Podiceps Cristatus Research Articles

Author Correction: Multiscale nest-site selection and breeding biology: infrared camera monitoring of the great crested grebe Podiceps cristatus in a plateau freshwater lake in southwestern China

Author Correction: Multiscale nest-site selection and breeding biology: infrared camera monitoring of the great crested grebe Podiceps cristatus in a plateau freshwater lake in southwestern China

Multiscale nest-site selection and breeding biology: infrared camera monitoring of the great crested grebe Podiceps cristatus in a plateau freshwater lake in southwestern China

Multiscale nest-site selection and breeding biology: infrared camera monitoring of the great crested grebe Podiceps cristatus in a plateau freshwater lake in southwestern China

Parasites as Indicators of Biotic Interrelations between Fishes and Waterbirds

The paper deals with the structural features of the waterbirds' cenoses, the fish population composition and distribution of metacercariae of trematodes, whose final hosts are waterbirds, in the model shallow lentic ecosystems of the city of Kyiv (Almazne, Martyshev, Verbne lakes and Sovski ponds). The waterbird cenosis was dominated by ichthyophagous (58.5-75.7%) and pantophagous birds (16.4-41.42%). The black-headed gull <i>Chroicocephalus ridibundus</i> (21.9-56.7%) prevailed in terms of relative abundance everywhere. The ornithocenoses differed in terms of the subdominant species: in the Almazne lake it was <i>Podiceps cristatus</i>, in the Martyshev Lake - <i>Sterna hirundo </i>(14.6%), in the Sovski ponds and Verbne Lake - <i>Anas platyrhynchos</i> (12.8-20.2%). Differences in the coastal ornithocenoses' composition were confirmed by results of the cluster analysis WPGMA (weighted pair-group centroid (median)); distance measure - 1-Pearson <i>r</i>). The coastal fish population comprised 24 species, including the native fresh-water (15 species), Ponto-Caspian and Mediterranean self-dispersers (4 species), and alien species - distant invaders (5 species). Parasitological studies revealed trematode metacercariae localized in lens (<i>Diplostomum</i> sp.) and vitreous body (<i>Tylodelphys clavata</i>) of the eye, ripples (<i>Apatemon gracilis</i>), and in the integument of the body (<i>Posthodiplostomum cuticola</i>). The discriminant analysis enabled to reveal significant differences in the species composition and abundance of trematode metacercariae in the water bodies with different structure of the water ornithocenoses (Wilks' Lambda: approx. 0.92235; <i>F</i>(8, 510) = 2.6293f) - 2.6293; the dispersion analysis showed confidently lower total number of trematode metacercariae in the Almazne Lake (Wilks' Lambda = 0.87377; <i>F</i>(6, 432) = 5.0253; <i>p</i><0.00005).

Water Bodies of Kazan and Their Significance in the City’s Avifauna Conservation

Water bodies that serve as habitats for semi-aquatic birds have been preserved in the city of Kazan, which contributes to the conservation of the city's avifauna diversity. Previously, special studies of birds in the water bodies of Kazan were not conducted. The study is aimed at the investigation of the species composition and distribution of the avifauna in water bodies of Kazan, as well as the ecological features of specific semiaquatic fauna species of the city. The research carried out over the past twenty-five years has made it possible to identify the species composition, their distribution, and ecological features of particular bird species associated with aquatic ecosystems. In total, 64 bird species of nine bird orders are recorded within the city of Kazan. The number of particular species and their spatial distribution in the city's water bodies depends on the specific conditions of the water object, where human activity is the major limiting factor. The most numerous species during the breeding period are the black-headed gull and the mallard. Nesting of 26 species has been recorded. A number of species, such as the mallard, show broad potential for synanthropization. The great-crested grebe, the coot and several species of ducks actively colonize the city reservoirs. A number of rare bird species listed in the Red Book of Tatarstan were recorded, including nesting of the mute swan, the moorhen.

