James H. Devries

Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: A review

Neonicotinoids, broad-spectrum systemic insecticides, are the fastest growing class of insecticides worldwide and are now registered for use on hundreds of field crops in over 120 different countries. The environmental profile of this class of pesticides indicate that they are persistent, have high leaching and runoff potential, and are highly toxic to a wide range of invertebrates. Therefore, neonicotinoids represent a significant risk to surface waters and the diverse aquatic and terrestrial fauna that these ecosystems support. This review synthesizes the current state of knowledge on the reported concentrations of neonicotinoids in surface waters from 29 studies in 9 countries world-wide in tandem with published data on their acute and chronic toxicity to 49 species of aquatic insects and crustaceans spanning 12 invertebrate orders. Strong evidence exists that water-borne neonicotinoid exposures are frequent, long-term and at levels (geometric means=0.13μg/L (averages) and 0.63μg/L (maxima)) which commonly exceed several existing water quality guidelines. Imidacloprid is by far the most widely studied neonicotinoid (66% of the 214 toxicity tests reviewed) with differences in sensitivity among aquatic invertebrate species ranging several orders of magnitude; other neonicotinoids display analogous modes of action and similar toxicities, although comparative data are limited. Of the species evaluated, insects belonging to the orders Ephemeroptera, Trichoptera and Diptera appear to be the most sensitive, while those of Crustacea (although not universally so) are less sensitive. In particular, the standard test species Daphnia magna appears to be very tolerant, with 24-96hour LC50 values exceeding 100,000μg/L (geometric mean>44,000μg/L), which is at least 2-3 orders of magnitude higher than the geometric mean of all other invertebrate species tested. Overall, neonicotinoids can exert adverse effects on survival, growth, emergence, mobility, and behavior of many sensitive aquatic invertebrate taxa at concentrations at or below 1μg/L under acute exposure and 0.1μg/L for chronic exposure. Using probabilistic approaches (species sensitivity distributions), we recommend here that ecological thresholds for neonicotinoid water concentrations need to be below 0.2μg/L (short-term acute) or 0.035μg/L (long-term chronic) to avoid lasting effects on aquatic invertebrate communities. The application of safety factors may still be warranted considering potential issues of slow recovery, additive or synergistic effects and multiple stressors that can occur in the field. Our analysis revealed that 81% (22/27) and 74% (14/19) of global surface water studies reporting maximum and average individual neonicotinoid concentrations respectively, exceeded these thresholds of 0.2 and 0.035μg/L. Therefore, it appears that environmentally relevant concentrations of neonicotinoids in surface waters worldwide are well within the range where both short- and long-term impacts on aquatic invertebrate species are possible over broad spatial scales.

Sensitivity analyses of the life cycle of midcontinent mallards

Relationships between vital rates and population growth rate (λ) are critical to understanding and managing population dynamics. Considerable study of the midcontinent mallard (Anas platyrhynchos) population has been directed to understanding how vital rates respond to environmental fluctuations and management, but inference to the relative importance of specific vital rates to λ remains weak. We used analytic and simulation-based sensitivity analyses of a stage-based matrix model of female midcontinent mallards to compare the relative importance of vital rates to λ. For each vital rate, we estimated mean values and process variation (biological variation across space and time) for females breeding on sites of approximately 70 km 2 in the Prairie Pothole Region (PPR) of the United States (Montana, North Dakota, South Dakota, Minnesota) and Canada (Saskatchewan, Manitoba, Alberta). We conducted perturbation analyses (i.e., analytic sensitivities and elasticities) to predict the relative influence of changes in vital rates on λ. We conducted variance decomposition analyses to assess the proportion of spatial and temporal variation in λ explained by process variation in each vital rate. At mean values of vital rates, analytic sensitivity of λ was highest to nest success and survival of adult females during the breeding season and non-breeding season; hence, equal absolute changes in these vital rates would be predicted to result in the largest Δλ, relative to other vital rates. Variation in sensitivities and elasticities across process variation in vital rates was primarily explained by variation in nest success and survival of ducklings. Process variation in breeding parameters was driving variation in λ: vital rates explaining the most variation were nest success (43%), survival of adult females during the breeding season (19%), and survival of ducklings (14%). Survival of adult females outside the breeding season accounted for only 9% of variation in λ. Our analyses suggested that predation processes on the breeding grounds were the primary proximate factors limiting population growth.

