Sub-lethal effects of the insecticide, imidacloprid, on the responses of damselfly larvae to chemosensory cues indicating predation risk.

Insecticides, including the widely used neonicotinoids, can affect both pest and non-target species. In addition to lethal effects, these insecticides at sub-lethal levels may cause disruption to sensory perception and processing leading to behavioural impairments. In this laboratory experiment, we investigated the effects of a 10-day exposure to the neonicotinoid insecticide, imidacloprid, on the behaviour of larvae of the damselfly, Lestes congener. In tests of baseline activity, imidacloprid concentrations of 1.0 and 10.0 µg/L caused significant reductions in foraging behaviour. Moreover, in response to chemical cues that indicate a potential risk to the larvae, imidacloprid caused the loss of an appropriate antipredator response (reduced foraging) depending on the concentration and duration of exposure. Imidacloprid at 0.1 µg/L caused the loss of responses toward the odour of a beetle (Dytiscus spp.) predator after 10 days of exposure, whereas 1.0 µg/L caused lost responses toward both the predator odour and injured conspecific cues (i.e., alarm cues) and after only 2 days of exposure. However, at 10.0 µg/L, larvae responded appropriately to both cues throughout the duration of the study, suggesting compensatory responses to imidacloprid at higher concentrations. Hence, the lack of appropriate responses at 1.0 µg/L likely resulted from a cognitive impairment rather than chemical alteration of these important chemosensory cues. In the natural environment, such effects will likely cause decreased survivorship in predator encounters. Hence, imidacloprid exposure, even at low concentrations, could have adverse consequences for chemosensory ecology of this damselfly species.

Exposure to the insecticide, imidacloprid, impairs predator-recognition learning in damselfly larvae.

Many aquatic organisms use chemosensory information to learn about local predation threats, but contaminants in their environment may impair such cognitive processes. Neonicotinoids are a class of water-soluble systemic insecticides that have become a major concern in aquatic systems. In this study, we explored how a 10-day exposure to various concentrations (0, 0.1, 1.0, or 10.0 µg/L) of the neonicotinoid imidacloprid affects the learned recognition of predator odour by non-target damselfly larvae (Lestes spp). Unexposed larvae and those exposed to the low concentration (0.1 µg/L) demonstrated an appropriate learned response to a novel predator odour following a conditioning with the odour paired with chemical alarm cues. However, such learning failed to occur for larvae that were exposed to imidacloprid concentrations of 1.0 and 10.0 µg/L. Thus, either the cognitive processing of the chemical information was impaired or the chemistry of one or both of the conditioning cues was altered, making them ineffective for learning. In a second experiment, we found evidence for this latter hypothesis. In the absence of background imidacloprid exposure, larvae did not show significant learned responses to the predator odour when the conditioning cues were mixed with imidacloprid (initial pulse solution of 3.0 µg/L) at the start of conditioning (reaching a final concentration of 0.01 µg/L). These findings indicate that even low levels of imidacloprid can have important implications for chemosensory cognition of non-target species in aquatic environments.

Spatial variation in the association between agricultural activities and bird communities in Canada.

Agriculture is one the main drivers of bird decline in both Europe and North America. While it is clear that agricultural practices and changes in the rural landscape directly and indirectly affect bird communities, we still do not know the extent to which these impacts might change across broad spatial and temporal scales. To address this question, we combined information on agricultural activities with occurrence and abundance of 358 bird species across five time periods spanning 20 years in Canada. As a proxy for agricultural impact, we used a combined index that included different agricultural metrics, such as cropland and tillage area and area treated with pesticides. We found that agriculture impact was negatively associated with bird diversity and evenness across all 20 years studied, but these associations seemed to vary by region. We found good support for an overall negative association between agriculture impact and bird diversity and evenness in the Eastern and Atlantic regions but weaker associations in the Prairies and Pacific. These findings suggest that agricultural activities result in bird communities that are less diverse and disproportionately benefit certain species. The spatial variation in the impact of agriculture on bird diversity and evenness we observed is likely a result of regional differences in the native vegetation, the type of crops and commodities produced, the historical context of agriculture, as well as the native bird community and the extent of their association with open habitat. Thus, our work provides support for the idea that the on-going agricultural impact on bird communities, while largely negative, is not uniform, and can vary across broad geographic regions.

