Eurasian Dipper Research Articles

Populations of high‐value predators reflect the traits of their prey

The extent to which prey traits combine to influence the abundance of predators is still poorly understood, particularly for mixed predators in sympatry and in aquatic ecosystems. In this study, we characterise prey use and distribution in iconic bird (grey wagtails and Eurasian dippers) and fish species (brown trout and Atlantic salmon) to assess whether prey traits could predict populations of these four riverine predators. Specifically, we hypothesised that: 1) prey key traits would predict predator populations more effectively than 2) diversity of prey traits, 3) the taxonomic abundance or richness of prey (known as traditional or mass‐effect types of biodiversity) or 4) the prevailing environmental conditions. Combined predator population sizes were predicted better by a few key traits – specifically those revealing prey habitat use, size and drifting behaviour – than by prey diversity or prey trait diversity or environmental conditions. Our findings demonstrate that the complex relationships between prey assemblages and multiple predator species can be represented mechanistically when the key prey traits that govern encounter and consumption rates are identified. Given their apparent potential to reveal trophic relationships, and to complement more traditional measures of prey abundance, we advocate further development of trait‐based approaches in predator–prey research.

Food web transfer of plastics to an apex riverine predator.

As a rapidly accelerating expression of global change, plastics now occur extensively in freshwater ecosystems, yet there is barely any evidence of their transfer through food webs. Following previous observations that plastics occur widely in their prey, we used a field study of free-living Eurasian dippers (Cinclus cinclus), to test the hypotheses that (1) plastics are transferred from prey to predators in rivers, (2) plastics contained in prey are transferred by adults to altricial offspring during provisioning and (3) plastic concentrations in faecal and regurgitated pellets from dippers increase with urbanization. Plastic occurred in 50% of regurgitates (n=74) and 45% of faecal samples (n=92) collected non-invasively from adult and nestling dippers at 15 sites across South Wales (UK). Over 95% of particles were fibres, and concentrations in samples increased with urban land cover. Fourier transform infrared spectroscopy identified multiple polymers, including polyester, polypropylene, polyvinyl chloride and vinyl chloride copolymers. Although characterized by uncertainty, steady-state models using energetic data along with plastic concentration in prey and excreta suggest that around 200 plastic particles are ingested daily by dippers, but also excreted at rates that suggest transitory throughput. As some of the first evidence revealing that plastic is now being transferred through freshwater food webs, and between adult passerines and their offspring, these data emphasize the need to appraise the potential ecotoxicological consequences of increasing plastic pollution.

Persistent contaminants as potential constraints on the recovery of urban river food webs from gross pollution

Urban areas contribute substantially to xenobiotic contaminant loads in rivers, but their effects have been investigated more for individual organisms and sensitive taxa, rather than through the emergent properties of communities. Here, we use replicated, catchment-scale sampling of benthic invertebrates and novel multivariate techniques to assess whether urban wastewater contaminants affected the structure and function of river food webs. We postulated that the continued occurrence of selected contaminants in river systems might explain the incomplete recovery of urban rivers from legacy gross pollution. Benthic invertebrate communities were sampled monthly over a year (2016–2017) at 18 sites across 3 river systems in South Wales (United Kingdom). Contaminant sources were characterised using remote sensing, water quality data from routine monitoring and measured concentrations of selected persistent xenobiotic pollutants (polychlorinated biphenyls and polybrominated diphenyl ethers). Urban wastewater discharges had relatively limited effects on river water quality, with small increases in nitrate, phosphate, temperature, conductivity and total dissolved solids in urban systems. Concentrations of polychlorinated biphenyls and polybrominated diphenyl ethers in invertebrates, however, were significantly higher under greater urban land cover and wastewater discharge. Food webs at the most highly contaminated urban sites were characterised by: (i) reduced taxonomic and functional diversity; (ii) simplified food web structure with reduced network connectance; and (iii) reductions in the abundance of prey important for apex predators such as the Eurasian dipper (Cinclus cinclus). Although correlative and partially confounded by other effects, these data provide support for the hypothesis that impairment to food webs resulting from urban pollutants might explain population, community and ecosystem-level effects in urban river systems, and hence incomplete recovery from past pollution.

