Larus Delawarensis Research Articles

Rubber shots not as effective as selective culling in deterring gulls from landfill sites

Landfill managers often need to implement scaring programmes to deter gulls from feeding at their sites because the birds can be a significant nuisance for both site employees and residents of the surrounding area. Our objective was to assess the efficiency of firing rubber shots, a method assumed to be non-lethal but never tested in a bird deterrence context. This method was compared to selective culling, a well-known lethal technique that some people find ethically unacceptable. Both methods were employed in combination with the use of pyrotechnics. Our study was conducted at the Ste-Sophie landfill site near Montreal (Canada) located 37km from a Ring-billed gull (Larus delawarensis) colony supporting 48,000 pairs. Daily counts and behavioural observations were conducted throughout the breeding and post-breeding periods. Firing rubber shots was ineffective in deterring gulls as we observed the same number of birds at the landfill during periods with and without deterrence (P=0.949). However, we counted 38% less birds during the culling periods than during the rubber shot treatment (P=0.014). We detected no sign of habituation during the 7-day culling trials. Culling was also more effective in getting the gulls to leave the site than was rubber shots (47 vs. 11%; P<0.001) and the birds took longer before returning to the site (16 vs. 2min; P<0.001). Finally, the non-lethal method required an increased use of pyrotechnics to reduce the number of gulls to an acceptable level when compared to culling (P<0.001). The difference between culling and rubber shots may be related to the louder noise produced when firing steel shots and the view of dead or injured birds falling on the ground, which may be a deterrent factor for gulls. We also noted that the number of gulls was greater during the rearing stage when the birds have to feed their juveniles (P=0.005) and after 15:00h when the deterrence activities were adjourned (P=0.003). Our results clearly suggest that the deterrence efforts have to be adapted to seasonal variations in bird numbers as dietary needs are higher during the chicks’ rearing period. Any scaring programme should also be performed from dawn to dusk. In conclusion, the use of non-lethal rubber shots as applied in this study to deter gulls from feeding at landfill sites cannot be used as an effective alternative technique to culling.

North American Birds as Potential Amplifying Hosts of Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) is an emerging arbovirus, and inter-continental spread is an impending threat. The virus is maintained in a transmission cycle between mosquito vectors and vertebrate hosts, including birds. We detected variation in interspecies responses among North American birds to infection with strains of two different JEV genotypes (I and III). Several native North American passerine species and ring-billed gulls had the highest average peak viremia titers after inoculation with a Vietnamese (genotype I) JEV strain. Oral JEV shedding was minimal and cloacal shedding was rarely detected. The majority of birds, both viremic (72 of 74; 97.3%) and non-viremic (31 of 37; 83.8%), seroconverted by 14 days post-inoculation and West Nile virus-immune individuals had cross-protection against JEV viremia. Reservoir competence and serologic data for a variety of avian taxa are important for development of JEV surveillance and control strategies and will aid in understanding transmission ecology in the event of JEV expansion to North America.

Novel Flame Retardants in Urban-Feeding Ring-Billed Gulls from the St. Lawrence River, Canada

This study investigated the occurrence of a comprehensive suite of polybrominated diphenyl ethers (PBDEs) and current-use flame retardants (FRs) in ring-billed gulls breeding in a highly industrialized section of the St. Lawrence River, downstream from Montreal (QC, Canada). Despite major point-sources and diffuse contamination by FRs, nearly no FR data have been reported in birds from this area. Bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (BEHTBP) was detected in 89% of ring-billed gull livers (mean: 2.16 ng/g ww; max: 17.6 ng/g ww). To our knowledge, this is the highest detection frequency and highest concentrations reported thus far in any avian species or populations. Dechlorane Plus (DP) isomers were also particularly abundant (anti-DP detected in 100% and syn-DP in 93% of livers). Other detected FR compounds (3-14% detection) included 2-ethylhexyl-2,3,4,5-tetrabromobenzoate (EHTBB), hexachlorocyclopentenyl-dibromocyclooctane (HCDBCO) and β-1,2-dibromo-4-(1.2-dibromoethyl)-cyclohexane (β-TBECH). Mean BDE-209 (57.2 ± 12.2 ng/g ww) in ring-billed gull livers was unexpectedly high for this midtrophic gull species, exceeding levels reported in several apex raptors such as peregrine falcons. BDE-209's relative contribution to ∑PBDEs was on average 25% (exceeding BDE-47 and BDE-99) and contrasted with profiles typically reported for fish-eating gull species. The present study highlighted preoccupying gaps in upcoming FR regulations and stressed the need for further investigation of the sources of FR exposure in highly urbanized areas.

