A flyway perspective on food resource abundance in a long-distance migrant, the Eurasian teal (Anas crecca)

Two frequent assumptions about the evolution of long-distance migration in birds are that they travel long distances annually to reach food-rich areas for breeding, and that they time their migratory journey to be at staging sites when the latter provide the best feeding conditions. These assumptions have rarely been properly tested, and there is no study in which a species’ major food types have been measured by standardized methods throughout a flyway and over a large part of the year. We here present such data for Eurasian teal (Anas crecca), converted to a common energetic currency, and collected at wintering, spring staging and breeding sites. Teal did not time migration to maximize local food abundance; most birds left wintering and spring staging sites before a sharp increase in invertebrate food abundance occurred. On the other hand, hatching of ducklings coincided with a peak in invertebrate food abundance on boreal breeding lakes. Mean overall food abundance (invertebrates and seeds combined) did not differ between wintering sites in southern France and breeding sites in northern Sweden at the time of breeding. Our results are inconsistent with the hypothesis that long-distance migration in dabbling ducks has evolved because adult birds gain an immediate pay-off in increased food abundance by flying north in spring. However, our data confirm a selective advantage for breeding at higher latitudes, because hatching of ducklings may coincide with a peak in invertebrate emergence and because longer days may increase the duration of efficient foraging.     

Variation in the Diet of Ducks During Spring Migration

Because management practices that promote the production of plant foods may differ from management practices that promote the production of aquatic invertebrates, a thorough understanding of the diet is needed to develop management strategies for various stages of the annual cycle for dabbling and diving ducks. Diet of dabbling (tribe Anatini) and diving (tribe Aythyini) ducks during breeding, autumn migration, and winter has been documented. Our goal was to estimate and compare the diet of blue-winged teal (Spatula discors), gadwall (Mareca strepera), mallard (Anas platyrhyncos), lesser scaup (Aythya affinis), and ring-necked duck (Aythya collaris) during spring migration in the Mississippi Flyway in the United States and evaluate variation among species. We collected 919 ducks for diet analysis from multiple wetlands at 6 sites across 4 states during the spring migration of 2006 and 2007. We collected ≥10 individuals of each species at each of the 6 study sites except we collected only 1 gadwall at the Scioto River site and 2 lesser scaup at the Cache River site. We detected that the proportion of plant and animal material in foods of each spring migrating duck species was in general intermediate of that found in wintering and breeding birds. Furthermore, the proportion of plant and animal material in the diet of species varied even among closely related species, indicating species are partitioning food sources along a protein-carbohydrate gradient during spring migration. We recommend that resources for ducks be managed to provide diverse wetlands to support the varied diets of even closely related species. © 2021 The Wildlife Society.     

Occupancy Patterns of Breeding American Black Ducks

Occupancy patterns can assist with the determination of habitat limitation during breeding or wintering periods and can help guide population and habitat management efforts. American black ducks (Anas rubripes; black ducks) are thought to be limited by habitat and food availability during the winter, but breeding sites may also limit the size or growth potential of the population. The Canadian Wildlife Service conducts an annual breeding waterfowl survey that we used to explore the hypothesis that black duck carrying capacity is limited by wetlands available for breeding in Québec, Canada. We applied single-visit, multi-species occupancy models to the 1990–2015 population survey data to determine if there was evidence the black duck population was limited by breeding habitat. Using a dynamic (multi-season) occupancy modeling approach, we estimated latent occupancy (occupancy accounting for imperfect detection) of black ducks and then used latent occupancy estimates to derive occupancy, colonization, and extirpation rates. We jointly modeled the occupancy dynamics of black ducks and other duck species in wetlands where both species were present. Throughout the duration of the survey, 44% of wetlands were never observed to be occupied by black ducks. Occupancy models showed wetland size was positively associated with occupancy at the first time step (initial occupancy) and colonization. All 2-species models indicated initial black duck occupancy, persistence (continued occupancy), and colonization were positively associated with the presence of a second species. Colonization rate over the 26-year period ranged from 7% to 27% across all models. Extirpation rates were similar and were constant through time within each model. Low occupancy rates, combined with approximately equal colonization and extirpation rates, suggest there are available wetlands for breeding black ducks in their core breeding area. If breeding habitats are not saturated, this suggests migration or wintering areas may be more limiting to black duck population abundance. © 2019 The Wildlife Society.     