Developmental impairment in eurasian dipper nestlings exposed to urban stream pollutants

Avian studies of endocrine disruption traditionally have focused on reproductive impairment, given that many environmental contaminants affect sex steroid hormones. There is also increasing interest in altered thyroid function, and associated early development, particularly in altricial species with extended developmental windows. Both types of effect are relevant under the complex pollutant conditions created in streams draining urban areas, but case studies are scarce. Therefore, the authors measured breeding performance, as well as nestling growth, condition, and plasma thyroid hormones, in 87 Eurasian dipper (Cinclus cinclus) nests on 36 urban and rural streams in south and mid-Wales (UK); invertebrate prey data were also collected. The objective of the present study was to evaluate whether urban stream pollution or food scarcity might affect reproduction or development in this specialized aquatic songbird. Clutch sizes and egg fertility were similar on rural and urban streams, whereas nest success was actually higher at urban sites and food abundance was not significantly reduced. However, subtle but important differences were apparent. Urban nestlings were significantly lighter than rural nestlings for their body size (condition index), and brood sex ratios were increasingly male biased with increasing urbanization. The nestling thyroid hormone profile closely reflected urban land use, whereas depressed triiodothyronine (T3) hormones and poorer body condition were associated with higher exposure to polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) at urbanized sites. These data suggest that PCBs, PBDEs, and/or accompanying contaminants in urban streams could be affecting dipper nestling development, with potential consequences for the birds' fitness.

Eurasian Dipper Eggs Indicate Elevated Organohalogenated Contaminants in Urban Rivers

Many urban European streams are recovering from industrial, mining, and sewage pollution during the 20th century. However, associated recolonization by clean water organisms can potentially result in exposure to legacy or novel toxic pollutants that persist in the environment. Between 2008 and 2010, we sampled eggs of a river passerine, the Eurasian dipper (Cinclus cinclus), from 33 rivers in South Wales and the English borders (UK) which varied in catchment land use from rural to highly urbanized. Dipper egg δ(15)N and δ(13)C stable isotopes were enriched from urban rivers while δ(34)S was strongly depleted, effectively discriminating their urban or rural origins at thresholds of 10% urban land cover or 1000 people/km(2). Concentrations of total polychlorinated biphenyls (PCBs) and polybrominated biphenyl ethers (PBDEs) were positively related to urban land cover and human population density while legacy organochlorine pesticides such as p,p'-DDE, lindane, and hexachlorobenzene were found in higher concentrations at rural sites. Levels of PBDEs in urban dipper eggs (range of 136-9299 ng/g lw) were among the highest ever reported in passerines, and some egg contaminants were at or approaching levels sufficient for adverse effects on avian development. With the exception of dieldrin, our data shows PCBs and other organochlorine pesticides have remained stable or increased in the past 20 years in dipper eggs, despite discontinued use.

Local to Continental Influences on Nutrient and Contaminant Sources to River Birds

Stable isotope and contaminant analyses revealed differences in nutrient sources and contaminant pathways in two species of dipper, Cinclus mexicanus and Cinclus cinclus in western Canada and western Britain. We collected dipper prey and eggs from relatively pristine British Columbian rivers contrasting in the presence of salmon-derived nutrients, and rural Welsh rivers with varying food-web complexity associated with stream acidity. Enriched delta(13)C and to a lesser extent delta(15)N in American dipper eggs and prey confirmed that streams with migrating Pacific salmon were enriched with marine-derived nutrients, but overall contaminant concentrations did not differ strongly in dipper eggs between rivers with and without salmon. However dipper contaminant profiles, particularly PBDEs, mercury and SigmaDDTs, were related to delta(13)C, reflecting the marine influence and greater fish consumption at salmon sites. Irrespective of catchment influences and despite feeding at a higher trophic level, American dipper eggs (n = 17) contained lower levels of organohalogens than Eurasian dippers (n = 37), but with similar PCB (153 and 138) and PBDE (47 and 99) congeners dominanating. Eurasian dipper eggs from circumneutral streams contained more dieldrin, SigmaDDT and Sigmahexachlorocyclohexanes while Sigmachlordanes, mirex, SigmaPBDEs and SigmaPCBs predominated at acid sites. Our data reveal how dippers indicate contaminant levels and sources under contrasting conditions at scales ranging from local to intercontinental, but local environmental conditions apparently alter feeding ecology and exposure pathways even in these closely related species.