Sex‐biased resource allocation in ovo in a sexually size‐dimorphic species

Sex‐biased resource allocation in eggs is increasingly recognized as one strategy oviparous mothers can employ to invest differentially in one sex, depending on nutritional requirements. Previous studies have used egg size as an index of nutrient allocation, but few have examined egg contents directly. We used molecular sexing of early‐stage ring‐billed gull Larus delawarensis embryos, a species with sexual size dimorphism, to test whether sex‐specific nutrient allocation occurs in ovo. Despite no sex difference in size, eggs with male embryos contained more albumen, while eggs with female embryos contained more yolk, lipid and non‐lipid (protein and carbohydrate). It is unclear why such sex‐biased resource allocation in ovo is utilized by ring‐billed gulls. However, our data indicate that a cursive examination of egg mass or size may not necessarily reflect nutrient allocation strategies mothers use in ovo, and that sex‐biased investment in ovo may be more widespread than currently appreciated.

Evidence of social information on food location in a ring-billed gull colony, but the birds do not use it

Bird colonies are potentially rich sources of social information that can be used to compensate for the numerous disadvantages of communal life. This information can reduce uncertainty about nest locations, mates or food sources. However, there is little empirical evidence that colonies can actually serve as an information exchange point. We asked whether a large nesting colony of ring-billed gulls, Larus delawarensis , could provide its members with social information about the quality and location of food resources during the chick-rearing period. We first determined whether social information was available in the colony, then whether it was signalled by some reliable cue, and finally, whether the birds used it by following knowledgeable individuals. We combined observations of flight departure bearings at the colony with flight tracks obtained from birds fitted with global positioning system (GPS) data loggers. We found that reliable information about feeding site locations could be obtained by observing the vanishing bearings of gulls leaving their nest. Birds nesting in different parts of the colony flew in different directions to reach their feeding grounds, but this did not influence the type of food brought to the chicks. To test whether gulls actually followed departing individuals, we searched for temporal clumping of departures and bearings for different time intervals during a day. We found that departures of gulls nesting in the same neighbourhood were not temporally clustered, nor did the gulls tend to leave in the same direction as their previously departing neighbours. We conclude that ring-billed gulls do not appear to use social information at the nest site to locate foraging opportunities. However, stopovers on nearby water or along the colony edge after a short flight from the nest could allow exchange of information that we could not document. ► Reliable information about feeding sites is available in a gull colony. ► Information could be obtained from vanishing bearings of gulls leaving their nest. ► Departures of neighbourhood gulls were not temporally clumped. ► Gulls did not leave in the same direction as their previously departing neighbours. ► We conclude that no information appears to be obtained at the nest site.

Egg Oiling to Reduce Hatch-Year Ring-Billed Gull Numbers on Chicago’s Beaches During Swim Season and Water Quality Test Results

