Flock size and habitat-dependent food and energy intake of foraging Goldfinches

Summary During the breeding season Goldfinches (Carduelis carduelis L.) feed on milky ripe seeds of about 20 food plants. Individual Goldfinches joining a flock reduce the time spent vigilant with increasing flock size. Therefore birds feeding in flocks get an increased intake of kernels per time unit. This was measured for five different food plants (Dactylis glomerata (Gramineae), Knautia arvensis (Dipsacaceae), Senecio vulgaris, Taraxacum officinale, Tragopogon pratensis (Compositae)). In large-sized flocks, birds fed up to 2.3 times more kernels, than when feeding solitarily. In addition, visibility in the vegetation leads to a further increase of kernel intake. Thus feeding under good conditions as in recently mown areas, can raise kernel intake to the seven fold per time unit as compared to solitary feeding. The maximum ingestion rate of kernels was 98 per min which implies a head up-and-down movement every 0.6 s. The calculated energy intake of birds per time unit is lowest in Senecio and highest in Tragopogon. Thus the birds, when feeding on Tragopogon in larger flocks, can gain an energy intake 16 times higher than that reached when feeding on Senecio, despite of a higher kernel intake rate. The energy intake individual Goldfinches gain at the particular plant species is markedly increased with flock sizes up to eight birds, with larger flocks the intake increases only slightly.     

Leg disorders in broiler chickens: prevalence, risk factors and prevention

Broiler (meat) chickens have been subjected to intense genetic selection. In the past 50 years, broiler growth rates have increased by over 300% (from 25 g per day to 100 g per day). There is growing societal concern that many broiler chickens have impaired locomotion or are even unable to walk. Here we present the results of a comprehensive survey of commercial flocks which quantifies the risk factors for poor locomotion in broiler chickens. We assessed the walking ability of 51,000 birds, representing 4.8 million birds within 176 flocks. We also obtained information on approximately 150 different management factors associated with each flock. At a mean age of 40 days, over 27.6% of birds in our study showed poor locomotion and 3.3% were almost unable to walk. The high prevalence of poor locomotion occurred despite culling policies designed to remove severely lame birds from flocks. We show that the primary risk factors associated with impaired locomotion and poor leg health are those specifically associated with rate of growth. Factors significantly associated with high gait score included the age of the bird (older birds), visit (second visit to same flock), bird genotype, not feeding whole wheat, a shorter dark period during the day, higher stocking density at the time of assessment, no use of antibiotic, and the use of intact feed pellets. The welfare implications are profound. Worldwide approximately 2 x 10(10) broilers are reared within similar husbandry systems. We identify a range of management factors that could be altered to reduce leg health problems, but implementation of these changes would be likely to reduce growth rate and production. A debate on the sustainability of current practice in the production of this important food source is required.     

Flock size and breeding success in flamingos

Using data on flocks of flamingos in Britain and Ireland, the relationship between flock size and breeding in captive flamingos was examined. Breeding flamingo flocks were significantly larger than nonbreeding flocks and larger flocks bred more frequently than smaller flocks. All Chilean flocks containing more than 40 birds have bred successfully; however, one flock of only 4 Chilean Flamingos has reared at least one chick. All Caribbean flocks over 20 birds have successfully reared a chick, yet the smallest flock to rear a chick was one of 14 birds. © 1992 Wiley-Liss Inc.     

Strained energy budget of winter floaters in the Willow Tit as indicated by ptilochronology

Most Willow Tits Parus montanus live within flock territories during the non-breeding season, but many juveniles roam around or switch between several flocks. Such floaters behave submissively and spend time watching other flock members in addition to scanning for predators. During September–December 1989–2000, I studied individually colour-ringed Willow Tits living in a subalpine forest area in central Norway. When among flock members, the floaters foraged less in favourable parts of trees and were more vigilant than the lowest-ranked juvenile flock members. The nutritional condition of the birds was assessed by examining the growth bar widths of their tail feathers. Birds in better condition have wider growth bars than those in poorer condition. The daily growth bars of induced feathers of male and female floaters, laid down under winter conditions, were significantly narrower than those of the lowest ranked flock members. These results suggest that juvenile floater Willow Tits maintain a poorer nutritional status than low-ranking juvenile flock members during winter.     

