During 2022, at least three females were observed entering rock cavities overhanging streams or woods. At least one female has been observed accompanying five flightless chicks. Article in Italian
Common Mergansers Mergus merganser dive into lakes, rivers, and coastal waters to feed on fish and other aquatic prey. This species and others in the genus Mergus are traditionally classified as ...foot-propelled divers. When submerged, mergansers are expected to swim by kicking their feet, holding their wings close to their bodies. Here, we report, with video evidence, an event in which four mergansers used their wings underwater to chase down and capture a large fish. Documentation of wing use by this classically defined "foot-propelled diver" illustrates the gaps in our understanding of avian diving physiology, hydrodynamics, and behavior.
The Goosander
was not recorded breeding in Bulgaria till recently. We present herewith the very first record of the species breeding in the country and estimate the size of its breeding population in ...Bulgaria. Thus, we propose a change in its status in the country with more effort to be invested in the survey of this small, isolated population.
The Eurasian subspecies of the Goosander
Mergus merganser
consists of three subclades (Fennoscandian–British, E European–N Asian, and Alpine). Recently, this species expressed a rapid expansion in ...the Carpathians. In this study, we used mitochondrial DNA to track the origins of this population. Sequencing revealed that the majority of the Carpathian birds are related to the N Polish and Russian populations, whereas one sample has a haplotype known from the Alps. This mixed ancestry was probably caused by an outbreeding enhancement and/or enlarged habitat requirements that allowed the birds to settle in the mountain rivers of the Carpathians.
Genetic studies of waterfowl (Anatidae) have observed the full spectrum of mitochondrial (mt) DNA population divergence, from apparent panmixia to deep, reciprocally monophyletic lineages. Yet, these ...studies often found weak or no nuclear (nu) DNA structure, which was often attributed to male‐biased gene flow, a common behaviour within this family. An alternative explanation for this ‘conflict’ is that the smaller effective population size and faster sorting rate of mtDNA relative to nuDNA lead to different signals of population structure. We tested these alternatives by sequencing 12 nuDNA introns for a Holarctic pair of waterfowl subspecies, the European goosander (Mergus merganser merganser) and the North American common merganser (M. m. americanus), which exhibit strong population structure in mtDNA. We inferred effective population sizes, gene flow and divergence times from published mtDNA sequences and simulated expected differentiation for nuDNA based on those histories. Between Europe and North America, nuDNA ФST was 3.4‐fold lower than mtDNA ФST, a result consistent with differences in sorting rates. However, despite geographically structured and monophyletic mtDNA lineages within continents, nuDNA ФST values were generally zero and significantly lower than predicted. This between‐ and within‐continent contrast held when comparing mtDNA and nuDNA among published studies of ducks. Thus, male‐mediated gene flow is a better explanation than slower sorting rates for limited nuDNA differentiation within continents, which is also supported by nonmolecular data. This study illustrates the value of quantitatively testing discrepancies between mtDNA and nuDNA to reject the null hypothesis that conflict simply reflects different sorting rates.
Transmission paths in the distribution of proliferative kidney disease (PKD) of salmonids are still largely unknown. In this study, the role of goosander (Mergus merganser) as possible transport host ...for Tetracapsuloides bryosalmonae through faeces was examined. Goosander fledglings were fed exclusively with diseased brown trout (Salmo trutta fario). In all trout used for feeding, intratubular sporogonic stage of the parasite was confirmed histologically. Between one to 10 hours post‐feeding, the goosander faeces were sampled and tested for T. bryosalmonae DNA. In qPCR, only DNA fragments were found, and in conventional PCR, no amplification was confirmed. Therefore, we hypothesize that the role of goosander as transport hosts for T. bryosalmonae via their faeces can be neglected.
Earlier studies based on censuses of adult birds in spring suggest that the Common Merganser
Mergus merganser
population in Finland has been rather stable during the last few decades. However, in the ...beginning of the 1990s, a population increase was followed by a decline. Contrary to the trends detected in breeding populations, wintering populations of the species have increased in Finland and elsewhere in Europe. Along with warming winters, wintering areas have shifted gradually towards northeast. In the present study, a coastal population of the Common Merganser breeding in nest boxes was monitored between 2004 and 2022 in southern Finland. The role of winter weather conditions in population fluctuations and changes was examined. The weather conditions during two preceding winters reflected in the population fluctuations of mergansers. The number of nests in nest boxes increased following increasing winter temperatures in the northeastern end of the wintering area (near the breeding area). The breeding population decreased after warm winters in the southwestern end of the wintering area (far from the breeding area). The present results suggest that established populations decrease after warm winters, because young birds that have not yet bred have shifted to overwinter and breed further eastwards than in general.
