Common Terns Research Articles

Quantifying the Effects of Research Band Resighting Activities on Staging Terns in Comparison to Other Disturbances

Abstract. Avian research that involves potential disturbance to the study species may have unintended fitness consequences and could lead to biases in measurements of interest. The effects of band resighting on the behavior of mixed-species flocks of staging waterbirds were evaluated against recreational pedestrian activity that was expected to cause flushing. We found a model with additive effects of distance (near, 0-50 m, or far, 50-200 m) and disturbance type (researcher or pedestrian) best explained flock behaviors. The proportion of staging flocks that flushed in response to pedestrians was greatest when pedestrians were within 50 m of the flock. Virtually no flushes were observed in response to researchers, regardless of distance. These results could assist in alleviating concerns that accepted protocols used for intensive band resighting studies on staging seabirds of special conservation status, such as Roseate (Sterna dougallii) and Common (S. hirundo) terns, may have adverse effects. Our framew...

Changes in White Blood Cell Parameters of Common Terns (Sterna hirundo) Exposed to Low Levels of Oil

Abstract. Little is known about sublethal effects on birds of low level exposure to oil. White blood cell parameters (total leukocyte counts and/or differentials) were measured in blood samples from Common Terns (Sterna hirundo; n = 71) exposed to low levels of oil from an oil spill in Buzzards Bay, Massachusetts, in 2003. Data from Common Terns (n = 16) sampled at the same site in a non-spill year were used for reference. Total leukocytes and lymphocytes were severely depressed when individuals were first sampled, 14–20 days after the spill, and returned to near to or above reference levels by day 39. Heterophils and heterophil/lymphocyte ratios were markedly elevated 14–20 days after the spill, and returned to below reference levels by day 39. These changes were closely parallel to changes in hematocrit in the same birds, but hematocrits were not correlated with white blood cell parameters, suggesting that mechanisms of action were different. The combination of immune suppression and anemia during the p...

The Influence of Spring Flood Water Levels on the Distribution and Numbers of Terns (On the Example of the Lower Desna River)

The floodplain reservoirs of the lower Desna River are known to represent suitable breeding habitats for the Black Tern (Chlidonias niger) and the White-winged Tern (Chlidonias leucoptera), while the Common Tern (Sterna hirundo) and the Little Tern (Sterna albifrons) nest on sandy islands and river spits at the river bed. We combined analysis of Landsat 8 satellite images and the breeding abundance of the lower Desna River resident terns to investigate if the levels of the floodplain inundation affect the terns’ distribution and numbers. Under the high flood conditions of 2013, we observed a significant decrease in the numbers of colonies and nesting pairs of the Common and Little Terns, which was probably caused by the delayed exposure of their breeding habitats at the river bed. In contrast, in the low water conditions of 2014, areas of sandy islands and river spits increase in the form of temporary sandbanks. Under low-water conditions, we observed a marked increase of the number of colonies and nesting pairs of the Little Tern, while the White-winged Tern disappeared from nesting sites and the Black Tern decreased in numbers.

Adult Survival and Breeding Dispersal of Common Terns (Sterna hirundo) in a Declining Population

Abstract. The population of Common Terns (Sterna hirundo) in Barnegat Bay, New Jersey, USA, has recently experienced poor productivity with complete or near-complete breeding failure at multiple colonies, and the number of breeding pairs has declined. Adult Common Terns were captured and banded at Pettit Island from 2010 through 2014 and at four additional islands from 2011 through 2014. Although the number of breeding pairs on Pettit Island decreased and reproductive success was generally poor, this colony was more productive than the other colonies. Data from the other colonies were too sparse to treat each site separately, and the analysis is instead based on two “locations”: Pettit Island and all other sites. Apparent survival and movement probabilities were estimated using multistate capture-recapture modeling based on recaptures combined with resighting of color-banded Common Terns. The two best supported models included location, transience, and presence or absence of color bands as variables and p...