A burgeoning ring-billed gull population along Chicago's Lake Michigan beaches contributes to degraded water quality through fecal contamination. Egg oiling was conducted at Chicago's gull colonies to reduce production and the influx of hatch-year (HY) gulls using Chicago's beaches, with a second, long-term objective of eventually reducing adult gull numbers through attrition. We also investigated swim season water quality trends through the course of this work. From 2007 to 2009, 52, 80, and 81%, of nests at the two primary nest colonies had their eggs rendered inviable by corn oil application. Counts of HY and after hatch-year (AHY) gulls were analyzed during treatment years for 10 beaches. Water quality data were available from the Chicago Park District during our three treatment years and the prior year (baseline) for 19 beaches. HY counts declined at all 10 surveyed beaches from the initial year (52% nests with oiled eggs) to subsequent years with ~80% of nests oiled. Overall, HY gulls numbers on beaches decreased 86% from 2007 to 2009. Decreases in beach usage by AHY gulls were not detected. Compared to pretreatment, the number of beaches with improved water quality test rates increased each year through the course of the study. The frequency of water quality tests showing bacterial exceedances compared to 2006 declined at 18 of 19 beaches by 2009. Egg oiling resulted in fewer HY gulls using Chicago's beaches and was likely a beneficial factor for reduced frequencies of swim advisories and swim bans.

Are Lice Associated with Ring-Billed Gull Chick Immune Responses?

Abstract. Little is known about whether chewing lice (Insecta: Phthiraptera) suppress or activate immunity in birds. Here, relationships between lice (Quadraceps punctatus, Saemundsonnia lari and Austromenopon transversum) and immune parameters were evaluated in Ring-billed Gull (Larus delawarensis) chicks. Eosinophils made up greater proportions of leukocytes in chicks with more lice (partial r = 0.64, P < 0.001), suggesting louse-induced immunoactivation via either eosinophil production or redistribution to peripheral blood. However, there were no significant relationships between lice and other immune parameters (proportion heterophils, proportion lymphocytes, heterophil:lymphocyte ratio, response to injection with phytohaemagglutinin). Collectively, results suggest only minor immune responses to lice, but experimental manipulations of louse infestations are needed to better quantify these responses and evaluate their potential consequences for fitness.

First record of Ring-billed Gull Larus delawarensis for The Gambia

First record of Ring-billed Gull Larus delawarensis for The Gambia

The decay of parasite community similarity in ring‐billed gulls Larus delawarensis and other hosts

The similarity of parasite communities often decays with increasing geographic distance. Here, geographic distance decay is evaluated in parasite communities of 145 ring‐billed gulls from six localities in Quebec, Canada, among both individual gulls and gull populations. Spatial decay in similarity is compared to temporal decay, using host age differences as a distance measure. The similarity of parasite communities of individual gulls from localities spanning 300 km within Quebec is more strongly associated with host age differences than with geographic distance. Among gull populations in Quebec, only geographic distance is significantly related to parasite community similarity. The explanatory power of geographic distance is higher still when data from Quebec are combined with those from a study conducted 3000 km away, indicating an effect of spatial scale on geographic distance decay. The rate at which parasite community similarity decays with distance in gulls is compared with that of 17 other host species using data from published studies. Spatial scale explains two thirds of the variance in distance decay rates, and some of the remaining variance is explained by latitude. The rate of decay in parasite community similarity with distance is greater in larger scale studies and further away from the equator. Traits of host species traits such as vagility, body weight and trophic level have little or no effect on distance decay rates.

Waterfowl Abundance Does Not Predict the Dominant Avian Source of Beach Escherichia coli

The horizontal, fluorophore enhanced, rep-PCR (HFERP) DNA fingerprinting technique was used to identify potential sources of in water, nearshore sand, and sediment at two beaches in the Duluth-Superior Harbor, near Duluth, MN, and Superior, WI, during May, July, and September 2006. An animal or environmental source could be identified for 35, 29, and 30% of strains in water, sand, and sediments, respectively. Waterfowl, including Canada geese, ring-billed gulls, and mallard ducks, were the largest source of that could be identified in water (55-100%), sand (59-100%), and sediment (92-100%) at both beaches. Although ring-billed gulls were more abundant in this harbor, Canada geese were usually the dominant source of waterfowl found at these beaches. The percentage of identified from treated wastewater was always less than the percentage of originating from waterfowl. At both beaches, the percentage of in water contributed by treated wastewater was higher in May compared with July and September. The larger proportion of wastewater-derived seen in May probably reflected a smaller contribution of from geese when these birds were less abundant rather than an absolute increase in from treated wastewater. Microbial source analysis and bird census data both indicated that waterfowl were a major source of at beaches in the Duluth-Superior Harbor. These data also indicated it is risky to assume that the most abundant waterfowl species present in waterways will also be the largest source of avian-derived in water, nearshore sand, and sediments at beaches.

