Mixed Flocks Research Articles

Vertical nest stratification of four heron species in southern Brazil

Herons generally breed in mixed flocks and their nests are made in shrub wetlands and on islands. Waterbirds can select different tree species in the heronries which can influence the vertical stratification of the heron nests. The aim of the present study was to determine the vertical nest stratification among four Ardeidae species in heronries in southern Brazil. The study was carried out during four breeding seasons between 2004 and 2009. No significant species-specific difference in mean nest height was observed between the three heronries. However, there was some variation in nest heights per species in the four years of the study and among the heron species. Nest height was correlated with the body size of the heron species. The smaller species, Bubulcus ibis, Egretta thula, and Nycticorax nycticorax, occupied mainly the lower stratum and the largest, Ardea alba, the higher stratum. The colonist species B. ibis did not show a clear preference, occupying both Mimosa bimucronata and Cephalanthus glabratus for nest building, while the other three herons selected mainly M. bimucronata if the two tree species were available.

Gene Flow and Hybridization between Numerically Imbalanced Populations of Two Duck Species on the Subantarctic Island of South Georgia

Hybridization is common between species of animals, particularly in waterfowl (Anatidae). One factor shown to promote hybridization is restricted mate choice, which can occur when 2 species occur in sympatry but one is rare. According to the Hubbs principle, or "desperation hypothesis," the rarer species is more likely to mate with heterospecifics. We report the second of 2 independent examples of hybridization between 2 species of ducks inhabiting island ecosystems in the Subantarctic and South Atlantic Ocean. Yellow-billed pintails (Anas georgica) and speckled teal (Anas flavirostris) are abundant in continental South America, where they are sympatric and coexist in mixed flocks. But on South Georgia, an isolated island in the Subantarctic, the pintail population of approximately 6000 pairs outnumbers a small breeding population of speckled teal 300∶1. Using 6 genetic loci (mtDNA and 5 nuclear introns) and Bayesian assignment tests coupled with coalescent analyses, we identified hybrid-origin speckled teal alleles in 2 pintails on South Georgia. While it is unclear whether introgression has also occurred into the speckled teal population, our data suggest that this hybridization was not a recent event, but occurred some time ago. We also failed to identify unequivocal evidence of introgression in a much larger sample of pintails and speckled teal from Argentina using a 3-population "Isolation-with-Migration" coalescent analysis. Combined with parallel findings of hybridization between these same 2 duck species in the Falkland Islands, where population ratios are reversed and pintails are outnumbered by speckled teal 1:10, our results provide further support for the desperation hypothesis, which predicts that scarcity in one population and abundance of another will often lead to hybridization. While the South Georgia pintail population appears to be thriving, it's possible that low density of conspecific mates and inverse density dependence (Allee effect) may be one factor limiting the reproductive output of the speckled teal population, and this situation may persist unless speckled teal increase in abundance on South Georgia.

Toxoplasma gondii and Neospora caninum seroprevalence in dairy sheep and goats mixed stock farming

Toxoplasma and Neospora infections are important causes of abortions and economic losses in animal production. Mixed stock farming of sheep and goats is a common practice in Mediterranean countries and could serve as a suitable model for the evaluation of differences between the two animal species regarding parasitic infections. In order to investigate the seroprevalence of T. gondii and N. caninum among flocks of small ruminants in Greece and to evaluate any prevalence difference between sheep and goats kept in mixed flocks, 833 sera samples (458 sheep and 375 goats) from 50 mixed flocks in different areas of the country were examined by ELISA for the detection of specific antibodies. Specific IgG against T. gondii were detected in 53.71% and 61.3% and against N. caninum in 16.8% and 6.9% of the sheep and goats, respectively. Goats had higher Toxoplasma seroprevalence than sheep (p<0.05), while sheep had higher Neospora seroprevalence than goats (p<0.05). The present study is the first report world wide, on the seroprevalence of T. gondii and N. caninum in sheep and goats that are kept together in mixed flocks.

