Gull Chroicocephalus Ridibundus Research Articles

Occurrence of rats and their impacts on colonial waterbirds in a Danish fjord

Human development around the globe has led to great expansion of the Brown Rat (Rattus norvegicus), which has implications for local wildlife and especially ground-breeding birds. In this study, we analyse the colonisation and persistence of rats on small islets important to breeding waterbirds in a Danish fjord, and investigate the effect of rat presence on the number of breeding pairs of eight waterbird species. The islets had an annual rat colonisation probability of 6% and an annual rat population persistence rate of 65% (equalling an annual population survival rate of 62% when adjusting for re-colonisations upon extinctions). Contrary to our hypotheses, rat colonisation and persistence was uncorrelated with islet size, distance from the mainland and the presence of shrub cover. Rat presence had a significant negative effect on the number of breeding pairs of four waterbird species, including Avocet (Recurvirostra avosetta, reduced to 30% compared to years without rats), Black-headed Gull (Chroicocephalus ridibundus, reduced to 45%) and Common Tern (Sterna hirundo, reduced to 52%). The smaller bird species in particular seemed to be affected by the presence of rats, and control efforts aimed at reducing rat presence on important breeding bird islets may consequently have a positive effect on the occurrence and breeding success of these species. We found no evidence of birds acting on a memory of where rats had been present in the previous year, and further research is needed to investigate the precise mechanisms behind the recorded negative effects in the contemporary year, i.e. how do prospecting as well as settled breeders detect and behaviourally respond to the presence of rats.

Unravelling diet composition and niche segregation of colonial waterbirds in a Mediterranean wetland using stable isotopes

Rice fields and waterbirds are an example of a synergy that can occur between agriculture and conservation. This connection is especially relevant during the farming period, when nesting waterbirds need to obtain resources to cover their energy requirements and those of their chicks in rice fields. However, new farming techniques may potentially put fulfilling this role at risk. Studies on how species use rice fields to feed during this critical period are essential to understand waterbird population dynamics and to optimize conservation measures. At present, several species of colonial birds in l’Albufera de València (Spain) that depend on trophic resources available in rice fields have decling populations and decreases in productivity. We therefore assessed trophic niche segregation in the diet of chicks of a waterbird community composed of seven species through stable isotope analyses of carbon (δ13C) and nitrogen (δ15N) obtained from chick blood and tissue samples of potential prey. According to trophic niche widths, chicks of Black‐headed GullChroicocephalus ridibundusand Gull‐billed TernGelochelidon niloticashowed a similar diet, although Gull‐billed Tern had a major trophic specialization. The Western Cattle EgretBubulcus ibisfed its chicks in a wider range of different habitats, with organisms located at the base of the food chain and with a greater importance of terrestrial prey than other species. Conversely, the Glossy IbisPlegadis falcinellushad a more differentiated diet, mostly in freshwater habitats and mainly consuming odonates. Grey HeronArdea cinerea, Little EgretEgretta garzettaand Squacco HeronArdeola ralloidesshowed overlap between their niches, largely explained by the presence and abundance of cyprinid fish and odonates in their diets. Our results suggest a less important role than expected of Red‐swamp CrayfishProcambarus clarkii, and a more important role of odonates despite being a less energy‐rich prey. In conclusion, the diet of generalistic species of waterbirds in this study suggests that their trophic niches can overlap when relative prey abundance is high.

A vagrant Black-headed Gull (Chroicocephalus ridibundus) documented from Saint Peter and Saint Paul Archipelago: Brazil’s first record

A vagrant Black-headed Gull (Chroicocephalus ridibundus) documented from Saint Peter and Saint Paul Archipelago: Brazil’s first record

Recent changes in breeding abundance and distribution of the Common Pochard (Aythya ferina) in its eastern range

BackgroundThe Common Pochard (Aythya ferina) (hereafter Pochard), a widespread and common freshwater diving duck in the Palearctic, was reclassified in 2015 from Least Concern to Vulnerable IUCN status based on rapid declines throughout its range. Analysis of its status, distribution and the potential causes for the decline in Europe has been undertaken, but there has never been a review of its status in the major part of its breeding range across Russia to the Pacific coast.MethodsWe reviewed the scientific literature and unpublished reports, and canvassed expert opinion throughout Russia to assess available knowledge about changes in the species distribution and abundance since the 1980s.ResultsWhile accepting available information may not be representative throughout the entire eastern range of the species, the review found marked declines in Pochard breeding abundance in the last two decades throughout European Russia. Pochard have also declined throughout Siberia. Declines throughout the steppe region seemed related to local drought severity in recent years, necessitating further research to confirm this climate link at larger spatial scales. Declines in the forest and forest-steppe regions appeared related to the major abandonment of fish farms in western Russia that had formerly provided habitat for breeding Pochard. However, hyper-eutrophication of shallow eutrophic lakes, cessation of grazing and haymaking in floodplain systems necessary to maintain suitable nesting habitat and disappearance of colonies of the Black-headed Gull (Chroicocephalus ridibundus) in a number of wetlands were also implicated. Increasing invasive alien predator species (e.g. American Mink Neovison vison and Raccoon Dog Nyctereutes procyonoides) and increasing spring hunting were also thought to contribute to declines. Reports of expansion in numbers and range only came from small numbers occurring in the Russian Far East, including on the border with China and the long-established isolated population on Kamchatka Peninsula.ConclusionsWidespread declines throughout the eastern breeding range of the Pochard give continued cause for concern. Although we could address all the potential causal factors identified above by management interventions, we urgently need better information relating to key factors affecting site-specific Pochard breeding success and abundance, to be able to implement effective actions to restore the species to more favourable conservation status throughout its breeding range.