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.     

Variation in home-range size and movements of wintering dabbling ducks

Despite a long historical record of radio-tracking analyses, basic home-range information is still lacking for most common waterfowl species, especially during the winter. We investigated how dabbling duck home ranges and daily foraging movements are influenced by extrinsic (site, temperature, date) and intrinsic factors (species, sex, age). We radio-tagged and monitored 125 individuals of three duck species (mallard Anas platyrhynchos, Eurasian teal A. crecca crecca and northern pintail A. acuta) in three French wetlands over four winters. Home-range sizes for a given species varied greatly among our study sites. Moreover, species differed according to home-range structure and distance traveled to reach their foraging grounds (teal had a more patchy home range and traveled farther distances than mallards). Foraging distances increased with temperature and time (over the winter season), but this effect differed among species, suggesting that they behave differently in response to food depletion and/or cold weather. The commuting behavior (i.e., the decision to leave the roost at night for foraging) differed among species and season. Teals were more risk-prone because they were more likely to leave the roost at night. In our study, ducks foraged at distances of 1–2 km from roosts, whereas distances of 2–48 km have been recorded in North America. We suggest that food supply, hunting pressure or population density may account for these inter-continental differences.     

The Potential Distance of Highly Pathogenic Avian Influenza Virus Dispersal by Mallard, Common Teal and Eurasian Pochard

Waterbirds represent the major natural reservoir for low pathogenic (LP) avian influenza viruses (AIV). Among the wide diversity of subtypes that have been described, two of them (H5 and H7) may become highly pathogenic (HP) after their introduction into domestic bird populations and cause severe outbreaks, as is the case for HP H5N1 in South-Eastern Asia. Recent experimental studies demonstrated that HP H5N1 AIV infection in ducks does not necessarily have significant pathological effects. These results suggest that wild migratory ducks may asymptomatically carry HP AIV and potentially spread viruses over large geographical distances. In this study, we investigated the potential spreading distance of HP AIV by common teal (Anas crecca), mallard (A. platyrhynchos), and Eurasian pochard (Aythya ferina). Based on capture-mark-recapture method, we characterized their wintering movements from a western Mediterranean wetland (Camargue, South of France) and identified the potential distance and direction of virus dispersal. Such data may be crucial in determining higher-risk areas in the case of HP AIV infection detection in this major wintering quarter, and may serve as a valuable reference for virus outbreaks elsewhere.     

鄱阳湖区稻田生境中灰鹤越冬行为的时间分配与觅食行为

2013年11月—2014年2月,采用瞬时扫描和焦点动物法研究了鄱阳湖区稻田生境中灰鹤越冬行为的时间分配、活动节律与觅食行为。结果显示,觅食(64.09%)行为所占比例最大,其次为警戒(15.97%)、飞行(8.67%)和修整(7.37%)行为。4种主要行为中,觅食行为时间分配随越冬前期(11月)、中期(12月—翌年1月)、后期(2月)逐渐增加,其余行为时间均逐渐减少。各环境因子对主要行为的影响存在显著交互效应,修整行为随各环境因子变化最为明显,日最低温度升高、日最高温度降低、日照长度增加及湿度降低都会使修整行为增加;日照长度增加和湿度降低时,觅食行为增加;日照长度增加时,警戒行为减少。环境因子对成鹤影响效果与总体相同。环境因子仅对幼鹤的觅食行为影响显著,即日照长度增加和湿度降低,幼鹤觅食行为增加。环境因子对行为的影响为非线性关系,致使其影响趋势在不同范围内有所变化。行为节律上,灰鹤昼间各时段觅食行为保持较高水平,觅食高峰出现在11:00—11:59和17:00—17:30。灰鹤觅食生境与其夜宿地分离,致其上午觅食高峰有所推后。幼鹤昼间各时段行为节律与成鹤有较大差异,且各时段觅食行为比例均高于成鹤。灰鹤越冬期在稻田生境的平均啄食频率为(32.06±0.47)次/min,平均步行频率为(6.55±0.35)步/min。啄食频率与步行频率呈极显著负相关。时段和集群类型对啄食频率的影响存在显著交互效应。稻田中食物资源的可利用性逐渐下降,灰鹤的啄食频率随时间逐渐降低,为保证越冬期间获取足够的能量供应,灰鹤采取逐渐增加步行频率和觅食时间的策略。有觅食间隔的抽样单元中,平均警戒次数为(1.37±0.04)次/单元,平均警戒持续时间为(6.02±0.37)s/单元。成鹤花费在警戒的时间多于幼鹤,家庭群中的个体警戒持续时间多于聚集群中的个体。     

