Sitting ducks: diet of wintering wildfowl in Lake Tonga,northeast Algeria

Dietary studies of five species of Anatidae (Gadwall Anas strepera, Shoveler Anas clypeata, Pochard Aythya ferina, Ferruginous Duck Aythya nyroca, and White-headed Duck Oxyura leucocephala) were carried out at Lake Tonga, northeast Algeria, from December 2011 to March 2012. Diet analysis of all five wintering species indicated a heavy reliance on seeds, which included a wide variety of aquatic plants, such as Myriophyllum spicatum, Ceratophyllum demersum, Sparganium erectum, Scirpus lacustris and Potamogeton pectinatus. Noteworthy is the paucity of ingested macroinvertebrates. Despite dietary overlap, the type, abundance and frequency of food consumed clearly indicated differences in resource use among the ducks. Incidentally, the study also highlighted the high vulnerability of threatened ducks to poaching (harvesting and disturbance) in a protected area. We discuss the implications of these findings for the management and conservation of wintering wildfowl and their North African habitats.     

Ecotourism disturbance to wildfowl in protected areas: historical, empirical and experimental approaches in the Camargue, Southern France

Ecotourism is becoming very popular, especially in protected areas where wildlife concentrate and is easier to observe, but the consequences of associated disturbance have seldom be quantified other than in the short-term, making the sustainability of this activity untested. We combined a historical, an empirical and an experimental approach to assess the long-, medium- and short-term consequences of disturbance to wintering wildfowl (Anatidae) in a wetland of international importance in the Camargue, Southern France. In the short-term, disturbance made teal (Anas crecca) move away temporarily from observation blinds without leaving the waterbody. Wildfowl fed more after disturbance, disrupting their normal resting activities. In the medium-term, waterbodies with more tourists did not host fewer birds: conversely the most heavily disturbed one hosted the highest wildfowl density. In the long term, wildfowl numbers were not related with the number of visitors. When practiced with appropriate guiding of people, and where appropriate facilities are provided to limit human disturbance as done here, ecotourism may not affect wintering wildfowl other than reversibly in the very short term. The legitimate demand of the public for access, even in fragile protected areas, may therefore be sustainable under some conditions.     

Species‐specific habitat use of wing‐moulting waterbirds in response to temporary flightlessness

The choice of the moulting habitat is of paramount importance for wing‐moulting waterbirds that have to cope with a flightless period of several weeks. However, some species might have more restricted habitat requirements during moult than others, for example due to a highly specialized feeding ecology. The moult‐related habitat use of five species (Gadwall Anas strepera, Red‐crested Pochard Netta rufina, Common Pochard Aythya ferina, Tufted Duck Aythya fuligula, Coot Fulica atra) was compared at a European inland moulting site that offered a variety of water bodies characterized by different levels of nutrient concentration, water depth, shoreline vegetation density and disturbance. To determine location‐ and species‐specific densities, birds were regularly counted throughout the moulting seasons of 2010 and 2011. In 2011, additional data on Gadwalls were used to assess differences in requirements between the flightless phase of moult and the periods before and after. Furthermore, habitat choice of 38 tagged Gadwalls was compared among two to four successive years. During the moulting season, all species showed clear preferences for specific levels of nutrient content, suggesting an active choice of suitable food sources in both food specialists and generalists. Species showing the strongest attachment to shallow water (Gadwall and Coot) were most sensitive to human disturbance and increasing water depths, and species averse to diving (Gadwall) used ponds with dense shore vegetation while flightless. For Gadwalls, habitat conditions rather than nutrient supply became increasingly important during the flightless phase. Average return rates of 59 and 54% were recorded for male and female Gadwalls, respectively, and the repeated use of familiar locations could be demonstrated in the majority of returning birds (65%). Familiarity with the habitat apparently plays an important role and may enable individuals to compensate for suboptimal conditions at the moulting site.     

