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Several alien predator species have spread widely in Europe during the last five decades and pose a potential enhanced risk to native nesting ducks and their eggs. Because predation is an important factor limiting Northern Hemisphere duck nest survival, we ask the question, do alien species increase the nest loss risk to ground nesting ducks? We created 418 artificial duck nests in low densities around inland waters in Finland and Denmark during 2017–2019 and monitored them for seven days after construction using wildlife cameras to record whether alien species visit and prey on the nests more often than native species. We sampled various duck breeding habitats from eutrophic agricultural lakes and wetlands to oligotrophic lakes and urban environments. The results differed between habitats and the two countries, which likely reflect the local population densities of the predator species. The raccoon dog (Nyctereutes procyonoides), an alien species, was the most common mammalian nest visitor in all habitats and its occurrence reduced nest survival. Only in wetland habitats was the native red fox (Vulpes vulpes) an equally common nest visitor, where another alien species, the American mink (Neovison vison), also occurred among nest visitors. Although cautious about concluding too much from visitations to artificial nests, these results imply that duck breeding habitats in Northern Europe already support abundant and effective alien nest predators, whose relative frequency of visitation to artificial nests suggest that they potentially add to the nest predation risk to ducks over native predators.

Certain species experience rapid population increases in human-modified and -affected environments. Conservation actions and increased wintertime food availability have led to a population increase of several large herbivorous waterbird species. In Northern Europe, this trend is opposite to the overall decrease of several smaller waterbird species. We examined whether the recovery of a flagship species, the whooper swan (Cygnus cygnus), and the spreading of the nonnative Canada goose (Branta canadensis), cause asymmetric competition with other sympatric waterbirds at their breeding sites. We used data from the national Finnish waterbird surveys collected in the late 1980s and early 2020 s at 942 sites, to assess the site-level effects of large herbivore occurrence on other waterbird species, while considering their trophic overlap. We hypothesised that there could be competitive effects of large herbivorous on smaller species, especially those with similar foraging niches. We however found that other waterbird populations have decreased less at sites occupied by whooper swans since the 1980 s. Canada goose site occupation was not associated with the abundance of other waterbirds. Thereby, our findings are not consistent with the suggestion that population increases of large herbivore species lead to asymmetric competition on the breeding wetlands. The whooper swan may potentially act as an indicator of habitat quality and further on as a flagship umbrella species with multidisciplinary conservation benefits, of which may accrue benefits also to other waterbirds exhibiting declining population trends. Our findings underline the importance of considering species interactions when designing and implementing management actions in conservation strategies.

Predation is the most important factor limiting Northern Hemisphere duck nest survival. While most avian nest predators take only eggs, mammalian predators also pose mortality risks to incubating ducks. Partial depredation of duck clutches elevates subsequent nest desertion probability, especially where eggshells provide evidence of the depredationevent. Avian predators tend to consume egg contents at the nest, which may not intrinsically pose a risk to hens, but leave egg remains. This begs the question: does primary avian depredation of duck eggs actively facilitate nest visits by secondary mammalian predators, with potential survival consequences for the remaining clutch, but also sittinghens? We created 335 artificial duck nests in Finland and Denmark during 2017-2019 and monitored them for seven days using wildlife cameras to test whether initial avian predators breaking the eggs facilitated visits by secondary mammalian predators in various duck breeding habitats. Visitation rates of mammalian predators likely to take duck hens increased significantly after avian egg depredation events that involved egg breakage, although rates differed between habitats. Most common mammalian nest visitors at nests depredated by avian predators were red fox (Vulpes vulpes), followed by two alien species, raccoon dog (Nyctereutes procyonoides) and American mink (Neovison vison). Although we should be prudent about extrapolating conclusions from artificial experiment to real duck nests, our results strongly suggest inter-guild facilitation between avian and mammalian predators at duck nest sites. We suggest that by breaking the eggs, avian predators may offer olfactory, visual or other cues for secondary predators. Nest visits by mammalian predators could potentially increase egg depredation risk, but also elevate mortality risks for incubating females, dependent upon prevailing predator guilds.