Potential use of weather radar to study movements of wintering waterfowl

To protect and restore wintering waterfowl habitat, managers require knowledge of routine wintering waterfowl movements and habitat use. During preliminary screening of Doppler weather radar data we observed biological movements consistent with routine foraging flights of wintering waterfowl known to occur near Lacassine National Wildlife Refuge (NWR), Louisiana. During the winters of 2004–2005 and 2005–2006, we conducted field surveys to identify the source of the radar echoes emanating from Lacassine NWR. We compared field data to weather radar reflectivity data. Spatial and temporal patterns consistent with foraging flight movements appeared in weather radar data on all dates of field surveys. Dabbling ducks were the dominant taxa flying within the radar beam during the foraging flight period. Using linear regression, we found a positive log-linear relationship between average radar reflectivity (Z) and number of birds detected over the study area (P < 0.001, r² = 0.62, n = 40). Ground observations and the statistically significant relationship between radar data and field data confirm that Doppler weather radar recorded the foraging flights of dabbling ducks. Weather radars may be effective tools for wintering waterfowl management because they provide broad-scale views of both diurnal and nocturnal movements. In addition, an extensive data archive enables the study of wintering waterfowl response to habitat loss, agricultural practices, wetland restoration, and other research questions that require multiple years of data. © 2011 The Wildlife Society.     

Agroecosystems and conservation of migratory waterbirds: importance of coastal pastures and factors influencing their use by wintering shorebirds

Coastal pastures are common agroecosystems adjacent to estuarine areas that can provide valuable habitat for wildlife, particularly for migratory shorebirds. Disentangling the factors that influence coastal pasture use by wintering shorebirds will provide new insights into its role for buffering human disturbances and habitat loss in intertidal areas. We examined whether numbers of two shorebirds (Eurasian curlew and Black-tailed godwit) foraging actively on coastal pastures was affected by weather conditions, tidal stage (low/high tide) and number of harvesters at intertidal areas throughout winter. Both species frequently used coastal pastures and most individuals foraged actively there. The average percentage of the total wintering population of curlews and godwits foraging on coastal pastures was 27.4 and 7.8 %, respectively, and was significantly higher during high tide compared to low tide. The number of harvesters on mudflats also had a positive significant effect in explaining the presence of curlews, and to a lesser extent for godwits, on coastal pastures, and accumulated rainfall had a positive effect for both species too. These supratidal areas were consistently used as alternative foraging grounds during low tide by curlews, as well as supplementary foraging areas during high tide by wintering populations of both large shorebirds. By supplementary foraging, wintering curlews, and probably godwits, seemed to compensate for a negative effect of the presence of harvesters on their foraging activity. We recommend managing of those coastal agricultural fields adjacent to intertidal foraging grounds in order to increase the availability of supratidal foraging habitats for declining shorebird populations. These habitats may thus have a beneficial role in sustaining populations of wintering shorebirds, but further studies are needed to estimate if birds can compensate for any shortfall in daily energy budget by supplementary foraging on coastal pastures, thus providing insights into whether they are involved in large-scale population regulation of migratory birds.     

Variability in the area,energy and time costs of wintering waders responding to disturbance