Understanding the ecological drivers of avian influenza virus infection in wildfowl: a continental-scale study across Africa

Despite considerable effort for surveillance of wild birds for avian influenza viruses (AIVs), empirical investigations of ecological drivers of AIV prevalence in wild birds are still scarce. Here we used a continental-scale dataset, collected in tropical wetlands of 15 African countries, to test the relative roles of a range of ecological factors on patterns of AIV prevalence in wildfowl. Seasonal and geographical variations in prevalence were positively related to the local density of the wildfowl community and to the wintering period of Eurasian migratory birds in Africa. The predominant influence of wildfowl density with no influence of climatic conditions suggests, in contrast to temperate regions, a predominant role for inter-individual transmission rather than transmission via long-lived virus persisting in the environment. Higher prevalences were found in Anas species than in non-Anas species even when we account for differences in their foraging behaviour (primarily dabbling or not) or their geographical origin (Eurasian or Afro-tropical), suggesting the existence of intrinsic differences between wildfowl taxonomic groups in receptivity to infection. Birds were found infected as often in oropharyngeal as in cloacal samples, but rarely for both types of sample concurrently, indicating that both respiratory and digestive tracts may be important for AIV replication.     

Correlations of daily activity with avian cholera mortality among wildfowl.

We tested the hypothesis that wildfowl activities can influence the risk of avian cholera (Pasteurella multocida infection) for susceptible birds at Centerville, Humboldt County, California (USA). Avian cholera mortality characteristics from past epizootics were correlated with variations in flock size, habitat use and 11 feeding and nonfeeding behaviors among six empirically defined groups of wildfowl: American coots (Fulica americana), tundra swans (Cygnus columbianus), American wigeon (Anas americana), northern pintails (A. acuta), northern shovelers (A. clypeata)/mallards (A. platyrhynchos), and teal (A. discors, A. crecca, A. cyanoptera). The position of these wildfowl groups in past mortality sequences was directly correlated with mean flock size, time spent on land, and time spent grazing on land or in shallow water. We propose that variations in bird density, habitat use and frequency of grazing may serve as predisposing factors to avian cholera among wildfowl.     

Compared distribution within a disturbed fishpond ecosystem of breeding ducks and bird species indicators of habitat quality

The distribution of breeding ducks versus three other bird species (Mute Swan Cygnus olor, Black-headed Gull Larus ridibundus and Purple Heron Ardea purpurea) among waterbodies was investigated in the Dombes area, Eastern France, where breeding duck populations have undergone a severe decline following a large-scale transformation of meadow habitat into cropland. Higher Pochard Aythya ferina, Tufted Duck Aythya fuligula, Red-crested Pochard Netta rufina and Gadwall Anas strepera pair densities were recorded in fishponds where Black-headed Gulls were nesting. In these ponds however, nesting success (assessed by the number of broods divided by the number of pairs) was not significantly higher. Similarly, Pochard pair density was higher in ponds with a Purple Heron colony, but brood densities were not. We hypothesise that, in the study region, clutch concentration in the most attractive areas could compensate for the anti-predation effect of gull colonies or overwater nesting in shore vegetation. We could not confirm the expected negative impact of Mute Swan aggressive behaviour on duck distribution. Even though Mallard Anas platyrhynchos pair density was lower in ponds with breeding swans, we did not observe difference for Mallard broods. Moreover, Red-crested Pochard pair density and nesting success were higher in ponds where swans were breeding, probably as a consequence of shared habitat preferences.     