Simple and inexpensive devices to measure heart rates of incubating birds

Heart rate is a useful physiological index for studies of stress, locomotion, and activity patterns. Measuring heart rates of birds without the need to handle individuals is desirable when trapping is problematic or may cause unwanted disturbance. Heart-rate recorders housed in dummy eggs offer an effective solution, but the usefulness of previously described devices is limited by their size, complex construction, and reliance on analog media. We constructed egg-based, heart-rate monitors through simple modifications of inexpensive, commercially available MP3 players and Bluetooth headsets. We compared the merits of each device during tests in the laboratory, an aviary, and the field in 2008. Field testing was undertaken at Presqu'ile Provincial Park, Ontario, Canada, where we recorded heart rates of Common Terns (Sterna hirundo), Caspian Terns (Hydroprogne caspia), and Ring-billed Gulls (Larus delawarensis). Birds incubated dummy eggs normally, with no differences in behavior (all P > 0.05) when incubating either wired (MP3 players) or wireless (Bluetooth) devices. MP3 devices were more reliable in the field. Bluetooth devices often lost pairing with laptop computers (33% of files analyzed contained no signal), produced files with more obscuring noise, and only two could be deployed simultaneously with a single computer; there was no limit on how many MP3 devices could be deployed simultaneously. Common Terns, the smallest of our three focal species, had significantly higher (P < 0.001) mean heart rates (268.6 ± 9.3 beats per min (bpm)) than either Ring-billed Gulls (198.0 ± 7.1 bpm) or Caspian Terns (204.2 ± 8.0 bpm). Heart rates of all three species were consistent with those reported or predicted from previous studies. The MP3 devices we describe provide investigators with a simple, inexpensive, and minimally invasive way to digitally record heart rates of birds of almost any size.

Population Trends of Ring-billed Gulls Breeding on the North American Great Lakes, 1976 to 2009

After near extirpation in the early 20th century, Ring-billed Gulls (Larus delawarensis) are currently (2009) the most abundant colonial waterbird nesting on the Great Lakes. Nest count data are reported from four decadal censuses (1976–2009) conducted by the Canadian Wildlife Service and the U.S. Fish and Wildlife Service. Numbers increased from 305,790 nests (1976–80) to a peak of 718,887 nests (1989–90), then decreased to 652,664 (1997–2000) and to 585,984 nests (2007–09). Changes varied spatially after the second census with greatest losses (-38.6%) at North Channel, Georgian Bay and northern Lake Huron colonies, and greatest gains ( 324.2%) at Lake Michigan colonies. A total of 472 sites had nests in at least one census (Canada N = 319; U.S. N = 153). Eighteen (3.8%) colonies had >2,000 nests in all four censuses, and had 37.5–41.9% of all nests in each census. Site occupancy was fluid. A high proportion (56.8%, N = 268) of sites contained nests in only one of the four censuses, and few (N = 40, 8.5%) had nests in all censuses. Thirty-nine sites had >2,000 nests gains/losses between census periods; 14 (35.9%) were on urban/industrial lands with artificial substrates. Human management and predator activities at some colonies contributed to declines in nest numbers at these locations. Movement of breeding birds among colonies and changes in local food supply may have influenced changes in nest numbers elsewhere. Reasons for the overall nest losses across the Great Lakes after the second census are unknown.