Birds’ responses to human disturbance are interesting due to their similarities to anti‐predator behaviour, and understanding this behaviour has practical applications for conservation management by informing measures such as buffer zones to protect priority species. To understand better the costs of disturbance and whether it will impact on population size, studies should quantify time‐related responses as well as the more commonly reported flight initiation distance (FID). Using waders wintering on an estuarine area, we experimentally disturbed foraging birds on the Wash Embayment, UK, by walking towards them and recording their responses (FID, alert time, time spent in flight, time taken to resume feeding, and total feeding time lost). We present data for 10 species of conservation concern: Curlew Numenius arquata, Oystercatcher Haematopus ostralegus, Bar‐tailed Godwit Limosa lapponica, Grey Plover Pluvialis squatarola, Redshank Tringa totanus, Knot Calidris canutus, Turnstone Arenaria interpres, Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Dunlin Calidris alpina. Larger species responded more strongly, response magnitude was greater under milder environmental conditions, and responses varied over both small and large spatial scales. The energetic costs of individual responses, however, were low relative to daily requirements and disturbance events were unlikely to be frequent enough to seriously limit foraging time. We suggest, therefore, that wintering wader populations on the Wash are not currently significantly negatively impacted by human disturbance during the intertidal foraging period. This is also likely to be the case at other estuarine sites with comparable access levels, visitor patterns, invertebrate food availability and environmental conditions.     

The influence of wave exposure on the foraging activity of marine otter, <Emphasis Type="Italic">Lontra felina</Emphasis> (Molina, 1782) (Carnivora: Mustelidae) in northern Chile

The marine otter Lontra felina has been said to prefer wave-exposed habitats over more protected sites in response to a greater prey abundance in exposed habitat. We examined how the foraging activity of L. felina is affected by the regime of wave exposure and prey availability at Isla Choros, northern Chile. Through focal sampling we recorded time spent by otters in foraging, the duration of dives, and the hunting success on a wave-exposed and a wave-protected site on the island. In addition, we quantified the abundance of prey in both habitats. Marine otters spent more time foraging in the wave-protected site compared with the wave-exposed habitat. Successful dives reached 26.9% in the wave-exposed habitats, and 38.2% in the wave-protected habitat. Foraging dives were 18% shorter in wave-exposed as compared with wave-protected habitat. Numerically, available prey did not differ significantly with habitat. Our results are more consistent with the hypothesis that wave-exposed habitats represent a sub-optimal habitat to foraging marine otters. Marine otters’ use of wave-exposed patches through northern and central Chile coastal areas probably reflects a low availability of suitable protected areas and greater human disturbance of more protected habitat.     

DISPERSAL OF AQUATIC ORGANISMS: VIABILITY OF SEEDS RECOVERED FROM THE DROPPINGS OF CAPTIVE KILLDEER AND MALLARD DUCKS

Seeds of aquatic and semiaquatic angiosperms were fed to two representative waterbirds: killdeer (Charadrius vociferus) and mallard ducks (Anas platyrhynchos). The viability and maximum period of retention for seeds recovered from the droppings were determined. Results indicate that resistance of the seeds to avian digestive processes depends both upon the nature of the seed coat and the species of bird through which they pass. Periods of maximum retention, greater in killdeer than in mallard ducks, were much longer than had previously been supposed. Plants with highly resistant seeds are for the most part of wide geographic distribution suggesting that the extensive range of many aquatic plants can be accredited, at least in part, to their adaptation to internal transport by birds.     

Pintail and Mallard Survival in California Relative to Habitat,Abundance, and Hunting

ABSTRACT The influence of habitat, waterfowl abundance, and hunting on winter survival of waterfowl is not well understood. We studied late August-March survival of 163 after-hatch-year (AHY) and 128 hatch-year (HY) female mallards (Anas platyrhynchos) radiotagged in Sacramento Valley (SACV) and 885 AHY female northern pintails (A. acuta) radiotagged throughout the Central Valley of California, USA, relative to flooded habitat (HAB), January abundance of each species (JMAL or JPIN), hunter-days (HDY), and a hunting pressure index (HPI) that combined these variables. From EARLY (1987–1994) to LATE (1998–2000), HAB increased 39%, JPIN increased 45%, JMAL increased 53%, HDY increased 21%, duck-hunting season increased from 59 days to 100 days, and the female daily bag limit doubled to 2 for mallards but remained 1 for pintails. Survival (± SE) was greater during LATE versus EARLY for pintails radiotagged in each region (SACV: 93.2 ± 2.1% vs. 87.6 ± 3.0%; Suisun Marsh: 86.6 ± 3.2% vs. 77.0 ± 3.7%; San Joaquin Valley: 86.6 ± 3.1% vs. 76.9 ± 4.1%) but not for SACV mallards (AHY: 70.6 ± 7.2% to 74.4 ± 7.7% vs. 80.1 ± 7.2% to 82.8 ± 5.6%; HY: 48.7 ± 9.1% [1999–2000 only] vs. 63.5 ± 8.8% to 67.6 ± 8.0%). Most pintail (72%) and mallard (91%) deaths were from hunting, and lower HPI and higher JPIN or JMAL were associated with reduced mortality. Increased HAB was associated with reduced winter mortality for pintails but not for SACV mallards. Pintail survival rates that we measured were within the range reported for other North American wintering areas, and during LATE were higher than most, even though our study duration was 68–110 days longer. Winter survival rates of SACV mallards were also within the reported range. However, with higher bag limits and longer seasons, mallard survival during LATE was lower than in most other wintering areas, especially during 1999–2000, when high winds on opening weekend resulted in high hunting mortality. Habitat conservation and favorable agriculture practices helped create a Central Valley wintering environment where natural mortality of mallards and pintails was low and survival varied with hunting mortality. We recommend regulations and habitat management that continue to minimize natural mortality while allowing sustainable harvest at a level that helps maintain strong incentive for management of Central Valley waterfowl habitats, including the large portion that is privately owned.     