Nesting effort by wild mallards with 3 types of radio transmitters

Although radio transmitters have been used extensively in waterfowl research for 20 years, effects of these devices on wild breeding mallards (Anas platyrhynchos) are largely unknown. Therefore, we compared various measures of nesting effort for mallards radiomarked with harnessed backpacks, sutured backpacks, and abdominal implants. The proportion of females that nested varied (P < 0.05) by transmitter type: 5 of 9, 16 of 16, and 5 of 5 females nested with harnessed backpacks, implants, and sutured backpacks, respectively. Females with harnessed backpacks initiated fewer (P < 0.0001) nests than birds with other transmitter types and devoted fewer (P = 0.007) days to egg laying and incubation than birds with implants. Our results suggest that studies using harnessed backpacks may underestimate nesting effort, hen success, and recruitment

Effects of transmitters on reproduction and survival of wild mallards

Radiotelemetry is an important tool in many studies of waterfowl ecology and management, but some studies have indicated that harnessed-radiopackages affected the behavior and survival of marked birds. Transmitters attached mid-dorsally with sutures, glue, and a subcutaneous, stainless steel anchor-shaped wire (hereafter anchored backpacks) may eliminate such problems. Therefore, we compared various measures of reproduction and survival rates of wild mallards (Anas platyrhynchos) radiomarked with abdominal implants and anchored backpacks at 5 study sites located in the aspen-parkland biome of the Prairie Pothole Region of Canada. We also compared our tracking ability between abdominal implants and anchored backpacks and determined retention time of anchored backpacks. Females with anchored backpacks devoted significantly fewer days to egg laying and incubation and initiated fewer nests than did females with implants. At one site, females with backpacks had significantly lower survival rates than females with implants. At 3 of the remaining 4 sites, females with anchored backpacks had lower survival rates than females with implants, but these results were not significant. We detected no difference in our tracking ability between anchored backpacks and abdominal implants (63 of 136 [46%] with anchored backpacks, and 140 of 319 [43%] with implants were monitored successfully from the time they were trapped to 30 June at each site). Two anchored backpacks were known to have fallen off and 11 were suspected to have fallen off, out of 198 backpacks (average retention time for anchored backpacks was 43 ± 5.8 days for those that lost their transmitter). Our results suggest that anchored backpacks may have negatively affected reproduction and survival rates of wild mallards.

Breeding-season survival of mallard females in the prairie pothole region of Canada

As part of the Prairie Habitat Joint Venture (PHJV) Habitat Assessment Project, we radiomarked and tracked daily 2,249 female mallard ducks (Anas platyrhynchos) in the Prairie Pothole Region (PPR) of Canada. We conducted our study at 19 different 54- to 78-km 2 sites for 1 year per site from 1993 to 1998. We estimated female survival probability during the 90-day period following arrival on the breeding area and employed information-theoretic approaches to select among competing models that described factors affecting survival probability. We investigated the relationship between female survival and 3 periods of the nesting season, female age (yearling vs. older), upland habitat treatments, longitude, and habitat variables. Our model estimates of female survival probability ranged between 0.62 (SE = 0.028) and 0.84 (SE = 0.018) and averaged 0.76 (SE = 0.004) for the 90-day period. The best approximating model indicated that female survival was (1) lowest when most females were nesting, and (2) depended on longitude and percent wetland habitat such that survival was lowest at western sites with low wetland densities. Management efforts to reduce wetland loss, especially in western regions of the Canadian PPR, may positively influence female survival. Upland habitat restorations designed to improve nest survival may not have a concurrent impact on female survival unless a significant portion of the nesting population is affected.