Facultative Interspecific Brood Parasitism in Colonial Breeding Waterbirds in Biebrza National Park, Poland

Abstract. Interspecific brood parasitism occurs when the eggs of one species are laid in the nest of a different species, but evidence of this phenomenon is scarce. Facultative interspecific brood parasitism has been described in Charadriiformes. However, to our knowledge, our study provides the first documentation of facultative interspecific brood parasitism in the colonially breeding species we studied. The factors affecting its frequency in relation to colony species composition, nest density, and period of the breeding season was analyzed. Between 2006 and 2012, we monitored 2,493 nests of five species: Northern Lapwing (Vanellus vanellus; n = 745), Common Redshank (Tringa totanus; n = 467), Black-tailed Godwit (Limosa limosa; n = 237), Black-headed Gull (Chroicocephalus ridibundus; n = 932) and Common Tern (Sterna hirundo; n = 112). Facultative interspecific brood parasitism was observed in 1.3% of all nests. Typically, a single egg was laid in a host nest (59.4% of parasitized nests), and a maximum...

Effects of aircraft and recreation on colonial waterbird nesting behavior

ABSTRACTBecause of the variability in the types of human activities to which animals are exposed and the associated responses by different species, there is a lack of consensus on the effects of humans on wildlife behavior. We studied the effects of military air traffic, all‐terrain vehicles, off‐road vehicles, and pedestrians on the nesting behaviors of least terns (Sternula antillarum), common terns (Sterna hirundo), gull‐billed terns (Gelochelidon nilotica), and black skimmers (Rynchops niger) at North Core Banks, Cape Lookout National Seashore (CALO), North Carolina. We deployed digital audio recorders and time‐lapse cameras within 9 colonies from May to August 2010–2011 and sampled nesting behaviors before, during, and after human activities. There was no evidence that military or civilian aircraft adversely affected incubation behavior for any of the focal species. The mean incubation rate by least terns was less during pedestrian events than control periods (91% vs. 79%, S = −2.2, P = 0.04). The current patterns of aircraft operations are unlikely to affect colonial waterbird demographics. Current beach management policies restricting human activity to >50 m from colony boundaries mitigated adverse impacts to nesting colonial waterbirds. © 2015 The Wildlife Society.

Sex-specific pathways of parental age effects on offspring lifetime reproductive success in a long-lived seabird.

The conditions under which individuals are reared vary and sensitivity of offspring to such variation is often sex-dependent. Parental age is one important natal condition with consequences for aspects of offspring fitness, but reports are mostly limited to short-term fitness consequences and do not take into account offspring sex. Here we used individual-based data from a large colony of a long-lived seabird, the common tern Sterna hirundo, to investigate longitudinal long-term fitness consequences of parental age in relation to both offspring and parental sex. We found that recruited daughters from older mothers suffered from reduced annual reproductive success. Recruited sons from older fathers were found to suffer from reduced life span. Both effects translated to reductions in offspring lifetime reproductive success. Besides revealing novel sex-specific pathways of transgenerational parental age effects on offspring fitness, which inspire studies of potential underlying mechanisms, our analyses show that reproductive senescence is only observed in the common tern when including transgenerational age effects. In general, our study shows that estimates of selective pressures underlying the evolution of senescence, as well as processes such as age-dependent mate choice and sex allocation, will depend on whether causal transgenerational effects exist and are taken into account.

Variation in Population Synchrony in a Multi-Species Seabird Community: Response to Changes in Predator Abundance.

