Duckling Survival Research Articles

Mallard brood movements and survival in an urbanized landscape

AbstractWhen selecting a nest site, mallards (Anas platyrhynchos) balance differing habitat requirements for the nesting and brood‐rearing periods, such that the juxtaposition of these habitats in the landscape may influence the female's reproductive strategy and reproductive success. Mallard populations in the northeastern United States have declined since the mid‐1990s, and increasing urban development in this region may pose risks to broods and cause high duckling mortality. We assessed mallard brood and duckling survival in the urbanized landscapes of Connecticut, USA, and evaluated whether differences in brood movements, home ranges, and habitat use in urbanized areas influence brood survival. We monitored 32 mallard broods from females with global positioning system (GPS) transmitters in Connecticut in 2021 and 2022. Apparent brood survival to 30 days (0.48, n = 29 broods) was comparable to previous estimates in the Northeast (range = 0.21–0.72), but individual duckling survival (0.18, n = 257 ducklings) was lower than many previous estimates for this region (range = 0.14–0.44), suggesting this parameter warrants continued evaluation because it may be contributing to population declines in Connecticut and the greater Northeast region. Mallard females demonstrated different reproductive strategies and seemed to prioritize either high‐quality nesting habitat or proximity to high‐quality brood‐rearing habitat. High‐quality nesting habitat is not necessarily near high‐quality brood‐rearing habitat, and 61% (17/28) of females moved their ducklings an average of 1.1 ± 0.9 km (SD) shortly after hatch to a brood‐rearing site, often traveling along small streams. A similar proportion of successful (9/12) and failed (7/13) broods moved. We provide evidence of limited availability of brood‐rearing habitat, as females moved long distances to brood‐rearing wetlands and only 1 brood made additional inter‐wetland moves. Management actions that create or modify nesting and brood‐rearing habitat should consider connectivity between these sites; females may choose to nest away from wetlands to minimize exposure to predators but may depend on small streams for travel to brood‐rearing wetlands.

Survival of northern pintail ducklings in grasslands and croplands: implications for fall‐seeded cereals

AbstractSpecies‐specific management strategies have been implemented to address persistently low continental populations of several duck species, including the northern pintail (Anas acuta). In the Canadian Prairie Pothole Region (PPR), addressing threats from spring‐seeded cereals on pintail productivity may provide sufficient gains to recover populations. Research on pintail duckling ecology has revealed that duckling survival may be greater in grassland‐dominated landscapes than in annual cropland‐dominated landscapes, possibly limiting the benefits of fall‐seeded cropping practices. Winter wheat crops increase nest success and may assist nesting pintail populations through provision of nesting refuges from spring tillage operations, earlier hatch, and greater nest densities compared to traditional spring‐seeded cereal crops. Yet inadequate duckling survival may reduce these benefits. Our principal objective was to examine if pintail reproductive success in winter wheat in cropland‐dominated landscapes was comparable to grassland‐dominated landscapes or, alternatively, if duckling survival rates in cropland‐dominated landscapes offset the gains of greater nesting success in winter wheat. We captured and radio‐marked 104 nesting female pintails in grasslands and croplands of southern Saskatchewan, during 2011–2012. We modeled cumulative survival to 30 days post hatch in relation to landscape composition and land cover type, specifically, the influence of nesting in fall‐seeded crops. Predicted 30‐day survival for ducklings hatched in perennial cover (40.8% [85% CI = 40.0–44.6%]) in grassland‐dominated landscapes and winter wheat (38.2% [32.0–44.4%]) in cropland‐dominated landscapes was more than double survival of ducklings hatched in spring‐seeded cropland (16.9% [12.6–21.6%]) in cropland‐dominated landscapes. Ducklings moving through local environments with more perennial cover and seasonal wetlands, but less wetland edge, had increased survival. The benefit of greater nest survival in winter wheat was not completely superseded by reduced duckling survival for broods raised in intensive agricultural landscapes. The retention of grassland landscapes and expansion and promotion of fall‐seeded crops in cropland‐dominated landscapes can benefit northern pintails across broad regions of the PPR.

