Nahrungsökologische Untersuchungen an Mantelmöwen(Larus marinus) auf Helgoland

This paper is based on observations and the analysis of 54 stomach contents of great black-backed gulls obtained from the island of Helgoland (North Sea) in 1971 and 1972. It deals with the following problems: How large is the share of food taken from the human area in progressing synanthropy of the great black-backed gull? Does this gull have any negative effect on the colony of guillemots(Uria aalge albionis) on Helgoland? Do great black-backed gulls bring further danger (in addition to weather, etc.) for smaller birds migrating over or resting on Helgoland in spring and autumn? 73.5% of the food taken up is of human origin, only 26.5% is considered to be natural food (Crustacea, Mollusca, Insecta). 36 (66.7%) stomachs contained remainders of fish, mainly cod(Gadus morhua), whiting(Merlangius merlangus) and poor cod(Trisopterus minutus). Together with herring gulls(Larus argentatus), great black-backed gulls often swoop down on fishing guillemots to recover the just captured fish from them. They also attack homing guillemots in the range of their breeding rocks. Only in one case the remainders of a smaller bird were found, but presumably a greater number of smaller birds is killed by great gulls.     

Comprehensive and Comparative Analysis of the Helminth Fauna of the Dominant Colonial Seabird Species on the Murman Coast

This work reports the results of the long-term study of the helminth fauna of the dominant colonial seabird species (common guillemots, Brünnich’s guillemots, kittiwakes, great black-backed gulls, and herring gulls) in the western, central, and eastern parts of the Murman coast. The presence of 52 parasitic worm species (18 trematode species, 21 cestode species, 11 nematode species, and 2 acanthocephalan species) was demonstrated. In the western, central, and eastern regions, the respective numbers of 32, 43, and 34 helminth species were registered. Twenty species of seabird parasites were found to be ubiquitous along the Murman coastal zone. Local foci of the trematode Maritrema arenaria and cestode Laricanthus lateralis infestation along the western part of the Murmansk coast were revealed. The highest helminth species diversity (38 species) was demonstrated for the herring gull; the lowest (7 species), for the common guillemot. Four parasite species were common for the helminth fauna of all bird species. A significant number of helminth infections were mixed ones (complexes of two or three bird species with the common helminth species in different combinations). The highest similarity of the helminth fauna was revealed in the pairs of the common guillemot and the Brünnich’s guillemot and of the great black-backed gull and the herring gull. A few parasitic worm species detected only in a single bird species were registered. The particularities and the possible causes of the geographical distribution and specificity of helminthes were analyzed, and a comprehensive assessment of the parasitological situation in the Murman coastal zone was performed.     

Interspecific differences in foraging preferences, breeding performance and demography in herring (Larus argentatus) and lesser black-backed gulls (Larus fuscus) at a mixed colony

Herring gulls Larus argentatus and lesser black-backed gulls Larus fuscus breeding at Walney Island, Cumbria, the largest breeding colony of the two species in the UK, have recently shown very different population trends. The former has declined sharply, whereas numbers of the latter have been maintained for several years. Here we compare aspects of the feeding and breeding ecology of the two species in order to examine whether or not this suggests explanations for their different population trends. Comparison of the ratio of the two species in flight lines leading to different feeding sites and their diet composition showed that the lesser black-backed gulls fed more at sea and the herring gulls fed more in the intertidal zone. Urban resources were used by both these species. These differences have been consistent over the last three decades. Susceptibility to death from botulism at the breeding colony was the same for the two species. The availability of the intertidal zone for foraging appears to have declined in recent years, and this may have had a more negative impact on the herring gull. However, the breeding success of the two species remains relatively high. This study suggests that differences in foraging behaviour and food availability during the breeding season are unlikely to be responsible for the marked differences in demographic trends in the two species. Changes in local food availability during the winter would be expected to have more effect on the resident herring gull. This work highlights the need for more detailed studies of the ecology of both species during the breeding season and in winter in regions showing differing patterns of population change.     