Annual Winter Site Fidelity of Barrow's Goldeneyes in the Pacific

Coastal regions on the Pacific north coast of North America provide important wintering habitat for many species of sea ducks. Although winter range and habitat preferences are well described for most species, fidelity to coastal wintering sites is generally undocumented. Fidelity is an important factor necessary for understanding interactions with coastal developments and activities and corresponding management strategies. We used data from Barrow's goldeneyes (Bucephala islandica), a sea duck that winters predominantly in nearshore habitats along the Pacific north coast, to investigate inter-annual fidelity to, and intra-annual fidelity within, coastal wintering sites. Between 2006 and 2015, we marked goldeneyes on breeding, molting, and wintering sites with satellite transmitters. We retained 4,931 locations in coastal habitats from 221 goldeneyes across 4 coastal regions for our analyses. These birds demonstrated high inter-annual fidelity to coastal wintering sites; 75% of selected wintering sites were within 29 km of sites used the previous winter. Inter-annual fidelity to wintering sites was similar between sex and age classes but differed by coastal region. Goldeneyes from southcentral Alaska, USA, expressed greater inter-annual fidelity relative to birds from northern or southern British Columbia, Canada, and southeast Alaska. Goldeneyes also expressed high intra-annual fidelity within wintering sites, with 75% of individuals averaging within-season movements of ≤9 km. Intra-annual fidelity was lesser for female than male goldeneyes but did not differ between hatch-year and after-hatch-year birds. We found regional variation in intra-annual fidelity, with goldeneyes from southcentral Alaska expressing greater intra-annual fidelity compared to birds from other regions. High inter- and intra-annual winter site fidelity by Barrow's goldeneyes suggests that, at a population level, habitat use is predictable and can be used to inform risk assessment or to evaluate factors affecting habitat choice. Also, low dispersal among wintering sites suggests that recovery from population perturbations, whether caused by natural or anthropogenic events, will be protracted. © 2019 The Wildlife Society.     

Fine‐scale habitat use during the non‐breeding season suggests that winter habitat does not limit breeding populations of a declining long‐distance Palearctic migrant

For migrant birds, which habitats are suitable during the non‐breeding season influences habitat availability, population resilience to habitat loss, and ultimately survival. Consequently, habitat preferences during winter and whether habitat segregation according to age and sex occurs directly influences migration ecology, survival and breeding success. We tested the fine‐scale habitat preferences of a declining Palearctic migrant, the whinchat Saxicola rubetra, on its wintering grounds in west Africa. We explored the influence of habitat at the territory‐scale and whether dominance‐based habitat occupancy occurs by describing the variation in habitat characteristics across wintering territories, the degree of habitat change within territories held throughout winter, and whether habitat characteristics influenced territory size and space‐use within territories or differed with age and sex. Habitat characteristics varied substantially across territories and birds maintained the same territories even though habitat changed significantly throughout winter. We found no evidence of dominance‐based habitat occupancy; instead, territories were smaller if they contained more perching shrubs or maize crops, and areas with more perching shrubs were used more often within territories, likely because perches are important for foraging and territory defence. Our findings suggest that whinchats have non‐specialised habitat requirements within their wintering habitat of open savannah and farmland, and respond to habitat variation by adjusting territory size and space‐use within their territories instead of competing with conspecifics. Whinchats show a tolerance for human‐modified habitats and results support previous findings that some crop types may provide high‐quality wintering habitat by increasing perch density and foraging opportunities. By having non‐specialised requirements within broad winter habitat types, migrants are likely to be flexible to changing wintering conditions in Africa, both within and across winters, so possibly engendering some resilience to the rapid anthropogenic habitat degradation occurring throughout their wintering range.     

Lead exposure and recovery rates of black ducks banded in Tennessee.

American black ducks (Anas rubripes) wintering in Tennessee during 1986 to 1988 were tested for exposure to lead. Twelve percent of the birds had blood lead concentrations exceeding 0.2 ppm. Significant differences in the prevalence of lead exposure were found for adults (14.4%) and juveniles (8.2%). Exposed birds had higher blood lead concentrations at one study site, corresponding with a lower survival index.     

Ingestion of lead and nontoxic shot by Green-winged Teal (Anas crecca) and Northern Shovelers (Anas clypeata) from the mid-Gulf Coast of Texas, USA

Ninety-eight Green-winged Teal (Anas crecca) and 84 Northern Shoveler (Anas clypeata) gizzards were examined for ingested shot. One Northern Shoveler had lead and three had steel shot; 24 teal and 17 shovelers had composite nontoxic shot or nonlead metal fragments. Prevalence of ingested lead appears minimal and consistent with other studies conducted after lead-shot bans.     