Ecologically similar sympatric species, subject to typical environmental conditions, may be expected to exhibit synchronous temporal fluctuations in demographic parameters, while populations of dissimilar species might be expected to show less synchrony. Previous studies have tested for synchrony in different populations of single species, and those including data from more than one species have compared fluctuations in only one demographic parameter. We tested for synchrony in inter-annual changes in breeding population abundance and productivity among four tern species on Coquet Island, northeast England. We also examined how manipulation of one independent environmental variable (predator abundance) influenced temporal changes in ecologically similar and dissimilar tern species. Changes in breeding abundance and productivity of ecologically similar species (Arctic Sterna paradisaea, Common S. hirundo and Roseate Terns S. dougallii) were synchronous with one another over time, but not with a species with different foraging and breeding behaviour (Sandwich Terns Thalasseus sandvicensis). With respect to changes in predator abundance, there was no clear pattern. Roseate Tern abundance was negatively correlated with that of large gulls breeding on the island from 1975 to 2013, while Common Tern abundance was positively correlated with number of large gulls, and no significant correlations were found between large gull and Arctic and Sandwich Tern populations. Large gull abundance was negatively correlated with productivity of Arctic and Common Terns two years later, possibly due to predation risk after fledging, while no correlation with Roseate Tern productivity was found. The varying effect of predator abundance is most likely due to specific differences in the behaviour and ecology of even these closely-related species. Examining synchrony in multi-species assemblages improves our understanding of how whole communities react to long-term changes in the environment and suggests that changes in predator abundance may differentially affect populations of sympatric seabird species.

In search of the gap: temporal and spatial dynamics of settling in natal common tern recruits

In colonial birds, criteria used for the first choice of a nest site and its temporal and spatial dynamics are rarely studied. This paper addresses first settlement of natal recruits in common terns Sterna hirundo at a stable colony site subdivided into six islands of equal size and habitat. Using extensive individual-based data of aged and sexed individuals with known recruitment age, I focus on timing of laying, island selection in relation to density and centrality, and movements after first breeding. Recruits’ laying date was timed between that of experienced and replacement breeders. The proportion of early clutches, density, and age of breeders were higher at the islands’ edge (the preferred area), whereas late clutches predominated at the center. Sixty-eight percent of recruits settled at the center and only 32 % at the islands’ edge. With advancing age, breeders shifted nest sites from the island center towards the edge. In 7 out of 18 years, annual recruit numbers were not evenly distributed among the islands. Density did not affect island selection, but in years with low numbers of recruits, their aggregation was more distinct. Recruits’ preference of a specific island rarely lasted more than 2 years. Depletion of the central area in the year after recruitment initially attracted new recruits before succeeding cohorts switched to another island. The dynamics of recruits’ settlement indicate diverging tendencies of attracting or repelling recruits at a specific subcolony, affected by group adherence and cohort size, density, and advancing laying date with age and shifts of nest sites towards the preferred subcolony periphery.

Migration routes and non-breeding areas of Common Terns (Sterna hirundo) from the Azores

We describe the migration routes and non-breeding areas of Common Terns (Sterna hirundo) from the Azores Archipelago, based on ringing (banding) recoveries and tracking of three birds using geolocators. Over 20 years, there have been 55 transatlantic recoveries of Common Terns from the Azores population: six from Argentina and 49 from Brazil. The three tracked birds migrated south in different months (August, September, November), but the northern migration was more synchronous, with all leaving in April. The birds were tracked to three areas of the South American coast: the male spent November—April on the northern Brazilian coast (13°N–2°S), whereas the two females first spent some time off central-eastern Brazil (4–16°S; one for 1 week, the other for 3 months) and then moved south to the coast of south-eastern Brazil, Uruguay and northern Argentina (24–39°S). Although caution is needed given the small sample size and errors associated with geolocation, the three tracked terns potentially travelled a total of ∼23 200 km to and returning from their non-breeding areas, representing an average movement of ∼500 km day−1. With the exception of Belém, in northern Brazil, and Lagoa do Peixe, in southern Brazil, the coastal areas used by the tracked birds were also those with concentrations of ringing recoveries, confirming their importance as non-breeding areas for birds from the Azores.

Playing the field.