Waterbird community changes in the Wilderness Lakes, South Africa (Part 3 of 3): Diving piscivores and scavengers

Estuarine waterbodies typically support diverse and abundant waterbird communities. However, global environmental degradation as a result of anthropogenic activities is leading to species level changes in biodiversity, with top predators such as piscivorous waterbirds being particularly vulnerable to ecosystem changes. The study aimed to document long-term spatial and temporal patterns of abundance of piscivorous and scavenging waterbirds in the Wilderness Lakes Complex (WLC) in the Garden Route National Park, South Africa, and where possible identify potential causes for observed trends. The abundance of waterbirds on these wetlands was determined biannually from 1992 to 2019, with counts conducted from a boat following a standardised route. Historical waterbird abundance data from the 1980s were also used to describe long-term abundance changes. Eight of the species exhibited seasonal variability in abundance with most, excluding Common Tern Sterna hirundo, being more abundant in winter. Substantial changes occurred in the abundance of several species over the four-decade study period, notably increases in Cape Cormorant Phalacrocorax capensis and Great Crested Grebe Podiceps cristatus, and decreases in Common Tern and Black-necked Grebe Podiceps nigricollis. Long-term abundance trends indicate a combination of declining, increasing, and stable populations. Although some species have undergone contrasting abundance changes on different waterbodies in the WLC the dominant pattern was a similar direction of change on most or all waterbodies and in different seasons. Local reasons for changes probably include loss of sandbanks, changing prey availability, and the absence of recreational disturbance on some waterbodies.Conservation implications: Drivers of changes in the abundances of piscivores are likely to be multifaceted, functioning on multiple spatial and temporal scales, and affecting different species in different ways. Recommended local corrective actions include managing emergent macrophyte encroachment on sandbanks, reducing recreational disturbance, managing processes affecting indigenous fish stocks, and protecting nesting sites.

Changes in Avian Top-Predator Diet in the 21st Century in Northeast (NE) Poland

The White-Tailed Eagle (WTE) Haliaeetus albicilla is a top avian predator that has rapidly increased in numbers and range in large parts of Europe in recent decades. In Poland, over the past 30 years, it has recolonized previously abandoned areas. In 1991, the first breeding pair in a large forest complex, the Augustów Forest (Northeast (NE) Poland), was recorded. In 2022, there were 13 breeding pairs. We analyzed changes in the diet composition of WTE in 2000–2023, divided into three periods: 2000–2005, 2009–2017, and 2018–2023. Throughout the 24 years of study, birds were the most frequently recorded food item, accounting for an average of 58% of food items, followed by fish (34%) and mammals (7%). During the study period, the most numerous food items were the Northern Pike Esox lucius, Coot Fulica atra, Common Bream Abramis brama, Mallard Anas platyrhynchos, and storks Ciconia sp. These species together accounted for 52% of food items. We recorded a long-term increasing share of Northern Pike, storks, and Great Crested Grebe Podiceps cristatus. Opposite changes, with declining frequency, were found for Coots and ducks. The share of the Coot, ducks, and Great Crested Grebe, as well as the total share of food connected with lakes in the WTE’s diet, increased along the growing area of lakes in the territory of the WTE. The proportion of fish in the food did not show a relationship with the increase in the area of lakes, while the most frequently eaten fish species changed. Observed changes in food composition appear related to the settlement of the habitat-diverse areas by individual breeding pairs and changes the availability of main food categories.

Mangcuo Lake in Hengduan Mountains: An Important Alpine Breeding and Stopover Site along Central Asian Flyway