Apparent resilience of a declining Afro‐Palaearctic migrant to forest loss on the wintering grounds

Populations of long‐distance migrant birds are declining but it is unknown what role land cover change in non‐breeding areas may be playing in this process. Using compositional analysis, we assessed habitat selection by one such migrant, the Wood Warbler Phylloscopus sibilatrix, at a wintering site in the forest–savannah transition zone in Eastern Region, Ghana. There was a preference for forest, a habitat that is in marked decline at this site. Annual habitat mapping revealed that the area of forest declined by 26% between 2011/12 and 2013/14, mainly through clearance for conversion to arable land. Numbers of birds changed throughout the season, but despite the reduction in the preferred forest habitat, there was no change in the total number of birds recorded at the site over the study period. The number of birds recorded at a point was positively related to the proportion of cleared land, plantation and, to a lesser extent, dense forest within 100 m. Investigation of the fine‐scale habitat preferences of radiotagged Wood Warblers suggested that there was an optimum number of trees, around 66–143 per hectare, at which estimated probability of occupancy was 0.5, falling to a probability of 0.2 at 25 trees per hectare. We suggest that Wood Warblers may be buffered against the loss of forest habitat by their ability to utilize degraded habitats, such as well‐wooded farmland, that still retain a substantial number of trees. However, the continued loss of trees, from both forest and farmland is ultimately likely to have a negative impact on wintering Wood Warblers in the long‐term.     

Epizootiological features of avian cholera on the north coast of California

An avian cholera (Pasteurella multocida) epizootic was observed among wildfowl at the Centerville Gun Club, Humboldt County, California (USA) in January 1978. Compared to their live populations and use of the area, coots (Fulica americana) died in proportionately greater numbers than any other species. Coots collected by gunshot were evaluated for sex and age composition, and morphometry from November 1977 through mid-January 1978 at this site. There was no substantial difference in the sex, age or morphometry between birds dying of avian cholera and from those dying from gunshot. Assuming coots dying of gunshot are representative of the general population, it appears there was little selection among coots by P. multocida. There was evidence for a sequential mortality similar to that reported previously at this site: coots were the first birds to die, followed by American wigeon (Anas americana) and northern pintails (A. acuta acuta); northern shovelers (A. clypeata) and mallards (A. platyrhynchos) died late in the epizootic.     

极端洪水作用下升金湖消落带生境变化对越冬水鸟群落结构的影响

水鸟是湿地生境质量的重要指示性动物类群,可敏感地反映湿地环境变化。浅水通江湖泊消落带具有复杂多样的生境和丰富的食物资源,是水鸟特别是越冬水鸟的重要聚集区,其食物资源的丰富度和可获得性受水文节律影响。在极端洪水作用下,消落带生境变化对越冬水鸟群落结构及其多样性的影响是一个值得关注的水鸟及湿地生态学问题。选择了具有典型消落带生境的升金湖作为研究区域,对2019年(正常水位)和2020年(异常水位)两个越冬季水鸟的数量、种类进行调查统计,分析了消落带的生境变化情况对越冬水鸟群落结构的影响。2019年越冬期,记录到水鸟(50984.20±9595.71)只(n=5),隶属7目13科51种;2020年越冬期,记录到水鸟(27923.00±13808.47)只(n=5),隶属7目12科53种。整个越冬季消落带的水鸟种类略增但数量减少,2019年游禽中的优势种为豆雁,2020年游禽中的优势种增加为豆雁和斑嘴鸭,但涉禽中的优势种由白琵鹭、反嘴鹬、凤头麦鸡转变为苍鹭、大白鹭和反嘴鹬。洪水导致的草滩-水域混合区生境面积减小使湿生植物退化,可能是导致以豆雁为主的食苔草水鸟数量大幅度减少的重要原因;因湖水延迟...     

