Mergus Merganser Research Articles

Size-dependent foraging behaviour and use of cover in juvenile coho salmon under predation risk

Foraging and use of cover by juvenile coho salmon (Oncorhynchus kisutch) were affected by predation threat in both seminatural channels and laboratory streams. In the field, coho salmon preferred stream sections with brushy cover only when under threat from hunting common mergansers. The mergansers had their highest capture success in pools without cover. Predation threat also caused coho salmon to use cover more as foraging habitat and to aggregate more in favourable positions at the head of the pool. In the laboratory, under simulated predation threat, fish using a refuge were significantly larger than those in the risky habitat. This pattern persisted for 2 days after the predation threat was discontinued. The average growth of coho salmon under predation threat was depressed and the difference in growth between large and small individuals was less than in control groups. We argue that larger fish were more averse to predation risk than smaller fish and that the smaller fish took advantage of feeding opportunities indirectly provided as a result of the predation risk. We speculate that in natural environments, predation may depress growth rates because of risk-avoidance behaviour but may also serve to reduce growth-rate differences among size classes within a cohort.

Effects of the Exxon Valdez Oil Spill on Habitat Use by Birds along the Kenai Peninsula, Alaska

We examined habitat use by 34 species of marine-oriented birds along the Kenai Peninsula, Alaska, in 1989-1991 to measure effects of the Exxon Valdez oil spill of March 1989 outside of the immediate spill area in Prince William Sound. Overall, 22 species (65%) did not exhibit statistically significant initial negative impacts on their use of oil-affected habitats. Of the 12 species that did exhibit significant negative impacts on habitat use, 6 showed evidence of recovery by the end of the study in late 1991. Of the 6 species that failed to show clear evidence of recovery, two (Common Merganser and Glaucous-winged Gull) showed no evidence of recovery by 1991, three (Common Loon, Double-crested Cormorant, and Sharp-shinned Hawk) may have begun recovery by 1991, and evaluation of recovery of the sixth species (Ancient Murrelet) was precluded by a lack of data. On individual surveys, the proportion of species recorded that exhibited negative impacts declined through time, from 36% on the first survey after the spill in 1989 to 19% in late 1991. These results indicate that the Exxon Valdez oil spill had significant initial effects on habitat use by some marine-oriented birds along the Kenai, although the majority of species analyzed showed no obvious spill-related effects on habitat use and impacts on several other species were not prolonged.

Identifying inter‐dive intervals in time‐activity budget studies of diving ducks

In order to identify inter‐dive intervals in diving ducks, i.e. the time spent regaining breath between consecutive feeding dives, the position of the tail, carpal joints and head was recorded in different behavioural categories for eight species on the southwestern coast of Norway in March. Inter‐dive intervals are part of the feeding behaviour and are easily confused with the behavioural categories of swimming and loafing. During inter‐dive intervals the ducks adopt a more or less hunch‐backed position, preparing for the next dive. In this position the tail touches the water surface and the head is held in a more forward position than during loafing and swimming. Some species expose carpal joints in inter‐dive intervals, while most of the wings are covered by the flank feathers during non‐feeding behaviour. Logistic regressions showed that a near perfect classification was obtained from the position of the wings alone in common eider Somateria mollissima, velvet scoter Melanitta fusca, and long‐tailed duck Clangula hyemalis. An almost equally good classification was obtained for the two last mentioned on the position of the tail, for scaup Aythya marila on the position of the head, and for red‐breasted merganser Mergus merganser on the position of the head and the stretching of the neck. Less reliable classifications were obtained for goldeneye Bucephala clangula and tufted duck Aythya fuligula, whereas in common scoter Melanitta nigra none of the variables fulfilled the criteria for entering a logistic regression function.

Monitoring nest box use by cavity‐nesting ducks on acid‐stressed lakes in Ontario, Canada