COMPOSITION, STRUCTURE AND ORGANIZATION OF MIXED-SPECIES BIRD FLOCKS IN WALAUWA TTA-WA TURANA SWAMP FOREST, KALUTARA DISTRICT, WESTERN PROVINCE OF SRI LANKA

Mixed- species foraging bird flocks in Walauwatta-Waturan Swamp Forest (WWSF) were studiedfor a period of six months from February to July in 2001. Field data was collected from 07:00 to18:00 hrs and flocks were followed as long as possible to record their composition. Scan samplingmethod (Altman, 1975) was used to record their behavioural activity, height of feeding, feedingsite and the role of each individual within the flock. Two minute scan samples were done with fiveminute intervals and almost all the birds participating in the flock were scanned within the twominutes time period.The flocking tendency of birds in WWSF was 28.7% and 27 flocks were studied. A total of 31 birdspecies were recorded to participate in mixed-species flocks in WWSF. These include 28 residentand 3 migrate species. Five species were endemic to Sri Lanka. The flock composition varied from3 to 15 species (5.89±2.61) and 4 to 31 individuals (I2.96±7.41). There was a positive correlationbetween the number of species and ~ock size (r= 0.796).Crested Drongo (77.78%) and Black-naped Monarch (70.37%) were the most frequent birds foundin flocks while Sri Lanka Orange-billed Babbler was the most abundant (8.78±3.67 individuals perflock). Territorial species such as Purple-romped Sunbird joined the flock when it was passingthrough their territory. Birds in mixed-species flocks in WWSF were classified as nuclear species,lead species, regular species, and occasional species. 2 major nuclear species (Crested Drongo &amp;Sri Lanka Orange-billed Babbler), 4 lead species (Above two with Malabar Trogon and AsianParadise Flycatcher), 12 regular species, and IS occasional species were identified. Associations ofbird species participating in mixed species flocks in WWSF were studied using cluster analysis.Two main clusters could be identified, one of which could be again divided into two subassociations.The first cluster comprised of Crested Drongo and Black-naped Monarch who showedthe highest level of association. Black Bulbul and Sri Lanka Orange-billed Babbler could not bepooled into any clusters.Different species in mixed species flocks had different optimum height levels of movementthrough the forest and appeared to have characteristic feeding sites. The vertical distribution of theregular species in flocks was consistent. Sri Lanka Orange-billed Babbler was found at a widerange of foraging heights. But, Scarlet Minivet and Black Bulbul were observed mostly in thecanopy and the Crested Drongo was observed in the middle strata of the forest (10 to 20 ft). TheAsian Paradise Flycatcher was observed in the same range. However, other fly catching species(Black-naped Monarch and Tickell's Blue flycatcher) were observed mostly in the 10 to 15ftvertical range. There was an extensive overlap of height ranges between some species. But theywere observed to use different activity/feeding sites. Black-naped Monarch and Velvet-frontedBlue Nuthatch were found in the same height range, but feeding sites utilized by them wasdifferent (foliage and tree trunk respectively). Crested Drongo and Asian Paradise Flycatcher wereobserved to occupy the same vertical height range and feeding sites, but they were using differentfeeding techniques. Even being a small area of 12 ha (CEA, 1994) IIWTOUIIdedby Rubber plantations and homegardens, the Swamp Forest have a considerable flocking tendency with compared to Sinharaja Forest Reserve 30%)(Kotagama et. AI., 1986) and Knuckles Conservation Forest (30.S) (Sbriyani, 2000), thus worth conserve thehabitat

Phylogenetic analysis of small ruminant lentiviruses in mixed flocks: Multiple evidence of dual infection and natural transmission of types A2 and B1 between sheep and goats

Previous molecular analyses of small ruminant lentivirus (SRLV) populations in single species herds in Quebec, Canada, have revealed a relatively simple structure where goats and sheep appeared exclusively infected with B1 and A2 subtypes respectively. The present work aimed at extending these earlier findings with the analysis of SRLVs in mixed flocks. Molecular analyses revealed a more complex picture of SRLV population structure in mixed herds compared to single species herds. Notably, phylogenetic analyses of long gag sequences strongly support transmission of A2 subtype from sheep to goats as well as transmission of B1 subtype from goats to sheep. Hence, this work uncovered for the first time natural transmission between sheep and goats of North American subtype A2. In addition, multiple evidences of mixed infection of sheep and goats with A2 and B1 subtypes were found. The data reported in this study reinforces the concept of a genetic continuum of SRLVs where strains are exchanged between sheep and goats under favourable conditions and in the absence of specific species barriers. Most interestingly, this study suggests that dual infection, which is a hallmark of the lentivirus paradigm HIV, may not be such rare events in small ruminants but may simply be understudied and underreported. Overall, the present data shows that sheep and goats in Canada can be infected with both SRLV A and B types, sometimes simultaneously, and that mixed flocks may represent a breeding ground for their evolution.