The stopovers provide food and habitat for migratory birds and therefore play an important role in facilitating the birds' completion of their migration. The Hengduan Mountains, which have a complex topography, are located in a large corridor of the Central Asian migratory flyway, so the lakes along the Hengduan Mountains are important for waterbird migration. The existing research on lakes in the Hengduan Mountain area is mostly concentrated in the central and southern parts of the mountains, which proves that many lakes are wintering grounds for migrating birds. We wonder whether the ecological functions of lakes will change more with further elevation. With this question, we conducted four surveys for the seasonal bird survey in Mangcuo Lake, which is located in the northwest of the Hengduan Mountains, in Markam County of Qamdo City, between October 2019 and July 2020. We recorded a total of 6109 birds from 20 species of waterbirds, including 20 species of migratory waterbirds, accounting for 100% of all bird species. The diversity and richness of waterbirds in Mangtso Lake is shown as spring > autumn ≥, summer > winter, with no waterbirds in winter. The black-necked grebe (Podiceps nigricollis), great crested grebe (Podiceps cristatus), bar-headed goose (Anser indicus), and ruddy shelduck (Tadorna ferruginea) were the dominant species in the waterbird community. The highest number of waterbird species and total individuals were found in the transition zone between the marsh wetlands and lakes, and the number of waterbird species differed significantly among habitats (X2 = 14.405, p = 0.000), with habitat complexity being an important factor influencing waterfowl abundance and distribution. The IUCN Red-listed species recorded include the black-necked crane (Grus nigricollis), painted stork (Mycteria leucocephala), and common pochard (Aythya ferina). By comparing with other lakes in Hengduan Mountain, we found that the ecological functions of the plateau lakes in the Hengduan Mountains, to support the life histories of migrating waterbirds, are gradually transforming as the altitude rises, and can be divided into approximately three levels, with the first level of Qionghai, Chenghai, Erhai, and Jianhu at altitudes of 1500-2200 m being the most important ecological function in terms of providing wintering grounds for migrating birds. The second layer, at an altitude of 2400-3300 m, includes Lashihai, Lugu Lake, and Napahai, which are not only wintering wetlands for migratory birds but also important stopover sites. The third layer of Mangcuo Lake, which is above 4000 m above sea level, provides a breeding ground for some migratory waterbirds in summer and a migratory resting place for migratory waterbirds in spring and autumn. We advocate for the importance of Mangcuo Lake in the alpine region along the central Asian flyway, as well as emerging nature conservation action that was previously neglected.

Mink predation in great crested grebe colonies: random robbery or a well-planned hunt?

The study aimed to recognize whether the activity of a semi-aquatic invasive carnivore – the American mink Neovison vison – is related to the distribution of waterbird colonies. For this reason, we monitored mink occurrence in lake reedbeds and the fate of artificial nests imitating those of the great crested grebe Podiceps cristatus. The location of artificial nests in the grebe colony increased the probability of their survival compared to those placed outside the grebe colony. During the study, mink activity increased over time. In general, it was lower in colonies than outside of them, suggesting that the presence of natural nests does not increase the probability of mink occurrence in lake reedbeds. However, mink activity was negatively correlated with the distance from the lake shoreline and differed spatially according to the presence or absence of natural grebe nests. In grebe colonies, the probability of mink occurrence at greater distances from the lake shoreline was higher than outside, which can be explained by optimizing swimming effort while searching for prey. In conclusion, mink activity in colonies was lower than in areas with no waterbird nests, and nest location in a colony decreased predation risk by mink.

The Application of Quantitative Metabolomics for the Taxonomic Differentiation of Birds.