Nest boxes erected on 75 small lakes near Sudbury, Canada were monitored annually between 1987 and 1996 to measure the response of cavity‐nesting waterfowl to changing chemical and biological conditions of their nesting habitat from the effects of acidification. Nest boxes were used mainly by common goldeneyes Bucephala clangula and hooded mergansers Lophodytes cucullatus, although a few were occupied by common mergansers Mergus merganser and wood ducks Aix sponsa. Use by hooded mergansers and wood ducks increased from 1987 to 1996, while use by goldeneyes remained stable. Patterns in nest box use reflected general population trends observed in the area. Interspecific nest parasitism also increased to 33% of all nests in 1996, probably a consequence of more hooded merganser nests. Clutch size, nesting and hatching success of goldeneye and hooded merganser eggs were similar to values reported for conspecifics in other studies. Overall, interspecific nest parasitism did not appear to affect the nesting success of either species. Although goldeneyes nested more often on fishless lakes early in the study, overall, fish presence, pH‐value, lake area and connectivity were not related to nesting attempts or measures of nesting success for either species. Therefore, it is believed that for common goldeneyes and hooded mergansers currently breeding in the acid‐stressed Sudbury area, habitat characteristics have little influence on nest site selection, particularly when compared to their documented effects on brood‐rearing. However, monitoring of nest boxes may prove a less expensive method than aerial surveys to track population responses of cavity‐nesting species to chemical improvements.

Abundance, distribution and habitat use of breeding Goosanders Mergus merganser and Red-breasted Mergansers Mergus serrator on British rivers

The abundance and distribution of breeding Goosanders and Red-breasted Mergansers were surveyed along river habitats throughout Britain in the spring and summer of 1987. Broad-scale habitat information was recorded and a total of around 9300 km of rivers was surveyed. The densities of Goosanders were highest in the Borders and northwest England, and those of Red-breasted Mergansers in the Highlands and western Scotland. The influence of river characteristics, including width, flow type, extent of bankside cover, elevation and gradient on the choice of habitats by sawbills was assessed using logistic regression models. River width had a significant influence on the presence of Goosanders and Mergansers, with wider river sections more likely to hold birds. The probability of recording Goosanders decreased with increasing river gradient while Mergansers preferred slower, smoother river sections. Taking these results into account, regional and national populations of both species were estimated by extrapolation from river sections surveyed to the total extent of river habitat available, as estimated by map measurements. Standing waters, by which both species nest, were not included in this survey. The limitations of this approach are discussed. National populations on river habitats were estimated to be 2600 (95% confidence limits CLs at 2333 and 2890) adult male and 3700 (95% CLs at 3272 and 4072) redhead Goosanders, and 800 (95% CLs at 562 and 1051) adult male and 750 (95% CLs at 562 and 964) redhead Mergansers.

Carlin tag recoveries as an indicator of predation on salmon smolts by goosanders and red‐breasted mergansers

Between 1984 and 1990 a total 221 Carlin tags used to mark salmon Salmo salar smolts in the River North Esk, NE Scotland, were recovered from the stomachs of goosanders Mergus merganser and red‐breasted mergansers M. serrator. Both Carlin‐tagging and adipose‐clipping affected the predation of salmon smolts by sawbill ducks. The mean (± S.D.) sizes of tagged smolts taken by both species were similar (117 ± 3 mm) and significantly smaller than the mean sizes of smolts in the river, possibly due to a reduction in the swimming performance of small smolts bearing tags. Large adipose‐clipped smolts (±mean smolt size) were predated significantly more than unclipped smolts, but no such difference was observed for small smolts (<mean smolt size). Data suggested that some ducks cued into smolt release sites where they took a disproportionately high number of tagged smolts on or near the day of release and continued to do so for several days. Although tag recoveries are commonly used to estimate the impact of piscivores on fish stocks, our study suggests that some predators respond to the presence of tagged fish in ways that directly reflect the tagging procedure and that caution should be exercised when extrapolating conclusions based on such data to untagged fish.

PCBs, dioxins and furans in Hooded Merganser ( Lophodytes cucullatus), Common Merganser ( Mergus merganser) and mink ( Mustela vison) collected along the St.Maurice River near La Tuque, Quebec

A pulp and paper mill located in La Tuque on the St.Maurice River, Quebec, and using the kraft bleaching process was historically the largest pulp and paper industry point source of chlorinated dibenzo- p-dioxins and dibenzofurans in Quebec. A study was undertaken to document the bioaccumulation of PCBs, dioxins and furans in piscivorous birds and mammals in this area. Hooded and Common Merganser eggs were collected in nest boxes along the St.Maurice River and Common Merganser fledglings were collected at two sites on the river. Wild minks were trapped along the St.Maurice River and in a control area upstream. Analysis of pooled merganser eggs showed contamination with dioxins, furans and PCBs. Liver samples of fledglings were contaminated with 2,3,7,8-tetrachlorodibenzofuran at the downstream site. Analysis of mink livers showed a significant higher contamination with dioxins and furans in some downstream samples compared with the upstream samples.