Heterogeneous structure in mixed-species corvid flocks in flight

Flocks of birds in flight represent a striking example of collective behaviour. Models of self-organization suggest that repeated interactions among individuals following simple rules can generate the complex patterns and coordinated movements exhibited by flocks. However, such models often assume that individuals are identical and interchangeable, and fail to account for individual differences and social relationships among group members. Here, we show that heterogeneity resulting from species differences and social structure can affect flock spatial dynamics. Using high-resolution photographs of mixed flocks of jackdaws, Corvus monedula, and rooks, Corvus frugilegus, we show that birds preferentially associated with conspecifics and that, like high-ranking members of single-species groups, the larger and more socially dominant rooks positioned themselves near the leading edge of flocks. Neighbouring birds showed closer directional alignment if they were of the same species, and neighbouring jackdaws in particular flew very close to one another. Moreover, birds of both species often flew especially close to a single same-species neighbour, probably reflecting the monogamous pair bonds that characterize these corvid social systems. Together, our findings demonstrate that the characteristics of individuals and their social systems are likely to result in preferential associations that critically influence flock structure. 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved. How do large aggregations of individuals, each of which may differ in its preferred outcome, coordinate their movements? The spectacular displays of flocking birds led the naturalist Edmund Selous (1931) to postulate a role for ‘thought transference’, but recent advances have begun to unravel the mysteries of collective movement without appealing to the supernatural (Couzin & Krause 2003; Conradt & Roper 2005; Sumpter 2006). Models of selforganizing systems suggest that repeated interactions among individuals following simple rules can generate complex patterns and coordinated group movements. Models of agents following simple rules of (1) long-range attraction to group members, (2) shortrange repulsion and (3) alignment between close neighbours have generated realistic representations of collective animal movements (reviewed in Sumpter 2006; Petit & Bon 2010). However, empirical verification of their assumptions remains scarce and largelyconfined to model systems such as starlings, Sturnus vulgaris

A New Record of James's Flamingo (Phoenicoparrus jamesi) from Laguna Melincué, a Lowland Wetland in East-Central Argentina

James's Flamingos (Phoenicoparrus jamesi), also known as Puna Flamingos, are distributed primarily in the Andean wetlands of southern South America during the breeding season, and dispersed through the lowland wetlands in Argentina during the non-breeding season. However, the main sites where they concentrate during the non-breeding season still remain unknown. Here, we report the first records of James's Flamingos observed in two consecutive years (two adults in Aug 2010, one adult and two subadults in Jul 2011) at Laguna Melincué, a Ramsar site in Santa Fe Province, Argentina (33° 25′ S, 61° 28′ W, 84 m asl). James's Flamingos were feeding in a mixed flock of Andean and Chilean flamingos (Phoenicoparrus andinus and Phoenicopterus chilensis, respectively). Our observations constitute the southernmost record for presence of this flamingo species at any lowland site and indicate the high dispersal ability of this species and its plasticity in occupying different wetland types during the non-breeding season.

Long‐term Changes in Bird Communities after Wildfires in the Central Brazilian Amazon

AbstractWe examined long‐term responses of an Amazonian bird assemblage to wildfire disturbance, investigating how understory birds reacted to forest regeneration 1, 3, and 10 years after a widespread fire event. The bird community was sampled along the Arapiuns and Maró river catchments in central Brazilian Amazonia. Sampling took place in 1998, 2000, and 2008 using mist‐nets in eight plots (four burned, four unburned sites). Species richness did not change significantly in unburned sites. In burned sites, however, we found significantly lower richness in 1998, higher richness in 2000, and similar richness in 2008. Multi‐dimensional scaling ordination showed consistent differences in bird communities both within burned sites sampled in different sampling years, and between burned and unburned sites in all years. Of the 30 most abundant species, 12 had not recovered 10 years after the fires, including habitat specialists such as mixed flocks specialists and ant‐followers. Fire‐disturbance favored three species (two hummingbirds and a manakin) in the short term only. All other species were either favored throughout the study (seven species of omnivores and small insectivores) or did not show a clear response (eight species). In burned sites, we also found significantly lower abundance of species sensitive to disturbances and habitat specialists over the entire study period. Although the bird community seems to be recovering in terms of richness, the overall community composition and abundance of some species in post‐burned and unburned sites remain very different, and have not recovered after 10 years of forest regeneration.