Comparison of flock characteristics,journey duration and pathology between flocks with a normal and a high percentage of broilers ‘dead-on-arrival’ at abattoirs

This study investigated high mortality in broilers transported to slaughter in Norway by comparing data from flocks with normal and high mortality during transportation. The data sources consisted of necropsy findings in 535 broilers dead-on-arrival (DOA), production data and slaughterhouse data, along with average journey duration for the 61 associated flocks. The mean Norwegian DOA% for 2015 was 0.10. In this study, normal-mortality flocks were defined as flocks with a mean DOA% up to 0.30 and high mortality as flocks with a mean DOA% above 0.30. DOA% was calculated per flock. The most frequent pathological finding was lung congestion which was observed in 75.5% of the DOA broilers. This postmortem finding was significantly more common in broilers from high-mortality flocks (89.3%) than in DOA broilers from normal-mortality flocks (58%). The following variables had a significantly (P<0.05) higher median in the high-mortality flocks: flock size, 1^st week mortality, foot pad lesion score, carcass rejection numbers and journey duration. The results indicate that high broiler mortality during transportation to the abattoir may be linked to several steps in the broiler production chain. The results suggest that preventive measures are to be considered in improvement of health and environmental factors during the production period and throughout the journey duration.     

The prevalence of Campylobacter amongst a free-range broiler breeder flock was primarily affected by flock age

Campylobacter successfully colonizes broiler chickens, but little is known about the longer term natural history of colonization, since most flocks are slaughtered at an immature age. In this study, the prevalence and genetic diversity of Campylobacter colonizing a single free-range broiler breeder flock was investigated over the course of a year. The age of the flock was the most important factor in determining both the prevalence and diversity of Campylobacter over time. There was no correlation with season, temperature, the amount of rain and sunshine, or the dynamics of colonization amongst geographically and temporally matched broiler flocks. The higher prevalence rates coincided with the age at which broiler chickens are typically slaughtered, but then in the absence of bio-security or other intervention methods, and despite changes in flock management, the prevalence fell to significantly lower levels for the remainder of the study. The genetic diversity of Campylobacter increased as the flock aged, implying that genotypes were accumulated within the flock and may persist for a long time. A better understanding of the ecology of Campylobacter within commercial chicken flocks will allow the design of more effective farm-based interventions.     

Microcosm study for revegetation of barren land with wild plants by some plant growth-promoting rhizobacteria

Growth promotion of wild plants by some plant growth-promoting rhizobacteria (PGPR) was examined in the microcosms composed of soils collected separately from a grass-covered site and a nongrass-covered site in a lakeside barren area at Lake Paro, Korea. After sowing the seeds of eight kinds of wild plants and inoculation of several strains of PGPR, the total bacterial number and microbial activity were measured during 5 months of study period, and the plant biomasses grown were compared at the end of the study. Acridine orange direct counts in the inoculated microcosms, 1.3-9.8 x 10(9) cells x g soil(-1) in the soil from the grass-covered area and 0.9-7.2 x 10(9) cells x g soil(-1) in the soil from the nongrass-covered site, were almost twice higher than those in the uninoculated microcosms. The number of Pseudomonas sp., well-known bacteria as PGPR, and the soil dehydrogenase activity were also higher in the inoculated soils than the uninoculated soils. The first germination of sowed seeds in the inoculated microcosm was 5 days earlier than the uninoculated microcosm. Average lengths of all plants grown during the study period were 26% and 29% longer in the inoculated microcosms starting with the grass-covered soil and the nongrass-covered soil, respectively, compared with those in the uninoculated microcosms. Dry weights of whole plants grown were 67-82% higher in the inoculated microcosms than the uninoculated microcosms. Microbial population and activity and growth promoting effect by PGPR were all higher in the soils collected from the grass-covered area than in the nongrass-covered area. The growth enhancement of wild plants seemed to occur by the activities of inoculated microorganisms, and this capability of PGPR may be utilized for rapid revegetation of some barren lands.     