Diet shifts during egg laying: Implications for measuring contaminants in bird eggs

We combined stable isotope tracers of blood plasma, blood cells and egg contents with faecal analysis during pre-breeding and egg laying phases in two dipper species Cinclus cinclus and Cinclus mexicanus to determine the occurrence of dietary shifts during egg production and to assess consequences for egg contaminant loads. In both species, changes in δ 13C ( C. cinclus) or δ 15N ( C. mexicanus) in female plasma relative to red blood cells indicated a dietary shift during laying that was not observed in males. Eurasian dippers increased prey consumption as breeding approached, shifting from primarily trichopteran insect larvae to ephemeropterans and plecopterans. In American dippers, egg-laying females switched to feeding at a higher trophic level by consuming more fish. Eggs derived from higher trophic level diets contained more mercury (American dipper), polychlorinated biphenyls and some organochlorines, especially DDT metabolites. The results demonstrate how dietary changes during egg laying accompany the demands for egg production with consequences for contaminant deposition in avian eggs.

Comparison of Plumages of White-Throated DipperCinclus cinclusand BlackbirdTurdus merula

Abstract. This study compares the plumage of a single Eurasian White-throated Dipper Cinclus cinclus with that of three Common (European) Blackbirds Turdus merula (all road casualties). As expected, the Dipper had far more down and contour feathers (3,322) than the Blackbirds (mean 1,704), with Dipper down and contour feathers being significantly shorter than those of Blackbirds. However, contrary to published information, the plumage of dippers is not exceptionally dense; the mean follicle density of the Dipper was 59.2 follicles cm-2, that of the Blackbirds 58.6–61.7 follicles cm-2. Instead, the enhanced insulation of diving Dippers stems from a) much more extensive plumage (the apterylae between feather tracts are fully feathered, whilst naked in Blackbirds), b) substantial down cover of head (absent in Blackbirds), c) extensive down cover of wings. Much of the higher number of feathers in the Dipper is made up of contour feathers rather than down/semiplume feathers (the ratio between Dipper contour an...

Influence of the Mating System of the Eurasian Dipper on Sex-Specific Local Survival Rates

The mating system of the Eurasian dipper (Cinclus cinclus) involves males defending resources, such as nesting sites or food, and females choosing sites based on quality. Strong territoriality and unequal quality of sites may induce polygyny. Depending on stream flow, external factors such as floods or drought may alter the quality of some breeding territories, leading to breeding dispersal. Emigration resulting from breeding dispersal should he reflected in annual local adult survival rates. In a study of the Eurasian dipper in northeastern France from 1981 to 1998, I verified that pairing and territoriality may influence local survival and that site choice may be mediated significantly by variation in extrinsic factors using mark-resighting data and selection of models using an information-theoretic framework. I found a decrease of about 0.09 in the annual adult local survival rates for both sexes of Eurasian dippers during flood years. During dry years and for monogamous dippers settled along <2m-wide brooks, female annual local survival rate decreased from 0.56 to 0.39, possibly reflecting permanent emigration, whereas the male resighting probability fell from 0.97 to 0.59, indicating delays in male breeding or temporary emigration. Unlike monogamous breeders, polygamous birds had constant local survival estimates and resighting probabilities, suggesting that they bred in sites secure from both flood and drought. Because the Eurasian dipper adapts poorly to environmental stress, 1 encourage managers to shorten stream diversions and other water management practices affecting stream flow.

Foraging behavior predicts age at independence in juvenile Eurasian dippers (Cinclus cinclus)

Timing of foraging independence may be controlled by parents, offspring, or both and may have consequences for dispersal, reproduction, and survival. In a study of juvenile Eurasian dippers {Cinclus cinclus), I examined the relationship between individual differences in parental provisioning, the development of foraging, and the liming of independence. Young dippers forage very differently from adults, specializing on small, stationary prey, such as simuliid larvae (Diptera), and avoiding energetically costly and highly skilled foraging techniques, such as diving, by which adults obtain larger prey. In my Welsh study area, age at independence varied substantially within and between broods. Juveniles that relied more on simuliids and less on larger prey were independent sooner, as were juveniles with higher rates of intake while foraging; the effect was obvious 3—4 days after fledging. Provisioning rate and total caloric intake over the dependent period was unrelated to age at independence, although greater reliance on parental feeding was associated with higher total caloric intake. Higher rates of intake from begging were correlated with reduced foraging time. The results demonstrate that the acquisition of the adult foraging strategy is not a prerequisite for independence or, hence, dispersal. In fact, mastering the skills necessary to capture larger prey may delay independence. Individual juvenile dippers seem to find different solutions to the trade-off between gaining sufficient food (either from begging or from foraging for simuliids) and the eventual necessity of learning to forage like an adult. Kty words: Cinclus cinclus, development, Eurasian dippers, foraging, individual differences, parental provisioning, passerines, skill acquisition. [Bthav Ecol 9:471-477 (1998)]