Benefits of mixed flocks

Benefits of mixed flocks

Differentiation of sheeppox and goatpox viruses by polymerase Chain reaction-restriction fragment length polymorphism

In the present study, the partial gene sequences of P32 protein, an immunogenic envelope protein of Capripoxviruses (CaPV), were analyzed to assess the genetic relationship among sheeppox and goatpox virus isolates, and restriction enzyme specific PCR-RFLP was developed to differentiate CaPV strains. A total of six goatpox virus (GTPV) and nine sheeppox virus (SPPV) isolates of Indian origin were included in the sequence analysis of the attachment gene. The sequence analysis revealed a high degree of sequence identity among all the Indian SPPV and GTPV isolates at both nucleotide and amino acid levels. Phylogenetic analysis showed three distinct clusters of SPPV, GTPV and Lumpy skin disease virus (LSDV) isolates. Further, multiple sequence alignment revealed a unique change at G120A in all GTPV isolates resulting in the formation of Dra I restriction site in lieu of EcoR I, which is present in SPPV isolates studied. This change was unique and exploited to develop restriction enzyme specific PCR-RFLP for detection and differentiation of SPPV and GTPV strains. The optimized PCR-RFLP was validated using a total of fourteen (n=14) cell culture isolates and twenty two (n=22) known clinical samples of CaPV. The Restriction Enzyme specific PCR-RFLP to differentiate both species will allow a rapid differential diagnosis during CaPV outbreaks particularly in mixed flocks of sheep and goats and could be an adjunct/supportive tool for complete gene or virus genome sequencing methods.

Diverse host–virus interactions following caprine arthritis-encephalitis virus infection in sheep and goats

Interspecies transmissions substantially contribute to the epidemiology of small ruminant lentiviruses (SRLVs), including caprine arthritis encephalitis virus (CAEV) and visna-maëdi virus. However, comprehensive studies of host-virus interactions during SRLV adaptation to the new host are lacking. In this study, virological and serological features were analysed over a 6 month period in five sheep and three goats experimentally infected with a CAEV strain. Provirus load at the early stage of infection was significantly higher in sheep than in goats. A broad antibody reactivity against the matrix and capsid proteins was detected in goats, whereas the response to these antigens was mostly type-specific in sheep. The humoral response to the major immunodominant domain of the surface unit glycoprotein was type-specific, regardless of the host species. These species-specific immune responses were then confirmed in naturally infected sheep and goats using sera from mixed flocks in which interspecies transmissions were reported. Taken together, these results provide evidence that SRLV infections evolve in a host-dependent manner, with distinct host-virus interactions in sheep and goats, and highlight the need to consider both SRLV genotypes in diagnosis, particularly in sheep.

Virological and phylogenetic characterization of attenuated small ruminant lentivirus isolates eluding efficient serological detection

Three field isolates of small ruminant lentiviruses (SRLVs) were derived from a mixed flock of goats and sheep certified for many years as free of caprine arthritis encephalitis virus (CAEV). The phylogenetic analysis of pol sequences permitted to classify these isolates as A4 subtype. None of the animals showed clinical signs of SRLV infection, confirming previous observations which had suggested that this particular subtype is highly attenuated, at least for goats. A quantitative real time PCR strategy based on primers and probes derived from a highly variable env region permitted us to classify the animals as uninfected, singly or doubly infected. The performance of different serological tools based on this classification revealed their profound inadequacy in monitoring animals infected with this particular SRLV subtype. In vitro, the isolates showed differences in their cytopathicity and a tendency to replicate more efficiently in goat than sheep cells, especially in goat macrophages. By contrast, in vivo, these viruses reached significantly higher viral loads in sheep than in goats. Both env subtypes infected goats and sheep with equal efficiency. One of these, however, reached significantly higher viral loads in both species. In conclusion, we characterized three isolates of the SRLV subtype A4 that efficiently circulate in a mixed herd of goats and sheep in spite of their apparent attenuation and a strict physical separation between goats and sheep. The poor performance of the serological tools applied indicates that, to support an SRLV eradication campaign, it is imperative to develop novel, subtype specific tools.