Simple SummaryModern evolutionary biology offers a wide variety of methods to explore the evolution of species and to describe their relationships. The methods of DNA/RNA sequence analysis have been developing for decades and have become increasingly popular and reasonably reliable. Nevertheless, final phylogenetic trees for many taxa are still under debate because both classical and genomics-based approaches have their own limitations for phylogenetic tree reconstruction. Here, we propose the use of younger ‘omics’ methods, namely quantitative metabolomics, to aid the phylogeny reconstruction of vertebrates. We show that metabolomics-based hierarchical clustering analysis trees match, although not perfectly, to the genomics-based trees.In the current pilot study, we propose the use of quantitative metabolomics to reconstruct the phylogeny of vertebrates, namely birds. We determined the concentrations of the 67 most abundant metabolites in the eye lenses of the following 14 species from 6 orders of the class Aves (Birds): the Black kite (Milvus migrans), Eurasian magpie (Pica pica), Northern raven (Corvus corax), Eurasian coot (Fulica atra), Godlewski’s bunting (Emberiza godlewskii), Great crested grebe (Podiceps cristatus), Great tit (Parus major), Hawfinch (Coccothraustes coccothraustes), Hooded crow (Corvus cornix), House sparrow (Passer domesticus), Rock dove (Columba livia), Rook (Corvus frugilegus), Short-eared owl (Asio flammeus) and Ural owl (Strix uralensis). Further analysis shows that the statistical approaches generally used in metabolomics can be applied for differentiation between species, and the most fruitful results were obtained with hierarchical clustering analysis (HCA). We observed the grouping of conspecific samples independently of the sampling place and date. The HCA tree structure supports the key role of genomics in the formation of the lens metabolome, but it also indicates the influence of the species lifestyle. A combination of genomics-based and metabolomics-based phylogeny could potentially resolve arising issues and yield a more reliable tree of life.

Occurrence and tissue distribution of alkylphenols (APs) in selected waterbirds from the Southern Baltic

The aim of the present study was to determine the concentrations of nonylphenols (NPs) and 4-t-octylphenol (4tOP) in the muscles, liver, and kidneys of selected waterbird species. Three species with different feeding habits were selected, i.e., greater scaup (Aythya marila), great crested grebe (Podiceps cristatus), and great cormorant (Phalacrocorax carbo) to investigate the potential effects of diet on the level of contaminants tested. The determination and quantification of analytes were performed using gas chromatography with mass spectrometric detection (GC-MS).The highest NP concentrations were noted in the kidneys of greater scaups and great crested grebes (208.3 and 160.8 μg kg−1 ww, resp.), which were six to fourteen-fold higher than those in the muscles (15.0 and 25.6 μg kg−1 ww, resp.) and livers (22.9 and 13.8 μg kg−1 ww, resp.) of these species. In greater scaups, the mean concentration of NPs in the livers was lower than in the muscles, while in great crested grebes, it was the opposite and higher concentrations were noted in the muscles. The mean concentrations of NPs in the muscles and livers of great cormorants were at similarly low levels (12.5 and 9.7 μg kg−1 ww, resp.). The concentrations of 4tOP in all samples were low, ranging from <LOQ to 0.29 μg kg−1 ww. The results of our study indicated that sex and diet did not affect the NP tissue concentrations in different waterbird species, but the phenological period (migration vs breeding) might influence the contamination levels in the kidneys.

First record of the Great Crested Grebe (Podiceps cristatus) from Sundarban Tiger Reserve, West Bengal, India

This is the first occurrence report of Great Crested Grebe (Podiceps cristatus) from Sundarban Tiger Reserve, West Bengal, India. A Great Crested Grebe was observed at a river in the Sajnekhali Wildlife Sanctuary, while conducting the annual biodiversity survey within the Sundarban Tiger Reserve in November 2020. The species is a winter migrant to mostly man-made reservoirs at the northern districts of the state, and compared to the previous records, this is the southernmost occurrence report from West Bengal. The discovery of Podiceps cristatus at an undisturbed and favorable habitat inside a well-protected mangrove ecosystem within the Sundarban Tiger Reserve may prove significantly informative for the possible range extension and future conservation approaches of the species.

Gastrointestinal helminth parasites of the threatened Australasian crested grebe (Podiceps cristatus australis, Gould 1844) in New Zealand, with descriptions of Baruscapillaria kamanae n. sp. (Nematoda: Trichuridae) and Cryptocotyle micromorpha n. sp. (Trematoda: Opisthorchiidae)