Behavioural responses to human intruders of herring gulls (Larus Argentatus) and great black-backed gulls (L. Marinus) with varying exposure to human disturbance

This study examined differences in response to humans approaching the nest for incubating herring and great black–backed gulls with varying amounts of prior exposure to humans. Gulls nesting in frequently disturbed areas sat more tenaciously, responded more slowly, and returned to the nest more quickly following the intruder's retreat, than birds nesting in less disturbed areas. The species differed in their responses in different areas. Stage of incubation had little effect, except that late in incubation herring gulls returned to the nest more quickly. Weather variables affected responses of great black-backed gulls. For both species the behaviours we scored when the experimenter approached the nest were correlated, as were those following departure, but there was no correlation between these two sets of responses. Our study provides evidence on the relationships among components of an alarm and escape response, and provides a measure of influence of human disturbance for two species of gulls.     

Geographical variation in the yellow‐legged gull: introgression or convergence from the herring gull?

Yellow-legged gulls Larus michahellis from the Atlantic Iberian coast exhibit some phenotypic similarities with the herring gull L. argentatus from Western Europe. To assess this phenomenon and its possible origin, we compared Mediterranean yellow-legged gulls, Atlantic Iberian yellow-legged gulls and herring gulls for several phenotypic traits (morphology, plumage), and used genetic data to determine the evolutionary history of the Atlantic Iberian yellow-legged gulls. Data from mitochondrial cytochrome b gene and microsatellite loci clearly indicate that Atlantic Iberian gulls are closely related to Mediterranean yellow-legged gulls, and do not show stronger signs of introgression with herring gulls relative to other populations of yellow-legged gulls. Atlantic Iberian yellow-legged gulls are more similar to herring gulls in body size and shape than to other yellow-legged gulls populations, but not in mantle colour and wing-tip pattern. Body size and other phenotypic and life history similarities with the herring gull ( L. argentatus argenteus ) such as voice, winter plumage and breeding phenology, previously described in several studies, might thus be interpreted as convergent characters. Within the yellow-legged gull, the high F _st-values obtained from four nuclear microsatellite loci indicate substantial population structure and reduced levels of gene flow between gull populations in Mediterranean France and Atlantic Iberia. Differences among these populations in breeding phenology and migration patterns, likely resulting from different local selection pressures, might contribute to this low level of gene flow.     

Characterization of Escherichia coli populations from gulls, landfill trash, and wastewater using ribotyping

Due to their opportunistic and gregarious nature, gulls may be important reservoirs and vectors for anthropogenically derived fecal pathogens in coastal areas. We used ribotyping, a genotypic bacterial source tracking method, to compare populations of Escherichia coli among herring gulls Larus argentatus, great black-backed gulls L. marinus, wastewater, and landfill trash in New Hampshire and Maine, USA. Concentrations of E. coli in gull feces varied widely among individuals, but were generally high (6.0 x 10(1) to 2.5 x 10(9) g(-1) wet weight). Of 39 E. coli isolates from L. argentatus, 67% had banding patterns that were > or = 90% similar to those from wastewater and trash, whereas only 39% of 36 L. marinus isolates exhibited > or = 90% similarity to these sources. Strains of E. coli from gulls matched (> or = 90% similarity) more strains from wastewater (39% matching) than from trash (15% matching). E. coli isolates from L. marinus feces exhibited a greater diversity of banding patterns than did isolates from L. argentatus. There were more unique E. coli banding patterns in trash samples than in wastewater, and higher diversity indices in the former compared to the latter. These findings suggest that both species of gulls, especially L. argentatus, obtain fecal bacteria from wastewater and landfill trash, which they may transport to recreational beaches and waters. Our results also indicate that E. coli populations may vary widely between gull species, and between the anthropogenic habitats that they frequent, i.e. landfills and wastewater treatment facilities.     

The biological function of gulls' attraction towards predators

Many species of birds and mammals are attracted towards some of their natural predators, often without overt aggression. The biological function of this predator attraction was studied in a colony of herring gulls and lesser black-backed gulls, with the aid of predator models. More birds flocked above the predator model when it was presented together with a dead gull; also the birds did not land as close to a predator with a dead gull as they did to a predator alone. Having seen a predator with a dead gull had a clear effect on the distance at which birds later avoided that particular predator on the ground when it was presented to them alone. It is suggested that predator-attraction enables animals to collect information about a potential enemy; in this information the experience of conspecifics with the predator is taken into account; subsequent behaviour of the animals depends partly on this information. The increase in the avoidance distance with respect to a predator with a dead bird may be an adaptation to carnivores' habit of surplus killing.     