Confirmed Winter Residency of Common Goldeneye and Common Merganser in the Northwest Territories

Confirmed Winter Residency of Common Goldeneye and Common Merganser in the Northwest Territories

Prevalence and Transmission of Cercariae Causing Schistosome Dermatitis in Flathead Lake, Montana

Numerous studies have been conducted on swimmer's itch, but very few have been in Montana and none on Flathead Lake, the largest, natural freshwater lake in the western United States. We conducted a study to determine the prevalence of hosts transmitting cercariae causing swimmer's itch in this lake. Hosts for this life cycle were determined by direct observation of fresh waterfowl fecal material for the presence of miracidia, and snails for the presence of cercariae. Swimmer's itch-producing cercariae were verified directly by placing various species on the arms of human volunteers and waiting for a reaction. Results of the study were further substantiated using a controlled experiment in which snails were individually infected with miracidia from the suspected waterfowl host and then checked for infection after a 6-wk incubation period. Our findings show that the common merganser (Mergus merganser) and the snail Stagnicola elrodi were natural hosts of the swimmer's itch parasite (Trichobiharzia ocellata) with prevalences of 84% and 2.0%, respectively. To our knowledge this is the first documented case of S. elrodi transmitting the swimmer's itch cercariae.

Diel activity patterns of lake chubs and other fishes in a temperate stream

Baited and unbaited minnow traps were set in Catamaran Brook and the Little Southwest Miramichi River, New Brunswick, and checked every 4 h to determine the diel activity pattern of four species of stream-dwelling fish (threespine stickleback (Gasterosteus aculeatus), juvenile white sucker (Catostomus commersoni), blacknose dace (Rhinichthys atratulus), and lake chub (Couesius plumbeus)). Secondary goals were to determine whether the presence of bait inside minnow traps affected the diel patterns of captures and to compare patterns of lake chub captures in minnow traps with movement through a nearby fish-counting fence. All fish except lake chubs were diurnal, although strict diurnality was less obvious when bait was present in the traps. Lake chubs, which are normally diurnal in the laboratory, were captured mostly near dawn or dusk in unbaited traps, throughout the day in baited traps, and mostly at night at the fish-counting fence. We infer that chubs are active mostly at dawn or dusk, except (i) when strong food cues are present, in which case their activity may extend into the day, and (ii) during the spawning migration, when they move mostly at night. Relative inactivity by chubs during the day may be caused by the presence of piscivorous birds such as kingfishers and common mergansers, whose hunting efficiency may be higher under brighter light.

Heavy metals in seaducks and mussels from misty fjords national monument in Southeast Alaska

Quartz Hill, in Misty Fjords National Monument near Ketchikan, Alaska, is the site of a proposed molybdenum-producing mine. To provide baseline data for use in post-development comparisons, we analyzed tissues of Barrow's goldeneyes (Bucephala islandica), common mergansers (Mergus merganser), and blue mussels (Mytilus edulis) for seven heavy metals that could potentially be released into the environment as a result of mining operations. Specimens were collected in 1980, 1981, and 1982 from two fjords likely to be used for discharge of tailings from the proposed mine and from two control fjords. Concentrations of arsenic, cadmium, copper, chromium, molybdenum, lead, and zinc were measured in soft tissues of mussels and in kidney, liver, and muscle of birds. The highest mean concentrations of metals found in bird tissues were 55.7 ppm dry weight cadmium in kidneys and 154 ppm dry weight zinc in livers of Barrow's goldeneyes. Concentrations of several metals in blue mussels differed among seasons and locations, but the most significant finding in mussels was a maximum mean cadmium concentration of 9.6 ppm dry weight, a level higher than normally found in undisturbed areas. With the exception of 104 ppm dry weight cadmium in the kidney of one common merganser and 12.7 ppm dry weight lead in the kidney of another, concentrations of other metals in seaduck and mussel tissues were low, consistent with what would be expected for a pre-development environment. Molybdenum was found in low concentrations (<10 ppm dry weight) in all avian kidney samples and most liver samples, but was not detected in blue mussels.