Quantifying Transmission of Campylobacter jejuni in Commercial Broiler Flocks

Since meat from poultry colonized with Campylobacter spp. is a major cause of bacterial gastroenteritis, human exposure should be reduced by, among other things, prevention of colonization of broiler flocks. To obtain more insight into possible sources of introduction of Campylobacter into broiler flocks, it is essential to estimate the moment that the first bird in a flock is colonized. If the rate of transmission within a flock were known, such an estimate could be determined from the change in the prevalence of colonized birds in a flock over time. The aim of this study was to determine the rate of transmission of Campylobacter using field data gathered for 5 years for Australian broiler flocks. We used unique sampling data for 42 Campylobacter jejuni-colonized flocks and estimated the transmission rate, which is defined as the number of secondary infections caused by one colonized bird per day. The estimate was 2.37 ± 0.295 infections per infectious bird per day, which implies that in our study population colonized flocks consisting of 20,000 broilers would have an increase in within-flock prevalence to 95% within 4.4 to 7.2 days after colonization of the first broiler. Using Bayesian analysis, the moment of colonization of the first bird in a flock was estimated to be from 21 days of age onward in all flocks in the study. This study provides an important quantitative estimate of the rate of transmission of Campylobacter in broiler flocks, which could be helpful in future studies on the epidemiology of Campylobacter in the field.     

The Effects of Predation Risk, Food Abundance, and Population Size on Group Size of Brown-Headed Cowbirds (Molothrus ater)

Social and ecological conditions can influence flock formation (e.g. number of flocks, flock size, etc.) depending on the degree of social attraction of a species. We studied group formation in brown‐headed cowbirds (Molothrus ater) over short time periods (30 min) in two semi‐natural experiments conducted under controlled conditions. First, we determined the shape of the relationship between intake rate and flock size by manipulating group size in a single enclosure. Second, we assessed the role of population size, food abundance, and predation risk, and their interactions, in flock size formation in a system of four enclosures (two with and two without food) connected to a central refuge patch. In the first experiment, we found that pecking rates peaked at intermediate flock sizes (three to six individuals), which was influenced by greater availability of foraging time and more aggressive interactions in large groups. In the second experiment, flock sizes in the patches with food increased with population size likely due to the benefits of patch exploitation in groups. Flock size decreased after predator attack probably because refuge availability reduced perceived predation risk more than flocking in larger groups. Food abundance had minor effects, varying flock sizes between the two patches with food, under high food availability conditions when population size was high, probably due to social cohesion effects. Our results suggest that: (1) this species has an inverted‐U food intake–group size relationship with a range of intake‐maximizing flock sizes rather than a single peak, (2) the presence of a near refuge modifies the expected benefits of group patch exploitation under high predation risk, and (3) an increase in population size would more likely be translated into rapid increases in the size of the flocks rather than in more new flocks.     

Flock Health Indicators and Campylobacter spp. in Commercial Housed Broilers Reared in Great Britain

This study investigated the relationship between flock health and Campylobacter infection of housed commercial broilers in Great Britain. Thirty ceca were collected at slaughter from batches of broilers from 789 flocks, at either full or partial depopulation, between December 2003 and March 2006 and examined individually for Campylobacter by direct plating onto selective media. Management and health data were collected from each flock and included information on mortality or culling during rearing, the number of birds rejected for infectious or noninfectious causes at slaughter, the proportion of birds with digital dermatitis (also termed hock burn), and other general characteristics of the flock. Campylobacter spp. were isolated from 280 (35%) flocks. The relationship between bird health and welfare and Campylobacter status of flocks was assessed using random-effects logistic regression models, adjusting for region, month, year, and rearing regime. Campylobacter-positive batches of ceca were associated with higher levels of rejection due to infection (odds ratio [OR], 1.5; 95% confidence interval [CI_95%], 0.98 to 2.30) and digital dermatitis (OR, 2.08; CI_95%, 1.20 to 3.61). Furthermore, higher levels of these conditions were also associated with the highest-level category of within-flock Campylobacter prevalence (70 to 100%). These results could indicate that improving health and welfare may also reduce Campylobacter in broilers.     