Perfluoroalkyl carboxylates and sulfonates and precursors in relation to dietary source tracers in the eggs of four species of gulls ( Larids) from breeding sites spanning Atlantic to Pacific Canada

In the present study, we identified and examined the spatial trends, sources and dietary relationships of bioaccumulative perfluorinated sulfonate (PFSA; C 6, C 8, and C 10 chain lengths) and carboxylate (PFCA; C 6 to C 15 chain lengths) contaminants, as well as precursor compounds including several perfluorinated sulfonamides, and fluorotelomer acids and alcohols, in individual eggs (collected in 2008) from four gull species [glaucous-winged ( Larus glaucescens), California ( Larus californicus), ring-billed ( Larus delawarensis) and herring ( Larus argentatus) gulls] from 15 marine and freshwater colony sites in provinces across Canada. The pattern of PFSAs was dominated by perfluorooctane sulfonate (PFOS; > 89% of ΣPFSA concentration) regardless of egg collection location. The highest ΣPFSA concentrations were found in the eggs collected in the urbanized areas in the Great Lakes and the St. Lawrence River area [Big Chicken Island 308 ng/g ww, Toronto Harbour 486 ng/g ww, and Ile Deslauriers (HG) 299 ng/g ww]. Also, eggs from all freshwater colony sites had higher ΣPFSA concentrations, which were significant ( p < 0.05) in many cases, compared to the marine sites with the exception of the Sable Island colony in Atlantic Canada off the coast of Nova Scotia. C 6 to C 15 chain length PFCAs were detected in the eggs, although the pattern was variable among the 15 sites, where PFUnA and PFTrA dominated the pattern for most colonies. Like the ΣPFSA, the highest concentrations of ΣPFCA were found in the eggs from Big Chicken Island, Toronto Harbour, Ile Deslauriers (HG), and Sable Island, although not all freshwater sites had higher concentrations compared to marine sites. Dietary tracers [δ 15N and δ 13C stable isotopes (SIs)] revealed that PFSA and PFCA exposure is colony dependent. SI signatures suggested that gulls from most marine colony sites were exposed to PFCs via marine prey. The exception was the Mandarte Island colony in Pacific British Columbia, where PFSA and PFCA exposure appeared to be via terrestrial and/or freshwater prey consumption. The same was true for the freshwater sites where egg SIs suggested both aquatic and terrestrial prey consumption as the source for PFC exposure depending on the colony. Both aquatic (marine and freshwater) and terrestrial prey are likely sources of PFC exposure to gulls but exposure scenarios are colony-specific.

Reporting Difference for Colored Patagial Tags on Ring‐Billed Gulls

ABSTRACT The possible role of tag color in mediating behaviors that could bias resighting rate has not been examined. In a study that began in 2007, we marked 725 ring‐billed gulls (Larus delawarensis) with Bondcote royal blue, green, yellow, or orange patagial tags. Reports we gathered over 2 years indicated approximately a 3.4:1 bias in resighting rate toward yellow or orange tags. The observed bias is inconsistent with color‐associated visibility bias or differential mortality among color‐tagged breeding adults. Potential behavioral effects of tag color on individuals and conspecifics should be considered by biologists when planning marking studies.

Avian Influenza Virus H13 Circulating in Ring-Billed Gulls (Larus delawarensis) in Southern Ontario, Canada

Avian influenza virus (AIV) was studied in ring-billed gulls (Larus delawarensis) in one breeding colony on Lake Erie in 2000, and two on Lake Ontario in both 2000 and 2004. Antibodies to H13 AIV were detected in 92% of adults in 2000 and 82% in 2004. Antibody prevalence in 3-wk-old chicks was 5%-30% (overall 15%) in 2000 and 21% and 76% (overall 48%) in 2004. In 5-wk-old chicks, antibody prevalence was 23%-75% (overall 53%) in 2000 and 53% and 79% (overall 66%) in 2004. Geometric mean antibody titers at 3 and 5 wk did not differ in 2000, but increased significantly at one colony in 2004. In 2000, overall prevalence of AIV isolation from cloaca in embryonated chicken eggs was 32% (3 wk old), 13% (5 wk old), and 0 (adults), but AIV was also isolated from kidney and lung in a high proportion of tissues cultured from 3-wk-old birds in one colony. Isolates from cloaca were characterized as subtype H13 by serology; all 15 tested for neuraminidase were H13N6. However, three AIV detections considered on the basis of nucleotide sequence to be subtype H16 were among the 28 detected retrospectively by PCR in archived cloacal swabs; the remainder were subtype H13. Outcome of virus isolation was not related to presence of antibody titers in chicks. The presence of antibody to AIV in chicks was associated significantly with inflammation in heart, kidney, pancreas, and liver. AIV was not isolated in 2004. AIV infected chicks annually within the first 3 wk of life, ultimately infecting the majority of birds in most colonies, but did not appear to cause clinical disease.