Central–periphery gradient of individual quality within a colony of Black‐headed Gulls

Central nesting sites within avian colonies are often more profitable in terms of fitness, as they can offer better protection against predators compared with colony edges. Thus, central sites are expected to attract high‐quality individuals, which should produce a clear central–periphery gradient in the phenotypic quality of nesting individuals and reproductive output within colonies. The aim of this study was to assess spatial patterns of individual quality within a colony of a common larid, the Black‐headed GullChroicocephalus ridibundus. We found that laying was advanced in the central zone of the colony when compared with the periphery, and central pairs tended to lay larger eggs and had higher hatching success than peripheral pairs. Centrally nesting individuals had higher blood haemoglobin concentrations, size‐corrected body mass and heterozygosity (males only), indicating their better condition and higher genetic quality. In contrast, central females had lower plasma albumin concentration, which could possibly be attributed to their greater investment in egg production. Finally, pairs breeding in the central zone of the colony had an elevated heterophil/lymphocyte ratio, suggesting that social stress can be recognized as an important cost of nesting in dense aggregations. The results provide empirical support for central–periphery gradients in the individual quality of colonially nesting Black‐headed Gulls, indicating that spatial gradients in pair quality should be carefully taken into account when conducting research on colonial birds.

Black-headed gulls (Chroicocephalus ridibundus) - a natural reservoir of potentially pathogenic microfungi?

Mycological studies of selected populations of black-headed gulls were carried out in response to the increasing interest in wild birds as reservoirs of potentially pathogenic fungi and links in the epidemiological chain of mycoses hazardous to human and animals. The biological material comprised swabs from the beaks and cloacae of adult and young birds subjected to standard mycological diagnostics. 79.5% of samples were positive, comprising 22 fungal species belonging to 10 genera, mainly Candida, Rhodotorula, Aspergillus, Fusarium, Cryptococcus, and Trichosporon. The most frequently isolated species were Candida albicans and Rhodotorula rubra, found in the beaks of females and young birds and in the cloacae of young birds with comparable frequency. Cryptococcus laurentii, Cr. neoformans, Aspergillus niger, A. flavus, and Rh. muscilaginosa were isolated relatively frequently from all birds. The results highlight the ecological importance of wild birds in the circulation of potentially pathogenic fungi in the biosphere.

Sequencing and analysis of the complete mitochondrial genome of Rufous-tailed Shrike, Lanius isabellinus (Passeriformes, Laniidae)

The complete mitochondrial genome of the Rufous-tailed Shrike (Lanius isabellinus) was 16 819 bp in length. The GenBank accession number is KP995437 and the contents of A, T, C, and G are 31.1% (5234 bp), 25.5% (4293 bp), 28.7% (4826 bp), and 14.7% (2466 bp), respectively. Gene organization and length are similar to other species of birds. It comprises 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a control region. All protein-coding genes use the typical initiation codon ATG, except for COX1 that uses GTG. All the complete stop codons were co-incident with the Black-headed Gull (Chroicocephalus ridibundus) and the Grey-backed Shrike (Lanius tephronotus), except for ND2 that was terminated with TAG. In addition, the phylogenetic relationships of Passeriformes based on complete mitochondrial genome showed that genetic distance of Laniidae and Corvidae was closer than other species.

Sequencing and analysis of the complete mitochondrial genome of Brown Shrike, Lanius cristatus (Passeriformes, Laniidae)

The complete mitochondrial genome of the Brown Shrike (Lanius cristatus) was 16 821 bp in length. The accession number was KT004451 and the contents of A, T, C, and G were 31.10%(5237 bp), 25.60%(4309 bp), 28.60%(4814 bp), and 14.60%(2461 bp), respectively. Gene organization and length was similar to other species of birds. It comprises of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and 1 control region. All protein-coding genes use the typical initiation codon ATG, except for COX1 which was initiated with GTG. All the complete stop codon was coincident with the Black-headed Gull (Chroicocephalus ridibundus) and the Grey-backed Shrike (Lanius tephronotus), except for ND2, which was terminated with TAG. In addition, the phylogenetic relationships of Passeriformes based on complete mitochondrial genomes showed that the genetic distance of Laniidae and Corvidae was closer than others.

Tissue tropism and pathology of natural influenza virus infection in black-headed gulls (Chroicocephalus ridibundus)

Black-headed gulls (Chroicocephalus ridibundus) are a suitable host species to study the epidemiology of low-pathogenic avian influenza virus (LPAIV) infection in wild waterbirds because they are a common colony-breeding species in which LPAIV infection is detected frequently, limited mainly to the H13 and H16 subtypes. However, the sites of virus replication and associated lesions are poorly understood. We therefore performed virological and pathological analyses on tissues of black-headed gulls naturally infected with LPAIV. We found that 24 of 111 black-headed gulls collected from breeding colonies were infected with LPAIV (10 birds with H16N3, one bird with H13N8, 13 birds undetermined), based on virus and viral genome detection in pharyngeal and cloacal swabs. Of these 24 gulls, 15 expressed virus antigen in their tissues. Virus antigen expression was limited to epithelial cells of intestine and cloacal bursa. No histological lesions were detected in association with virus antigen expression. Our findings show that LPAIV replication in the intestinal tract of black-headed gulls is mainly a superficial infection in absence of detectable lesions, as determined recently for natural LPAIV infection in free-living mallards (Anas platyrhynchos). These findings imply that LPAIV in black-headed gulls has adapted to minimal pathogenicity to its host and that potentially the primary transmission route is faecal–oral.