Extensive regional variation in the phenology of insects and their response to temperature across North America.

Climate change models often assume similar responses to temperatures across the range of a species, but local adaptation or phenotypic plasticity can lead plants and animals to respond differently to temperature in different parts of their range. To date, there have been few tests of this assumption at the scale of continents, so it is unclear if this is a large-scale problem. Here, we examined the assumption that insect taxa show similar responses to temperature at 96 sites in grassy habitats across North America. We sampled insects with Malaise traps during 2019-2021 (N = 1041 samples) and examined the biomass of insects in relation to temperature and time of season. Our samples mostly contained Diptera (33%), Lepidoptera (19%), Hymenoptera (18%), and Coleoptera (10%). We found strong regional differences in the phenology of insects and their response to temperature, even within the same taxonomic group, habitat type, and time of season. For example, the biomass of nematoceran flies increased across the season in the central part of the continent, but it only showed a small increase in the Northeast and a seasonal decline in the Southeast and West. At a smaller scale, insect biomass at different traps operating on the same days was correlated up to ~75 km apart. Large-scale geographic and phenological variation in insect biomass and abundance has not been studied well, and it is a major source of controversy in previous analyses of insect declines that have aggregated studies from different locations and time periods. Our study illustrates that large-scale predictions about changes in insect populations, and their causes, will need to incorporate regional and taxonomic differences in the response to temperature.

Increased reliance on insecticide applications in Canada linked to simplified agricultural landscapes.

Intensification of agriculture and increased insecticide use have been implicated in global losses of farmland biodiversity and ecosystem services. We hypothesized that increased insecticide applications (proportion of area treated with insecticides) in Canada's expansive agricultural landscapes are due, in part, to shifts toward more simplified landscapes. To assess this relationship, we analyzed data from the Canadian Census of Agriculture spanning 20 years including five census periods (1996-2016) and across 225 census units within the four major agricultural regions of Pacific, Prairie, Central, and Atlantic Canada. Generalized mixed effects models were used to evaluate if changes in landscape simplification - defined as the proportion of farmland in crops (cereals, oilseeds, pulses and fruit/vegetables) - alongside other farming and climatic variables, influenced insecticide applications over time. Bayesian spatial-temporal models were further used to estimate the strength of the relationship with landscape simplification over time. We found that landscape simplification increased in 89% and insecticide applications increased in 70% of the Census Division spatial units during the 1996-2016 period. Nationally, significant increases in landscape simplification were observed in the two most agriculturally intensive regions of Prairie (from 55% to 63%) and Central (from 51% to 60%) Canada. For both regions, landscape simplification was a strong and significant predictor of higher insecticide applications, even after accounting for other factors such as climate, farm economics, farm size and land use practices (e.g., area in cash crops and tillage). If current trends continue, we estimated that insecticide applications will increase another 10%-20% by 2036 as a result of landscape simplification alone. To avoid increased reliance on toxic insecticides, agri-environmental policies need to consider that losing diverse natural habitat can increase insect pest pressure and resistance with negative environmental consequences extending beyond the field.

Pre-fledging quality and recruitment in an aerial insectivore reflect dynamics of insects, wetlands and climate.

Wetland systems, including shallow palustrine ponds, are hotspots for emergent aquatic insects but are globally threatened by land-use practices and climate change. Loss of insects is hypothesized as a key driver of population declines in aerial insectivores, but studies of climate-driven fluctuations in pond abundance during wet-dry periods and aerial insects on nestling quality and apparent recruitment are lacking. Using tree swallow (Tachycineta bicolor) data spanning 14-28 years we evaluated: (1) whether nestling quality based on pre-fledging (~ 12 days old) body mass changed over the time series; (2) how annual estimates of aerial insect biomass and variability, temperature, and pond abundance influenced nestling mass; and (3) whether the annual number of recruits produced was related to the annual mean mass of nestlings, aerial insects, and pond abundance in their year of hatching. Average nestling body mass varied annually but no long-term temporal trends were detected. Nestlings were heavier when raised during periods of stable insect biomass, warmer temperatures, and higher pond abundance. Pond abundance consistently had strong effects on nestling mass and inter-annual apparent recruitment, suggesting that this metric provides a complementary index of either higher prey abundance or higher-quality aquatic prey. Overall, pre-fledging quality and annual recruitment of nestling tree swallows reflects dynamic interannual changes in climate, pond availability, and aerial insect food supply. Our findings further suggest the abundance of ponds in this semi-arid prairie landscape is likely a strong predictor of regional population stability in tree swallows and possibly other ecologically similar species.

