Colonial breeding reduces nest predation in the common gull (Larus canus)

It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.     

Can rats prey on gull eggs? An experimental approach

Black rat Rattus rattus populations can reach high densities on the Mediterranean islands, as has been the case on the Chafarinas Islands (Western Mediterranean coast) in the last decade. This archipelago holds the second largest breeding population of Audouin's gull Larus audouinii and an important population of yellow-legged gull Larus cachinnans. Circumstantial evidences of rat predation upon Audouin's gull eggs led to conservation concerns about the impact of rat predation on gull productivity. We studied the impact of rats on gull nests experimentally by building artificial nests into the breeding area of yellow-legged gulls. Two kinds of eggs were placed in the artificial nests: manipulated eggs, in which the shell had been previously opened, and intact (unmanipulated) eggs. Rats preyed extensively on opened eggs but only once on intact eggs, apparently due to lack of skills to prey on intact eggs, suggesting that rats do not normally have access to fresh gull eggs. Rats inhabiting breeding areas of gulls can scavenge on broken eggs rolled out of the nest or on eggs with softened shells after nest desertion, but it is unlikely that they prey on natural gull nests guarded by parents. We suggest that introduced black rats on Mediterranean islands can only marginally affect the productivity of gulls owing to egg predation.     

Nest predation and nest site selection among Eiders Somateria mollissima: the influence of gulls

Hooded Crows Corvus cornix, Great Black-backed Gulls Larus marinus and Herring Gulls L. argentatus were the main nest predators in an Eider population in southwest Sweden. The clutch sizes of Eider nests within gull colonies did not differ from those outside gull colonies. The proportion of Eider nests destroyed by predators was significantly lower within than outside gull colonies, especially on islands with Lesser Black-backed Gulls L. fuscus. Although the difference was not significant, the survival time of simulated Eider nests was higher within than outside gull colonies. On Eider islands with gull colonies, foraying crows spent more time within the colony area than expected by chance. However, crows apparently avoided an area around each gull nest, and we suggest that the colonies, to some extent, protected Eider nests against predation. The density of Eider nests was higher on gull islands than on gull- free islands, and higher within than outside the gull colonies. However, the association with gulls was weak compared to that displayed by some other waterfowl.     

Management-Induced Reproductive Failure and Breeding Dispersal in Double-Crested Cormorants on Lake Champlain

ABSTRACT We studied breeding dispersal of double-crested cormorants (Phalacrocorax auritus) associated with management practices that suppressed their reproduction on Lake Champlain in the northeastern United States. We implemented an experiment on one colony by spraying corn oil on cormorant eggs in portions of the colony and leaving other portions untreated. Gulls (Larus spp.) consumed cormorant eggs during the oiling process, but we reduced and then eliminated predation levels after the first year of the study. We used mark-recapture techniques within the experimental framework to measure rates of breeding dispersal for cormorants from the experimental colony and an unmanaged colony in Lake Champlain. Egg oiling increased the movement rate to the unmanaged colony by 3% during the year with no egg predation by gulls. When gulls depredated cormorant eggs at high rates during egg oiling, movement to the unmanaged colony increased by 20%. When cormorants are managed to reduce population sizes, methods that limit dispersal away from the managed colony may be most effective. Such methods would mitigate effects to nontarget populations and allow for a greater portion of the metapopulation to be managed.     

Changes in the species composition and number of gulls in tundra colonies in the western Chukotka over the last 40 years

Long-term data reflecting the abundance and species composition of large colonies of gulls (more than five nests, distance between the nests less than 50 m) on Aiopechan Island, West Chukotka, were compared. A comparative analysis of the data published in 1970–1984 and our data for 1989, 2000–2013 revealed significant changes in the composition and abundance of colonies over the 40-year period with simultaneous shift in the spring phonological characteristics to earlier dates. Growth in the number of the Vega gull (Larus vegae) and decrease in the number of Sabine’s gull (Xema sabini) were revealed. The number of glaucous gulls (Larus hyperboreus) was stable. A change of the dominant species in the colonies and disappearance of some colonies of the Sabine’s gull under the influence of the expansion of the Vega gull were registered. It was found that the increase in the abundance of the Vega gull occurs not owing to the increase of long-term colonies but due to the appearance of new ones.     