The versatility of graded acoustic measures in classification of predation threats by the tufted titmouse Baeolophus bicolor: exploring a mixed framework for threat communication

Many mammal and bird species respond to predator encounters with alarm vocalizations that generate risk‐appropriate responses in listeners. Two conceptual frameworks are typically applied to the information encoded in alarm calls and to associated anti‐predator behaviors. ‘Functionally referential’ alarm systems encode nominal classes or categories of risk in distinct call types that refer to distinct predation‐risk situations. ‘Risk‐based’ alarms encode graded or ranked threat‐levels by varying the production patterns of the same call types as the urgency of predation threat changes. Recent work suggests that viewing alarm‐response interactions as either referential or risk‐based may oversimplify how animals use information in decision‐making. Specifically, we explore whether graded alarm cues may be useful in classifying risks, supporting a referential decision‐making framework. We presented predator (hawk, owl, cat, snake) and control treatments to captive adult tufted titmice Baeolophus bicolor and recorded their vocalizations, which included ‘chick‐a‐dee’ mobbing calls (composed of chick and D notes), ‘seet’ notes, two types of contact notes (‘chip’, ‘chink’), and song. No single call type was uniquely associated with any treatment and the majority of acoustic measures varied significantly among treatments (46 of 60). The strongest models (ANOVA and classification tree analysis) grouped hawk with cat and owl, and control with snake, and were based on the number or proportion of a) chick and D notes per chick‐a‐dee call, b) chip versus chink notes produced following treatment exposure, and c) the frequency metrics of other note types. We conclude that (1) the predation‐threat information available in complex titmouse alarm calls was largely encoded in graded acoustic measures that were (2) numerous and variable across treatments and (3) could be used singly or in combinations for either ranking or classification of threats. We call attention to the potential use of mixed threat identification strategies, where risk‐based signal information may be used in referential decision‐making contexts.     

A comparison of foraging at refuse tips by three species of gull (Laridae)

The comparative foraging of Black-headed ( Larus ridibundus ), Herring ( L. argentalus ) and Great black-backed gulls ( L. marinus ) was investigated at refuse tips in north-east England. Between October and February, two races of Herring gulls are present, those which breed in Britain ( L. a. argenteus ) and the larger Scandinavian herring gulls ( L. a. argentatus).
Three types of feeding at a refuse tip were distinguished: undisturbed primary feeding (highly competitive feeding on freshly dumped rubbish), disturbed primary feeding (agile surface dipping for food from the air, close to the working bulldozer) and secondary feeding (low density feeding on dispersed and partially buried rubbish).
In undisturbed feeding the largest individuals (i.e. Great black-backed gulls) were competitively superior and achieved the highest feeding success. The smallest individuals (i.e. Black-headed gulls) were rapidly excluded by the larger gulls. Scandinavian herring gulls were competitively superior in intraspecific interactions, but they were selectively attacked by Great black-backed gulls. Disturbed feeding, in contrast, was used most by Black-headed gulls and not at all by Great black-backed gulls. Large body size is a disadvantage in disturbed feeding, due to increased wing loading acting as a constraint on manoeuvrability. Overall, the separation between species, in terms of the proportion of food gained by different feeding methods, was estimated at 30–50%.
Cold and windy conditions led to increased numbers of Herring and Great black-backed gulls at tips, and numbers of Great black-backed gulls were also higher when fish landings at the coast were low. There were significant differences between tips in the number of Great black-backed and Black-headed gulls, possibly due to differences in working regime which influence the feeding opportunities which were available.     