The effectiveness of the biologically active additive «Activio» using when feeding young ducks

Agricultural poultry has a number of biological features: intensive metabolism and rapid growth, rapid maturity and significant reproductive potential, high body temperature, resistance to many infectious diseases, etc. The scientific article presents the results of an experimental study of the effect of the biologically active additive Activio, which contains essential oils of cinnamon, rosemary, oregano and chili pepper extract, on the productive qualities of young ducks. To realize the set goal, two experimental groups of ducks were formed: 1st group - Peking ducks, 2nd group - Cherry Valley ducks, which were fed the drug Activio as part of a complete and balanced diet in terms of nutrients and energy, at the rate of 100 g ha 1 t of compound feed . It has been established that the introduction of the drug Activio into the diet of young ducks contributes to the increase in feed consumption, live weight gains and the survival of ducklings, which is primarily due to the fact that the essential oils of cinnamon, rosemary, oregano, chili pepper extract have positive, stimulating biological effects. improve the functioning of the digestive, immune, nervous systems and musculoskeletal system. During the breeding of poultry, an important indicator is the average daily feed consumption, which according to the data of the article in the period from 1 to 7 days was 27.15 g/head/day in the ducks of the first group, and 28.41 g/head/day in the ducks of the second group, and in the period from the 22nd to the 28th day, the value of the average daily feed consumption is 259.36 g/go/day in the first group, and 270.36 g/go/day in the ducks of the second group. The use of the drug Activio did not have a negative effect on the body of young ducklings and made it possible to realize the genetic potential of the productivity of ducks, which was more clearly expressed in the young ducklings of the Cherry Valley breed, which was obtained on the basis of Peking ducks through in depth selection using the paternal line 151 and maternal line 102 and has higher growth energy compared to Peking ducks. Key words: ducks, Peking breed, Cherry Valley, feed supplement, «Activio», gains, live weight, preservation.

Integrated population modeling identifies low duckling survival as a key driver of decline in a European population of the Mallard

Abstract Europe’s highest densities of breeding Mallards (Anas platyrhynchos) are found in the Netherlands, but the breeding population there has declined by ~30% since the 1990s. The exact cause of this decline has remained unclear. Here, we used an integrated population model to jointly analyze Mallard population survey, nest survey, duckling survival, and band-recovery data. We used this approach to holistically estimate all relevant vital rates, including duckling survival rates for years for which no explicit data were available. Mean vital rate estimates were high for nest success (0.38 ± 0.01) and egg hatch rate (0.96 ± 0.001), but relatively low for clutch size (8.2 ± 0.05) compared to populations in other regions. Estimates for duckling survival rate for the three years for which explicit data were available were low (0.16–0.27) compared to historical observations, but were comparable to rates reported for other regions with declining populations. Finally, the mean survival rate was low for ducklings (0.18 ± 0.02), but high and stable for adults (0.71 ± 0.03). Population growth rate was only affected by variation in duckling survival, but since this is a predominantly latent state variable, this result should be interpreted with caution. However, it does strongly indicate that none of the other vital rates, all of which were supported by data, was able to sufficiently explain the population decline. Together with a comparison with historic vital rates, these findings point to a reduced duckling survival rate as the likely cause of the decline. Candidate drivers of reduced duckling survival are increased predation pressure and reduced food availability, but this requires future study. Integrated population modeling can provide valuable insights into population dynamics even when empirical data for a key parameter are partly missing.

Reproductive Ecology of the Brazilian Merganser (Mergus octosetaceus) in Serra da Canastra National Park and Adjacent Areas, Minas Gerais, Brazil

The Brazilian Merganser (Mergus octosetaceus) is globally classified as a Critically Endangered species and is one of the world's rarest waterbirds. The breeding ecology of this species was studied between 2005 and 2016 in the region of the Serra da Canastra National Park, Minas Gerais, Brazil. Between two and six nests were followed each year, with mean of 4.1 (n = 18 nests). Mean clutch size was 6.7 ± 0.9 (n = 31 clutches) with a range of five to eight eggs per nest. Average incubation constancy was 88.3% (n = 3 nests) and ranged from 86.7% to 90.7%. Mean incubation temperature and humidity were obtained from three nests and ranged from 33.6 °C to 33.8 °C and 65.9% to 70.2% respectively. The nest success was 77.1%, and the duckling survival (up to 8 weeks) was 53.8%. Nest predation was relatively low at 7.9%, and the annual reproductive output was 4.7 ducklings/female. Data on breeding ecology is fundamental in guiding conservation strategies, both in the field and in captivity.