Consumption of Atlantic salmon smolts and parr by goosanders: estimates from doubly‐labelled water measurements of captive birds released on two Scottish rivers

The field metabolic rates (FMRs) of nine captive goosanders, Mergus merganser, released on two Scottish rivers were estimated using the doubly‐labelled water (DLW) technique. Mean (± S.E.) FMR was 2.322±0.239ml CO2 g−1 h−1 and daily energy expenditure (DEE) 1939 ± 184 kJ per day. This was significantly greater (x 1.5) than previous estimates which assumed DEE to be three times the basal metabolic rate (BMR) based on regression equations predicting BMR from body mass. FMR of captives and dietary data from previous studies were used to estimate daily consumption of salmon, Salmo salar, smolts and parr by natural populations of these ducks on the river North Esk, north‐east Scotland. Goosanders are likely to consume 480‐522 g fish per day of which two‐thirds are juvenile salmon; equivalent to a daily intake of 10‐11 smolts and 48‐52 parr. Annual predation of smolts by goosanders was estimated to be between 8000 and 15 000 or 3 and 16% of annual production.

Influence of Movement by Coho Salmon (Oncorhynchus kisutch) Parr on Their Detection by Common Mergansers (Mergus merganser)

AbstractA common reaction in juvenile salmonids that detect predators is to decrease activity. To test whether there is a survival advantage to reduced movement under such circumstances, juvenile coho salmon (Oncorhynchus kisutch) were placed with common mergansers (Mergus merganser) under laboratory conditions that precluded crypsis. Mergansers were more likely to attack fish that moved than fish that remained stationary, and the relation between the lag time for detection by the birds and fish movement rate is best described as inversely exponential. The lag time for detection was not correlated with fish size. The risk of detection of prey by visual predators should be determined by both predator and prey behaviour, but our results suggest that in this case prey behaviour is more important. In the field, territorial coho juveniles do feed more and grow faster than other, non‐territorial fish. They also spend a smaller proportion of their time moving. The present experiment suggests that territorial coho may also suffer less mortality than non‐territorial fish, which would lower their ratio of mortality risk to growth rate.

Declines in organochlorines in eggs of red-breasted mergansers from Lake Michigan, 1977?1978 versus 1990

From 1977-1978 to 1990, concentrations of polychlorinated biphenyls (PCBs) and most organochlorine pesticides declined in eggs of red-breasted mergansers (Mergus serrator) nesting on islands in northwestern Lake Michigan. Total PCBs decreased 60% (from 21 ppm in 1977-1978 to 8.5 ppm in 1990) and p,p'-DDE decreased 66% (from 6.5 to 2.2 ppm). Dieldrin decreased only 16% (from 0.82 to 0.69 ppm). In 1990, 79.1% of incubated eggs hatched, which was not significantly different from the 83.5% that hatched in 1977-1978.

Variation in the morphology of adult Apatemon gracilis Rudolphi, 1819 (Digenea: Strigeidae) reared in different avian hosts

Adult Apatemon gracilis (Rudolphi, 1819) were reared experimentally in three different avian hosts: herring gulls Larus argentatus Gmelin, domestic chicks Gallus gallus (L.) and eider ducklings Somateria mollissima (L.). Comparisons of size, body proportions and fecundity were made between these and specimens obtained from a naturally infected goosander Mergus merganser L. The eider duck proved to be a suitable experimental host, rearing adults of comparable size and fecundity to those from the natural host. The growth and development of the parasite in domestic chicks and herring gulls were significantly reduced. Similar conditions are likely to exist in the natural environment and this should be taken into consideration when choosing experimental hosts for use in the laboratory or when identifying species.

Water-bird population changes in 1976–1990 on Besnard Lake, Saskatchewan: increases in loons, gulls, and pelicans

Declines in Common Loon (Gavia immer) populations associated with increasing human use of lakes have been reported from many areas of North America. In the present report we describe a lake in northern Saskatchewan, Besnard Lake, where there has been a substantial increase in the number of loons, from about 85 in 1976–1979 to about 165 in 1990. A comparison was made with numbers of other birds associated with water. Increases were also seen in American White Pelicans (Pelecanus erythrorhynchos), Osprey (Pandion haliaetus), Great Blue Herons (Ardea herodias), Herring Gulls (Larus argentatus), Ring-billed Gulls (L. delawarensis), and Bonaparte's Gulls (L. Philadelphia). No change was seen in mergansers (Mergus merganser and M. serrator), Bald Eagles (Haliaeetus leucocephalus), or Common Terns (Sterna hirundo). The period 1976–1990 has also seen increased human use on Besnard Lake. The reason for increased loon numbers is uncertain, but could possibly be related to an increase in the numbers of small fish in Besnard Lake as a result of increased fishing pressure disproportionately removing the larger, predatory fish.