Effects of Spring Body Condition and Age on Reproduction in Mallards (Anas Platyrhynchos)

Abstract We explored predictive models relating body condition and age to nesting propensity, timing of nest initiation, clutch size of first nests, aggregated nest survival, hatching success, and timing of hatch in Mallards (Anas platyrhynchos). Nesting propensity had a positive linear relationship with body condition, and second-year (SY) females had a lower probability of nesting than after-second-year (ASY) females (84% and 94%, respectively, at average body condition). Females in better body condition initiated nesting ∼15 days earlier than those in poor condition, and SY females nested ∼4 days later than ASY females at average body condition. Clutch size of first nests exhibited a curvilinear decline with body condition, such that large clutches were characteristic of females in the best condition that nested early. Nest survival and hatching probability were unaffected by body condition. Younger females had somewhat lower nest survival (11%) than older females (14%), which, in combination with renesting effort, resulted in an age difference in hatching probability (22% and 33%, respectively). Females in better condition hatched nests ∼15 days earlier than those in poor condition, and SY females hatched nests ∼4 days later, on average, than ASY females. Our results indicate that factors influencing the body condition of female Mallards arriving on breeding areas could influence subsequent reproductive investment and success. Condition effects are primarily through the mechanisms of nesting propensity, clutch size, and timing of nest initiation and hatch. Additionally, we provide evidence that Mallards in their first breeding season have lower reproductive potential than older females.

Waterfowl Use of Dense Nesting Cover in the Canadian Parklands

Abstract Dense nesting cover (DNC) has been a conspicuous component of habitat management for upland-nesting ducks for >30 years, but its benefits for nesting ducks have been contentious. During 1994–1999 we monitored 3,058 dabbling duck (Anas spp.) nests in 84 DNC fields located throughout the Canadian Parklands to examine sources of among-field variation in nest density and nesting success. Nest density averaged 1.51 (SE = 0.15) nests/ha and overall nesting success was 20.4%, but there was pronounced annual variation in both estimates. Nesting success increased with increasing field size (range = 6–111 ha), but nest density remained constant. Nest density increased with percent wetland habitat within DNC fields and declined with percent perennial cover in the surrounding 2.4 × 2.4-km landscape, but these variables were not important for predicting nesting success. Nest abundance and nesting success roughly doubled in fields seeded with alfalfa (Medicago sativa) or sweet clovers (Melilotus spp.), but there was no benefit from using native as opposed to tame grasses. We recommend that waterfowl managers in the Canadian Parklands establish DNC with alfalfa in large fields in landscapes with abundant wetlands but minimal competing cover.

Factors that affect renesting in Mallards (Anas platyrhynchos)

ABSTRACT. Renesting is an important strategy for coping with nest loss in many species of birds. We investigated renesting behavior of radiomarked Mallards (Anas platyrhynchos) breeding in the Canadian Prairie Parklands and found that females were persistent renesters, replacing >57% of 4,112 destroyed nests. Renesting propensity was most affected by nest initiation date, with ∼90% of unsuccessful females renesting if destroyed clutches had been initiated in April but <10% renesting for clutches initiated after 20 June. Probability of renesting declined with successive number of nesting attempts, but this was primarily an effect of initiation date. Renesting propensity increased with female age and body condition and declined for birds that had invested more time tending their previous clutch, but the latter effect was pronounced only among late-nesting females. The amount of time required to produce a replacement clutch was primarily a function of whether females were engaged in rapid follicle growth when nest failure occurred: 44% of females (383 of 870) that lost nests during early laying renested within 4 days, whereas only 2% (12 of 639) that lost nests after clutch completion renested within 4 days. Although clutch size was smaller in renests, this was entirely an artifact of later laying dates. Our results suggest that seasonal timing had the most influence on renesting behavior. Female age, body condition, and prior nesting effort had smaller, but demonstrable, influence.

Long-term response of northern pintails to changes in wetlands and agriculture in the Canadian prairie pothole region