First Report of a Snow Bunting × Lapland Longspur Hybrid

In late April 2011, photographs of an apparent male snow bunting ( Plectrophenax nivalis ) × Lapland longspur ( Calcarius lapponicus ) hybrid were taken at St. Lewis Inlet, Newfoundland and Labrador, Canada, while the bird was foraging in a mixed flock of both species along a previously documented spring migratory route. As far as we are aware, this is the first hybridization of these species documented anywhere in the world. The bird was identified as a male on the basis of longspur nape coloration, and it appears to have the head, beak, and back coloration and patterning of a Lapland longspur, but the chin, chest and throat, and overall appearance of a snow bunting. Although our research team has banded more than 50 000 birds of both species over the past 30 years across the latitudinal range of both species, we have never observed such a hybrid. While these Arctic-breeding species overlap spatially and temporally during wintering, migration, and breeding, longspurs and buntings have distinct sexual characters and breed in different ecological niches, which may account for the reproductive isolation or low rates of hybridization of these species. While we were unable to conduct detailed morphological or genetic comparisons on this particular individual for phylogenic interpretation, this report highlights the importance of reporting field observations that may indicate ecological changes affecting the hybridization rates of these inaccessible Arctic species.

Spring and summer habitat preferences of little bustard in an agro-pastoral area in Sardinia (Italy)

The little bustard Tetrax tetrax (Aves, Gruiformes) is a threatened bird species, which is highly reliant on extensively grazed semi-natural grasslands. It is one of the more rapidly declining species in Europe due to the widespread intensification of agricultural practices and consequent abandonment of agro-pastoral activities. Therefore, understanding its habitat requirements in different seasons is crucial to implement adequate habitat management measures. Previous knowledge of habitat preference of the little bustard in Sardinia, which nowadays supports the only remnant isolated population present in Italy, is only available for the breeding season. We conducted surveys of displaying males in spring and of mixed flocks (of different age and sex classes) in summer and quantified habitat requirements in the two seasons using logistic regression analysis. Overall, we detected 85 displaying males in spring and seven mixed flocks (totalling 77 individuals) in summer within the study area. Interestingly, habitat preference models evidenced contrasting needs between the two different seasons: Males occurrence in spring was higher with greater fallow cover and further from water, whereas in summer flock occurrence was negatively related to fallow cover. This seasonal change in fallow preference is likely due to the effect of grazing livestock on this land-use. Extensive grazing is known to shape adequate habitat structure for displaying males in spring. On the other hand, grazing animals in summer may deplete the already limited food resources (i.e. green plants) available during this dry period of the year and when energy requirement for the little bustard is high due to feather moulting. This may explain the observed avoidance of fallow cover in summer. Conservation efforts in Sardinia should aim at maintaining a mosaic of diverse habitats that may provide complementary resources at any given time of the year that would benefit this and other grassland species of conservation concern.

Asymmetries in Mobbing Behavior Among Nuclear Flockmates

Abstract Tufted Titmice (Baeolophus bicolor) and Carolina Chickadees (Poecile carolinensis) often occur together in mixed species flocks during the non-breeding season and, as nuclear species, often initiate mobbing bouts. We compared the mobbing behavior of Tufted Titmice and Carolina Chickadees and, specifically, their tendency to approach five potential predators. We exposed flocks of chickadees and titmice to study skins of five species of raptors in 2008; raptors were categorized as either low-threat (rarely preying on chickadees or titmice) or high-threat (more likely to prey on chickadees or titmice). We noted the distance of closest approach by titmice and chickadees during trials, and whether a chickadee or titmouse spent more time within 5 m of the raptor. Titmice were more likely to remain within 5 m of both low (p = 0.0008) and high-threat (p = 0.0015) raptors. Titmice approached low-threat raptors closer than chickadees (p = 0.014). There was no difference in the mean distance of closes...

The composition of mixed-species bird flocks in northern Australian savannas

The study of the ecology of species assemblages provides information on the function and resilience of ecosystems and helps predict the response of species to environmental change. Mixed-species flocks are a particular mode of avian assemblage and are suggested to have benefits for foraging and predator vigilance. In this study we examine for the first time the composition of mixed-species flocks in Australian savannas using data from 335 mixed-species flocks recorded across northern Queensland. A total of 122 species, both passerines and non-passerines, were observed in flocks. Individual flocks comprised 2–21 species and 2–237 individuals, with small, insectivorous birds dominant. Although flock composition was largely undifferentiated, six broad groups of mixed-species flocks were identified, their similarity driven by a few key species. Our study found that mixed-species flocks are a common component of the tropical savannas and are similar in individual bird abundance and richness compared with studies in other biomes. One important next step is to examine the relationship of mixed flocks to the entire species pool, and their ecological significance within tropical savannas.