Annual Finnish breeding duck surveys over the last 30 years show declining abundance among several species and greater declines on eutrophic waters than oligotrophic lakes. It has been suggested that habitat-related differences in the rate of increase in predation pressure is a potential explanation for contrasting duck population trajectories between habitats. We assessed potential duck nest predation risk and predator presence in various duck breeding habitats in Finland and Denmark by monitoring 333 artificial duck nests with wildlife cameras during 2017-2019. Predation rates differed between landscapes and habitats: nest predation rate and predator diversity were lowest in forested and highest in agricultural landscapes. Forest nests further from water bodies survived better than nests around shorelines of permanent lakes. Of the 16 different predator species detected, the most common were Eurasian magpie (Picapica), hooded crow (Corvus corone) and raccoon dog (Nyctereutes procyonoides). While predation by specific native predator species was typically associated with particular habitats and landscapes, the alien raccoon dog appeared to be a true habitat generalist, ubiquitous and common across all habitats and landscapes. Based on these results, the higher duck nest predation pressure along shorelines, especially in agricultural landscape lakes, due to increased diversity and abundance within the predator community, may contribute to the declining population trends of ducks. (C) 2020 Gesellschaft fir okologie. Published by Elsevier GmbH. All rights reserved.

Increasing anthropogenic pressures have affected the status of surface freshwater ecosystems. Eutrophication, water browning, acidification, and several other processes may be channelled through the food web. In this study, we evaluate the role of hydrology impacting anthropogenic pressures, flows from urban, farmland and ditched forest areas, and how they explain the physico-chemical quality of lakes and ponds in the boreal biome of Finland. We study the long-term effect around 445 waterfowl survey sites that had physico-chemical measurements (total phosphorus, total nitrogen, pH, water clarity and colour) produced by Finnish environmental authorities done in years 1986-2020. Furthermore, we investigate whether a long-term national-level citizen science study focusing on rather robust visible habitat structures measured by the volunteers can reveal physicochemical water quality using data from >270 lakes where the waterfowl habitat survey and physico-chemical measurements could be spatio-temporally matched. Farmland occurrence around the lakes was positively associated with pH, colour and nutrient concentrations but negatively associated with water clarity. Furthermore, ditch length was positively associated with nitrogen concentration and water colour, while being negatively associated with pH and water clarity. Overall, the studied lakes showed a negative trend in nutrients and clarity but a positive trend in pH and colour. As expected, nutrient concentration increased and clarity decreased along the gradient from oligotrophic to eutrophic lake habitat classifications, which suggests that the citizen science classification seem to reflect the subsurface physico-chemical status of the lakes. We conclude that farming and forest ditching practices in particular seem to associate with the state of the study lakes and that the ecological impacts of intensified turbidity and brownification in wetland ecosystems should be studied further in the future. Sustainable improvement of water quality rests upon scientific understanding of biogeochemical processes in lake ecosystems and the primary sources of the nutrient and sediment loading. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Zusammenfassung: Wiedererstarken der Singschwäne-Populationen verursacht durch das Grasen im gleichen Habitat keinen Rückgang der Pfeifente The Whooper Swan (Cygnus cygnus) is a good example of successful conservation, with rapidly growing numbers in Fennoscandia in recent decades. To the contrary, Eurasian Wigeon (Mareca penelope) shows a strong negative trend in breeding numbers, which raises conservation concerns. Previous research suggests a causal link between recent population trajectories of the two species. Both preferentially breed on wetlands with abundant horsetail (Equisetum spp.), a plant providing food for Whooper Swan and crucial feeding microhabitat for Eurasian Wigeon broods. We here test predictions based on the hypothesis that grazing on Equisetum by Whooper Swan reduces breeding habitat or breeding habitat quality for Eurasian Wigeon. We use data from 60 lakes in which waterfowl were counted in 1990-1991 and 2016, and Equisetum was mapped in 1990-1991 and 2013-2014. Lakes colonized by Whooper Swan typically had more abundant Equisetum vegetation in the past than lakes not colonized. Lake-specific decrease of Equisetum was not associated with colonization by Whooper Swan. The number of lakes occupied by Eurasian Wigeon decreased, but the decrease was not stronger on lakes colonized by Whooper Swan than on those that were not. Contrary to our prediction, current Eurasian Wigeon abundance was positively associated with Whooper Swan abundance. Moreover, Eurasian Wigeon did not decrease more on lakes from which Equisetum disappeared than on lakes in which there was still Equisetum left. This study does not support the idea that Whooper Swan affects Eurasian Wigeon negatively by grazing on Equisetum.