Survival and habitat selection of wood duck ducklings

ABSTRACTSurvival and habitat selection during brood‐rearing influences reproductive success and waterfowl population dynamics. For effective management, it is important to understand vital rates and habitat choice range wide. We investigated survival and habitat selection of female wood ducks (Aix sponsa) and ducklings at Long Point, Lake Erie, Ontario, Canada in 2014. We captured incubating females (n = 40) in nest boxes and used radio‐telemetry to monitor survival and habitat use to 30 days post‐hatch. Four female mortalities occurred during brood‐rearing and apparent brood and duckling survival were 0.42 (85% CI = 0.33, 0.51) and 0.16 (85% CI = 0.14, 0.18), respectively. Duckling survival was negatively associated with brood size and distance of first movement, whereas survival was positively associated with precipitation. Successful brood‐rearing wood ducks selected forested wetlands and habitats that provided dense vegetative cover. Conservation and restoration of forested wetlands and similar cover should increase the availability of brood‐rearing habitat. Placement of nest boxes close to selected land cover types and strategies associated with reducing inflated clutch sizes may improve offspring survival. Our spatially explicit habitat selection model informs spatial prioritization of habitat conservation and nest box placement strategies within the Great Lakes region. © 2018 The Wildlife Society.

Duckling survival of mallards in Southland, New Zealand

ABSTRACTThe southern portion of New Zealand's South Island is a productive area for mallards (Anas platyrhynchos) despite a notable lack of permanent or semi‐permanent wetlands. Most broods are reared in pastures that may or may not be flooded with ephemeral water. In recent years, there has been an increased conversion from continuous to sporadic grazing that has resulted in a functional change in the emergent and upland vegetation available for broods. In 2014, we investigated mallard duckling survival on different pastures relative to a suite of characteristics pertaining to the adult female, clutch, brood, weather, and habitat. We monitored 438 ducklings from 50 radio‐marked females to 30 days post‐hatch. Duckling survival was unaffected by pasture type but increased with duckling age, the presence of ephemeral water, and with greater distance from the nearest anthropogenic structure. Survival was lower for broods of second year (SY) females than for broods of after‐second year (ASY) females, in areas with more dense cover, and when ducklings moved, on average, greater daily distances. Cumulative 30‐day duckling survival ranged from 0.11 for ducklings of SY females without ephemeral water present to 0.46 for ducklings of ASY females with ephemeral water present. Therefore, increasing available seasonal water sources may increase duckling survival. Further, narrow, linear patches of dense cover present in our study could support a greater abundance of predators or increase their foraging efficiency. As such, managers could consider increasing patch sizes of dense cover to reduce predator efficiency, and employing predator removal in these areas to improve duckling survival. © 2017 The Wildlife Society.

White-cheeked Pintail duckling and brood survival across wetland types at Humacao Nature Reserve, Puerto Rico

ABSTRACT Duckling survival is an important influence on recruitment in several North American Anas species. White-cheeked Pintail (Anas bahamensis) breeding in Puerto Rico encounter a variety of wetland types that may influence duckling survival. We monitored fates of 92 radio-tagged ducklings in 31 broods in 5 wetland habitat types at Humacao Nature Reserve in southeastern Puerto Rico from 2000 to 2002. Wetlands included 2 separate coastal lagoon complexes, mangrove forest, and managed and unmanaged wetland impoundments containing herbaceous vegetation. We used known-fate models to estimate daily and interval survival rates of ducklings and broods. We conducted conservative and liberal analyses of survival because of uncertain fates of 36 ducklings. In the conservative analysis, the most parsimonious model for duckling survival contained wetland type and a positive influence of daily precipitation. In the liberal analysis, duckling survival also varied among wetlands, was positively influenced by daily p...