The Chicago Ring-Billed Gull Damage Management Project

The population of ring-billed gulls in the upper Midwest has increased exponentially in recent decades leading to a variety of conflicts including property damage, negative economic impacts, threats to human safety, and potential threats to human health. Some studies have suggested a link between gull fecal droppings and elevated Escherichia coli levels, which result in swim advisories and bans on public beaches. The objectives of the Chicago ring-billed gull damage management project were to reduce the local production of ring-billed gulls, to evaluate the affects limiting gull production has on gull use of beaches, and to reduce the severity of conflicts with gulls including the issuance of swim advisories and swim bans. Between 2007 and 2009, we applied corn oil to 52 - 80% of nests in 2 large gull colonies in Chicago and successfully reduced hatching success and subsequent fledging of 18,000 - 42,000 gulls per year without causing colony abandonment. Fewer hatch year gulls were observed in 2009 on Chicago’s beaches compared to 2007. The reduction in the number of gulls using Chicago beaches has contributed to a reduction in conflicts with gulls, including a decrease in the frequency of swim advisories/bans on Chicago’s beaches in comparison to 2006.

Sources of Food Delivered to Ring-Billed, Herring and Great Black-Backed Gull Chicks in Marine Environments

Beginning in the 1960s, Ring-billed Gulls' (Larus delawarensis) historic breeding range expanded from inland habitats and freshwater wetlands to marine sites in Atlantic North America. Adults winter on salt water but salt tolerance may entail costs (e.g. maintenance of salt glands) and favor reduced parental use of marine resources for feeding chicks. Diets of Ring-billed Gull chicks nesting on a marine island off Prince Edward Island, Canada, were investigated using soft regurgitant collection and stable isotope (δ13C and δ15N) analysis of both regurgitants and blood samples. Isotopic signatures in blood of chicks of Ring-billed and sympatrically-nesting Herring (L. argentatus) and Great Black-backed Gulls (L. marinus) were also compared. Regurgitants of Ring-billed Gull chicks contained freshwater/ terrestrial and marine invertebrates and fish. A stable isotope mixing model incorporating both δ13C and δ15N in chick regurgitants and blood estimated that 42.2% of Ring-billed Gull chick diet came from the marine environment, whereas estimates from blood for Herring and Great Black-backed Gulls were 43.6%, and 73.5%, respectively. Further, differences existed among gull species in estimates for dietary contribution from various food sources from marine and terrestrial/freshwater environments. Although Ring-billed Gulls can use marine food sources to feed their young, whether salt in marine food imposes a physiological cost on these young in comparison to young reared exclusively on non-marine foods is unclear.

Distribution and abundance of nesting common and Caspian terns on the North American Great Lakes, 1976 to 1999

Canadian and US federal wildlife agencies completed three surveys (1976–1980, 1989–1991, and 1997–2000) to census colonial waterbirds breeding on the Great Lakes. We here summarize and comment on nest numbers and colony site distribution of common terns ( Sterna hirundo) and Caspian terns ( Hydroprogne caspia). Common terns are in serious trouble on the Great Lakes. Numbers declined with substantial losses in nests (− 19.1%) and colony sites (− 23.2%) between the first and third censuses. An increase in numbers at US sites (+ 26.6%) did not compensate for losses (− 33.1%) at Canadian sites. Caspian terns increased in nest numbers (+ 65.9%) and colony sites (+ 50.0%) over the same period. The increase at US sites (136.5%) was greater than at Canadian sites (11.5%). Most (70.7%, n = 186) common tern sites had nests during only one census; 17 sites (6.5%) had nests during all censuses. In contrast, 9 of 33 (27.2%) Caspian tern sites had nests during all censuses and contained a majority of nests (50–82%) in each census. Pairs of both species nested on natural substrates across the Great Lakes. Common terns nested mostly on artificial (human-constructed) substrates on the lower Great Lakes. We identify site characteristics that may have contributed to long-term (three census) occupancy by common terns (small size, artificial substrates, absence of ring-billed gulls) and Caspian terns (natural substrates on large, remote islands). We suggest an urgent need for protection and conservation of common tern colonies and identify specific priority sites for implementation of management protocols.

