Black-headed Gull Larus Ridibundus Research Articles

PATHOMORPHOLOGICAL CHANGES IN THE KIDNEYS OF THE BLACK-HEADED GULL WITH URURIC DIATESIS

The article provides data on pathomorphological changes in the kidneys of the black-headed gull (Larus Ridibundus L., 1766) with uric acid diathesis. The material (kidney pieces) was collected from clinically healthy birds removed from their natural habitat using the generally accepted method. Macroscopic and histological studies were carried out in the dissecting room and laboratory of the Department of Pathological Anatomy and Histology of the Vitebsk State Academy of Veterinary Medicine. Preparation of histological sections and their staining were carried out according to generally accepted methods. With uric acid diathesis, the black-headed gull's kidneys were enlarged in size with diffusely located foci of urate deposition. Microscopic changes were characterized by the appearance of basophiliceosinophilic cylinders of crystalline and round-oval shape in the urine-forming tubules, collecting ducts and the lumen of the vascular glomeruli. The deposition of uric acid salts led to atrophy of the kidney structures, their necrosis and desquamation. In the parenchyma of the organ, proliferation of connective tissue with the formation of interstitial nephritis was detected.

Sexual Differentiation of Aggressive Behavior in the Chicks of the Black-Headed Gull (Larus ridibundus, Laridae, Charadriiformes) in the Natural Environment

Sexual Differentiation of Aggressive Behavior in the Chicks of the Black-Headed Gull (Larus ridibundus, Laridae, Charadriiformes) in the Natural Environment

Ecological and evolutionary aspects of the nesting life of black-headed gulls <i>Larus ridibundus</i>) as a colonial breeding species

This article analyzes the ecological and evolutionary aspects of the nesting life of the black-headed gull (Larus ridibundus), which leads a synanthropic lifestyle and forms colonies during the breeding season. The number of individuals belonging to this species began to increase rapidly at the end of the 19th century, which is a manifestation of one of the criteria for biological progress. This direction of evolution is associated with an increase in the level of adaptability of descendants in comparison with their ancestors. The progressive nature of the development of the species affects the stages of the annual life cycle, which includes the pre-breeding and nesting periods. During the pre-nesting period, birds arrive in the nesting area and select a site for the colonial settlement. Arrival dates are determined by temperature, the state of aquatic ecosystems and the physiological characteristics of birds. The nesting period includes the construction of a nest in a certain part of the territory on which the colony is being built. The process of colony formation occurs in stages: single nests, microcolonies, biological center. After the formation of the biological center, nests are built on the periphery. The formation of this part of the colony according to the same stages as the biological center. The biological center deals with the birds that arrive first on the territory of the colony. This area within the colony differs from the periphery in early terms of formation and high density of nests. In the formed colony, the biological center and periphery are distinguished. The colony as a supraorganismal structure is built under the influence of environmental factors that provide a sufficient level of adaptability of this group of individuals to the environment. The obtained materials will make it possible to study monospecific and polyspecific colonies as groups of individuals that exist on the basis of the manifestation of biocoenotic relationships.

The Richness of Sarcocystis Species in the Common Gull (Larus canus) and Black-Headed Gull (Larus ridibundus) from Lithuania

The common gull (Larus canus) and the black-headed gull (Larus ridibundus) are common waterbird species in Lithuania. Until now, the composition of Sarcocystis species in these birds was unknown. The current study aimed to identify Sarcocystis spp. by the morphological examination of sarcocysts found in the muscle tissues and by DNA sequence analysis. Between 2011 and 2019, the leg muscles of 42 common gulls and 63 black-headed gulls were tested for Sarcocystis spp. Based on the methylene blue staining of squashed muscle samples, sarcocysts were detected in six common gulls (14.3%) and in six black-headed gulls (9.5%). Under a light microscope, one type of microcyst was observed. Sarcocysts were thread-like (2860–8250 × 40–180 μm) and had a smooth and thin (0.8–1.4 μm) cyst wall, while bradyzoites were banana-shaped and 5.0–9.2 × 1.3–2.4 μm in size. The sequencing of complete ITS1 showed the presence of S. columbae, S. halieti and S. wobeseri in the common gull and S. columbae and S. halieti in the black-headed gull. The highest intraspecific genetic variability was established for S. halieti, which is characterized by a wide host range. This species is considered to be pathogenic, therefore further histopathological examination of the various organs of gulls is needed.