Using sightability‐adjusted brood‐pair ratios to estimate waterfowl productivity

ABSTRACTHistorically, biologists used brood‐pair ratios (BPRs) as an index to waterfowl productivity to help guide management decisions and evaluate conservation practices. However, BPRs are biased by imperfect detection probabilities, especially for broods. We conducted roadside surveys for breeding waterfowl pairs on 7–8 study sites in the springs of 2006–2008 in northeastern North Dakota, USA. Later each year, we conducted replicate counts of broods on the same wetlands and used mark–recapture methods to estimate sightability‐adjusted BPRs (SA‐BPRs). Traditional roadside brood surveys detected only 30–45% of the available broods, depending on species. We explored the potential for using SA‐BPRs to measure hen success (i.e., the probability a female hatches ≥1 egg across all nesting attempts) for mallards (Anas platyrhynchos) and other upland‐nesting dabbling ducks (Anas spp.). We found that SA‐BPRs explained 40% of the variation in hen success over 5 species of dabbling ducks, and we were able to detect an effect of predator reduction on hen success in combined dabblers, but not in mallards alone. However, we found no relationship between SA‐BPRs and mallard fledging rates (hen success × initial brood size × duckling survival). Our results suggest that SA‐BPRs can provide a cost‐effective alternative to traditional measures of productivity such as nesting success, but not to measures of duckling survival. Nevertheless, SA‐BPRs may be useful in areas where traditional measures of waterfowl productivity are logistically or financially challenging. © 2014 The Wildlife Society.

Multi-scale habitat selection affects offspring survival in a precocial species

In theory, habitat preferences should be adaptive. Accordingly, fitness is often assumed to be greater in preferred habitats; however, this assumption is rarely tested and, when it is, the results are often equivocal. Habitat preferences may not directly convey fitness advantages if animals are constrained by tradeoffs with other selective pressures like predation or food availability. We address unresolved questions about the survival consequences of habitat choices made during brood-rearing in a precocial species with exclusive maternal care (mallard Anas platyrhynchos, n = 582 radio-marked females on 27 sites over 8 years). We directly linked duckling survival with habitat selection patterns at two spatial scales using logistic regression and model selection techniques. At the landscape scale (55-80 km(2)), females that demonstrated stronger selection of areas with more cover type 4 wetlands and greater total cover type 3 wetland area (wetlands with large expanses of open water surrounded by either a narrow or wide peripheral band of vegetation, respectively) had lower duckling survival rates than did females that demonstrated weaker selection of these habitats. At finer scales (0.32-7.16 km(2)), females selected brood-rearing areas with a greater proportion of wetland habitat with no consequences for duckling survival. However, females that avoided woody perennial habitats composed of trees and shrubs fledged more ducklings. The relationship between habitat selection and survival depended on both spatial scale and habitats considered. Females did not consistently select brood-rearing habitats that conferred the greatest benefits, an unexpected finding, although one that has also been reported in other recent studies of breeding birds.

Radiomarking brood‐rearing mallard females: Implications for juvenile survival

AbstractRadiotelemetry is frequently used to measure habitat use, movements, and survival in birds; presumably, outfitting adult females with radiotransmitters does not influence juvenile survival, but this critical assumption is rarely tested. We evaluated whether the timing or type of transmitter deployed on adult female mallards (Anas platyrhynchos) reduced duckling survival estimates in the Canadian Prairie Pothole Region, 1993–1995. The best‐approximating model suggests that, compared with 2 other trap–transmitter combinations, ducklings raised by mallard females trapped prior to nest initiation and outfitted with anchor–suture transmitters had poor survival. The 30‐day survival rate of ducklings raised by female mallards equipped with anchor–suture transmitters prior to nest initiation was lower than survival of ducklings attended by females equipped prior to nest initiation with abdominally implanted transmitters or females marked during late incubation with anchor–suture transmitters. Studies of reproductive success deploying anchor–suture transmitters on female waterfowl trapped prior to nest initiation may have biased results because of possible negative consequences to offspring survival. © 2012 The Wildlife Society.