Predation risk associated with nesting in gull colonies by two Aythya species: observations and an experimental test

To reduce nest predation certain duck species nest in association with more aggressive species. For instance, Pochard Aythya ferina and Tufted Duck Aythya fuligula often nest in association with small larids, such as the Black-headed Gull Larus ridibundus . I studied nest predation, nesting association and nest site requirements of Pochard and Tufted Duck in central Finland (63°N, 27°E) observing natural and artifical nests. Predation of Pochard and Tufted Duck nests was of similar extent and stronger outside than within gull colonies. An experiment with artficial nests also showed that a higher proportion of nests was preyed upon outside than within gull colonies (0.98 and 0.13, respectively). The results are consistent with the hypothesis that nest predation is lower within than outside gull colonies. Tufted Ducks nest more often with gulls than do Pochards; 61.5% of Tufted Duck nests and 29.3% of Pochard nests were found within gull colonies.     

Breeding adaptations of Franklin's gull (larus pipixcan) to a marsh habitat

The behaviour and ecology of Franklin's gull were studied at Agassiz National Wildlife Refuge in northwestern Minnesota to determine the adaptations of the species for nesting in marshes. Two factors seemed to be important in colony site selection: cattail dispersion pattern and cattail density. Franklin's gulls prefer to nest in cattail areas closest to open water. The number of nests per unit area decreased as cattail density increased. Nest site selection is dependent on aggression and visibility. Visibility from nest level is the result of cattail placement and height. The distance between nests was directly correlated with visibility. Aggression by gulls on nests was lowered experimentally by decreasing visibility and raised by increasing visibility. Nest platforms were constructed of cattail material, and were attached to cattail stems. Nest material was added to the nests throughout the incubation and brooding period. Material was usually added following nest relief. The egg laying period was from 6 to 28 May. There was more synchrony of egg laying in sub-areas of the colony than in the colony as a whole. Successive eggs in clutches were laid at 24- to 48-hr intervals. The distance between nests decreased during the season as pairs filled in areas that were not defended. Territorial pairs defended an area up to 10 m from their stations prior to egg laying, but defended only the area within 3 m of their nests during incubation. Both members of pairs incubated the eggs and cared for the young. The incubation period was 24 days. The primary predators on adults and young were marsh hawk, great horned owl and mink. Franklin's gulls do not eat eggs or young of gulls. Adults fed on earthworms, insects and grain. Most marked adults fed within 16 km of the colony. Chicks were fed primarily on earthworms. The hatching period was from 30 May to 21 June. Chicks of all ages tested on a visual cliff apparatus were able to perceive the drop. Chicks tested on a 30-degree incline apparatus walked up it when 6 days old and younger, and walked down at 12 days of age and older. Brood mobility was less than in ground nesting species of gulls. In an undisturbed colony the chicks remained on the nest platforms until they were 25 to 30 days old although they were capable of swimming shortly after hatching. Individual recognition between parents and chicks appeared later in this species than in ground-nesting gulls. Adults accepted alien chicks (experimentally exchanged) that were younger than about 14 days old until their own chicks were over that age. Adults accepted larger and older broods than their own, as well as broods of mixed ages. Chicks began to react differently to strange adults at about 16 days of age. The breeding chronology of Franklin's gull is compressed when compared to that of other gulls. Possible selection pressures affecting this synchrony are discussed. The behaviour of the marsh-nesting Franklin's gull is compared with that of typical ground-and cliffnesting gulls; the possibility that the ancestral gull may have been a marsh nester is discussed.     