Understanding drivers of variation and trends in biodiversity change is a general scientific challenge, but also crucial for conservation and management. Previous research shows that patterns of increase and decrease are not always consistent at different spatial scales, calling for approaches combining the latter. We here explore the idea that functional traits of species may help explaining divergent population trends. Complementing a previous community level study, we here analyse data about breeding waterbirds on 58 wetlands in boreal Fennoscandia, covering gradients in latitude as well as trophic status. We used linear mixed models to address how change in local abundance over 25 years in 25 waterbird species are associated with life history traits, diet, distribution, breeding phenology, and habitat affinity. Mean abundance increased in 10 species from 1990/1991 to 2016, whereas it decreased in 15 species. Local population increases were associated with species that are early breeders and have small clutches, an affinity for luxurious wetlands, an herbivorous diet, and a wide breeding range rather than a southern distribution. Local decreases, by contrast, were associated with species having large clutches and invertivorous diet, as well as being late breeders and less confined to luxurious wetlands. The three species occurring on the highest number of wetlands all decreased in mean abundance. The fact that early breeders have done better than late fits well with previous research about adaptability to climate change, that is, response to earlier springs. We found only limited support for the idea that life history traits are good predictors of wetland level population change. Instead, diet turned out to be a strong candidate for an important driver of population change, as supported by a general decrease of invertivores and a concomitant increase of large herbivores. In a wider perspective, future research needs to address whether population growth of large-bodied aquatic herbivores affects abundance of co-occurring invertivorous species, and if so, if this is due to habitat alteration, or to interference or exploitative competition.

Surface water browning affects boreal lakes in the Northern Hemisphere. This process is expected to increase with global warming. Boreal lakes are the most numerous lakes on Earth. These ecosystems are particularly sensitive to disturbances due to their low biodiversity compared to other aquatic environments. The recent darkening of surface water is expected to hinder key ecosystem processes, particularly through lower primary productivity and loss of biodiversity. However, studies based on long-term data collections have rarely been conducted on the ecological consequences of water browning on aquatic food webs, especially concerning its impacts on invertebrate communities. For the first time, our analysis based on two decades of data collection in Finnish lakes highlighted a relation between water browning and a decline in aquatic macroinvertebrate abundances. Aquatic invertebrates are the main food resource for many secondary predators such as fish and waterbirds, hence such effect on their populations may have major consequences for boreal ecosystem functioning.

We explored whether the recent large-scale population decline of Eurasian wigeon (Anas penelope) in Europe may be linked to long-term vegetation changes in their boreal breeding wetlands. First, we assessed the importance of Equisetum, Phragmites, and Carex stands in lake selection by pairs and in foraging habitat selection by broods. Second, in 2013–2014 we revisited 58 lakes in Sweden and Finland studied in 1990–1991, to examine if there had been any long-term change in the abundance of habitat types preferred by wigeon. Finally, using continuous long-term data on breeding numbers of wigeon in 18 of the lakes studied in 1990–1991, we examined if wigeon numbers had changed at lakes where the habitat also had changed. We found that lake occupation of nesting wigeon pairs and foraging habitat use of broods were associated with the extent of Equisetum stands. The presence and abundance of this preferred habitat declined dramatically from 1990–1991 to 2013–2014 in the lakes from which the presence–absence data of wigeon emanate. Breeding numbers of wigeon showed a long-term declining trend in lakes where Equisetum has decreased. Our results imply that the recent population decline of wigeon in Europe may be linked to decrease of Equisetum habitat.