Kin structure and choice of brood care in a Common Eider (Somateria m. mollissima) population

We investigated the presence of kin-biased cooperative breeding in the Common Eider (Somateria m. mollissima), a colonial seaduck commonly presumed to have a high rate of natal philopatry. Based on a 23-year- long time series of individually marked mothers and daughters, we found that on average 18% of the study population consisted of first-order relatives: mothers, daughters, and female siblings. However, there were years with no or only a few first-order kin pairs present. This was due to the overall low duckling survival in this species and the high rate of natal dispersal in this population. There was no apparent tendency for timely nesting relatives (laying within 3 days of each other) to approach each other, indicating no firm kin recognition. In a 3-year sampling of DNA from egg shell membranes, the annual rate of intra- specific brood parasitism in the population varied between 25 and 67%. However, becoming parasitized had no effect on the subsequent choice of brood tending tactics, i.e., whether to tend alone or communally. Neither was the choice of brood tending tactics affected by the number of own eggs in the clutch or by the female body condition. However, becoming a communal brood-tender was jointly contributed by the presence of alien eggs in the nest and the presence of first-order kin in the colony during early breeding. The greatest effect on females favoring com- munal brood care instead of rearing alone was due to the number of similar-aged broods nearby at the time of nest exodus. We found no evidence of firm kin recognition among individuals in our study population.

Population dynamics of king eiders breeding in northern Alaska

The North American population of king eiders (Somateria spectabilis) has declined by more than 50% since the late 1970s for unknown reasons. King eiders spend most of their lives in remote areas, forcing managers to make regulatory and conservation decisions based on very little information. We incorporated available published estimates of vital rates with new estimates to build a female, stage-based matrix population model for king eiders and examine the processes underlying population dynamics of king eiders breeding at 2 sites, Teshekpuk and Kuparuk, on the coastal plain of northern Alaska and wintering around the Bering Sea (2001–2010). We predicted a decreasing population (λ = 0.981, 95% CI: 0.978–0.985), and that population growth was most sensitive to changes in adult female survival (sensitivity = 0.92). Low duckling survival may be a bottleneck to productivity (variation in ducking survival accounted for 66% of retrospective variation in λ). Adult survival was high (0.94) and invariant ( = 0.0002, 95% CI: 0.0000–0.0007); however, catastrophic events could have a major impact and we need to consider how to mitigate and manage threats to adult survival. A hypothetical oil spill affecting breeding females in a primary spring staging area resulted in a severe population decline; although, transient population dynamics were relatively stable. However, if no catastrophic events occur, the more variable reproductive parameters (duckling and nest survival) may be more responsive to management actions. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Landscape‐level correlates of mallard duckling survival: Implications for conservation programs

AbstractDespite recent work, uncertainty remains concerning how abiotic and biotic factors affect duckling survival. Additionally, upland habitat characteristics may affect duckling survival rates but this potential relationship has largely been ignored. We evaluated several unresolved hypotheses about causes of mallard (Anas platyrhynchos) duckling survival variation, with an emphasis on assessing effects of managed and remnant natural upland habitats. During 1993–2000, 617 radio‐marked females provided information about brood habitat use and duckling survival on 27 sites in prairie Canada. We contrasted a priori and exploratory models that incorporated effects of upland, wetland, weather, female, and brood‐related variables on duckling survival rates. Survival was highest for ducklings when a greater proportion of their surrounding landscape (i.e., within a 500‐m radius buffer around the brood) was comprised of wetlands characterized by a central expanse of open water and a peripheral ring of flooded emergent vegetation. Cold and wet weather in the first week of life resulted in lower duckling survival. In a post hoc analysis, duckling survival (of older ducklings) was negatively related to increasing proportions of managed hayland. © 2011 The Wildlife Society.