Performance of commercial laying hen genotypes on free range and organic farms in Switzerland, France and The Netherlands

1. A total of 257 farmers with free ranging laying hens (organic and conventional) in Switzerland, France and The Netherlands with 273 flocks were interviewed to determine the relationships between the genotype of the hens, management conditions and performance. 2. Almost 20 different genotypes (brands) were present on the farms. In France, all birds were brown feathered hens laying brown eggs. In Switzerland and The Netherlands, there were brown, white (white feathered hens laying white eggs) and silver (white feathered hens laying brown eggs) hens. In Switzerland, mixed flocks were also present. 3. The overall effect of system (organic vs. conventional free range) on egg production and mortality was significant, with higher mortality and lower egg production among organic hens. In pair wise comparisons within country, the difference was highly significant in The Netherlands, and showed a non-significant tendency in the same direction in Switzerland and France. 4. White hens tended to perform better than brown hens. Silver hens appeared to have a higher mortality and lower production per hen housed at 60 weeks of age. 5. There were no significant relationships between production, mortality, feather condition and use of outside run or with flock size. 6. There was more variation in mortality and egg production among farms with a small flock size than among farms with a large flock size.

Grazing land management and biodiversity in the Atlantic European heathlands: a review

Atlantic heaths are semi-natural habitats of high biodiversity interest which once covered large areas of the Atlantic Region. Nowadays these heathlands are dramatically reduced in many countries although they still cover wide areas in the north-west Iberian Peninsula, especially in the poorest and most socially marginal areas that are frequently affected by wildfires. We review the role of livestock grazing as a sustainable management strategy for heathlands in Europe. We have worked on a generalized conceptual framework for the management of a resource of nutritional and environmental value by drawing together evidence from studies of the livestock and the community ecology of grazed plants and the associated fauna. Key factors that influence grazing impact, such as type of livestock (animal species and breed) and their management are discussed. Goats thrive better than sheep, and horses than cattle, when heathland vegetation is the predominant resource available. Regardless of the type of livestock species managed, the low nutritive value of this vegetation hinders the maintenance of productive groups of suckler dams with offspring through the grazing season. The nutritional requirements of livestock can be met by adding improved pasture areas to heathlands. Under that strategy, sheep have the best productive performance and cattle the poorest. Management of mixed flocks with goats can lead to a more efficient use of vegetation, improve productivity and develop a patchier habitat which supports a richer associated fauna. Overall the results indicate that the sustainability of livestock grazing in these marginal lands will be achieved if they are managed effectively according to the available vegetation and their effects on the biodiversity.

Ecological correlates of song complexity in white-rumped munias

Male white-rumped munias sing syntactically simpler songs than their domestic counterparts, Bengalese finches. The differences in song structure may reflect differences in natural selection pressures between wild and domestic environments. Deacon (2010) proposed song simplicity of the wild strain could be subject to natural selection. We hypothesized the selection pressure may be species identification. Thus, we compared song variations in relation to ecological factors and dispersal history of white-rumped munias to understand song evolutionary processes. We found geographic variations of song syntactical complexity. The difference of song syntactical complexity did not corresponded to genetic distance, but did to that of the proportion of mixed flocks with sympatric related species. Birds that inhabited the areas with more mixed flocks sang simpler songs. The song complexity might be constrained to intensify distinct conspecific signals from related species. Our field work provided empirical evidence supporting a proposal made by Deacon (2010). Keywords: birdsong; evolution; masking hypothesis; Bengalese finches; song geographic variation; genetic variation

Effect of Immunosuppression on Newcastle Disease Virus Persistence in Ducks with Different Immune Status

This study was carried out to verify the possibility that ducks are sources of Newcastle disease (ND) virus infection for chickens in mixed flocks. Immunosuppressed (IS) and non immunosuppressed (NIS) birds, at three different antibody levels (medium, low and absent) were used; the titres having been induced through vaccination, and Immunosuppression done using dexamethazone. Each of the 3 respective groups was further divided into 2 groups of about 12 ducks each: one challenged with velogenic ND virus; the other not challenged. Selected ducks from all groups had their antibody titres monitored serially using hemagglutination inhibition test, while two birds from each of the challenged groups were killed and respective tissues processed for ND viral recovery, using chicken embryo fibroblasts. In general, antibody titres of IS and NIS challenged ducks were significantly higher than their unchallenged counterparts (P < 0.05). Non-challenged pre-immunised ducks had a progressive decrease in antibody levels; non-immunised ducks did not seroconvert. Newcastle disease virus was isolated from livers and kidneys of the challenged ducks throughout the experimental period; indicating a possibility of viral excretion, especially when the birds are stressed. It, therefore, provides another possible model of viral circulation within mixed flocks.