Breeding habitats strongly influence duck reproduction and survival. The boreal biome harbours a large share of the world’s wetlands, which are important breeding sites for several duck species. Based on 98 studies in the peer-reviewed literature, we here synthesize and evaluate which habitat characteristics affect habitat use and reproduction of ducks breeding in boreal freshwater wetlands with respect to (1) species and guild (dabbling, diving and piscivorous ducks) and (2) breeding cycle stage (settling by pairs, nesting and brood rearing). We consider the following aspects related to habitat: wetland morphology and spatial aggregation, water characteristics, habitat structure and vegetation, and biotic interactions. Most of the peer-reviewed studies of duck habitat use in boreal wetlands are from North America and Fennoscandia, while nearly half of the boreal area lacks such studies. Few species dominate research thus far while several others have not been studied at all. Nest site use and success are mainly related to predator avoidance. Food resources and habitat structure are the key characteristics affecting habitat use by duck pairs and broods as well as breeding success, although there are differences between duck guilds. Among the commonly studied variables, there is little evidence that water characteristics affect duck habitat use or survival. The most notable knowledge gaps are found in the effects of anthropogenic activities on habitat use and breeding success of ducks. Because boreal breeding environments are increasingly affected by human activities, we underline the need for future studies combining climate variation with natural and anthropogenic disturbances.

The growth rate of populations usually varies over time, often in a density-dependent manner. Despite the large amount of literature on density dependence, relatively little is known of the mechanisms underlying the density-dependent processes affecting populations, especially per capita natality. We performed a 20-year study on the density dependence of brood production in two duck species differing in the stability of habitat use. Our study was conducted in a boreal watershed in southern Finland. We predicted that a diving duck common goldeneye Bucephala clangula, with more stable habitat use, would show stronger density dependence than a dabbling duck common teal Anas crecca. We investigated reproductive output in relation to the duck pair density per se as well as in relation to per capita food availability. As predicted, the reproductive output of the goldeneye showed a more density-dependent pattern than that of the teal. The number of goldeneye broods per pair decreased when the pair density increased. This was not the case with the teal. However, when the breeding success was measured by taking into account per capita food availability, both species showed density dependence. Our results imply that the occurrence of density dependent processes may vary even in sympatric ducks breeding in the same, relatively stable landscape. Our analysis also emphasizes that it is important to take into account per capita resource availability when studying the density dependence of breeding success. Both findings have important implications for the management and conservation of species.

SUMMARY 1. Boreal forest lakes are normally considered stable environments, but from a duck’s point of view, both resource abundance and habitat quality in the lakes may differ from 1 year to another. Duck species differ in their flexibility to respond to variation in environmental factors, such as habitat quality, habitat variability and weather. Anas crecca, the common teal, has been suggested to be a species that can readily colonise newly formed habitat. 2. We studied the effect of habitat quality (invertebrate food resources, amount of spring flood, beaver flood abundance, predation pressure), weather (temperature, precipitation, timing of ice breakup) and pair abundance on breeding success of teal at the landscape scale in Southern Finland. We used 20 years of data (1989–2008) from a study area consisting of 50 lakes. This is typical boreal breeding area for the teal, whose population size is markedly variable. We express breeding success as number of broods in two different age classes. 3. The number of broods in both age classes was explained well by habitat quality, but different variables seem to operate during different phases of the breeding season. Increases in abundance of breeding pairs and of food led to increased production of younger broods. Habitat factors including food and flood abundance were the most important predictors for older broods, which are the more influential in terms of recruitment. These factors manifested in an age-specific manner, highlighting the importance of comprehensive breeding time surveys of boreal breeding ducks to understand variation in their recruitment. 4. Our research underlines the importance of high-quality habitats for breeding teal populations in the boreal forest landscape. The existence of these habitats depends substantially on human actions, such as managing beaver populations and preserving seasonal pond habitats.