The influence of a river bird, the dipper (Cinclus cinclus), on the behaviour and drift of its invertebrate prey

1. We examined the behavioural response of stream macroinvertebrates to real and simulated predatory activity by a river bird, the Eurasian dipper, Cinclus cinclus L.2. In the field, we assessed whether invertebrate drift changed in response to live dippers in enclosures; we found no effects on the drift of any of the five families for which individual analyses were possible, either because it was infrequent, or involved distances too short to be detected (&lt; 0.5 m).3. In a laboratory stream, we observed prey during encounters with a model dipper which simulated flight, swimming, bill contact with the prey, and stone turning. Invertebrate families varied in their response. Simuliids and hydropsychid caddis lacked effective escape behaviour, consistent with heavy losses through predation by dippers in the wild. Other families either drifted (Baetidae, Gammaridae) or moved away (Heptageniidae, Ephemerellidae, Leuctridae, Perlidae) from the model dipper, but responded only to bill contact or simulated stone turning. Such delayed responses would not protect individuals directly targeted by foraging dippers and partly explain the lack of detectable effects by dippers on drift in the field.4. We suggest why invertebrates do not show more marked escape responses to this important predator.

Development of foraging behaviour in the Eurasian dipper, Cinclus cinclus, from fledging until dispersal

Abstract. The acquisition of foraging behaviour patterns by young birds has not been thoroughly described. Furthermore, the study of the developmental and maturational processes underlying such acquisition is in its infancy, despite the consequences these processes might have for the survival, life-history patterns, and behaviour of both juveniles and adults. Acquisition of foraging behaviour by juvenile Eurasian dippers from fledging to dispersal was studied at a site in central Wales. Dippers are passerines associated with upland rivers and streams in which they forage for benthic macroinvertebrates and small fish. Juvenile foraging differed from that of adults on nearly every measure taken, and most differences persisted after independence. Juveniles foraged at different water speeds and depths than adults (e.g. juveniles did not dive) and, unlike adults, frequently dropped prey and stumbled while foraging. Even in foraging areas preferred by juveniles, capture rates of larger prey were low despite improvement with age. Juveniles specialized on simulid (blackfly) larvae, which are small, stationary and accessible. Handling times for larger prey were longer for juveniles than adults but profitability nevertheless increased with prey size at all ages. The high probability of dropping larger prey and the costs of energetically expensive foraging techniques may promote the observed juvenile strategy of foraging in slow, shallow water for small prey. Possible ecological and developmental variables that promote the juvenile strategy are discussed.

Patterns of contamination by organochlorines and mercury in the eggs of two river passerines in Britain and Ireland with reference to individual PCB congeners

Unhatched eggs were collected in 1988 and 1990 from nests of the Eurasian Dipper Cinclus cinclus and the Grey Wagtail Motacilla cinerea in Wales, eastern Scotland and south-western Ireland. Mercury concentrations in Dipper eggs (geometric means 0.45–0.91 ppm (μg g −1) dry mass) were significantly lower in eastern Scotland than in either south-western Ireland or Wales, where the incidence of detectable residues increased markedly between 1988 (2% of eggs) and 1990 (69%). By contrast, DDE (geometric means 0.63–3.54 ppm in lipid), TDE (<0.01–1.80 ppm), DDT (<0.01–0.65 ppm), total PCBs (3.99–10.47 ppm), HEOD (0.39–0.61 ppm) and HCB (0.02–0.13 ppm) were all significantly higher in Scottish eggs than others. Around 33–46% of the total PCB burden in Dipper and Grey Wagtail eggs could be accounted for by six congeners (IUPAC numbers 118, 180, 101, 153, 138 and 170). Amongst these attributable PCBs, Dipper eggs from eastern Scotland were dominated by congener 153 (2,2′,4,4′,5,5′-hexachlorobiphenyl), whilst Welsh and Irish eggs were dominated by congener 118 (2,3′,4,4′,5-pentachlorobiphenyl). With the latter exception, all the individual congeners were found at significantly higher concentrations in Scottish eggs than others. Grey Wagtail eggs were dominated by congeners 118 and 101 (2,2,4,5,5′-pentachlorobiphenyl). In general, these congeners are common, widespread, and dominant components in the eggs of other wild birds for which data are available. Consistent with the low to medium levels of contaminants found in Dipper eggs, there was only slight evidence of any toxic effects. These included moderate shell thinning in relation to increasing DDE, and some evidence that contaminants had contributed to egg failure.