Diversity and prevalence of Salmonella spp. in gulls caught at a landfill, Zagreb, Croatia

Gulls are a group of seabirds distributed worldwide that are an important reservoir of Salmonella spp. Salmonellosis is the second most commonly reported gastrointestinal infection in humans, and understanding the role wild birds have in spreading Salmonella can help to improve the health of humans and domestic animals. The mobility and migration capacity of gulls makes them an interesting group for research given their potential role in spreading pathogens. This paper presents the diversity and prevalence of Salmonella spp. in different gull species caught at a landfill in Zagreb in the winter months over a nine-year period from 2014-2022. In total, 1083 cloacal swabs were sampled from six gull species: Black-headed Gull (Larus ridibundus), Yellow-legged Gull (L. michahellis), Caspian Gull (L. cachinnans), Common Gull (L. canus), Lesser Black-back Gull (L. fuscus) and Herring Gull (L. argentatus). The prevalence of Salmonella was 5.82%, and 16 Salmonella serotypes were identified; S. Typhimurium had the highest prevalence (47.62%) followed by S. Enteritidis (12.69%) and S. Infantis (9.52%). To date, 82 Salmonella serotypes have been isolated in research on gulls in Europe, with S. Typhimurium as the most common, followed by S. Agona and S. Enteritidis. In this study, we found three serotypes not previously reported in gulls, S. Yalding, S. Reading and one with the antigenic formula O:17; H:z10; H:e,n,x,z15 (IIIb).

Мониторинг солнечного орла в национальном парке «Хвалынский» (Саратовская область, Россия)

Мониторинг солнечного орла в национальном парке «Хвалынский» (Саратовская область, Россия)

Behavioral plasticity mediates adaptation to changes in food provisioning following the COVID-19 lockdown in black-headed gulls (Larus ridibundus)

The 2020 COVID-19 lockdown provides an opportunity to assess how the anthropause affected the behavior of birds. Black-headed gulls (Larus ridibundus) wintering at Dianchi Lake (Yunnan Province, southwestern China) prefer to forage on easily accessible human-provided food at various sites along the lake. Following the closure of the lake because of the pandemic, synthetic food was provided at a single location. We expected that the home range size and distribution of gulls would change in response to these changes in food provisioning. A total of 91 gulls were tagged with satellite transmitters in November 2018 and March 2019, and their movements were tracked during the winter months. We analyzed their home range size and spatial distribution in four periods, SCP2019, SOP2019, SCP2020, and SOP2020 (Scenic Opening/Closing Period in 2019/2020), and the difference between SOP2019 and SCP2019 was used as the control group. The eutrophication level in the wintering periods “Nov. 2018–Apr. 2019” and “Oct. 2019–Apr. 2020” was determined using the Normalized Difference Vegetation Index (NDVI), and the coverage ratio of algal blooms and NDVI were used as indicators of the amount of naturally available food. The home range sizes of gulls were reduced in SCP2020 compared with SOP2019, SCP2019, and SOP2020. The gulls were most abundant in the 600–900 m buffer zone and least abundant in the 0–300 m buffer zone in SCP2019; they were most abundant in the 0–300 m buffer zone and least abundant in the 900–2000 m buffer zone in SCP2020. These patterns were consistent with variation in the NDVI and the coverage ratio of algal blooms among buffer zones. Changes in wintering behaviors in SCP2020 relative to other periods suggested that gulls modified their behavior following anthropause-related changes in the distribution and provisioning of food. Our findings provide insights into the role of behavioral plasticity in mediating adaptation to changes in human activities in birds.