I grew up in the New York suburbs, a world of small lawns and scattered parks, but I spent most of my summers in rural upstate New York, roaming the woods. The creatures I found there fascinated me, so I went to college to study biology. One summer, I spent 2 weeks at a field station—Great Gull Island in Long Island Sound, off the coast of Connecticut—banding terns. My time there planted the seed that matured into a rewarding career and, ultimately, took me back to the woods. ![Figure][1] “I lived in the rainforest and woke to the sound of howler monkeys.” ILLUSTRATION: ROBERT NEUBECKER Great Gull Island is owned by the American Museum of Natural History (AMNH). It's a former military base used mainly to study the common and roseate terns that nest there every summer. It isn't far offshore, but to me it felt remote. The boat came twice a week, on Fridays to bring food and weekend visitors and on Sundays to take the weekenders home. The buildings were old, with no electricity or running water. I didn't care. After graduating from college, I drifted a while, then returned to New York and took a waitressing job. I wanted to get back to biology, so I volunteered at AMNH. Great Gull Island was normally used only during summer, but I learned about a fall project studying bird migration along the Atlantic coast. I quit my job and returned to the island. During the day, I removed birds from mist nets and banded and released them. At night, I played cards with the other staff members by candlelight. I watched the seasons change. Every evening at dusk, a snowy owl emerged from the old gun emplacement where it hunkered down during the day and flew off over the ocean. I enrolled in a master's degree program at the Yale School of Forestry and Environmental Studies. While I was there, I took a semester off to work at another field station, on Barro Colorado Island in Panama, a former hilltop that was marooned when the Panama Canal flooded the area. I lived in the rainforest and woke to the sound of howler monkeys. I spent days watching lizards and recording their behavior. Once, I returned to my room at the end of the day and found it invaded by army ants. I moved to Cornell University for a Ph.D. studying interactions between herbivorous insects and host plants. Then came a search for faculty positions, which led me to a teaching post at a liberal arts college. What I enjoyed most about that work, I found, was taking students outside: getting them on snowshoes, sending them out to catch grasshoppers, taking them canoeing. But full-time teaching had never been my dream, and when I saw an ad for a field station job, I applied. Now I'm manager of the University of Wisconsin-Milwaukee Field Station in Saukville, Wisconsin. I've been here 15 years. It's the perfect job. I have a research program. I teach and advise. I facilitate research projects and support the teachers who bring classes here. I participate in the management of the land, at the field station and other university-owned areas: a regionally significant wetland, a virgin prairie remnant, an abandoned iron mine that's an important site for hibernating bats. My work is structured by seasons. As the snow melts, I track bud break and leaf development. In summer and fall, I administer workshops on topics ranging from creative writing to sedge and grass identification. Winter means hikes on the frozen wetlands that, at nearly 900 hectares, are a large part of the property. I've surveyed rare orchids and an endangered dragonfly, participated in prescribed burns at our prairie site, and taken students to watch through night vision telescopes as bats exit from our hibernaculum. I've watched sandhill cranes court outside my office window and seen them later shepherding their growing chicks. Experiences like these aren't just scientific; they're natural, and human. I've found a career that allows me to have such experiences and also share them with others. I like to think I'm helping inspire the next generation of students, as I was inspired by my own field station visits years ago. [1]: pending:yes

Are arrival date and body mass after spring migration influenced by large-scale environmental factors in a migratory seabird?

Changes in the timing of migratory events have been observed recently in many migratory species, most likely in response to climatic change. In the common tern Sterna hirundo we examined such changes in spring arrival date and body mass based on a 19 year individual-based longitudinal data from a transponder marked colony from 1994 - 2012. Although no long-term trend was observed in either trait, strong inter-annual and age-specific variation in arrival date and mass was evident. We investigated whether environmental factors such as (i) global climate phenomena North Atlantic and Southern Oscillation Indices NAOI and SOI, or (ii) local factors, such as food abundance in the wintering and breeding area, represented by fish stock or marine primary productivity, could explain this variation. We found that 2-year-old birds on their first spring migration advanced arrival relative to spring NAOI and delayed arrival relative to sprat Sprattus sprattus abundance. The arrival date of 3-year-olds also advanced in relation to NAOI and delayed in relation to winter SOI. In contrast, adults delayed arrival with NAOI and advanced relative to SOI. Within age groups, earlier annual arrival coincided with higher mass, indicating that a fast and/or early migration did not come at a cost to body condition. Changes in arrival mass relative to environmental covariates were found only in 2-year-olds on their first spring migration: in these birds arrival mass was positively related to herring Clupea harengus and sprat abundance in the breeding area as well as spring NAOI and negatively related to SOI. In conclusion, traits related to migration of common terns were linked with environmental conditions, but showed no long-term trends over the past two decades. Age-related differences were marked, suggesting that common terns might be subject to differing environmental constraints or respond differently to conditions during their annual cycle depending on age.