Exploitation of prey by a river bird, the dipper Cinclus cinclus (L.), along acidic and circumneutral streams in upland Wales

SUMMARY. 1. The diet of the Eurasian dipper Cinclus cinclus. a riverine bird from a globally widespread genus, was assessed through all stages of its annual cycle using published data and field studies from streams of contrasting chemistry. Time‐activity budgets were also compiled throughout the year and used to estimate annual energy requirements from the stream ecosystem.2. The annual energy requirements for a territorial pair ranged from 148,000 to 158,000 kJ yr−1 depending on whether one or two broods were reared. After allowing for assimilation efficiency, these requirements were estimated to represent 10.5–11.0 kg dry mass of fish and invertebrates. Using representative values for territory size (4680–11,250 m2), annual exploitation of secondary production was estimated at 0.93–2.35 g dry mass m−2.3. Several features combined to focus the predatory load on certain organisms over different stages of the annual cycle. These included the availability and selection of alternative prey, the need to provision nestlings with large items such as trichopteran larvae, and the use by females of calcium‐rich prey such as fish prior to egg formation.4. Across their range of territory size, annual exploitation (dry mass) by dippers was estimated at 0.06–0.29 g m−2 for Plecoptera. 0.02–0.22 g m−2 for Ephemeroptera. 0.59–1.11 g m−2 for Trichoptera and 0–0.78 g m−2 for fish. Exploitation of Ephemeroptera. I richoptera and fish were all highest in circumneutral streams, but exploitation of Plecoptera was highest in acidic streams because other prey were scarce.5. Cottids dominated the fish component of the diet. Influences on their density could be substantial according to available data on production in Welsh streams. Hydropsychids and limnephilids dominated the trichopteran component, with exploitation again representing potentially substantial amounts of production. Contemporaneous data are required on benthic production and exploitation by the birds.6. The ecological role of birds in rivers particularly, and aquatic ecosystems generally, is currently neglected but worthy of considerable research effort.

Infanticide in the Eurasian Dipper

Infanticide has been reported in several avian species (see Mock 1984, for a review). Direct observations of infanticide among individually marked animals are, however, scarce. Here I describe one definite case of infanticide by a male Eurasian Dipper (Cinclus cinclus), and three suspected cases. Dippers are passerines closely associated with fastflowing rivers in which they forage for invertebrates. Domed nests, made primarily of moss, are always located over water. Linear territories along rivers are defended vigorously by pairs during the breeding season, and maintained less assiduously by individuals the rest of the year. Though traditionally considered a monogamous species, polygyny has been reported (e.g., Galbraith 1979). Indeed, within my study area half of the males were polygynous (Yoerg et al., unpubl.). Thirteen contiguous territories along a tributary of the river Wye in mid-Wales comprised the study area. All adults (13 females and eight males) were individually color-marked with leg bands during February and March of 1989, and were observed from February through June in a study of foraging and breeding behavior. Observations were made from inside a hide. On 28 April 1989 I was 7 m from a nest where adults were provisioning young. The five nestlings were 5 days old; dippers typically fledge at 23 days of age. The resident male was the only trigamous male in my study area: in addition to helping to provision the brood in question, he was building a nest with another female, and helping a third female feed five nestlings due to fledge in 2 days. At 09:10 the female was brooding in the nest. The male from the downstream territory flew upstream landing 5 m downstream of the nest. This male was also polygynous. Both of his females were incubating eggs. For approximately 1 min he engaged in a soliciting display, dipping deeply with his wings low and neck outstretched. He then landed directly below the nest, where he called. (When the nestlings are small and the female likely to be brooding, a provisioning male will often call below the nest before attempting to deliver food.) After calling, the intruding male flew up and perched on the threshold of the nest opening. The female immediately chased the intruder downstream.