From 1955 through the late 1970s, northern pintail (Anas acuta) populations closely tracked the abundance of spring ponds. Declines in numbers of both northern pintails (hereafter, pintails) and ponds were evident during years of drought. However, since the early 1980s, the strength of the relationship between pintails and ponds has weakened greatly. Agricultural expansion on primary breeding grounds has been implicated as the cause of sustained pintail declines, but previous studies investigated pintail response only at large geographic scales (e.g., prairie-wide, stratum level). Potentially important effects of localized or multiscale changes in wetlands and agriculture on pintails are not well understood. Using data from the Canadian Prairie Pothole Region for 1961 to 1996, we investigated spatial and temporal covariation of pintail numbers with environmental factors (pond numbers and wetness indices) and agriculture at various scales. Models best supported by the data indicated that pintails responded positively to winter precipitation but with important regional variation and positively to pond numbers in some locations (southwestern Saskatchewan and southern Alberta). Results also indicated that pintail settling was better explained (increases in R 2 values of 0.05-0.06) using information about specific agricultural practices than about overall increases in farmed area. At a prairie-wide scale, we detected a negative association between settling and increased cropland area. At regional scales, settling was positively associated to various degrees with area in fallow (i.e., summerfallow-land tilled but not planted to crop in a given year). Both associations were strengthened with higher winter precipitation. Because cropland stubble is used readily as a nesting habitat by pintails and spring tillage of fields not used for summerfallow destroys nests, a shift from summerfallow to continuous cropping in the Prairie Pothole Region of Canada may have reduced the reproductive capacity of pintails in important breeding areas. In regions with characteristics that historically have attracted pintails to settle, we encourage land managers to promote agricultural practices that minimize use of spring tillage, convert cropland to perennial forages and pasture, and protect and restore wetland and upland habitat.

Costs of Reproduction in Breeding Female Mallards: Predation Risk during Incubation Drives Annual Mortality

The effort expended on reproduction may entail future costs, such as reduced survival or fecundity, and these costs can have an important influence on life-history optimization. For birds with precocial offspring, hypothesized costs of reproduction have typically emphasized nutritional and energetic investments in egg formation and incubation. We measured seasonal survival of 3856 radio-marked female Mallards (Anas platyrhynchos) from arrival on the breeding grounds through brood-rearing or cessation of breeding. There was a 2.5-fold direct increase in mortality risk associated with incubating nests in terrestrial habitats, whereas during brood-rearing when breeding females occupy aquatic habitats, mortality risk reached seasonal lows. Mortality risk also varied with calendar date and was highest during periods when large numbers of Mallards were nesting, suggesting that prey-switching behaviors by common predators may exacerbate risks to adults in all breeding stages. Although prior investments in egg laying and incubation affected mortality risk, most relationships were not consistent with the cost of reproduction hypothesis; birds with extensive prior investments in egg production or incubation typically survived better, suggesting that variation in individual quality drove both relationships. We conclude that for breeding female Mallards, the primary cost of reproduction is a fixed cost associated with placing oneself at risk to predators while incubating nests in terrestrial habitats. RESUME. L’effort investi a la reproduction peut avoir une incidence sur les couts futurs – comme un faible taux de survie ou de fertilite – et ces couts peuvent grandement influencer l’optimisation du cycle biologique. Chez les oiseaux dont les jeunes sont nidifuges, les couts hypothetiques de la reproduction sont surtout lies aux efforts nutritionnel et energetique investis dans la formation des œufs et a l’incubation. Dans le cadre de cette etude, nous avons mesure le taux de survie saisonnier de 3 856 Canards colverts (Anas platyrhynchos) femelles munies d’un emetteur radio, de leur arrivee sur les aires de nidification jusqu’a ce que l’elevage des jeunes soit complete ou jusqu’a l’echec de la nidification. Le taux de mortalite etait de 2,5 fois plus eleve chez les femelles qui couvaient leurs œufs en milieu terrestre, tandis qu’il a etait a son plus bas niveau saisonnier au moment de l’elevage des jeunes en milieu aquatique. Le taux de mortalite a aussi varie en fonction de la date : il etait a son maximum au moment ou de nombreux Canards colverts nichaient, ce qui laisse croire que le changement de proies dans la diete des predateurs communs pourrait exacerber le risque de mortalite chez les femelles a toutes les etapes de la nidification. Meme si les efforts investis dans la ponte et l’incubation ont eu un effet sur le taux de mortalite, la plupart des relations n’etaient pas conformes aux predictions de l’hypothese des couts de la reproduction; les femelles qui ont grandement investi dans la production d’œufs ou l’incubation ont eu un meilleur taux de survie, ce qui donne a penser que la variabilite de la qualite individuelle etait responsable des deux relations. Nous concluons que, chez les femelles nicheuses de Canard colvert, le cout principal de la reproduction est un cout fixe associe au risque de predation lie a l’incubation d’œufs en milieu terrestre.