The Australasian crested grebe Podiceps cristatus australis, Gould 1844 is restricted to Australia and New Zealand, where it is listed as Threatened and Nationally Vulnerable. For the first time in New Zealand, we report on the parasitic helminths infecting three individuals from Lake Wanaka, Otago, using morphological and molecular tools. Seven helminth species were found in the gastrointestinal tract: 2 nematodes (Contracaecum ovale and Baruscapillaria kamanaen. sp.), 4 trematodes (Australapatemon minor, Cryptocotyle micromorphan. sp., Tylodelphys darbyi and Neopetasiger neocomensis), and 1 cestode (Confluaria pseudofurcifera). Except for T. darbyi, all are new records for New Zealand. A change of orthography is proposed for Neopetasiger neocomensis and N. pseudoneocomensis. Cryptocotyle micromorphan. sp. (Opisthorchiidae) is distinguished from similar species by its small size, wholly extracaecal vitellaria and anteriorly looped uterus. Baruscapillaria kamanaen. sp. (Trichuridae) is distinguished from other freshwater species by a combination of vulva and spicule morphology. The helminth parasites found here are mostly the same as those from the grebe in the northern hemisphere, indicating that they have been carried with the host species in its spread to Australasia. However, the parasite fauna may be depauperate due to a diminishing reservoir of intermediate hosts in that geographical migration.

Phylogenetic Diversity of Ossification Patterns in the Avian Vertebral Column: A Review and New Data from the Domestic Pigeon and Two Species of Grebes.

Simple SummaryThere are still many unknowns in the development of the skeleton in birds. Traditionally, the neck vertebrae were considered to be the first ossifying elements in the spine. Later studies have shown that this is not always the case. In some species, the thoracic vertebrae ossify even before them. Evolutionary analyses indicate that ancestrally the spine starts ossifying from two different sites, one located in the neck, the other in the thorax. However, the Neoaves, a group that includes all living birds except the palaeognaths, landfowl and waterfowl, are very poorly studied. In this article, we review the information about ossification patterns of the spine in birds. We also describe its development in three neoavians, the pigeon and two grebes. In the pigeon, the neck vertebrae were the first to ossify, but in the grebe, the thoracic vertebrae ossified earlier. Our analyses confirm the ancestral presence of two sites from which the ossification of the spine starts in birds.Despite many decades of studies, our knowledge of skeletal development in birds is limited in many aspects. One of them is the development of the vertebral column. For many years it was widely believed that the column ossifies anteroposteriorly. However, later studies indicated that such a pattern is not universal in birds and in many groups the ossification starts in the thoracic rather than cervical region. Recent analyses suggest that two loci, located in the cervical and thoracic vertebrae, were ancestrally present in birds. However, the data on skeletal development are very scarce in the Neoaves, a clade that includes approximately 95% of extant species. We review the available information about the vertebral column development in birds and describe the ossification pattern in three neoavians, the domestic pigeon (Columba livia domestica), the great crested grebe (Podiceps cristatus) and the red-necked grebe (Podiceps grisegena). In P. cristatus, the vertebral column starts ossifying in the thoracic region. The second locus is present in the cervical vertebrae. In the pigeon, the cervical vertebrae ossify before the thoracics, but both the thoracic and cervical loci are present. Our ancestral state reconstructions confirm that both these loci were ancestrally present in birds, but the thoracic locus was later lost in psittacopasserans and at least some galloanserans.

DISTRIBUTION AND DIVERSITY OF DIPLOSTOMIDS IN NEW ZEALAND.

Parasitism is one of the most common consumer strategies and contributes a large portion to biological diversity. Trematodes in the family Diplostomidae are common in freshwater ecosystems worldwide, often residing in the eyes or brain of fish and then infecting fish-eating birds as adults. As a result, some species have broad geographic distributions due to the bird host's motility. In contrast to the cosmopolitan nature of diplostomids, only a single species, Tylodelphys darbyi, has been identified in New Zealand to date, and only from the South Island. Tylodelphys darbyi has a 3-host life cycle consisting of an unidentified snail, a freshwater fish (Gobiomorphus cotidianus), and the Australasian crested grebe (Podiceps cristatus australis). To date, T. darbyi has been found in 2 locations, Lake Hayes, in the eyes of G. cotidianus, and Lake Wanaka, adults recovered from grebes. Considering the near ubiquity of the fish host in New Zealand, it is likely the bird, listed as nationally vulnerable, is the limiting factor in the range of T. darbyi. Up to 10 G. cotidianus were sampled from 10 mountain lakes known to have populations of grebe in the Otago and Canterbury regions of New Zealand's South Island. The eyes of all fish were examined and any metacercariae present were set aside for genetic analysis. In addition to expanding the known range of T. darbyi to at least 4 water bodies across the South Island, 2 new taxa of diplostomid were identified. A lens-infecting metacercariae clustered with Diplostomum spathaceum, while the metacercariae from the humor clustered with Diplostomum baeri.