Ecological aspects of the nesting life of the black-necked grebe (<i>Podiceps nigricollis</i> C.L. Brehm) in the forest-steppe zone of the Trans-Urals

The black-necked grebe (Podiceps nigricollis C.L. Brehm) is a nesting, migratory bird species, the number of which in the Southern Urals reaches 12 thousand individuals. From an ecological point of view, the named bird species belongs to aquatic birds and prefers aquatic and semiaquatic habitats. Being a waterfowl, the black-necked grebe has a complex of diving adaptations and is characterized as a specialized waterfowl. The literature analysis has proved that the knowledge of the ecological aspects of the nesting life of the black-necked grebe is insufficient. The nesting period of the annual life cycle was studied on the Kurlady and Smolino lakes located in the forest-steppe zone of the Trans-Urals. The average date of birds arrival at the nesting area according to 19882013 data is 19 April. The choice of breeding site leads to the fact that black-necked grebes form colonies in stagnant water bodies or with a slow flow of water. The water is fresh or brackish, with a certain pattern of overgrowth of vegetation and depth in the area where the nests are located. The presence of nests of black-headed gulls (Larus ridibundus L.) plays a special role in choosing a place to build a nest. Black-necked grebes and black-headed gulls form polyspecific colonial settlements. The laying of the first egg is carried out by the black-necked grebe in an unfinished nest, floating on the water and having a flat shape. At the stage of the appearance of the first egg in the nest, the elimination of eggs occurs, which can reach 44,1% (the biological center of the colony, 1989). On the periphery of the colonial settlement, the percentage of dead clutches is significantly higher, which can be caused by unfavorable biotic and abiotic relationships. Nests of black-necked grebes are completed from the moment the first egg is laid until the laying is completed. At a statistically significant level, the diameter of the nest and tray, the height of the nest, and the depth of the tray increase. The nest with completed masonry has a truncated-conical shape with a cup-shaped tray. According to long-term observations, the average value of the completed clutch is 3,8 eggs per nest. The reproduction in the composition of a polyspecific colony is accompanied by the establishment of biocoenotic relationships. The manifestation of topical, phoric and factory relationships, which can lead to individual and group elimination, has been established.

Characterization of antibiotic resistance in Escherichia coli isolates from Black-headed gulls (Larus ridibundus) present in the city of Novi Sad, Serbia.

Despite common resistance to antimicrobials in Escherichia coli isolates from farm animals in Serbia, no data are currently accessible on its occurrence in E. coli isolated from gulls. Therefore, 67 cloacal swabs and 70 fecal samples from black-headed gulls were investigated for the presence of antibiotic-resistant E. coli isolates. Ninety-nine isolates were obtained during the study. Resistotyping and resistance gene typing has shown that 44 isolates harbor resistance to one or more antibiotics. Multidrug resistance was detected in 24 E. coli isolates. Ten isolates were resistant to extended-spectrum cephalosporin antibiotics and were studied in detail including virulence gene typing, phylogenetic and multilocus sequence typing, and mating. These ten isolates belonged to phylogenetic groups B2 (five isolates), D (four isolates) and B1 (one isolate). Five different sequence types (ST38, ST2307, ST224, ST162 and ST34) were detected in E. coli isolates with AmpC phenotype and genotype. One isolate carried the Inc I2/FIB replicon type plasmid with the blaCTX-M-1 gene. Nine isolates had blaCMY-2 genes, which were detected on conjugative plasmids in seven isolates. The virulence genes hly, iroN, iss, ompT and cvaC were detected in one transconjugant. Ten isolates were found to be resistant to ciprofloxacin, whose MIC ranged from 4 to 32mg/L. Genotyping revealed single or double mutations in the quinolone resistance determining region (QRDR) of the gyrA or gyrA, parC and parE genes, respectively. So, Black-headed gulls from Serbia may be colonized by multidrug-resistant E. coli, some of which are resistant to critically important antibiotics in medicine.