贵州草海湿地越冬黑颈鹤觅食地与农耕地的空间关系研究

贵州草海湿地是世界上最大的黑颈鹤东部种群越冬地之一。黑颈鹤在草海越冬期极其依赖农耕地觅食存活,但当地人鸟争地冲突严重、觅食地萎缩加剧。为此,运用空间点格局分析及缓冲区叠加分析,探究黑颈鹤觅食地与农耕地空间关联性,并精确确定出重点保护管理区域,结果表明：1）研究期间,两年共在草海湿地周边农地确定黑颈鹤觅食点216处,其中家庭鹤觅食地99处、集群鹤觅食地117处,越冬种群中83%的个体依赖农耕区觅食;2）区域尺度上,家庭鹤与集群鹤的觅食点分布均为聚集分布,但集群鹤觅食点聚集程度较家庭鹤更高;觅食地与农耕地在空间聚类上呈正相关关系,并在3.2 km距离尺度下聚类程度最高;3）基于空间关联性,通过缓冲区叠加分析,共确定最适宜的农地觅食地53.74 km²,并划定2处重点核心保护区域及2处次重核心保护区域范围。研究结果对于揭示区域尺度上黑颈鹤觅食地与农耕地空间关系,指导保护管理者加强重点区域管理,以及对区域土地利用规划和缓解人鸟争地矛盾,具有重要的理论与实践意义。     

Agonistic Interactions and the Distribution of Foraging Organisms: Individual Costs and Social Information

The results of a previous experiment we conducted suggested that agonistic interactions may, counterintuitively, attract organisms to food sites rather than drive them away. In this study we test whether interactions attract or deter organisms by manipulating the distribution of interactions in a natural population of mallard ducks (Anas platyrhynchos L.). We manipulated the distribution of interactions by changing the size of the bread fed to the ducks from two food sites. In the condition with large pieces of bread the distribution of interactions between the two food sites was more extreme than in the small bread condition. The attraction hypothesis predicted that the distribution of ducks should be more extreme in this condition, whereas the deterrence hypothesis predicted that the distribution of ducks should be less extreme. We found that the distribution of ducks was significantly more extreme in the large bread condition. This supports the hypothesis that agonistic interactions act as a net attraction to foraging organisms. The possible benefits organisms may gain from agonistic interactions are discussed.     

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.     

Multi-scale habitat selection and foraging ecology of the eurasian hoopoe (<Emphasis Type="Italic">Upupa epops</Emphasis>) in pine plantations

Bird conservation can be challenging in landscapes with high habitat turnover such as planted forests, especially for species that require large home ranges and juxtaposition of different habitats to complete their life cycle. The eurasian hoopoe (Upupa epops) has declined severely in western Europe but is still abundant in south-western France. We studied habitat selection of hoopoes in pine plantation forests using a multi-scale survey, including point-counts at the landscape level and radio-tracking at the home-range scale. We quantified habitat use by systematically observing bird behaviour and characterized foraging sites according to micro-habitat variables and abundance of the main prey in the study area, the pine processionary moth (Thaumetopoea pityocampa). At the landscape scale, hoopoes selected habitat mosaics of high diversity, including deciduous woods and hedgerows as main nesting sites. At the home-range scale, hoopoes showed strong selection for short grassland vegetation along sand tracks as main foraging habitats. Vegetation was significantly shorter and sparser at foraging sites than random, and foraging intensity appeared to be significantly correlated with moth winter nest abundance. Hoopoe nesting success decreased during the three study years in line with processionary moth abundance. Thus, we suggest that hoopoes need complementation between foraging and breeding habitats to establish successfully in pine plantations. Hoopoe conservation requires the maintenance of adjacent breeding (deciduous woods) and foraging habitats (short swards adjacent to plantation edges), and consequently depends on the maintenance of habitat diversity at the landscape scale.     