Population census of a large common tern colony with a small unmanned aircraft.

Small unmanned aircraft systems (UAS) may be useful for conducting high-precision, low-disturbance waterbird surveys, but limited data exist on their effectiveness. We evaluated the capacity of a small UAS to census a large (>6,000 nests) coastal Common tern (Sterna hirundo) colony of which ground surveys are particularly disruptive and time-consuming. We compared aerial photographic tern counts to ground nest counts in 45 plots (5-m radius) throughout the colony at three intervals over a nine-day period in order to identify sources of variation and establish a coefficient to estimate nest numbers from UAS surveys. We also compared a full colony ground count to full counts from two UAS surveys conducted the following day. Finally, we compared colony disturbance levels over the course of UAS flights to matched control periods. Linear regressions between aerial and ground counts in plots had very strong correlations in all three comparison periods (R 2 = 0.972–0.989, P < 0.001) and regression coefficients ranged from 0.928–0.977 terns/nest. Full colony aerial counts were 93.6% and 94.0%, respectively, of the ground count. Varying visibility of terns with ground cover, weather conditions and image quality, and changing nest attendance rates throughout incubation were likely sources of variation in aerial detection rates. Optimally timed UAS surveys of Common tern colonies following our method should yield population estimates in the 93–96% range of ground counts. Although the terns were initially disturbed by the UAS flying overhead, they rapidly habituated to it. Overall, we found no evidence of sustained disturbance to the colony by the UAS. We encourage colonial waterbird researchers and managers to consider taking advantage of this burgeoning technology.

Survival and local recruitment are driven by environmental carry-over effects from the wintering area in a migratory seabird.

We estimated annual apparent survival rates, as well as local recruitment rates in different age groups and for different breeding status in the common tern Sterna hirundo using mark-recapture analysis on a long-term individual-based dataset from a breeding colony in Germany. Strong inter-annual variability in survival rates became apparent, especially in prospectors. Local recruitment also varied strongly between years and age groups. To explain these fluctuations, we linked survival and recruitment estimates to several environmental covariates expected to be limiting during the wintering period and migration, including the global climate indices of North Atlantic Oscillation and Southern Oscillation, fish abundance indices, and marine primary productivity in the West African wintering area. Contrary to expectations, global indices did not seem to be linked strongly to vital rates. Results showed that primary productivity had the strongest effect on annual survival, especially in young and inexperienced individuals. Primary productivity in the wintering area was also strongly associated with the probability of recruitment in the following breeding season, indicating that conditions during winter can have carry-over effects on the life cycle of individuals.

Algal Turbidity Reduces Risk Assessment Ability of the Three‐Spined Stickleback

AbstractRecent anthropogenic increases in algal turbidity in aquatic habitats have been suggested to affect the ability of fish to assess predation risk. We investigated the response of feeding three‐spined sticklebacks (Gasterosteus aculeatus) exposed to a sudden appearance of an avian predator (the silhouette of common tern, Sterna hirundo), under clear and turbid water conditions. As stickleback use social cues to aid in predator avoidance, we also tested whether turbidity affected social information use by manipulating group size. We found that in turbid water, a smaller proportion of fish would escape from the feeding area, that the distance escaped was shorter and that a smaller proportion of fish fled into shelter. Larger group size was associated with longer escape distance and greater shelter use. However, there was no effect of group size on the proportion of fish that escaped the arena. The effect of group size was similar for turbid and clear water. Our finding that the fish showed a weaker antipredator response suggests that turbidity impedes their risk assessment capability. However, the sticklebacks were still able to benefit of the social facilitation provided by being in a group. This suggests that algal turbidity has detrimental effects on the ability of sticklebacks to assess predation risk from avian predators in shallow water. An implication is that in shallow water fish may be more vulnerable to avian predation under turbid conditions.