The Morphometric Examination of Head Area of Black Headed Gulls (Larus Ridibundus) from Marmara Region

The Black-headed gull (Larus ridibundus), a gull species commonly seen on shores of Küçükçekmece lake located in Marmara Region, does not exhibit sexual dimorphism as it has monomorphic feather traits like the other gull species. In order to perform sex discrimination in gulls, the effective discriminant function analysis (DFA) method is used for the measurements based on the external morphology and determining the variables discriminating the two sex groups. The head morphological measurements and the body weights of 28 adult Black-headed gulls were obtained. One discriminant function was determined based on the results. The accuracy rate in two sexes was determined to be 82.1% (85.7% female, 78.6% male) using the formula we obtained as a result of the discriminant function analysis in which the head length, determined to be more significant compared to the other variables, was used. The aim of the study is to assess the sexual dimorphism in population of Black-headed gull in Küçükçekmece Lake and its surrounding located in Marmara Region and represent a reliable method to make a sex discrimination along with discriminant analysis.

Usage of Urban Rivers by Gulls and Cormorants as Movement Pathways in Winter

For the long-term survival of bird populations in urban areas, it is necessary to protect both bird habitats fragmented by urbanization and potential pathways for movement between them. However, urban pathways for waterbirds have rarely been studied. Suspecting that certain waterbird species that visit inland waters would tend to move along rivers, as movement pathways, we surveyed waterbird movement along the Kanda River in Tokyo, Japan in the winter of 2017/2018. We defined those species that very frequently (more than 95% of all flights) flew along the river as “river travelers”. Three species, Great Cormorant Phalacrocorax carbo, Black-headed Gull Larus ridibundus, and Herring Gull L. argentatus proved to be river-dependent movers that frequently used the Kanda River as a pathway. The gulls relied more heavily on the river as a movement pathway than the cormorant. In this sense, urban rivers may play a role for these species that is analogous to that of linear vegetated spaces for terrestrial birds. In addition, the distribution of river travelers (especially Black-headed Gull) may have been affected by the extent of riverside vegetation alongside, and highways covering, the river. To protect movement pathways for gulls and cormorants in urban areas, it is necessary to consider the differences among bird species in terms of their relative dependence on urban rivers as movement pathways and their comparative susceptibilities to the impact of manmade structures covering the rivers.

МІГРАЦІЙНІ СКУПЧЕННЯ ВОДОПЛАВНИХ І НАВКОЛОВОДНИХПТАХІВ У ЦЕНТРАЛЬНІЙ ЧАСТИНІ КРЕМЕНЧУЦЬКОГО ВОДОСХОВИЩА В ОСІННІ ПЕРІОДИ 2015–2017 РР.