Impact of egg harvesting on breeding success of black-headed gulls,Larus ridibundus

Gull colonies world-wide have been harvested for their eggs for centuries with minimal knowledge of the impacts on breeding. Although most Laridae can replace lost eggs, they have comparatively high energetic demands for egg production. In this paper we assess the impacts of a licensed egg harvest on the breeding success of black-headed gulls Larus ridibundus, which nest colonially in an EU Special Protection Area in Hampshire, southern England. We compared egg volume, hatching and chick survival from harvested and un-harvested nests in central and fringe positions within colonies of various sizes, including colonies with no harvesting activity. Eggs from various laying stages were collected from harvested and un-harvested colonies of similar pre-harvest intrinsic quality, for comparison of their volumes, yolk-to-albumen ratios and eggshell thickness. Egg volume and the yolk-to-albumen ratio depended on laying time and location, with the largest eggs laid during the peak period by birds breeding in central positions on large colonies. Eggs produced by these peak layers also had the largest yolk-to-albumen ratios. Harvested sites were characterised by reductions in egg volume, yolk-to-albumen ratio and eggshell thickness, which translated to poorer hatching success and chick survival. Harvested sites also had a higher proportion of abnormal eggs, particularly taking the forms of small yolkless eggs and unpigmented eggs. The reduced breeding success on harvested colonies is likely to be linked to depletion of the female's endogenous reserves which can also reduce future survival and breeding propensity.     

Extent and Degree of Shoreline Oiling: Deepwater Horizon Oil Spill,Gulf of Mexico,USA

The oil from the 2010 Deepwater Horizon spill in the Gulf of Mexico was documented by shoreline assessment teams as stranding on 1,773 km of shoreline. Beaches comprised 50.8%, marshes 44.9%, and other shoreline types 4.3% of the oiled shoreline. Shoreline cleanup activities were authorized on 660 km, or 73.3% of oiled beaches and up to 71 km, or 8.9% of oiled marshes and associated habitats. One year after the spill began, oil remained on 847 km; two years later, oil remained on 687 km, though at much lesser degrees of oiling. For example, shorelines characterized as heavily oiled went from a maximum of 360 km, to 22.4 km one year later, and to 6.4 km two years later. Shoreline cleanup has been conducted to meet habitat-specific cleanup endpoints and will continue until all oiled shoreline segments meet endpoints. The entire shoreline cleanup program has been managed under the Shoreline Cleanup Assessment Technique (SCAT) Program, which is a systematic, objective, and inclusive process to collect data on shoreline oiling conditions and support decision making on appropriate cleanup methods and endpoints. It was a particularly valuable and effective process during such a complex spill.     

Nest sanitation behavior does not increase the likelihood of parasitic egg rejection in herring gulls

Birds’ behavioral response to brood parasitism can be influenced not only by evolution but also by context and individual experience. This could include nest sanitation, in which birds remove debris from their nests. Ultimately, nest sanitation behavior might be an evolutionary precursor to the rejection of parasitic eggs. Proximately, the context or experience of performing nest sanitation behavior might increase the detection or prime the removal of parasitic eggs, but evidence to date is limited. We tested incubation-stage nests of herring gulls Larus argentatus to ask whether nest sanitation increased parasitic egg rejection. In an initial set of 160 single-object experiments, small, red, blocky objects were usually rejected (18 of 20 nests), whereas life-sized, 3D-printed herring gull eggs were not rejected whether red (0 of 20) or the olive-tan base color of herring gull eggs (0 of 20). Next, we simultaneously presented a red, 3D-printed gull egg and a small, red block. These nests exhibited frequent nest sanitation (small, red block removed at 40 of 48 nests), but egg rejection remained uncommon (5 of those 40) and not significantly different from control nests (5 of 49) which received the parasitic egg but not the priming object. Thus, performance of nest sanitation did not shape individuals’ responses to parasitism. Interestingly, parents were more likely to reject the parasitic egg when they were present as we approached the nest to add the experimental objects. Depending on the underlying mechanism, this could also be a case of experience creating variation in responses to parasitism.     