Redshank Tringa totanus flocking behaviour, distance from cover and vulnerability to sparrowhawk Accipiter nisus predation

Over 11 winters I examined the interactions between sparrowhawk Accipiter nisus attack behaviour, the gregariousness of redshanks Tringa totanus and local geography to test hypotheses that suggest birds should flock to reduce their risk of predation and that predation risk should decline with the prey's distance from cover. Sparrowhawk attacks on redshanks feeding on beaches around the high tide mark (the strandline zone) were more frequent and more successful than attacks on redshanks feeding seaward of the strandline zone (in the intertidal zone). The results therefore confirmed hypothetical expectations that predation risk should decline with distance from cover. Flocking only appeared to influence the outcome of hawk attacks at shorter distances from cover on the strandline, with attacks on singletons and small flocks being more successful than attacks on larger flocks. Distance from cover had a stronger influence on the likelihood of attack success than did flock size. Mid-range flock sizes (6–45 birds) were attacked more frequently than expected, but singletons and large flocks were attacked less than expected. Despite these differences an individual redshank's likelihood of predation by a sparrowhawk declined with increasing flock size, thereby confirming the 'dilution effect' and 'vigilance' hypotheses for the evolution of flocking in birds. Food intake rates of redshanks declined with increasing flock size, further indicating that redshanks flocked to avoid predation rather than to increase their food intake rates. The strong interaction between two influences on predation risk revealed by the present study suggests other studies should take great care when considering a single influence on predation risk in isolation from others.     

Perches and elevated platforms in commercial broiler farms: use and effect on walking ability,incidence of tibial dyschondroplasia and bone mineral content

Modern fast-growing broilers spend excessive periods resting and their activity further decreases with age. Inactivity has been suggested to increase impaired gait and the incidence of leg disorders. Tibial dyschondroplasia (TD) is a common leg pathology in broilers. A more complex environment might facilitate more activity and improve leg health. Perches or elevated platforms bring variety to broilers’ environment and could motivate more locomotion. This study examined the impact of perches and elevated platforms on walking ability, the occurrence of TD and level of bone ash and mineral contents. The investigation was performed on four commercial broiler farms throughout six consecutive batches with platforms and four to five with perches. On each farm at least two separate houses were included, enabling the comparison of furnished flocks to control flocks during each batch. Plastic slats with ramp access elevated by 30 cm or wooden perches of 10 and 30 cm height were offered in the furnished house. Farmers recorded the platform and perch usage twice a week with a five-point scale. Gait was scored before slaughter on a six-point scale according to the Welfare Quality® assessment protocol for poultry. The severity of TD was determined using a four-point scale on farm from all birds gait scored as 3 and at slaughter from 200 birds/flock. Farmers estimated 50% to 100% of the platforms to be occupied in all flocks throughout the entire growing period. Only single birds were perching, thus perch structures were constantly evaluated to be empty. Due to the low use, the perch-equipped houses were excluded when analysing bone content, walking ability and TD. On average, 30% of the tested birds exhibited gait score ⩾3. Younger scoring age resulted in a lower mean gait score and a lower percentage of scores 3 and 4 to 5. Overall, 2.3% of the birds examined at slaughter and 3.5% of the birds with gait score 3 were affected by TD. Leg health was better in birds with access to platforms: mean gait score, the percentage of birds scoring 3, and TD percentage and severity were lower in birds in platform-equipped houses. Elevated structures such as platforms, offering additional possibilities for locomotion to broilers seem to improve their leg health.     

Effects of snow cover on the social and foraging behavior of the great tit Parus major

In the Joetsu region of central Honshu, Japan, snow lies on the ground 2–3 m deep from January to February every year. To test the effects of snow cover on the social and foraging behaviors of the great tit (Parus major Linnaeus) in the region, the following parameters were compared between the pre-snowy period (November and December) and the snowy period (January and February) at the individual level: population size, monospecific flock size and the stability of its membership, home range size, attendance rate with mixed-species flocks, and foraging height. Great tits lived alone or in pairs, but often joined mixed-species flocks. Throughout the study period, individuals exhibited strong site fidelity, which resulted in a stable population size. Neither the size of a monospecific flock nor its membership was affected by snow cover. The home range expanded when birds joined mixed-species flocks during both periods. Birds more frequently joined mixed-species flocks during the snowy period, and the size of mixed-species flocks was significantly larger than during the pre-snowy period. During the snowy period, birds shifted their foraging position from the ground to the upper parts of trees. They also used the upper parts of trees when they joined mixed-species flocks. These results suggest that the intraspecific sociality of great tits is relatively insensitive to snow cover, but that the home range size and foraging positions are affected by joining mixed-species flocks, rather than by snow cover.     