Function of the waterfowl nests as reproduction and living areas for leeches (Annelida: Hirudinea)

Some species of leeches migrate into waterfowl nests and use these both as general habitats and to deposit cocoons, but ecological associations between leeches and birds are not well understood. In the present study, characteristics of waterfowl nests both as living area for leeches (Hirudinea) and as reproduction areas for select hirudinid leeches (Hirudo verbana and Haemopis sanguisuga) was investigated in both natural and controlled laboratory conditions. A total of 48 leeches were detected in 23 of the 51 nests surveyed in natural habitats. The leeches were detected more frequently but there were less dense populations in the nests of the great crested grebe (Podiceps cristatus) (frequency: 57 %, population density: 0.71 ± 0.76 leeches/nest), and leeches were detected less frequently but there were more dense populations in the nests of coots (Fulica atra) (frequency: 36 %, population density: 0.91 ± 1.70 leeches/nest). Although the hirudinid leeches naturally reproduce between June and September, cocoons were only detected in August and September, when the nests were not actively used by the waterfowl and when water depths were less. In laboratory conditions, gravid medicinal leeches prefer moist peat rather than waterfowl nests for cocoon deposition. Results from the present study indicate leeches more frequently use the nests of coots, which have both dry and wet layers, compared to the nests of the great crested grebe, which have only a wet layer. Leeches were also found to be more prevalent in bird nests during spring months, during the reproductive periods of the waterfowl.

Underwater video and still‐image dataset of fishes and other aquatic animals in Lake Biwa, Japan, observed via carp‐mounted video loggers

AbstractThis is the first large dataset of underwater videos from which species occurrence and behavioral records of aquatic organisms were identified in Lake Biwa, the largest lake in Japan. We compiled 109 videos and 122 still‐images of fishes, diving birds and shrimps. The images were cropped from videos taken underwater with animal‐borne video cameras which were mounted on the backs of common carp (Cyprinus carpio). The attribute of each image and its occurrence of organisms were formatted according to the Darwin Core Archive which was developed by the Biodiversity Information Standards (TDWG), and the dataset is available via the Global Biodiversity Information Facility. Our dataset includes records of 10 species, 4 genera, 2 families and 1 infraorder which includes mostly fishes, several birds and a crustacean. The fish records include a threatened endemic fish, the “gengorou‐buna” crucian carp (Carassius cuvieri), and two alien fishes, largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus). We confirmed several types of intraspecific and interspecific relationships between video‐mounted carp and other organisms; for example, most video‐mounted carp frequently approached or chased conspecifics upon encountering, which sometimes led to two carp feeding side by side. At least three avian species also appeared in the dataset: Eurasian coot (Fulica atra), little grebe (Tachybaptus ruficollis), great crested grebe (Podiceps cristatus), but there was no apparent interaction between carp and these birds. Our underwater videos reveal and highlight the rich biodiversity of the lake today, providing clear evidence for behavior of aquatic organisms under natural conditions.The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2020-18.1/jalter-en.

