment 4 indicates that frequency-dependent selection may break down entirely if bait types are too similar, while experiment 3 indicates that some details of this trend with density will depend either on the protocol used or on exogenous changes in the birds’ feeding behaviour. Received: 1 September 1999 / Accepted: 22 March 2000     

Distribution and population density of the bushcricket Decticus verrucivorus in a damp-meadow biotope

Summary A population of Decticus verrucivorus (Orthoptera: Tettigoniidae) was studied in the field over two successive years. The majority of insects accumulate only in certain parts of a diverse habitat. In this area the mean population density of adult Decticus verrucivorus was 3.1/100 m². Analysis of nearest neighbour distances shows that males have a clumped distribution in the undisturbed habitat. It is concluded that larval distribution reflects the distribution of oviposition sites but that the distribution of adult males, though also depending on the distribution of natural resources and the climatic conditions, is produced mainly by the acoustic interactions with other males. The distribution of adult females does not appear to be determined by the acoustic behaviour of the males. The role of environmental factors such as the availability of food, humidity and temperature, and of the acoustic communication within this species, is discussed with respect to the problem of the high site fidelity of Decticus verrucivorus.     

Social organisation of female field volesMicrotus agrestis in a population in Southern England

The social organisation of a population ofMicrotus agrestis (Linnaeus, 1761) was studied by live trapping and radiotracking in southern England. Radiotracking revealed significant differences in both female home ranges and core areas with breeding condition. Lactating females had the smallest home ranges and core areas, and pregnant females the largest. There were no significant differences in female home range and core areas during the breeding season or between years despite different densities. Females were only territorial whilst lactating during which time their core areas were small. There were some overlaps of core areas among females at the beginning of the breeding season which are thought to be due to familiarity or kin associations. Associations between females were short-lived, lasting approximately one breeding event. As the breeding season progressed core areas became distinct suggesting a change to a territorial system although densities were low and most females were lactating. Patterns of social organisation among females were similar in both 1995 and 1996. Mean nearest neighbour distances tended to increase as the breeding season progressed and were uncorrelated with density.     

Densities and dispersion of breeding Eurasian Hobbies Falco subbuteo in southeast England

Capsule Breeding Hobbies are more numerous in parts of southeast England than previously recognized, and in suitable habitat their breeding dispersion shows a regular pattern.

Aims To establish the density and breeding dispersion pattern of a population of Hobbies in southeast England.

Methods Surveys to locate every pair of Hobbies present were conducted in six study areas of between 48.0 and 201.2 km² in three counties in southeast England during 2005–10.

Results Each study area held between 7 and 21 pairs. Densities were higher than in previous studies conducted in Britain, at between 9.0 and 15.0 pairs per 100 km². Mean densities per unit area of non-developed habitat were also consistently higher than expected, at between 10.1 and 17.3 pairs per 100 km². The mean nearest known neighbour distances fell within the range 1.8–2.8 km. In all six study areas, pairs were regularly spaced. The majority (68.0%) of nesting and territorial pairs occupied sites in woodland.

Conclusions Breeding Hobbies are considerably more numerous in parts of southeast England than previously recognized, and numbers appear to be continuing to increase. Accurate population estimates for Hobbies require species-specific fieldwork.     

Light intensity and schooling behaviour in larval gulf menhaden

Schooling behaviour was examined in larval gulf menhaden Brevoortia patronus under decreasing and increasing light intensities and related to movements of retinal photoreceptors and pigment. Nearest neighbour angles and nearest neighbour distances between fish were inversely related to light intensity and were independent of the direction of intensity change. Swimming speeds of individual fish were directly related to light intensity when intensity was decreased but did not increase when intensity was raised. The changes in nearest neighbour angles and distances more closely paralleled movements of retinal pigment cells than cone cell migration, suggesting that rod photoreceptors play a greater role than cones in determining the threshold light intensity for schooling. A general model is developed relating the threshold light intensity for schooling to eye diameter for a number of different species and the implications of this relationship are discussed.     

Effect of prey density on behaviour and development of the predatory mosquito,Toxorhynchites towadensis

The effect of prey density on feeding behaviour, killing behaviour, and development of the predatory mosquito,Toxorhynchites towadensis, was investigated in the laboratory. The number of prey consumed per larva increased toward an upper asymptote as prey density increased. Prey consumption curves during fourth instar were concave at low prey densities but convex at high prey densities. This phenomenon was not observed during other instars. Killing without consuming any part of prey occurred at prey densities of 20 per container and over. The number of prey killed but not consumed increased linearly with the number of unconsumed prey in the container. Prey acquisition behaviour was not affected by prey densities during the prepupal period. Developmental time from first instar to adult emergence decreased with increasing prey densities, but remained constant at densities of 10 per container and over. Adult size increased with increasing prey densities but there was no effect at prey densities of 20 and over.     

Implications of small scale variation in ecological conditions for the diet and density of red colobus monkeys

In this 3-year investigation we documented patterns of density, diet, and activity of red colobus monkeys (Procolobus tephrosceles) in six areas in or near Kibale National Park, Uganda and related these patterns to availability of food resources. There were large differences in the density and behavior of the red colobus among the sites. For example, the red colobus at one site with a diverse plant community of more than 61 tree species, had a diet that included at least 42 species. In contrast, at a second site red colobus spent 92% of their feeding time eating from one species that dominated the tree community. The density of important red colobus food trees varied among sites from 32 trees/ha to 204 trees/ha, and red colobus density ranged from 0.70 groups/km² to 7.41 groups/km². Among sites, red colobus density was related to the cumulative DBH of important food trees, when one apparently anomalous site was excluded, and populations with more plant species in their diets tended to be those that were found at higher densities. Activity budgets of the red colobus populations varied markedly among sites. For example, feeding time ranged among sites from 29 to 55%, and traveling varied from 5 to 20%. When faced with increased foraging demands, red colobus reduced the time spent resting, while the time spent socializing remained fairly constant. Comparative socioecological studies typically contrast species separated by large geographical distances to ensure there is sufficient variation in the environment to detect behavioral responses. The marked differences in ecological conditions and red colobus behavior we documented over short geographical distances, suggests that small-scale contrasts are a useful tool to examine ecological determinants of behavior and community structure.