Bird mixed‐species flock formation is driven by low temperatures between and within seasons in a Subtropical Andean‐foothill forest

According to both the predation avoidance and foraging efficiency hypotheses, birds within mixed flocks increase their foraging efficiency and/or can spend more time feeding and less time looking out for predators. These hypotheses predict that birds in mixed flocks obtain benefits. Thus, mixed flock formation could serve as a strategy to cope with difficult conditions imposed on birds such as climatic conditions that ultimately result in a change in predation pressure or food resources. We evaluate the hypotheses that forming part of a flock confers benefits to its members and the associated prediction that birds will take advantage of these benefits and flock more often under cold and dry weather conditions between and within seasons to cope with such conditions. We surveyed the presence of mixed flocks, flocking propensity, number of species and individuals in mixed flocks in the Subtropical Yungas foothill of Argentina, to examine seasonality, flocking behavior of birds and their responses to two climatic variables: temperature and humidity. Bird species presented a higher flocking propensity and mixed flocks occurred more frequently during the dry and cold seasons than during the more benign seasons, and lower values of temperature within seasons triggered the flocking behavior. Although effects between seasons were expected, birds also showed a short‐term response to small changes in temperature within seasons. These results strengthen the ideas proposed by the foraging hypothesis. Although benefits derived from flocking have yet to be determined, whatever they are should be understood in the context of seasonal variation in life‐history traits.     

Harvesting of Onion Grass,Romulea rosea L. by Sulphur‐crested Cockatoo,Cacatua galerita Latham

The harvesting of Onion Grass (Romulea rosea) corms by flocks of Sulphur‐crested Cockatoo (Cacatua galerita) is well known. Individual birds and large flocks feed on the weed in pastures, grasslands and recreational turf. Flocks of Sulphur‐crested Cockatoo were observed feeding on Onion Grass at seven sites along the Maribyrnong River at Keilor, Victoria. Flock size and feeding habits were noted, as were the depth of corms, the time taken to remove corms from the ground and the number of eaten and lifted but uneaten corms. From the data collected, it was estimated that an individual bird can extract and eat about 200 plants per hour and that even a small flock can consume several thousand plants in a feeding session. Corms were typically within 20 mm of the soil surface and were removed primarily by the cockatoo with its beak, but the left foot was sometimes used to excavate the corm from the soil. Flock feeding sessions lasted from about 0.5 to 2.5 hours, but feeding by individual or pairs of birds was often shorter. Plants that had been removed from the soil appeared to have intact corms, but all that was left were the outer scales. Of the plants removed from the soil, only 6% had intact corms attached. The removal of large numbers of Onion Grass plants could impact on their population numbers over time if there was repeated annual harvesting.     

Potential sources of Campylobacter infection on chicken farms: contamination and control of broiler-harvesting equipment, vehicles and personnel

Aims: To test the efficacy of enhanced biosecurity measures on poultry farms for reducing environmental contamination with Campylobacter during partial depopulation of broiler flocks prior to normal slaughter age. The study has also evaluated the risk of infection from live‐bird transport crates that are routinely cleaned at the slaughterhouse, but may remain contaminated. Methods and Results: On‐farm sampling and Campylobacter isolation was undertaken to compare the prevalence of contamination on vehicles, equipment and catching personnel during farm visits that took place under normal or enhanced biosecurity. Campylobacters were found in almost all types of sample examined and enhanced biosecurity reduced the prevalence. However, the additional measures failed to prevent colonisation of the flocks. For transport crates, challenge trials involved exposure of broilers to commercially cleaned crates and genotyping of any campylobacters isolated. The birds were rapidly colonised with the same genotypes as those isolated from the cleaned crates. Conclusions: The enhanced biosecurity measures were insufficient to prevent flock colonisation, and the problem was exacerbated by inadequate cleaning of transport crates at the slaughterhouse. Significance and Impact of the Study: Current commercial practices in the United Kingdom facilitate the spread of campylobacters among broiler chicken flocks. Prevention of flock infection appears to require more stringent biosecurity than that studied here.     