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The Lesser Crested Tern Thalasseus bengalensis emigratus breeding population in the Mediterranean is found exclusively in Libya, on the two coastal islands of Gara and Elba and one wetland on the mainland coast at Benghazi. In order to improve knowledge of the species migration to wintering quarters in West Africa, a ringing programme was conducted from 2006–2008 and 2009–2012. From a total of 1 354 nestlings ringed using metal and/or colour rings, 64 were recovered along their flyway and in their wintering range, representing 6.9% of birds ringed with both colour and metal rings. This provided the opportunity to collect information on post-natal movements (staging and wintering ranges), breeding philopatry and recruitment, in addition to a preliminary estimate of their migration journey duration. This paper indicates sighting and recovery distributions in space and time, highlighting the important areas for the species during its journey between breeding and wintering sites. The findings indicate that several areas where ringed terns stop-over during pre- and post-breeding migration journeys are not protected, causing an additional threat to their survival, as some wintering areas are also not protected. Conservation of this highly localised and threatened population needs not only to address protection at breeding sites but also at migratory stop-overs and wintering strongholds.     

Behavioural adjustment in response to increased predation risk: a study in three duck species

Predation directly triggers behavioural decisions designed to increase immediate survival. However, these behavioural modifications can have long term costs. There is therefore a trade-off between antipredator behaviours and other activities. This trade-off is generally considered between vigilance and only one other behaviour, thus neglecting potential compensations. In this study, we considered the effect of an increase in predation risk on the diurnal time-budget of three captive duck species during the wintering period. We artificially increased predation risk by disturbing two groups of 14 mallard and teals at different frequencies, and one group of 14 tufted ducks with a radio-controlled stressor. We recorded foraging, vigilance, preening and sleeping durations the week before, during and after disturbance sessions. Disturbed groups were compared to an undisturbed control group. We showed that in all three species, the increase in predation risk resulted in a decrease in foraging and preening and led to an increase in sleeping. It is worth noting that contrary to common observations, vigilance did not increase. However, ducks are known to be vigilant while sleeping. This complex behavioural adjustment therefore seems to be optimal as it may allow ducks to reduce their predation risk. Our results highlight the fact that it is necessary to encompass the whole individual time-budget when studying behavioural modifications under predation risk. Finally, we propose that studies of behavioural time-budget changes under predation risk should be included in the more general framework of the starvation-predation risk trade-off.     

Study on the foraging behaviour of the European nightjar Caprimulgus europaeus reveals the need for a change in conservation strategy in Belgium

Effective nature conservation requires coherent actions based on the best available evidence concerning protected species. Recent studies have suggested that European nightjars Caprimulgus europaeus forage outside their recognized breeding habitats, yet, for Flanders (northern Belgium) information on nightjar foraging behaviour and key foraging habitats is lacking. To assess whether the foraging ecology of nightjars in Flanders is similar to that observed in other parts of Europe, we studied the crepuscular behaviour of this species in Bosland (northeastern Flanders) during a five‐year radio telemetry study. Tracking of 48 individuals within a coniferous forest was standardized and home ranges were calculated using a kernel density estimator (fixed kernel). Habitat use was investigated by comparing kernel placement to available habitat. Average maximal foraging distance was 2603 ± 1094 m and home ranges extended up to 691 ha. We identified the key foraging habitats to be extensively‐cultivated grasslands and recreational areas, areas that were previously assumed unsuitable for Belgian nightjars. Our results indicate the importance of foraging sites outside the breeding territory, confirming the findings of previous studies performed elsewhere in Europe. Incorporating our findings into future conservation plans could, therefore, lead to improved efficiency of EU conservation measures, designed for the protection of this bird species in Flanders.