Introduction. Kremenchuk Reservoir plays an important part in maintaining populations of waterfowl and waterbirds in the migration period. They stop to rest and feed here. The upper part of the Reservoir is promising for inclusion in the Ramsar list. A significant part of this area is occupied by the Lypivsky Ornithological Reserve with a total area of 4631 hectares. We have been monitoring waterfowl and waterbirds around the reserve for over 20 years. The purpose of the study is to establish the species composition and relative number of waterfowl and waterbirds in the central part of the Kremenchuk Reservoir, to study their seasonal and long-term dynamics. Methods. The records cover the central part of the Kremenchuk Reservoir: along the right bank - within the city of Cherkasy, along the left one - from the village Kedyna Hora to the village of Blagodatne (former village of Chapaiivka) (Zolotonosha district of Cherkasy region), as well as along the dam that crosses the Reservoir. The study was conducted by the point count method from the shore and the dam. 17 records were conducted during autumn periods of 2015-2017. Results. In total for three years, we have found 44 species belonging to 8 series. The core of the avifauna consisted of Mallard (Anas plathyrhynchos), Coot (Fulica atra), the Tufted Duck (Aythya fuligula) and Great Cormorant (Phalacrocorax carbo) making 82.3% - 86.1% of the total number of birds in different years. The Shannon species diversity index in 2015 were 1 . 50-2 . 61 , in 2016 – 1 . 17-1 . 97 , in 2017 – 1 . 37-2 . 72 . The maximum number of birds stopping to rest and feed during a season in the central part of the Kremenchuk Reservoir was from about 13,600 up to about 29,500 birds in different years. During 2015-2017, among the mass species for three ones (Great Crested Grebe (Podiceps cristatus), the Tufted Duck and the Black-headed Gull (Larus ridibundus)), there was the highest number for more than 20 years of the research. 6 species listed in the Red Book of Ukraine were identified. Among them, the studied area plays a significant role in maintaining the populations of the Common Goldeneye (Bucephala clangula) and White-Tailed Eagle (Haliaeetus albicilla). Originality. The n umber and bird diversity of the ornithocomplex due to climate change has been described. The number of some numerous species is increasing compared to previous years . Conclusion. The results of the research confirm the importance of the Lypivsky Ornithological Reserve, where more birds than in the surrounding areas, are concentrated. Such preferences are associated with more attractive conditions for feeding and resting of mass species.

Breeding population dynamics of Common Tern Sterna hirundo and associated gull species with overview of conservation management in continental Slovenia

Abstract An overview of the long-term (1980–2019) population development of colonial Laridae species in continental part of Slovenia, their nest sites at anthropogenic water bodies, and various conservation measures with special focus on Common Tern Sterna hirundo along the Slovenian/border part of the Drava River is given. Breeding of these species occurs only on the westernmost fringes of the Pannonian plain, on lowland floodplains of the main rivers of the Danube Basin. Altogether, breeding of Common Tern and Black-headed Gull Larus ridibundus was recorded at 11 and 10 sites, respectively. Lake Ptuj is the single site with mixed-species colony residing there in all years of the study period, while at Ormož (two sites) it was established during the early 1990s in the Slovenian territory but moved completely to the Croatian side by the second half of the 2010s. At all other sites, a suitable breeding habitat became available or was provided by management in just a few years, or created only recently. The percentage of Common Tern national population breeding in continental Slovenia was usually well above 50% throughout the 1980s and 1990s (52–136 pairs), while in the last 16 years (77–258 pairs) it ranged between 40.8% and 69.0%. Breeding of Black-headed Gull remains largely limited to continental Slovenia. Overall, continental populations of both species in the last few years have been substantially higher compared to the most of the study period. Long-term trends were estimated as a moderate increase for Common Tern and a strong increase for Black-headed Gull. Since 2006, the Mediterranean Gull L. melanocephalus has been a regular breeder at Lake Ptuj (up to 28 pairs), the only such site in Slovenia. Three general types of conservation measures implemented at different nesting locations are described in detail: (1) measures to create/increase the total surface of breeding habitat – the construction of new breeding structures, such as artificial islands and nesting rafts, (2) measures to maintain and enhance breeding habitat through recurring management activities, and (3) measures aimed to increase chick/nest survival and improve breeding success.

Shortcomings of Discriminant Functions: A Case Study of Sex Identification in the Black-Headed Gull

The Black-headed Gull Larus ridibundus, like many other gulls, has monomorphic plumage, which impedes sex identification in the field. We analysed the size of the hood, eye ring and wing tip and found that putative ornaments did not differ between sexes in this species. We formulated a novel discriminant function for Black-headed Gulls using morphometric measurements of live individuals (i.e. total head length, bill depth, and the sixth rectrix length), intentionally excluding data from dead birds, which were on average significantly smaller than their living conspecifics. We also tested cross-application of discriminant functions previously developed for Black-headed Gulls, proving that sexing individuals from different populations, even geographic neighbours, based on a single discriminant function risks errors and showing that discriminant functions cannot be treated as a universal tool for sex identification across space and time. —Indykiewicz, P., Minias, P., Kowalski, J. & Podlaszczuk, P. (2019). Shortcomings of discriminant functions: a case study of sex identification in the Black-headed Gull. Ardeola, 66: 361-372.