The herring gull complex is not a ring species

Under what circumstances speciation in sexually reproducing animals can occur without geographical disjunction is still controversial. According to the ring-species model, a reproductive barrier may arise through 'isolation by distance' when peripheral populations of a species meet after expanding around some uninhabitable barrier. The classical example of this kind of speciation is the herring gull (Larus argentatus) complex, with a circumpolar distribution in the Northern Hemisphere. Based on mitochondrial DNA variation among 21 gull taxa, we show that members of this complex differentiated largely in allopatry following multiple vicariance and long-distance-colonization events, not primarily through isolation by distance. Reproductive isolation evolved more rapidly between some lineages than between others, irrespective of their genetic distance. Extant taxa are the result of divergent as well as reticulate evolution between two ancestral lineages originally separated in a North Atlantic refugium and a continental Eurasian refugium, respectively. Continental birds expanded along the entire north Eurasian coast and via Beringia into North America. Contrary to the ring-species model, we find no genetic evidence for a closure of the circumpolar ring through colonization of Europe by North American herring gulls. However, closure of the ring in the opposite direction may be imminent, with lesser black-backed gulls about to colonize North America.     

Conspecific alarm cues, but not predator cues alone, determine antipredator behavior of larval southern marbled newts, Triturus pygmaeus

Predation imposes selection on the ability of prey to recognize and respond to potential threats. Many prey species detect predators via chemoreception, particularly in aquatic environments. Also, chemical cues from injured prey are often perceived as an indication of predation risk. However, because antipredatory behavior can be costly, prey responses should depend on the current level of risk that each predator poses, which may depend on the type of chemical cues detected. We exposed larval newts, Triturus pygmaeus, to chemical cues from predator larval beetles or to alarm cues from conspecific larval newts and examined the behavioral changes of larval newts. Results showed that larval newts reduced activity levels when conspecific alarm cues were present but not when the predator cues alone were present. These results might suggest that larval newts are unable to recognize predator chemicals. To avoid costs of unnecessary antipredatory behaviors, larval newts may benefit by avoiding only predators that represent a current high level of threat, showing only antipredatory responses when they detect conspecific alarm cues indicating that an actual predatory attack has occurred.     

Ultraviolet photopigment sensitivity and ocular media transmittance in gulls,with an evolutionary perspective

Gulls (Laridae excluding Sternidae) appear to be the only shorebirds (Charadriiformes) that have a short wavelength sensitive type 1 (SWS1) cone pigment opsin tuned to ultraviolet (UV) instead of violet. However, the apparent UV-sensitivity has only been inferred indirectly, via the interpretation that the presence of cysteine at the key amino acid position 90 in the SWS1 opsin confers UV sensitivity. Unless the cornea and the lens efficiently transmit UV to the retina, gulls might in effect be similar to violet-sensitive birds in spectral sensitivity even if they have an ultraviolet sensitive (UVS) SWS1 visual pigment. We report that the spectral transmission of the cornea and lens of great black-backed Larus marinus and herring gulls L. argentatus allow UV-sensitivity, having a λ_T0.5 value, 344 nm, similar to the ocular media of UV sensitive birds. By molecular sequencing of the second α-helical transmembrane region of the SWS1 opsin gene we could also infer that 15 herring gulls and 16 yellow-legged gulls L. michahellis, all base-pair identical, are genetically UV-sensitive.     

Differential expression, induction, and stability of CYP1A4 and CYP1A5 mRNA in chicken and herring gull embryo hepatocytes

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces cytochrome P4501A (CYP1A) catalyzed ethoxyresorufin-O-deethylase (EROD) activity in chickens and other avian species. To investigate mechanisms underlying the effectiveness of EROD activity as a biomarker for exposure to dioxin-like compounds in avian models, we characterized inter-species differences in isoform-specific CYP1A mRNA expression, induction, and stability in chickens (Gallus gallus domesticus) and herring gulls (Larus argentatus). Exposure to 100 nM TCDD significantly increased CYP1A4 and CYP1A5 mRNA expression in chicken and herring gull embryo hepatocyte cultures. Chicken CYP1A4 and CYP1A5 were induced 61-fold and 25-fold respectively. The herring gull isoforms were induced 2.2- and 4.3-fold respectively. In both species, the isoform that was preferentially induced exhibited lower constitutive expression. Half-lives of chicken CYP1A4, chicken CYP1A5, and herring gull CYP1A5 mRNA ranged from 5.0 to 7.0 h in cultured hepatocytes. The half-life of herring gull CYP1A4 mRNA was 2.5 h. Our findings indicate that expression, induction, and stability of CYP1A4 and CYP1A5 mRNA are differentially regulated in chickens and herring gulls. In particular, CYP1A4 is preferentially induced in chickens, while CYP1A5 is preferentially induced in herring gulls. We propose that CYP1A5 mRNA expression may be a sensitive biomarker of exposure to dioxin-like compounds in some avian species.     