The boreal biome harbours a large share of the world s wetlands, and is the main breeding area for several duck species. Breeding habitats strongly influence duck reproduction. In this study, the habitat use of ducks and their breeding success was estimated in a boreal landscape in southern Finland. A review of duck habitat use in boreal wetlands was additionally made. Boreal forest lakes are normally considered stable environments, but from a duck s point of view both resource abundance and habitat quality in the lakes may differ from one year to another. In this study the vegetation of boreal freshwater lakes was found to slowly change during the 20-year study period. Beavers (Castor canadensis) caused pronounced alterations in the lakes by flooding them. Flooding rendered lake vegetation structure more luxuriant and increased the lake use by ducks. In general, duck brood lake use was positively associated with both the coverage of wide belts of tall emergent plants and the abundance of emerging insects and aquatic invertebrates. The relative importance of these factors varied between species. The brood production of common goldeneyes (Bucephala clangula) was regulated by density dependence per se, but fluctuated with food availability per capita. No spatial density-dependent effects were found for the common teal (Anas crecca), but the breeding success was instead explained well by habitat quality variation. Both food and flood abundance had a positive effect, but different variables seemed to operate during different phases of the breeding season. Many aspects of boreal breeding ducks are still poorly studied. Especially lacking are studies concerning duckling survival and the effects of anthropogenic actions on duck habitat use. This research underlines the importance of high quality habitats for breeding duck populations in the boreal landscape. The varying habitat requirements of duck species should be considered when implementing wetland management. Boreaalisen biomin vesistöt ovat monien sorsien tärkeimpiä lisääntymisympäristöjä. Tässä tutkimuksessa selvitettiin sorsien elinympäristön käyttöä ja lisääntymismenestystä boreaalisilla kosteikoilla Evolla Hämeessä. Lisäksi boreaalisten alueiden sorsia käsittelevistä julkaisuista koottiin kirjallisuuskatsaus. Boreaalisia järviä pidetään yleensä vakaina ympäristöinä, mutta sorsien kannalta sekä ravinnon saatavuus että ympäristön laatu voivat vaihdella vuodesta toiseen. Tässä tutkimuksessa havaittiin järvikasvillisuuden muuttuneen hitaasti 20 tutkimusvuoden aikana. Amerikanmajavan (Castor canadensis) aiheuttamat tulvat muuttivat kasvillisuutta nopeasti ja voimakkaasti. Tulvaaminen lisäsi järvien kasvillisuuden rehevyyttä ja houkutteli varsinkin sorsapoikueita. Sorsapoikueiden elinympäristönkäytössä korostuivat rantakasvillisuuden ja kuoriutuvien hyönteisten sekä veden selkärangattomien määrä. Näiden tekijöiden merkitys kuitenkin vaihteli sorsilla lajikohtaisesti. Eri sorsalajien elinympäristövaatimukset tulisi huomioida kosteikkojen hoidossa. Erilaisten ravintoresurssien käyttö sekä territoriaalisuus heijastuivat myös lajien ympäristön käytön vakauteen. Telkän (Bucephala clangula) ympäristönkäytön havaittiin olevan paljon vakaampaa kuin tavin (Anas crecca). Territoriaalisen telkän poikuetuottoa sääteli suora tiheysriippuvuus, mutta myös vuotuinen ravintoresurssien vaihtelu heijastui alueelliseen poikuemäärään. Tavilla suoraa tiheysriippuvuutta ei havaittu, vaan poikuetuotto vaihteli elinympäristön laadun mukaan. Sekä ravinto että tulvat vaikuttivat positiivisesti tavipoikueiden määrään, mutta tekijät toimivat eri tavoin eri lisääntymisvaiheissa. Boreaalisilla alueilla sorsien elinympäristön valintaa ja lisääntymismenestykseen vaikuttavia tekijöitä tunnetaan vielä huonosti. Varsinkaan poikasten selviytymiseen vaikuttavia tekijöitä ja puolisukeltajasorsien pesäpaikan valintaa ei ole tutkittu. Ihmistoimien, kuten maankäytön muutosten ja järvien virkistyskäytön, vaikutusta sorsien lisääntymismenestykseen ei ole tutkittu lähes lainkaan. Tämä tutkimus korostaa hyvälaatuisten elinympäristöjen, kuten tulvikoiden, merkitystä boreaalisilla alueilla lisääntyville sorsille. Tulvikoita on boreaalisessa maisemassa suhteellisen vähän ja lisäksi ilmastonmuutoksen otaksutaan vähentävän niiden määrää entisestään sekä heikentävän niiden laatua. Majavan luomien tulvikoiden määrä on kasvanut lajin palatessa entisille elinalueilleen. Majava-tulvikoita voidaan edelleen lisätä suosimalla majavaa kosteikoiden ennallistajana.