Feeding and aggressive behaviours in juvenile coho salmon (Oncorhynchus kisutch) under chemically-mediated risk of predation

Juvenile coho salmon (Oncorhynchus kisutch) spend the first year of their lives in their natal streams, where they may often hold feeding territories. They also face significant risk of predation by birds and fish, and should alter their behaviour to reduce risk of mortality when these predators are present. Although there is laboratory evidence that coho react to predator visual stimuli, chemoreception of avian predator presence has not previously been reported. We tested the influence of chemical stimuli of common merganser (Mergus merganser), preying on juvenile coho, on two aspects of coho territorial behaviour, foraging and aggression, in flow-through aquaria. After a mixture of merganser- and coho-conditioned water was introduced into the system, juvenile coho significantly reduced their attack distance on drifting prey. The fish also significantly decreased their aggressive behaviour directed towards mirrors (total number of acts, intensity of acts and time spent) when the same odour was present. They did not change their behaviour in either experiment after control introductions of water treated with fish alone. These results are interpreted within the framework of a trade-off between juvenile growth and mortality.

Feeding behaviour and diet of goosanders(Mergus merganser)in relation to salmonid seaward migration

Foraging activities of goosanders (Anatidae, Mergus merganser) were studied in relation to seaward migration of smolt in the River Halselva in northern Norway, 1987-1989. Birds aggregated in the estuary in June, during mass migration of smolts. When present in the estuary males and females spent 28.7 and 35.6% of their time feeding. Only 15% of dives resulted in birds' bringing prey to the surface and about 25% of prey found in goosander stomachs were salmonids. For hatchery-reared smolts released in the estuary, average length taken did not differ from that available; for wild smolts of Arctic char, however, smaller fishes than those available were taken. For 1989, we estimate that goosanders took 1% of the hatchery-reared smolts released in the estuary, and 2% of the wild smolts when smolts passed the estuary during seaward migration. As it is likely that less fit smolts (e.g. sick, injured, small) are most prone to predation, we argue that such a level of predation on migrating smolts from goosanders has only a minor impact on salmonid production. Suggestions to reduce predation are discussed.

Identification of Diplostomum spp. in the retina of perch Perca fluviatilis and the lens of roach Rutilus rutilus from the Baltic Sea — an experimental study

Metacercariae of the genus Diplostomum dwelling in the retina of perch Perca fluviatilis and the lens of roach Rutilus rutilus were identified on the basis of adults obtained by feeding various piscivorous birds of the families Laridae, Anatidae and Phasianidae with metacercariae on an experimental basis. Both morphological studies of the metacercariae and adults obtained from the intestine of the infected birds, as well as the suitability in these hosts, indicated that we were dealing with two different species of Diplostomum. The perch form was recognised as D. baeri Dubois, 1937. Although metacercariae of this species matured both in herring gull Larus argentatus and common tern Sterna hirundo, the principal final host seemed to be goosanders Mergus merganser. In contrast, the lens form in roach was identified as D. spathaceum (Rudolphi, 1819) and it seemed to be restricted to birds of the family Laridae. These experimental results agree with parasitological findings from birds infected in the wild.

Waterbird Surveys at Hamilton Harbour, Lake Ontario, 1985–1988

Waterbird surveys were conducted at Hamilton Harbour and Windermere Basin from 1985–88 to help assess current wildlife usage of Burlington Bay vis-à-vis the Remedial Action Plan (RAP) for Hamilton Harbour. A total of 43 and 32 waterbird species (not including shorebirds) was recorded at Hamilton Harbour and Windermere Basin, respectively. Generally, more species of loons and grebes and aquatic raptors such as osprey and bald eagle were found at Hamilton Harbour than at Windermere Basin. Species such as mallard and Canada goose which key into unnatural food sources at marinas and golf courses, and double-crested cormorants, associated with a growing colony, were present in large numbers at Hamilton Harbour. Large numbers of common mergansers congregated on the harbor in early winter before freeze-up. On average, waterbirds were found in greater numbers at Windermere Basin. The large numbers of scaup and dabbling ducks, such as black duck and mallard, present at Windermere Basin were attracted by the warm water, low disturbance, and abundant available food source. The ice-free conditions at Windermere Basin also attracted regionally rare wintering species such as northern pintail, northern shoveler, ruddy duck, and green-winged teal. Survey results were compared to unpublished survey data from Cootes Paradise and published results of the annual mid-winter waterfowl survey of western Lake Ontario. The importance of Hamilton Harbour and Windermere Basin to migratory waterbirds should be considered regarding future clean-up of Burlington Bay.