Preen oil chemical composition in herring gull Larus argentatus,common gull Larus canus and black-headed gull Chroicocephalus ridibundus confirms their status as two separate genera

Fatty acid and alcohol components of preen oil were determined in three gull species that belong to two systematic genera: herring gull Larus argentatus, common gull Larus canus and black-headed gull Chroicocephalus ridibundus. All gulls were captured in winter, in Gdańsk, Poland. All gulls produced monoesters composed of C₇–C₁₆ saturated fatty acids and C₁₁–C₂₀ saturated alcohols, with n-octanoic acid and n-hexadecanol as the major fatty acid and alcohol, respectively. Preen oils of black-headed gull had higher content of trimethyl fatty acids, 2,8-dimethylundecanoic acid, 2,6-dimethylundecanoic acid and 2,6-dimethylnonanoic acid, and lower content of 2-methyl fatty acids than oils of herring gull and common gull. Preen oils produced by black-headed gull also had lower content of 2-methyl alcohols. The relative contents of n-octanoic acid and n-hexadecanol did not differ among species. The differences among species are probably not a result of different diet, as all gulls fed mainly on household refuse. Hence, preen oil analysis confirmed the taxonomic relations among these gull species, that recently were placed into two different genera.     

The value of constant surveillance in a risky environment

In risky environments, where threats are unpredictable and the quality of information about threats is variable, all individuals face two fundamental challenges: balancing vigilance against other activities, and determining when to respond to warning signals. The solution to both is to obtain continuous estimates of background risk, enabling vigilance to be concentrated during the riskiest periods and informing about the likely cost of ignoring warnings. Human surveillance organizations routinely produce such estimates, frequently derived from indirect cues. Here we show that vigilant individuals in an animal society (the pied babbler, Turdoides bicolor) perform a similar role. We ask (i) whether, in the absence of direct predator threats, pied babbler sentinels react to indirect information associated with increased risk and whether they communicate this information to group mates; (ii) whether group mates use this information to adjust their own vigilance, and whether this influences foraging success; and (iii) whether information provided by sentinels reduces the likelihood of inappropriate responses to alarm calls. Using playback experiments, we show that: (i) sentinels reacted to indirect predator cues (in the form of heterospecific alarm calls) by giving graded surveillance calls; (ii) foragers adjusted their vigilance in reaction to changes in surveillance calls, with substantial effects on foraging success; and (iii) foragers reduced their probability of responding to alarm calls when surveillance calls indicated lowered risk. These results demonstrate that identifying attacks as they occur is only part of vigilance: equally important is continuous surveillance providing information necessary for individuals to make decisions about their own vigilance and evasive action. Moreover, they suggest that a major benefit of group living is not only the increased likelihood of detecting threats, but a marked improvement in the quality of information available to each individual.     

North Sea ecosystem change from swimming crabs to seagulls

A recent increase in sea temperature has established a new ecosystem dynamic regime in the North Sea. Climate-induced changes in decapods have played an important role. Here, we reveal a coincident increase in the abundance of swimming crabs and lesser black-backed gull colonies in the North Sea, both in time and in space. Swimming crabs are an important food source for lesser black-backed gulls during the breeding season. Inhabiting the land, but feeding mainly at sea, lesser black-backed gulls provide a link between marine and terrestrial ecosystems, since the bottom-up influence of allochthonous nutrient input from seabirds to coastal soils can structure the terrestrial food web. We, therefore, suggest that climate-driven changes in trophic interactions in the marine food web may also have ensuing ramifications for the coastal ecology of the North Sea.     

Hematologic and hematochemical characteristics of the herring gull (Larus argentatus) and the buzzard (Buteo buteo)

Some hematological and hematochemical parameters in eight herring gulls (Larus argentatus) and in six buzzards (Buteo buteo) were checked. The buzzards were fed with ovine meat exclusively, while the herring gulls were fed with fish and ovine meat. Considerable differences between the two species were noted, particularly as far as the hematological and lipidic parameters are concerned. These differences are probably related to the aquatic life of the herring gull.     