Managing the social environments of flamingos for reproductive success

Recent research has shown that large flamingo flocks are more likely to experience reproductive success than small flocks and that there is a positive relationship between behavioral stimulation from group displays and reproductive success. This study compares the group displays and reproductive success in a captive flock of Caribbean flamingos over 6 years at the National Zoological Park. Birds were added to the flock in two different years. In each case, the flock produced fertile eggs during the breeding season following the addition of new birds. Furthermore, the addition of new birds in 1988, and then again in 1991, significantly increased group display activity over the previous year when the flock size was lower. That the addition of birds stimulated group display activity suggests an alternative management strategy for promoting reproduction in captivity: separate birds in a flock and then reunite them prior to the breeding season. © 1994 Wiley-Liss, Inc.     

Quantifying transmission of Campylobacter spp. among broilers

Campylobacter species are frequently identified as a cause of human gastroenteritis, often from eating or mishandling contaminated poultry products. Quantitative knowledge of transmission of Campylobacter in broiler flocks is necessary, as this may help to determine the moment of introduction of Campylobacter in broiler flocks more precisely. The aim of this study was to determine the transmission rate parameter in broiler flocks. Four experiments were performed, each with four Campylobacter-inoculated chicks housed with 396 contact chicks per group. Colonization was monitored by regularly testing fecal samples for Campylobacter. A mathematical model was used to quantify the transmission rate, which was determined to be 1.04 new cases per colonized chick per day. This would imply that, for example, in a flock of 20,000 broilers, the prevalence of Campylobacter would increase from 5% to 95% within 6 days after Campylobacter introduction. The model and the estimated transmission rate parameter can be used to develop a suitable sampling scheme to determine transmission in commercial broiler flocks, to estimate whether control measures can reduce the transmission rate, or to estimate when Campylobacter was introduced into a colonized broiler flock on the basis of the time course of transmission in the flock.     

Plasma levels of luteinizing hormone and steroid hormones in free-living winter groups of willow tits (Parus montanus)

Plasma levels of LH, DHT, testosterone, and corticosterone were measured for all members in free-living winter flocks of willow tits, Parus montanus. Hormonal data were related to (1) flock size and (2) age/sex differences. The winter flock defends a large winter territory and shows a well-established social hierarchy in which adults consistently dominate first-year birds. One winter group normally consists of four individuals, two adults and two juveniles. In flocks containing four or five members juvenile willow tits had significantly higher corticosterone values than adults. In small-sized groups, containing three members, all individuals had high plasma levels of corticosterone. No other effects of flock size was found. When data were treated on an age/sex basis, i.e., flock size was not considered, juvenile females were found to have significantly higher plasma levels of testosterone than adult birds, and also significantly higher levels of DHT than juvenile males and adult females. Also, juvenile willow tits had significantly higher plasma levels of corticosterone than adult birds.     

Eimeria acervulina: The influence of inoculation dose on transmission between broiler chickens

The course and clinical appearance of an Eimeria species infection in chicken flocks depend on the response of an individual bird to infection and on population-dynamics of the infection in the flock. Differences in ingested numbers of oocysts may affect oocyst load in the flock and the subsequent infectious dose for not yet infected birds. To study the link between numbers of oocysts excreted by infected birds and transmission of Eimeria acervulina, experiments were carried out with 42 pairs of broiler chickens using inoculation doses with 5, 50, 500 or 50,000 sporulated oocysts. In each pair one bird was inoculated and the other bird was contact-exposed. All contact birds became infected, which occurred on average within 34 h after exposure to an inoculated bird. Although a higher inoculation dose resulted in higher oocyst excretion in inoculated and contact-infected birds, only small non-significant differences in transmission rates between groups were found.