Bacteroidales Diversity in Ring-Billed Gulls ( Laurus delawarensis ) Residing at Lake Michigan Beaches

This study investigated the occurrence and diversity of Bacteroidales fecal bacteria in gulls residing in the Great Lakes region. Members of this bacterial order have been widely employed as human and bovine host-specific markers of fecal pollution; however, few studies have focused on gulls, which can be a major source of fecal indicator bacteria and pathogens at beaches. We found a low but consistent occurrence of Bacteroidales in gulls at five beaches in three different counties spanning the Wisconsin shoreline of Lake Michigan. The percentages of gulls positive for Bacteroidales were 4 to 8% at beaches in the southern part of the state and 8 to 50% at beaches in the north. Sequencing of 931 clones from seven gull Bacteroidales 16S rRNA gene libraries revealed a large amount of diversity in both individual and pooled gull fecal samples. Two libraries constructed from pooled gull fecal samples (n = 5 and n = 6) did not have a greater richness of sequences than individual samples, suggesting that even within a single gull diversity is high and an extensive sequencing effort is needed to characterize the populations. Estimates of the numbers of operational taxonomic units (OTUs) for the libraries obtained using different similarity levels revealed a large amount of microdiveristy with a limited number of OTUs at the 95% similarity level. Gull sequences were clustered by the beach from which they were collected, suggesting that there were geographic effects on the distribution of Bacteriodales. More than 53% of the 16S rRNA gene sequences from gulls at the southern beaches were associated with the family Porphyromonadaceae, primarily the genus Parabacteroides, whereas sequences from gulls at the northern beaches were comprised of Bacteroidaceae and Prevotellaceae sequences. Comparison of gull sequences with sequences from goose, canine, raccoon, and sewage sources revealed distinct clusters of closely related gull sequences; however, these sequences were widely dispersed across a dendrogram that included all other sources, including previously characterized gull Bacteroidales from other studies, suggesting that geographic influence or simply sample representation plays a greater role in the observed population structure than strictly the host gut environment.

Egg coloration in ring-billed gulls (Larus delawarensis): a test of the sexual signaling hypothesis

Although many avian eggs appear to be cryptically colored, many species also lay vibrant blue green eggs. This seemingly conspicuous coloration has puzzled biologists since Wallace, as natural selection should favor reduced egg visibility to minimize predation pressure. The sexual signaling hypothesis posits that blue green egg coloration serves as a signal of female quality and that males exert post-mating sexual selection on this trait by investing more in the nests of females laying more intensely blue green eggs. This hypothesis has received mixed support to date, and most previous studies have been conducted in cavity-nesting species where male evaluation of his partner’s egg coloration, relative to that of other females, may be somewhat limited. In this study, we test the sexual signaling hypothesis in colonially nesting ring-billed gulls (Larus delawarensis) where males have ample opportunity to assess their mate’s egg coloration relative to that of other females. We used correlational data and an experimental manipulation to test four assumptions and predictions of the sexual signaling hypothesis: (1) blue green pigmentation should be limiting to females; (2) extent of blue green egg coloration should relate to female quality; (3) extent of blue green egg coloration should relate to offspring quality; and (4) males should provide more care to clutches with higher blue green chroma. Our data provide little support for these predictions of the sexual signaling hypothesis in ring-billed gulls. In light of this and other empirical data, we encourage future studies to consider additional hypotheses for the evolution of blue green egg coloration.