Experimental Evidence of Threat-Sensitive Collective Avoidance Responses in a Large Wild-Caught Herring School

Aggregation is commonly thought to improve animals'' security. Within aquatic ecosystems, group-living prey can learn about immediate threats using cues perceived directly from predators, or from collective behaviours, for example, by reacting to the escape behaviours of companions. Combining cues from different modalities may improve the accuracy of prey antipredatory decisions. In this study, we explored the sensory modalities that mediate collective antipredatory responses of herring (Clupea harengus) when in a large school (approximately 60 000 individuals). By conducting a simulated predator encounter experiment in a semi-controlled environment (a sea cage), we tested the hypothesis that the collective responses of herring are threat-sensitive. We investigated whether cues from potential threats obtained visually or from the perception of water displacement, used independently or in an additive way, affected the strength of the collective avoidance reactions. We modified the sensory nature of the simulated threat by exposing the herring to 4 predator models differing in shape and transparency. The collective vertical avoidance response was observed and quantified using active acoustics. The combination of sensory cues elicited the strongest avoidance reactions, suggesting that collective antipredator responses in herring are mediated by the sensory modalities involved during threat detection in an additive fashion. Thus, this study provides evidence for magnitude-graded threat responses in a large school of wild-caught herring which is consistent with the “threat-sensitive hypothesis”.     

First records of lesser black-backed gulls Larus fuscus crossing the Sahara non-stop

Lesser black-backed gulls Larus fuscus migrate regularly along coastlines or the Nile to their wintering grounds in sub-Saharan Africa. They usually avoid the interior of the Sahara, but occur occasionally far inland when moving upstream along rivers. We discovered several flocks of lesser black-backed gulls crossing the western Sahara about 500 km east of the Atlantic coast. Their concentrated flight directions along a northeast-southwest axis indicate that the gulls were on an intended migratory flight and not incidentally drifted inland. Ground speed of 8 flocks of gulls averaged 20 m/s and was considerably larger than the mean air speed (12 m/s) demonstrating that the gulls were strongly assisted by tailwinds. Highest ground speed was 26 m/s. Warmest temperature encountered when crossing the study site was 13° C due to relative high flight altitudes of 3,500 m above sea level. Thus, lesser black-backed gulls migrated under favourable conditions with respect to energy and water consumption. Our observations strongly suggest that the gulls performed long non-stop flights between the eastern Atlantic coast of sub-Saharan Africa and the Mediterranean Sea.     

A histochemical comparison of fibre types in the M. pectoralis and M. supracoracoideus of the great skua Catharacta skua and the herring gull Larus argentatus with reference to kleptoparasitic capabilities

Skuas, which are closely related to gulls, frequently use a specialized feeding method (kleptoparasitism) by which they rob other seabirds of their food. This paper tests the idea that skuas have evolved as specialist kleptoparasites.
The fibre type composition of the M. pectoralis, M. supracoracoideus and M. iliofibularis of a great skua Catharacta skua (Brünn.) and a herring gull Larus argentatus (Pontopp.) was determined by three enzyme histochemical methods commonly used for mammalian fibre classification; the reactions for alphaGPDH, NADH-TR and mATPase activity.
In both species slow fibres were present only in the M. iliofibularis, and fast twitch glycolytic fibres were not present in any of the muscles. The M. pectoralis and M. supracoracoideus of both species consisted entirely of the fast twitch oxidative-glycolytic fibres.
The overall metabolic enzyme activities of the muscles were assessed in terms of the proportions of fibres with high, intermediate and low metabolic enzyme activity. The overall levels of oxidative and glycolytic enzyme activity were significantly higher in the M. pectoralis than in the M. supracoracoideus and significantly higher in both of these than in the M. iliofibularis. This was true of both species.
The oxidative and glycolytic activities of all three muscles of the great skua were significantly higher than those of the homologous muscles of the herring gull. This was particularly true of the M. pectoralis and M. supracoracoideus. It is suggested that this difference between great skuas and herring gulls enables the former to be more effective aerial kleptoparasites than the latter.