Polycyclic Aromatic Hydrocarbons Alter the Hepatic Expression of Genes Involved in Sanderling (Calidris alba) Pre-migratory Fueling.

Polycyclic aromatic hydrocarbons (PAHs) impaired pre-migratory fueling in 49 orally dosed Sanderling (Calidris alba). In the present study, 8 genes related to fat deposition and PAH exposure were measured in liver subsamples from these same shorebirds. At the highest dose (1260 µg total PAH [tPAH]/kg body wt/day), PAH exposure decreased liver basic fatty acid binding protein 1 (Lbfabp) and hepatic lipase (Lipc) expression. The present study reveals candidate molecular-level pathways for observed avian pre-migratory refueling impairment. Environ Toxicol Chem 2021;40:1983-1991. © 2021 SETAC.

Characterizing imidacloprid and metabolites in songbird blood with applications for diagnosing field exposures.

Neonicotinoids are the most widely used insecticides globally, but their rapid metabolism in vertebrates makes diagnosing wildlife exposure challenging. More detailed information on the pattern of imidacloprid metabolites over time could be used to better approximate the timing and level of exposure. Here, we applied recently developed sensitive analytical methods to measure imidacloprid (IMI) parent compound along with an expanded suite of metabolites (5-OH-IMI, IMI-olefin, desnitro-IMI, IMI-urea, 6-chloronicotinic acid, 5-AMCP, 6-OH nicotinic acid) and six other neonicotinoids in adult red-winged blackbirds (Agelaius phoeniceus) that were experimentally exposed to one of two field-realistic concentrations of imidacloprid (0.8 or 6.9 mg/kg bw). We measured concentrations in small (25 µL) plasma samples collected pre-exposure and at 1-, 6-, 24- and 48-h post-exposure. Imidacloprid was rapidly absorbed and metabolized within 48 h at both doses, with the largest decrease within 6 h post-exposure. The average proportion of parent IMI decreased from 68% of total detectable residues at 1-h to 34% at 6-h post-exposure. Two primary metabolites in blood were 5-OH-IMI and IMI-olefin, and 5-OH-IMI was the most persistent marker of exposure at 48-h. Desnitro-IMI was consistently detected following very recent (≤ 1-h) IMI exposure, and a higher ratio of parent IMI to metabolites also indicated recent exposure. Other metabolites were only detected in the higher dose group, and could be used as indicators of exposure to higher IMI concentrations. This sensitive analytical method and the observed metabolite patterns could be used to inform a growing body of field studies linking neonicotinoid exposure and effects in free-living birds.

The relative contribution of individual quality and changing climate as drivers of lifetime reproductive success in a short-lived avian species.

Animal populations are influenced strongly by fluctuations in weather conditions, but long-term fitness costs are rarely explored, especially in short-lived avian species. We evaluated the relative contributions of individual characteristics and environmental conditions to lifetime reproductive success (LRS) of female tree swallows (Tachycineta bicolor) from two populations breeding in contrasting environments and geographies, Saskatchewan and British Columbia, Canada. Female swallows achieved higher LRS by breeding early in the season and producing more fledglings. Other measures of female quality had virtually no influence on LRS. Genetic factors did not predict LRS, as there was no correlation between life-history components for sister pairs nor between mothers and their daughters. Instead, climate variability-indexed by spring pond density (i.e., abundance of wetland basins holding water) during years when females bred-had strong positive effects on female LRS in more arid Saskatchewan but only weak positive effects of moisture conditions were detected in wetter British Columbia. Overall, several life history trait correlates of LRS were similar between populations, but local environmental factors experienced by individuals while breeding produced large differences in LRS. Consequently, variable and extreme environmental conditions associated with changing climate are predicted to influence individual fitness of distinct populations within a species' range.

Species traits predict the aryl hydrocarbon receptor 1 (AHR1) subtypes responsible for dioxin sensitivity in birds.