Nonbreeding and nests without eggs in the Lesser Black-backed Gull Larus fuscus

Estimates of the number of breeding Lesser Black-backed Gulls Larus fuscus at the Tarnbrook Fell gullery, Lancashire, have been made from annual counts of nests since 1981. During all of these surveys, the mean percentage of nests which did not contain eggs has been remarkably constant from year to year (54%± 1.9%). A study of specific nests at the colony in 1992 showed that the great majority of these "empty" nests did not subsequently receive eggs. in 1993, a study of a sample of territory-holding gulls was made on a 0.41-ha study plot to investigate and to quantify the occurrence of empty nests. Of the 62 pairs that defended a territory and constructed a complete nest, 27% subsequently failed to produce eggs. These birds attended their territory as a pair significantly less frequently than pairs that produced clutches and achieved significantly fewer apparently successful mountings. Sixty percent of pairs constructed more than one nest, and 58% of all nests built received no eggs. The construction of empty nests was not found to be related to the density of nesting gulls. Since 1981, estimates of the number of gulls in the colony have been based on the assumption that one nest represents one pair of gulls. This has been shown not to be the case, and a correction multiplier of 0.61 must be applied to counts of nests at the colony to obtain an estimate of the number of breeding gulls.     

An invasive gull displaces native waterbirds to breeding habitats more exposed to native predators

The effect of invasive opportunistic predators may include population changes in both native prey and native predators as well as alteration of predator–prey interactions. We analyzed the activity of native magpie Pica pica and changes in population, nest sites and nesting success probability of native waterbirds (namely: grebes, ducks, rails and native gulls) in response to the population growth of the invasive Caspian gull Larus cachinnans. The study was carried out at a reservoir in southern Poland and at a similar control reservoir where the Caspian gull was absent. Both the invasive gulls and the native magpie are opportunistic predators of nests of native waterbirds. The population increase of the invasive gull led to a decline in the population of native black-headed gulls Larus ridibundus only. However, the invasive gull displaced all the native species from the breeding islets located in the central part of the reservoir to islets located close to the shoreline. The latter were frequently visited by magpies, which depredated on nests along the shores, leading to an up to threefold decrease in nesting success as compared with nests located in the central area of the invaded reservoir. Predation by Caspian gulls was rarely observed. Thus, the invasion of Caspian gull caused complex direct and indirect effects on the waterbird community that included competition for breeding sites, changes in the spatial distribution of nests and alteration of predation rate by native predators. Moreover, the effects of invasion may not be reflected by changes in population size of native species.     

High connectivity in a long-lived high-Arctic seabird,the ivory gull <Emphasis Type="Italic">Pagophila eburnea</Emphasis>

Species may cope with rapid habitat changes by distribution shifts or adaptation to new conditions. A common feature of these responses is that they depend on how the process of dispersal connects populations, both demographically and genetically. We analyzed the genetic structure of a near-threatened high-Arctic seabird, the ivory gull (Pagophila eburnea) in order to infer the connectivity among gull colonies. We analyzed 343 individuals sampled from 16 localities across the circumpolar breeding range of ivory gulls, from northern Russia to the Canadian Arctic. To explore the roles of natal and breeding dispersal, we developed a population genetic model to relate dispersal behavior to the observed genetic structure of worldwide ivory gull populations. Our key finding is the striking genetic homogeneity of ivory gulls across their entire distribution range. The lack of population genetic structure found among colonies, in tandem with independent evidence of movement among colonies, suggests that ongoing effective dispersal is occurring across the Arctic Region. Our results contradict the dispersal patterns generally observed in seabirds where species movement capabilities are often not indicative of dispersal patterns. Model predictions show how natal and breeding dispersal may combine to shape the genetic homogeneity among ivory gull colonies separated by up to 2800 km. Although field data will be key to determine the role of dispersal for the demography of local colonies and refine the respective impacts of natal versus breeding dispersal, conservation planning needs to consider ivory gulls as a genetically homogeneous, Arctic-wide metapopulation effectively connected through dispersal.     