New species on the list of species with intraspecific nest parasitism

Abstract Intraspecific nest parasitism has only recently received more attention from ornithologists. In 2001, Yom-Tov published a list of 234 species that had exhibited this behaviour. I have since found literature data on four additional species in which intraspecific nest parasitism has been observed. No such record has so far been published from Hungary. This study presents records on 25 species from Hungary and on one species from Croatia, out of which I have not found any reference for intraspecific nest parasitism in the literature for Cattle Egret (Bubulcus ibis), Eurasian Thick-knee (Burhinus oedicnemus), Black-winged Stilt (Himantopus himantopus), Collared Pratincole (Glareola pratincola), Mediterranean Gull (Larus melanocephalus), Little Tern (Sternula albifrons), Whiskered Tern (Chlidonias hybrida), Eurasian Roller (Coracias garrulus) and Eurasian Jackdaw (Corvus monedula). In addition to records from Hungary, for Black-headed Gull (Larus ridibundus) and Mediterranean Gull I also present observations from Slovakia, and for Common Shelduck (Tadorna tadorna) from Germany.

Great Crested Grebe (Podiceps cristatus) synchronies egg laying with protective species

Great crested grebes (Podiceps cristatus) are opportunistic breeders nesting in colonies or solitarily in different biotopes with varying nesting dates in different circumstances. On the northern coast of the Neva Bay in the eastern part of the Gulf of Finland, great crested grebes breed solitarily, in colonies situated in reed beds and in a colony on the open water in direct vicinity of a colony of black-headed gulls (Larus ridibundus) and black terns (Chlidonias niger). In the vicinity of the larid colony, grebes profit from the protecting behaviour of gulls and terns in a similar way as they do in their mixed colonies with larids. Despite the fact that small larids have a shorter incubation period than great crested grebes, the latter synchronize their beginning of incubation with the gulls and terns. The incubation of all three species in two adjoining open-water colonies started on the same dates. The incubation of grebes nesting in the reed beds began significantly later. The average clutch sizes did not differ significantly between the colonies situated on the open water near larids and those in the reeds. The average lowest distances between the nests of great crested grebes in the open water colony were larger than in the reed bed colonies. The ability to synchronize the beginning of incubation with a small protecting species helps great crested grebes to occupy otherwise unsafe habitats.

First Report of Chlamydia Psittaci Seroprevalence in Black-headed Gulls (Larus Ridibundus) at Dianchi Lake, China.

Chlamydiosis is an important zoonosis which can transmit from birds to humans, and investigation first reported the seroprevalence of Chlamydia psittaci in black-headed gulls (Larus ridibundus) at the Dianchi Lake, China. A total of 1029 serum samples collected from black-headed gulls between 2012-2015 were analyzed. The gulls were randomly caught and blood collected at Dianchi Lake, China. All the samples were analyzed for the presence of antibodies to C. psittaci by indirect hemagglutination assay (IHA). In this survey, the total infection rate was 11.86% (122/1029). The results of the present survey documented the existence of relatively high C. psittaci seroprevalence in black-headed gulls, which have a potential risk to the wild bird health and human health. Comprehensive practical control approaches and measures should be executed.

Analysis of body mass changes in the Black-Headed Gull (Larus ridibundus) during the winter.