Differences in avian sensitivity to dioxin-like compounds (DLCs) are directly attributable to the identities of amino acids at two sites within the ligand binding domain (LBD) of the aryl hydrocarbon receptor 1 (AHR1). Recent work suggests that by influencing avian exposure to naturally occurring dioxins, differences in diet, habitat, and migration may have influenced the evolution of three AHR1 LBD genotypes in birds: type 1 (high sensitivity), type 2 (moderate sensitivity), and type 3 (low sensitivity). Using a boosted regression tree (BRT) analysis, we built on previous work by examining the relationship between a comprehensive set of 17 species traits, phylogeny, and the AHR1 LBD across 89 avian species. The 17 traits explained a combined 74% of the model deviance, while phylogenetic relatedness explained only 26%. The strongest predictors of AHR1 LBD were incubation period and habitat type. We found that type 3 birds tended to occupy aquatic habitats, and, uniquely, we also found that type 3 birds tended to have slower developmental rates. We speculate that this reflects higher evolutionary exposure to naturally occurring dioxins in waterbirds and species with K-selected life histories. This study highlights the value of trait-based approaches in helping to understand differing avian species sensitivities to environmental contaminants.

Incubation temperature and PCB-126 exposure interactively impair shorebird embryo and post-hatch development.

In oviparous wildlife, many critical physiological and behavioural components are strongly influenced by the embryonic and early post-hatch developmental environment. As such, early life stages in these species are highly vulnerable to both natural and anthropogenic stressors. For example, in birds, incubation temperature may influence the rate of egg development while also affecting contaminant metabolism and absorption in body tissues, resulting in potentially multiplicative impacts on embryonic and posthatch development. We tested the hypothesis that cumulative effects of early contaminant exposure and temperature stress can negatively affect avian development and may have interactive effects that are more detrimental than either stressor individually. Using a controlled egg injection and incubation study on killdeer (Charadrius vociferous), eggs were exposed to a known endocrine disruptor, 3,3',4,4',5-pentachlorobiphenyl (PCB-126) and incubated at either low (36 °C), intermediate (37.5 °C), or high (39 °C) temperatures. Our results indicated that eggs incubated at low temperature had earlier detection of heartbeat, longer incubation length, lower growth rate post-hatch, and higher post-hatch mortality, compared to eggs incubated under intermediate temperatures. Higher incubation temperatures resulted in shorter incubation length, earlier detection of heart rate and faster righting time. As predicted, embryo and chick mortality were greater in the PCB-dosed birds incubated at intermediate and high temperatures. Incidence of distended yolk sacs (%) also increased with PCB exposure in all temperature groups, with the largest increase in the high temperature group. Overall, our results show that low incubation temperature can cause greater adverse effects than PCB-126 exposure alone, but that negative effects of PCB-126 exposure are exacerbated by high incubation temperatures. These findings suggest that in natural settings, shorebird embryos may be more susceptible to contaminant exposure when incubated at temperatures either below or above the apparent optimum.

Environment and food web structure interact to alter the trophic magnification of persistent chemicals across river ecosystems.

Legacy organic pollutants persist in freshwater environments, but there is limited understanding of how their trophic transfer and effects vary across riverine ecosystems with different land use, biological communities and food webs. Here, we investigated the trophic magnification of polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs) and a suite of organochlorines (OCs) across nine riverine food webs in contrasting hydrological catchments across South Wales (United Kingdom). Pollutants biomagnified through the food webs in all catchments studied, in some cases reaching levels sufficient for biological effects on invertebrates, fish and river birds such as the Dipper (Cinclus cinclus). Trophic magnification differed across food webs depending on pollutant characteristics (e.g. octanol-water partitioning coefficient) and site-specific environmental conditions (e.g. land use, water chemistry and basal resource composition). The trophic magnification of PBDEs, PCBs and OCs also reflected food-web structure, with greater accumulation in more connected food webs with more generalist taxa. These data highlight interactions between pollutant properties, environmental conditions and biological network structure in the transfer and biomagnification of POPs in river ecosystems. We advocate the need for further investigations of system-specific transfers of contaminants through aquatic food webs as these factors appear to have important implications for risk assessment.

Spatial distribution of agricultural pesticide use and predicted wetland exposure in the Canadian Prairie Pothole Region.