Multiple maternity in black-headed gull Larus ridibundus clutches as revealed by protein fingerprinting

Social monogamy with biparental care is the norm in gulls Laridae , but egg colour variation suggests that some nests may contain mixed clutches laid by more than one female. Here we use protein fingerprinting of egg albumen to assess the occurrence of mixed maternity clutches in three colonies of black-headed gulls. Among 160 analysed clutches with >1 egg, 34% contained eggs from more than one female, and 15% of the eggs in clutches >1 came from other females than the major female (laying most eggs in nest). Among clutches with 2–3 eggs 28% were mixed, and among clutches with 4 or more eggs 89% contained eggs from two or more females. There were significantly fewer eggs from the major female in mixed nests (mean=2.06±0.63 SD) than in non-mixed nests (mean=2.82±0.43 SD). In nests without evidence of female conflict, hatching success of minority eggs was similar to that of eggs from the major female (12.5 and 8.4%, respectively). In 21% of mixed maternity nests, one or more minority eggs was buried or punctured, and 25% of eggs from major females were also found evicted, suggesting conflict between females and rejection of eggs. Intra-specific nest parasitism seems the most likely cause of mixed clutches, but there are also other possible causes.     

Egg production in a coastal seabird, the glaucous-winged gull (Larus glaucescens), declines during the last century

Seabirds integrate information about oceanic ecosystems across time and space, and are considered sensitive indicators of marine conditions. To assess whether hypothesized long-term foodweb changes such as forage fish declines may be reflected in a consumer's life history traits over time, I used meta-regression to evaluate multi-decadal changes in aspects of egg production in the glaucous-winged gull (Larus glaucescens), a common coastal bird. Study data were derived from literature searches of published papers and unpublished historical accounts, museum egg collections, and modern field studies, with inclusion criteria based on data quality and geographic area of the original study. Combined historical and modern data showed that gull egg size declined at an average of 0.04 cc y(-1) from 1902 (108 y), equivalent to a decline of 5% of mean egg volume, while clutch size decreased over 48 y from a mean of 2.82 eggs per clutch in 1962 to 2.25 in 2009. There was a negative relationship between lay date and mean clutch size in a given year, with smaller clutches occurring in years where egg laying commenced later. Lay date itself advanced over time, with commencement of laying presently (2008-2010) 7 d later than in previous studies (1959-1986). This study demonstrates that glaucous-winged gull investment in egg production has declined significantly over the past ～50-100 y, with such changes potentially contributing to recent population declines. Though gulls are generalist feeders that should readily be able to buffer themselves against food web changes, they are likely nutritionally constrained during the early breeding period, when egg production requirements are ideally met by consumption of high-quality prey such as forage fish. This study's results suggest a possible decline in the availability of such prey, and the incremental long-term impoverishment of a coastal marine ecosystem bordering one of North America's rapidly growing urban areas.     

Spatial contraction in a large gull colony in relation to the position of arctic fox dens

Many species of colonial ground-nesting birds are known to be sensitive to predation by terrestrial predators. The response of prey under the pressure of predation can either be direct (depletion of prey) or indirect due to prey avoiding the predator. We studied the recolonization of arctic foxes into a large and growing breeding colony of lesser black-backed gulls. The gull colony reached the size of 20,000 pairs during the period of no foxes. The number of breeding gulls continued to increase after the colonization of foxes and reached a maximum of 40,000 pairs about 15 years later. During the same time period, the spatial coverage of the gull colony shrunk from 31.4 down to 18.6 km², and the change in distribution was closely linked with position of fox dens, which ranged in number from one to three annually. In 2005, the number of breeding gulls decreased slightly with an ongoing shrinkage in spatial coverage. Food analyses from fox scats and stomachs showed that birds of the order Charadriiformes, particularly gulls, were the key prey item. Survival rates of gull nests were higher in the middle of the colony than at the colony edge close to a fox den. The colony area lost could be explained solely by the number of eggs removed by foxes but is unlikely, e.g., due to reclutching. We suggest that intraspecific predation contributes additionally to the effects of direct fox predation although to an unknown degree.     