The role of predator removal, density‐dependence, and environmental factors on mallard duckling survival in North Dakota

AbstractDuckling survival is an important component of mallard (Anas platyrhynchos) recruitment and population growth, yet many factors regulating duckling survival are poorly understood. We investigated factors affecting mallard duckling survival in the drift prairie of northeastern North Dakota, 2006–2007. Mammalian meso‐predators were removed by trapping on 4 92.3 km2 study sites and another 4 study sites served as controls. We monitored 169 broods using telemetry and periodic resighting, and we modeled cumulative survival to 30 days of age ${\left( {{\hat {S}}_{30\,{\rm d}} } \right)}$ using the nest survival module in Program MARK. Duckling survival was not affected by predator removal (${\hat {S}}_{30\,{\rm d \hbox{-} Control}} {\rm = 0}{\rm .208}$, 85% CI: 0.182–0.234; ${\hat {S}}_{30\,{\rm d \hbox{-} Trapped}} {\rm = 0}{\rm .183}$, 85% CI: 0.155–0.211) and was only weakly negatively correlated with duckling density. Duckling survival was higher in 2007 (${\hat {S}}_{30{\rm d \hbox{-} 2007}} = 0.264$, 85% CI: 0.193–0.355) than 2006 (${\hat {S}}_{30\,{\rm d \hbox{-} 2006}} = 0.157$, 85% CI: 0.084–0.252) and increased with total seasonal and semipermanent wetland area and declined with perennial cover in the surrounding landscape. Broods that hatched earlier in the season (especially in 2006) and ducklings that were heavier at hatch also had higher survival. Our estimates of duckling survival are among the lowest reported for mallards and contradict previous research in Saskatchewan that found predator removal increased duckling survival. However, our results are consistent with other studies suggesting that earlier hatch date, increased wetland availability, and better duckling condition lead to increased survival. Management actions that increase wetland density, improve nest success early in the season, and potentially target brood‐specific predators such as mink (Neovison vison) would likely lead to higher duckling survival. © 2011 The Wildlife Society.

Born to cope with climate change? Experimentally manipulated hatching time does not affect duckling survival in the mallard Anas platyrhynchos

Two main hypotheses proposed to explain the seasonal decline in reproductive performance in birds are (1) deterioration of environmental conditions and (2) lower parental quality of late breeders. Previous experimental work addressing these hypotheses generally have problematic biases pertaining to delay of hatching, costs of re-laying and incubation, as well as variation in the quality of eggs, territories, offspring and parental traits. We address these biases in an experimental test of the timing hypothesis (i.e. (1) above) in a precocial bird. Using a 2-year cross-over design and game-farm mallard (Anas platyrhynchos) eggs originating from a number of hens and a standardised delay procedure, we introduced early and late broods with a foster female onto boreal oligotrophic lakes and monitored subsequent duckling survival. Standardised invertebrate sampling was done concurrently to get a measure of lake-level abundance of aquatic prey, a likely causative agent of putative seasonal difference in duckling survival. Survival data and covariates (duckling age; days) were analysed by an information theoretic approach. There was no effect of treatment (i.e. manipulation of hatching date) on duckling survival, which was higher in 2005 than in 2004. In contrast to observational studies from more seasonal wetlands, our experiment demonstrates that duckling survival on boreal lakes was not affected by a 12-day delay in hatching date. Since we did not find any consistent trends in abundance of aquatic prey, i.e. neither clear peaks nor differences between treatment periods, we hypothesise that moderate climate change has minor effects on resource abundance and hence also on mallard duckling survival in boreal environments.

Pre-laying climatic cues can time reproduction to optimally match offspring hatching and ice conditions in an Arctic marine bird

Individuals breeding in seasonal environments are under strong selection to time reproduction to match offspring demand and the quality of the post-natal environment. Timing requires both the ability to accurately interpret the appropriate environmental cues, and the flexibility to respond to inter-annual variation in these cues. Determining which cues are linked to reproductive timing, what these cues are predicting and understanding the fitness consequences of variation in timing, is therefore of paramount interest to evolutionary and applied ecologists, especially in the face of global climate change. We investigated inter-annual relationships between climatic variation and the timing of reproduction in Canada's largest breeding population of Arctic common eiders (Somateria mollissima) in East Bay, Nunavut. Warmer spring temperatures predicted both earlier mean annual laying dates and the earlier ice-free conditions required by ducklings for post-natal growth. Warmer springs had higher variation in this temperature cue, and the population laying distribution became increasingly positively-skewed in warmer summers, potentially indicating that more low-quality females had the opportunity to commence laying in warmer years. Females that timed laying to match duckling hatching just prior to fully ice-free conditions obtained the highest duckling survival probability. Inter-annual data on repeated breeding attempts revealed that the individuals examined show a similar degree of laying flexibility in response to climatic variation; however, there was significant individual variation in the absolute timing of laying within an average year. This work sheds light on how reproductive timing is related to and influenced by variation in local climate and provides vital information on how climate-related variation in reproductive timing influence a fitness measure in an Arctic species. Results are especially relevant to future work in polar environments given that global climatic changes are predicted to be most intense at high latitudes.