THE WINTER FEEDING ECOLOGY OF WIGEON AT BRIDGWATER BAY, SOMERSET

The feeding ecology of Wigeon wintering in the vicinity of Bridgwater Bay National Nature Reserve is described. The birds roost on mudflats in the Bay during the day and feed, mainly at night, on saltings and wet pastures in the surrounding area. Their food, ascertained from gut analyses, consists largely of grass leaves; with roots, stolons, bulbils and seeds of secondary importance. Analyses including gizzard contents much exaggerated the importance of seeds because they are retained in the gizzard for longer than softer items.
An investigation of Wigeon feeding behaviour and food preferences on salting pasture is described, using the density of the birds' droppings on different vegetation zones to assess usage, and faecal analysis to determine the composition of the selected diet. The technique of faecal analysis is discussed in relation to feeding studies on grazing wildfowl.
Disturbance is a very important factor affecting the availability of feeding habitat, and this can mask the birds' food preferences. Early in the winter, Wigeon select Puccinellia maritima in preference to Agrostis stolonifera and Festuca rubra. They do this initially by selecting the broad zone in which they feed, by selecting feeding sites within zones, and particular plant species from a mixed sward. The birds are more selective when feeding in less preferred zones. The mechanisms and reasons for food selection are discussed in relation to characteristics of the habitat and of the plants. It is concluded that the nutritional value of the plants is important in determining the birds' preference, but that other factors also play a part.
Wigeon are flexible in their feeding habits and are increasingly found on inland habitats. They are adaptable in using new roosts, and in modifying their behaviour in response to changes in food supply and changes in disturbance pressures.     

Partial migration in inexperienced pied avocets Recurvirostra avosetta: distribution pattern and correlates

Birds exhibit a range of wintering behaviour from strictly migrant to strictly resident species. In partially migrating ones, some birds overwinter within their breeding region (resident birds) while others, although breeding in the same area, winter far away (migrant birds). Accordingly, choosing a wintering region is a key stage in the annual life cycle of birds, notably for inexperienced first‐year individuals. The present study aimed to investigate this issue, and more specifically to study the distribution pattern during winter and factors influencing the wintering behaviour of first‐year pied avocets Recurvirostra avosetta. Based on a 10‐yr ringing study carried out on five of the major French breeding colonies distributed along the Atlantic coast, we showed the coexistence of different wintering tactics. The resident tactic was predominant (approximately 86% of the 575 birds re‐sighted), while the other birds adopted migration. Among resident individuals, two different tactics occurred: 43% of birds overwintered within their natal colony, whereas the others wintered in another site located at relatively close proximity along the French Atlantic coast. Hatching date was a consistent predictor of all wintering tactics. More specifically, the probability of migrating was the highest for early‐hatched birds, and for resident ones, the probability of wintering within their natal colony rather than in another French site was the highest for both median‐ and late‐hatched individuals. In addition, a colony effect was demonstrated for resident birds. Several biological interpretations, including social system, variations in both individual body condition and habitat quality, were put forward to explain these correlates.     

Maintenance and dissemination of avian-origin influenza A virus within the northern Atlantic Flyway of North America

Wild waterbirds, the natural reservoirs for avian influenza viruses, undergo migratory movements each year, connecting breeding and wintering grounds within broad corridors known as flyways. In a continental or global view, the study of virus movements within and across flyways is important to understanding virus diversity, evolution, and movement. From 2015 to 2017, we sampled waterfowl from breeding (Maine) and wintering (Maryland) areas within the Atlantic Flyway (AF) along the east coast of North America to investigate the spatio-temporal trends in persistence and spread of influenza A viruses (IAV). We isolated 109 IAVs from 1,821 cloacal / oropharyngeal samples targeting mallards (Anas platyrhynchos) and American black ducks (Anas rubripes), two species having ecological and conservation importance in the flyway that are also host reservoirs of IAV. Isolates with >99% nucleotide similarity at all gene segments were found between eight pairs of birds in the northern site across years, indicating some degree of stability among genome constellations and the possibility of environmental persistence. No movement of whole genome constellations were identified between the two parts of the flyway, however, virus gene flow between the northern and southern study locations was evident. Examination of banding records indicate direct migratory waterfowl movements between the two locations within an annual season, providing a mechanism for the inferred viral gene flow. Bayesian phylogenetic analyses provided evidence for virus dissemination from other North American wild birds to AF dabbling ducks (Anatinae), shorebirds (Charidriformes), and poultry (Galliformes). Evidence was found for virus dissemination from shorebirds to gulls (Laridae), and dabbling ducks to shorebirds and poultry. The findings from this study contribute to the understanding of IAV ecology in waterfowl within the AF.     