Local use of landfills by a yellow‐legged gull population suggests distance‐dependent resource exploitation

Understanding the use of feeding sources at the local scale is crucial in comprehending the factors driving population dynamics, dispersal and territory use. Many gull (Larus spp.) populations have increased sharply, which is partly promoted by their use of landfills as a food resource. Although at the large scale it is known that birds from mainland colonies feed more on landfills than those from offshore colonies, at the local scale, this distance‐dependent exploitation has been little studied. Here, then, we study whether the extent of gulls’ use of landfill is distance‐dependent through the study of 3 different gull colonies and five separate landfill sites within a relatively small geographical area. After controlling for bird numbers by both age cohort and colony, we observed that the number of gulls found at each landfill was colony dependent and that it decreased non‐linearly with increased distance to place of birth.     

Nest site selection of the Kelp gull (Larus dominicanus) in the Beagle Channel, Tierra del Fuego, Argentina

Nest site selection of Kelp gulls Larus dominicanus breeding in Conejo and Bridges islands, Tierra del Fuego, Argentina, was assessed between 14 and 30 December 2005 to describe variability in nest site features and determine variables affecting nest choice. Fourteen microhabitat variables were quantified at 40 nest sites and at 40 random points in each island during the late incubation stage. Nests at the two colonies were placed on different kinds of substrates across areas with varying degrees of cover provided either by rocks or vegetation. Despite the variability observed in nest site features, rock cover and rocky substrates were the main factors determining nest site selection. At Conejo Island, nest sites presented more rock cover, less percentage of vegetation cover and of vegetation debris substrate, and were placed further from the nearest vegetation in comparison to random points. Similarly, gulls at Bridges Island selected nest sites with more rock cover which were placed mainly on rocky and vegetation substrates. This contrasts with results previously obtained in Argentina, which indicated that vegetation is a key factor influencing Kelp gull nest site selection. Over 80% of the nests at both study colonies were placed on the northern slopes of the islands, relatively more protected from the strong prevailing southwest winds, and nests at both colonies tended to be more protected on their southern side either by rocks or vegetation. Results obtained at Tierra del Fuego confirm the plasticity of microhabitat use by Kelp gulls, and their ability to take advantage of nesting sites according to availability and local environmental factors.     

Ecology of Slaty-Backed Gull (<Emphasis Type="Italic">Larus schistisagus</Emphasis>) Breeding on Kronotskoe Lake,Kamchatka Peninsula

The slaty-backed gull population of Kronotskoe Lake has not been subjected to anthropogenic impact for many decades. The number and distribution of the breeding colonies of the slaty-backed gulls on the islands of this largest freshwater reservoir of the Kamchatka Peninsula are presented. Data on the breeding phenology, the seasonal dynamics of the food composition of breeding gulls, the foraging distance, and breeding success are considered. These data are compared to the results obtained earlier for Kuril’skoe Lake. Both gull populations are unique in that they are the only freshwater colonies within the distribution range of this marine species. The breeding success of the slaty-backed gulls on Kronotskoe Lake suffers from predation, both intra- and interspecific, in the latter case from brown bears and sea eagles. The hatching period and the fledging time of chicks in this population are both shifted to the end of summer, when gulls have the most abundant food available within the lake area, which increases successful survival of the fledglings. Despite considerable differences between the ecosystems of Kronotskoe Lake and Kuril’skoe Lake, there are several common features in the diets of the gull populations living on the lakes: (1) Despite the fact that gulls perform foraging flights to the sea coast, they only take fish and almost never collect marine invertebrates there. (2) Nearly half of all food items are taken within a 40-km distance from the colony. (3) During the growth period of chicks, gulls from both lakes rely on salmonids (anadromous in Kuril’skoe Lake, resident in Kronotskoe Lake) that they hunt in the lakes near their colonies.