Waterbird species have different requirements with respect to their non‐breeding areas, aiming to survive and gain condition during the non‐breeding period. Selection of non‐breeding areas could ...change over time and space driven by climate change and species habitat requirements. To help explain the mechanism shaping non‐breeding area selection, we provide site‐specific analyses of distributional changes in wintering waterbirds in central Europe, located at the centre of their flyways. We use wintering waterbirds as a highly dynamic model group monitored over a long‐time scale of 50 years (1966–2015). We identified species habitat requirements and changes in habitat use at the level of 733 individual non‐breeding (specifically wintering) sites for 12 waterbird species using citizen‐science monitoring data. We calculated site‐specific mean numbers and estimated site‐specific trends in numbers. The site‐specific approach revealed a general effect of mean winter temperature of site (seven of 12 species), wetland type (all species) and land cover (all species) on site‐specific numbers. We found increasing site‐specific trends in numbers in the northern and/or eastern part of the study area (Mute Swan Cygnus olor, Eurasian Teal Anas crecca, Common Pochard Aythya ferina, Great Cormorant Phalacrocorax carbo and Eurasian Coot Fulica atra). Common Merganser Mergus merganser, Great Cormorant, Grey Heron Ardea cinerea, Common Pochard, Eurasian Coot and Common Moorhen Galinulla chloropus increased their site‐specific numbers on standing industrial waters with traditionally low fish stock. The site‐specific dynamics of bird numbers helped us to identify general preference for sites reducing winter harshness (warmer areas, running waters and more wetlands in the site vicinity), as well as indicating climate‐driven changes in spatial use of wintering sites (northern/north‐eastern range changes and changes in preference for industrial waters). This fine‐scale (site‐specific) approach can reveal large‐scale range and distribution shifts driven by climate and environmental changes regardless of the availability of large‐scale datasets.
Migrations allow animals to find food resources, rearing habitats, or mates, but often impose considerable predation risk. Several behavioural strategies may reduce this risk, including faster travel ...speed and taking routes with shorter total distance. Descriptions of the natural range of variation in migration strategies among individuals and populations is necessary before the ecological consequences of such variation can be established.
Movements of tagged juvenile coho, steelhead, sockeye, and Chinook salmon were quantified using a large-scale acoustic tracking array in southern British Columbia, Canada. Smolts from 13 watersheds (49 watershed/species/year combinations) were tagged between 2004-2008 and combined into a mixed-effects model analysis of travel speed. During the downstream migration, steelhead were slower on average than other species, possibly related to freshwater residualization. During the migration through the Strait of Georgia, coho were slower than steelhead and sockeye, likely related to some degree of inshore summer residency. Hatchery-reared smolts were slower than wild smolts during the downstream migration, but after ocean entry, average speeds were similar. In small rivers, downstream travel speed increased with body length, but in the larger Fraser River and during the coastal migration, average speed was independent of body length. Smolts leaving rivers located towards the northern end of the Strait of Georgia ecosystem migrated strictly northwards after ocean entry, but those from rivers towards the southern end displayed split-route migration patterns within populations, with some moving southward.
Our results reveal a tremendous diversity of behavioural migration strategies used by juvenile salmon, across species, rearing histories, and habitats, as well as within individual populations. During the downstream migration, factors that had strong effects on travel speeds included species, wild or hatchery-rearing history, watershed size and, in smaller rivers, body length. During the coastal migration, travel speeds were only strongly affected by species differences.
The aerial and ground methods of counting birds in a coastal area during different ice conditions were compared. Ice coverage of water was an important factor affecting the results of the two ...methods. When the water was ice-free, more birds were counted from the ground, whereas during ice conditions, higher numbers were obtained from the air. The first group of waterbirds with the smallest difference between the two methods (average 6%) contained seven species: Mute Swan
, Whooper Swan
, Greater Scaup
, Tufted Duck
, Common Goldeneye
, Smew
and Goosander
; these were treated as the core group. The second group with a moderate difference (average 20%) included another six species: Mallard
, Eurasian Wigeon
, Common Pochard
, Great Crested Grebe
and Eurasian Coot
. The third group with a large difference (average 85%) included five species, all of the Anatini tribe: Gadwall
, Northern Pintail
, Northern Shoveler
, Eurasian Teal
and Garganey
. During ice conditions, smaller numbers of most species were counted from the ground. The exception here was Mallard, more of which were counted from the ground, but the difference between two methods was relatively small in this species (7.5%). Under ice-free conditions, both methods can be used interchangeably for the most numerous birds occupying open water (core group) without any significant impact on the results. When water areas are frozen over, air counts are preferable as the results are more reliable. The cost analysis shows that a survey carried out by volunteer observers (reimbursement of travel expenses only) from the land is 58% cheaper, but if the observers are paid, then an aerial survey is 40% more economical.
PDF