An assessment of the potential impact of dredging activity on the Tamar Estuary over the last century: Bathymetric and hydrodynamic changes

The Tamar Estuary, S.W. England, is a commercial and military port and the site of a major naval dockyard. Parts of the estuary require regular maintenance dredging and some capital dredging has been undertaken. The estuary is also assigned Special Area of Conservation (SAC) status under the European Habitats Directive and is an important site for migrating wildfowl and wading birds. As part of an assessment undertaken for a consortium of the port operators and regulatory authorities, we have analysed the ecological, physical, chemical and socio-economic impacts of dredging on the Tamar Estuary ecosystem. This paper focuses on the physical changes through the analysis of historical survey data and the use of hydrodynamic modelling. The objective was to evaluate whether dredging has influenced the estuary morphology or hydrodynamic regime and thus impacted on the ecological habitat. Bathymetric survey data collected between 1895 and 1968 were compared with multi-beam echo sounder data obtained in 2001. The paper survey records were digitised, geo-referenced and adjusted to the modern datum and units. The accuracy and limitations of this approach are discussed. Both sets of data were contoured and analysed using a GIS package. Comparisons between 1895 and 2001 hydraulics were made using a 1-D hydrodynamic and sediment transport model set up for the bathymetry at those times but ‘driven’ using a single, common, year-long data set for tides and river flows. The results suggest that although the deep channel in the region that is mainly south of the Tamar road bridge, is on average 0.5 m deeper in 2001 than it was in 1895, this has had a negligible effect on the area of intertidal mud and, thus, on habitat available for wading birds, and minimal impact on the large-scale hydrodynamics of the estuary.     

Interspecific and intraspecific differences in habitat use and their conservation implications for Palaearctic harriers on Sahelian wintering grounds

The floodplains of the West‐African Sahel region have experienced extensive habitat transformation during the past four decades, coinciding with an impoverishment of raptor populations. We investigated foraging patterns of Palaearctic migratory Eurasian Marsh Harriers Circus aeruginosus, Pallid Harriers C. macrourus and Montagu’s Harriers C. pygargus on a floodplain system in northern Cameroon to assess species, sex‐ and age‐related habitat preferences. Sex and age have rarely been incorporated into general studies of raptor habitat associations, despite clear evidence of intrasexual and age‐related differences in foraging strategies and diet composition, potentially carrying strong conservation implications. We found evidence of sexual differences in foraging preference related to land use, particularly in the most sexually dimorphic Pallid Harrier, and evidence that juveniles used different habitats to adults. This constitutes the first quantitative documentation of such differentiation by Palaearctic raptors on African wintering grounds, indicating that general patterns of habitat use in wintering raptors may obscure sex‐ and age‐specific preferences. Contrary to expectations, we found limited evidence for interspecific foraging segregation. Food partitioning by prey mass was related to harrier body mass and facilitated by a diverse availability of prey on human‐transformed floodplains. Anticipated further large‐scale conversion of floodplain habitat into predominantly desiccated grasslands raises concerns about the survival of wintering harriers.     

Switching to a feeding method that obstructs vision increases head-up vigilance in dabbling ducks

A major assumption in most models of foraging is that feeding and vigilance are mutually exclusive. A recent experimental study challenged this hypothesis and demonstrated that birds are able to detect predators while pecking seeds on the ground (head-down vigilance). Experimental obstruction of head-down vigilance makes birds increase head-up vigilance (i.e. the classical overt vigilance posture). For many foragers in the wild, visibility varies between habitats and foraging methods. We compared the vigilance of Teal Anas crecca and Shoveler Anas clypeata when foraging with their eyes above the water surface (shallow feeding, only the bill submerged) and when foraging with their eyes underwater (deep feeding, head and neck underwater, or upending), at three wintering sites in western France. Birds of both species spent less time in head-up vigilance during shallow foraging than during deep foraging, with no significant difference between sites, which suggests that they are capable of some vigilance during shallow foraging. During deep foraging, the time spent vigilant increased because the frequency of scans was much higher, while scan length decreased. However, these differences could have resulted from variations in the availability of food at different depths. In an experiment where the food availability was constant, we observed the same pattern, with a higher frequency of scans during deep foraging. This study therefore provides strong support for the idea that vigilance and foraging are not always mutually exclusive and shows that switching between searching methods can cause vigilance time – and, as a consequence, loss of feeding time – to vary. This should be taken into account in future field and experimental studies of the trade-off animals make between vigilance and feeding.