Reproduction in mallards exposed to dietary concentrations of methylmercury

The purpose of this experiment was to use mallards (Anas platyrhynchos) tested under controlled conditions to determine how much harm to reproduction resulted from various concentrations of mercury in eggs. Breeding pairs of mallards were fed a control diet or diets containing 1, 2, 4, or 8 microg/g mercury, as methylmercury chloride. Mean concentrations of mercury in eggs laid by parents fed 0, 1, 2, 4, or 8 microg/g mercury were 0.0, 1.6, 3.7, 5.9, and 14 microg/g mercury on a wet-weight basis. There were no signs of mercury poisoning in the adults, and fertility and hatching success of eggs were not affected by mercury. Survival of ducklings and the number of ducklings produced per female were reduced by the 4 and 8-microg/g dietary mercury treatments (that resulted in 5.9 and 14 microg/g mercury in their eggs, respectively). Ducklings from parents fed the various mercury diets were just as heavy as controls at hatching, but by 6 days of age ducklings whose parents had been fed 4 or 8 microg/g mercury weighed less than controls. Because we do not know if absorption of mercury from our diets would be the same as absorption from natural foods, the mercury concentrations we report in eggs may be more useful in extrapolating to possible harmful effects in nature than are the dietary levels we fed. We conclude that mallard reproduction does not appear to be particularly sensitive to methylmercury.

Enhanced reproduction in mallards fed a low level of methylmercury: An apparent case of hormesis

Breeding pairs of mallards (Anas platyrhynchos) were fed a control diet or a diet containing 0.5 microg/g mercury (Hg) in the form of methylmercury chloride. There were no effects of Hg on adult weights and no overt signs of Hg poisoning in adults. The Hg-containing diet had no effect on fertility of eggs, but hatching success of eggs was significantly higher for females fed 0.5 microg/g Hg (71.8%) than for controls (57.5%). Survival of ducklings through 6 d of age was the same (97.8%) for controls and mallards fed 0.5 microg/g mercury. However, the mean number of ducklings produced per female was significantly higher for the pairs fed 0.5 microg/g Hg (21.4) than for controls (16.8). Although mercury in the parents' diet had no effect on mean duckling weights at hatching, ducklings from parents fed 0.5 microg/g Hg weighed significantly more (mean = 87.2 g) at 6 d of age than did control ducklings (81.0 g). The mean concentration of Hg in eggs laid by parents fed 0.5 microg/g mercury was 0.81 microg/g on a wet-weight basis. At this time, one cannot rule out the possibility that low concentrations of Hg in eggs may be beneficial, and this possibility should be considered when setting regulatory thresholds for methylmercury.

Nest Success and Duckling Survival of Greater Scaup, <em>Aythya marila</em>, at Grassy Island, New Brunswick

Nesting biology and duckling survival of Greater Scaup (Aythya marila) at Grassy Island on the Saint John River in southern New Brunswick were compared between 1995 and 1996. Grassy Island in New Brunswick is an area that is notably removed from other scaup breeding areas, being located farther south from main breeding areas in North America. The Mayfield estimates of nest success were 61% and 21% in 1995 and 1996, respectively. Mean daily survival rates were 0.99 in 1995 and 0.96 in 1996 and were significantly different (t = 4.86, P < 0.001). Duckling survival was estimated to range from 38 to 54% in 1995, and was 8% in 1996. The lower breeding success in 1996 may have been due to factors associated with decreased temperatures and increased precipitation, but the fact that the breeding location is atypical to other Greater Scaup breeding areas should not be overlooked.