Opposing selective pressures may act on the colony size in a waterbird species

In theory, larger colony size should be favoured by lower per-capita predation rates, whereas smaller colony size should be favoured by reduced parasitism, social stress and competition for food. We conducted an experimental cross-fostering of young between colonies of different size to test whether differences in fitness had an environmental or genetic basis. We induced formation of one large (ca. 100 breeding pairs) and three small (30–40 pairs) Common Tern Sterna hirundo colonies by providing different size patches of nesting area (floating rafts). The larger colony had about 30 % higher reproductive success than the smaller colonies. However, offspring raised in the large colony were in poorer condition, which was indicated by the higher heterophil/lymphocyte ratios, lower hemoglobin concentrations in blood and slower growth rates, suggesting higher parasite loads or higher levels of social stress. By performing a cross-fostering experiment we confirmed that differences in chick condition were not inherited, but could be directly attributed to different rearing conditions experienced in the colonies of varying size. These results suggest that colony size in the Common Tern may be regulated by the opposing selective pressures (predation vs. parasitism/social stress).

Foraging specificity and prey utilization: evaluating social and memory-based strategies in seabirds

This study explores the capacity for seabirds to exhibit behavioral plasticity in response to the predictability of resources. Using direct species-comparisons, I tested the hypothesis that roseate terns (Sterna dougallii), dietary specialists, rely more heavily on foraging site-fidelity to pursue persistent prey, whereas common terns (S. hirundo), prey generalists, depend more on local enhancement by exploiting mixed-species assemblages. I analysed chick-provisioning observations and the bearings of commuting trajectories between the shared breeding colony, foraging areas, and feeding flocks. Foraging route patterns in roseate terns were consistent with a strategy based more heavily on spatial memory than social cues, in contrast to common terns, which associated more readily with nearby feeding aggregations, in line with social facilitation. Only during years of high prey abundance did roseate terns outperform common terns in nest productivity and the quality of prey delivered to chicks, suggesting that opportunistic tactics support resilience to sparse prey availability.

Age-dependent trait variation: the relative contribution of within-individual change, selective appearance and disappearance in a long-lived seabird.

Within populations, the expression of phenotypic traits typically varies with age. Such age-dependent trait variation can be caused by within-individual change (improvement, senescence, terminal effects) and/or selective (dis)appearance of certain phenotypes among older age classes. In this study, we applied two methods (decomposition and mixed modelling) to attribute age-dependent variation in seven phenological and reproductive traits to within-individual change and selective (dis)appearance, in a long-lived seabird, the common tern (Sterna hirundo). At the population level, all traits, except the probability to breed, improved with age (i.e. phenology advanced and reproductive output increased). Both methods identified within-individual change as the main responsible process, and, within individuals, performance improved until age 6-13, before levelling off. In contrast, within individuals, breeding probability decreased to age 10, then levelled off. Effects of selective appearance and disappearance were small, but showed that longer-lived individuals had a higher breeding probability and bred earlier and that younger recruits performed better throughout life than older recruits in terms of both phenology and reproductive performance. In the year prior to death, individuals advanced reproduction, suggesting terminal investment. The decomposition method attributed more age-dependent trait variation to selective disappearance than the mixed-modelling method: 14-36% versus 0-8%, respectively, which we identify to be due to covariance between rates of within-individual change and selective (dis)appearance leading to biased results from the decomposition method. We conclude that the decomposition method is ideal for visualizing processes underlying population change in performance from one age class to the next, but that a mixed-modelling method is required to investigate the significance and relative contribution of age effects. Considerable variation in the contribution of the different age processes between the seven phenotypic traits studied, as well as notable differences between species in patterns of age-dependent trait expression, calls for better predictions regarding optimal allocation strategies with age.