Comparison of spring and summer clutches of Great Crested Grebes (Podiceps cristatus)

The intensively farmed fishponds of the Třeboň Basin in South Bohemia, Czech Republic host a substantial number Great Crested Grebe (Podiceps cristatus) pairs that nest later than the expected spring season and instead in summer, which may be associated with fishpond farming. A two-factor nested ANOVA of Great Crested Grebe egg and clutch characteristics showed no differences between spring (May-June) and summer (July - August) seasonal clutches. High egg total volume in spring nests was significantly related to both decreasing distance between nests and decreasing number of nests on the fishpond. The increase of total egg volume in summer nests was significantly related to the distance to the edge of littoral vegetation. There is no substantial difference between spring and summer egg characteristics, but total egg volume in spring nests is dependent on other characteristics that those in summer nests.

Estimation of native and alkylated polycyclic aromatic hydrocarbons (PAHs) in seabirds from the south coast of the Baltic Sea

Native and alkylated polycyclic aromatic hydrocarbons (PAHs) were examined in the muscle, liver, kidneys, and lungs of greater scaup (Aythya marila) and great crested grebe (Podiceps cristatus). Both species showed differences in distribution and profiles among the tissues. The highest ƩPAH concentrations were in the scaup lungs and the grebe kidneys (20 and 19 ng g−1 wet weight, respectively). Alkylated derivatives were in the range of 61 to 77% of ΣPAHs in both species. Differences in PAH profiles between birds, analyzed by PCA, were probably results of metabolic capability, not various diet. In comparison to available data from other regions of the world, PAH levels in investigated species are relatively low and do not pose a threat to birds themselves.

Prey Composition of Great Crested Grebe (Podiceps cristatus) and Red-Throated Diver (Gavia stellata) in Freshwater Reservoirs during Migration

The diet composition and prey length of the Great Crested Grebe (Podiceps cristatus) and the Red-throated Diver (Gavia stellata) co-occurring in late autumn in two reservoirs was studied. Their diet was analyzed based on carcasses from incidental mortality of individuals in fishery gill net surveys in two different freshwater reservoirs (one deep, one shallow) in southern Poland during autumn migration (October - December). Five fish species were identified in the diet of the Great Crested Grebe and nine fish species were identified in the diet of the Red-throated Diver. The proportion of a particular fish species in diet was different between the studied bird species. The ruffe (Gymnocephalus cernua) was the most common prey in the diet of the Great Crested Grebe at both reservoirs. The diet of Red-throated Diver was dominated by roach (Rutilus rutilus) at the deep reservoir and the zander (Sander lucioperca) at the shallow one. The Red-throated Diver consumed larger fish than the Great Crested Grebe at both reservoirs.

Breeding population increase and range expansion of the Great Crested Grebe Podiceps cristatus in southeastern Norway

The Great Crested Grebe Podiceps cristatus is listed as near-threatened on the Norwegian red list due to small population size, estimated in 2015 at 220–380 pairs. Population size is considered to be stable. Approximately one quarter of the population (50–100 pairs) is thought to occur in Oslo and Akershus, but this estimate is not based on detailed data, and the only previous systematic estimate was 90–100 pairs in 13 sites in 1982. In 2018, I conducted a comprehensive survey of all known and potential breeding sites to assess current population size in Oslo and Akershus. I recorded 233 pairs in 34 sites, suggesting a large increase in population size. To analyse the population increase in more detail, I collected all known records of Great Crested Grebes during the breeding season for the period 1995–2018. Analyses confirmed that there has been a strong increase, at a yearly rate of 4.2%. The increase was both due to increases in already established populations (69% of total increase), and establishment of new sites (31%). New sites were colonised in particular the last 10–15 years, and new sites were located gradually further away from the sites that were already used in 1982, indicating continuous range expansion. New sites were also located in smaller, less nutrient-rich lakes at higher elevations, perhaps indicating occupation of lower quality sites that could limit further population increase. Similar population increases have also occurred in other parts of the distribution range of Great Crested Grebes in Norway, and I present a new population size estimate for Norway at 531–634 pairs. Hence, the species no longer qualifies for red listing, and one may consider to downlist the species to least concern.&#x0D; &#x0D; Cover photo: A pair of Great Crested Grebes with chicks. Photo: Frode Falkenberg.