During the autumn migration of many waterfowls, body mass is lowest upon arrival at the wintering area and gradually increases during the winter. Consequently, body mass is highest before the spring migration. We studied the pattern of body mass changes in the Black-Headed Gull (Larus ridibundus) from December 2010 to December 2016 in the Shinhama area of Chiba, Japan. Based on 327 captured animals, body mass increased during the wintering period, but tended to decrease before migration. In 2014–2016, a muscle mass reduction in females was observed, explaining the change in body mass. However, the observed weight loss may be caused by many factors, which may be related to the migratory ecology of the regional population.

Сезонная динамика гидрофильного орнитокомплекса бухты Круглая (Севастополь, Чёрное море)

Актуальность изучения гидрофильных птиц в городских зонах черноморского побережья обусловлена их важной ролью в структуре прибрежных биоценозов и необходимостью сохранения биоразнообразия в условиях антропогенной трансформации береговой зоны Крыма. Исследована динамика видового состава и численности птиц бухты Круглая (Севастополь). Материал собран в 1995 и 2005–2016 гг. В бухте Круглая установлено пребывание 51 вида водных и околоводных птиц из 8 отрядов. Зимний орнитокомплекс наиболее разнообразен и многочислен (32 вида: 14 Anseriformes, 7 Charadriiformes, 5 Podicipediformes, 3 Gruiformes, 2 Pelecaniformes, 1 Gaviiformes). Регулярно зимуют и количественно доминируют 8 видов – Cygnus olor, Anas platyrhynchos, Aythya ferina, Aythya fuligula, Fulica atra, Larus ridibundus, Larus cachinnans и Larus canus. Определены численность всех видов птиц, возрастной состав Cygnus olor и половой состав Anas platyrhynchos, Aythya ferina и Aythya fuligula. Основу орнитокомплекса составляли бентофаги (не менее 13 видов), ихтиофаги (5) и эврифаги (4). Отмечено 30 пролётных и кочующих видов, преимущественно Charadriiformes (11), Anseriformes (7) и Ciconiiformes (5). Гнездовой орнитокомплекс отсутствовал, только в 2016 г. зарегистрировано гнездование Ixobrychus minutus. Весенний пролёт проходил с конца февраля до мая, осенний –– с августа до первой декады ноября. Для сохранения данной бухты как ценного природного и эколого-воспитательного объекта целесообразно придание ей статуса природного парка.

Reduction of variability of individual colonization programs in black-headed gulls (Larus ridibundus) leads to diminished reproductive success

The study is devoted to the problem of adaptive significance of territorial antagonism in colonial birds. Many of them are characterized by a high intensity and diversity of territorial demonstrations, along with tolerance of each other and a tendency to aggregate. Here we consider the effects of territorial behavior on the viability of a breeding colony. We analyze the breeding of black-headed gull in two colonies formed under the impact of a short-term temperature fall in 2008, which resulted in a 7-day shift in the timing of egg laying. Compared with the colonies at the same reservoirs, one in 2007 and one in 2009, the number of nests and their density in 2008 were much smaller, whereas the duration of settling, nest density growth, and average size of breeding territories did not change. The average body weight of adult birds during incubation was stable throughout all years; however, the correlations typical for 2007 and 2009 (negative between the female mass and date of clutching start and positive between masses of parents) were absent, suggesting that assortative mating by body mass and territory size was not the case in 2008. The average clutch, egg, and hatching sizes were on average smaller in 2008, while mortality due to attacks of aerial predators was much higher than in other years. In 2007 and 2009, birds that started egg-laying in the first 5 days after the first egg appeared in the colony (pioneer settlers) were larger than others (the so-called followers) and produced a larger offspring. These differences were not observed in 2008. According to our data, due to the impact of cold weather, some birds abandoned their nesting sites and others were sick, but they mostly behaved as pioneer settlers and formed underpopulated and sparse colonies. We assume that the formation of a viable colony requires the interaction of highly territorial “pioneers” and a certain number of less competitive followers. The withdrawal of the latter results in a general reproductive failure of the colony. Thus, the pattern of colony formation in black-headed gull turns natural selection towards a maintenance of the variety of individual programs of territorial competition.