Are Morphometrics Sufficient for Estimating Age of Pre-Fledging Birds in the Field? A Test Using Common Terns (Sterna hirundo)

Age is a key component of fitness, affecting survival and reproductive capacities. Where it is not possible to study known individuals from birth, morphometrics (predominantly patterns of plumage development for birds) are most often used to estimate age. Although criteria for age estimations exist for many species, the degree to which these criteria improve the precision of estimates remains to be tested, restricting their widespread acceptance. We develop a photographic tool for estimating ages of Common Tern (Sterna hirundo) chicks and test it using 100 human observers of varying prior experience across four breeding colonies (three North American sites and one European site) and under controlled laboratory conditions. We followed the design approach of other morphometric tools, expanding it to create a user-friendly guide (divided into six age groupings). The majority (86%) of observers improved in chick-aging accuracy when using the tool by an average of 20.1% (±1.4 SE) and correctly estimated 60.3% (±1.4) of chick ages. This was similar to the intrinsic aging ability of our best field observer (63.3%). Observers with limited experience showed the greatest increases in chick-aging accuracy over experienced observers who likely had established a method for estimating chick ages prior to using the tool. Even the best observers only correctly estimated ages of chicks 62.9% (±2.8) of the time in the field and 84.0% (±2.9) of the time in the lab when using the tool and typically underestimated ages. This indicates that developmental variation between individual chicks can prevent completely reliable age estimates and corroborates the few existing data that suggest that morphometric criteria fail to achieve robust levels of accuracy and may introduce error into studies that rely on them. We conclude that novel approaches for estimating age, not only morphometric criteria, must be pursued.

Tracing organophosphorus and brominated flame retardants and plasticizers in an estuarine food web

Nine organophosphorus flame retardants (PFRs) were detected in a pelagic and benthic food web of the Western Scheldt estuary, The Netherlands. Concentrations of several PFRs were an order of magnitude higher than those of the brominated flame retardants (BFRs). However, the detection frequency of the PFRs (6–56%) was lower than that of the BFRs (50–97%). Tris(2-butoxyethyl) phosphate (TBOEP), tris(isobutyl) phosphate (TIBP) and tris(2-chloroisopropyl) phosphate (TCIPP) were the dominant PFRs in sediment with median concentrations of 7.0, 8.1 and 1.8ng/g dry weight (dw), respectively. PFR levels in the suspended particular matter (SPM) were 2–12 times higher than that in sediment.TBOEP, TCIPP, TIBP, tris(2-chloroethyl) phosphate (TCEP) and tris(phenyl) phosphate (TPHP) were found in organisms higher in the estuarine food web. The highest PFR concentrations in the benthic food web were found in sculpin, goby and lugworm with median concentrations of 17, 7.4, 4.6 and 2.0ng/g wet weight (ww) for TBOEP, TIBP, TCIPP and TPHP, respectively. Comparable levels were observed in the pelagic food web, BDE209 was the predominant PBDE in sediment and SPM with median concentrations up to 9.7 and 385ng/g dw, respectively. BDE47 was predominant in the biotic compartment of the food web with highest median levels observed in sculpin and common tern eggs of 79ng/g lipid weight (lw) (2.5ng/g ww) and 80ng/g lw (11ng/g ww), respectively.Trophic magnification was observed for all PBDEs with the exception of BDE209. Indications of trophic magnification of PFRs were observed in the benthic food web for TBOEP, TCIPP and TCEP with tentative trophic magnification factors of 3.5, 2.2 and 2.6, respectively (p<0.05). Most of the other PFRs showed trophic dilution in both food webs. The relative high PFR levels in several fish species suggest high emissions and substantial exposure of organisms to PFRs in the Western Scheldt.