Agricultural pest control products are a major cause of degradation of water quality and biodiversity loss worldwide. In the Canadian Prairie Pothole Region, the landscape is characterized by millions of ecologically important wetlands, but also large farm sizes and high agrochemical use. Despite the region's agricultural intensity, the spatial extent of pesticide use and likelihood of pesticides contaminating surface water has been poorly studied. Here, we estimated the pesticide use patterns for three main groups (herbicides, fungicides and insecticides) using the most recent (2015) pesticide use survey data and digital crop maps. Furthermore, we developed a Wetland Pesticide Occurrence Index (WPOI; 1 km2 resolution), to robustly estimate potential wetland exposure using spatially explicit data on pesticide use density, wetland density, precipitation and pesticide-specific physicochemical properties. In total, 39,236 metric tonnes of pesticides consisting of 94 active ingredients were applied to the Prairies in 2015. Herbicides had the highest density of use (24-183 kg/km2), followed by fungicides (0.4-23.8 kg/km2) and insecticides (0.4-3.6 kg/km2). Pesticide use differed by province; however, the major pesticides applied (e.g., glyphosate, prothioconazole, and thiamethoxam) were consistent across the region and were largely associated with wheat and canola crops. Although insecticides and fungicides had lower mass applied than herbicides, they had slightly higher overall WPOI scores. The predicted pesticide occurrence for insecticides and fungicides in wetlands was higher in the wetter central and eastern part of the Prairie region (WPOI = 0.6-1) compared to the drier western and southwestern part (WPOI = 0.1-0.6), suggesting that wetlands in much of Saskatchewan and southern Manitoba may be more vulnerable to higher and frequent contamination. Identifying crops, chemicals and landscapes with the greatest likelihood of pesticide contamination to wetlands will help prioritize future environmental monitoring programs and aid in assessing the ecological risk of specific pest control products in Canada's most agriculturally intensive region.

Neonicotinoids and other agricultural stressors collectively modify aquatic insect communities.

Threats to wetland water quality and aquatic insect secondary production in agricultural landscapes are multifaceted and are known to vary spatially and temporally. We designed this study with the aim to disentangle the effects of multiple stressors on emerging aquatic insects from wetlands impacted by intensive agricultural practices and receiving runoff from neonicotinoid-treated canola. A total of 22 semi-permanent wetlands were monitored over two growing seasons (11 different wetlands per year) in central Saskatchewan, Canada. Over the two sampling years, dipterans from the families Chironomidae (60-67%), Muscidae (13-15%) and Ceratopogonidae (7-13%) made up the majority of emergent taxa, representing 80-95% of the total emergence. Multivariate ordination analyses of eight water quality and nine wetland habitat variables revealed that neonicotinoid concentration, turbidity, vegetation disturbance, and continuity of a vegetative grass buffer zone were significant factors influencing the aquatic insect taxa composition. Generalized linear mixed effects models indicated that total insect emergence over time was significantly predicted by neonicotinoid concentrations (imidacloprid toxic equivalency, TEQ) and vegetation disturbance. Higher neonicotinoid concentrations negatively affected insect emergence over time, whereas vegetation disturbance increased total emergence, likely due to the abundance of disturbance-tolerant taxa. Overall, we observed community-level responses driven by multiple indicators of wetland degradation (insecticides, turbidity, and vegetation disturbance). Collectively, these multivariate field data provide an in-depth understanding of how agricultural management practices, including neonicotinoid use, interact to shape wetland aquatic insect communities.

Nutrients and sediment modify the impacts of a neonicotinoid insecticide on freshwater community structure and ecosystem functioning.

Pesticides are important contributors to the global freshwater biodiversity crisis. Among pesticides, neonicotinoids are the best-selling class of agricultural insecticides and are suspected to represent significant risks to freshwater and terrestrial ecosystems worldwide. Despite growing recognition that neonicotinoid impacts may be modified by the presence of additional stressors, there is limited information about their interactions with other agricultural stressors in freshwater ecosystems. We conducted an outdoor pond-mesocosm experiment to investigate the individual and interactive effects of nutrients, fine sediment, and imidacloprid (a neonicotinoid insecticide) inputs on freshwater community structure (density, diversity, and composition of zooplankton and benthic invertebrates) and ecosystem functioning (ecosystem metabolism, primary production, and organic matter decomposition). We hypothesized antagonistic nutrient-imidacloprid, and synergistic sediment-imidacloprid interactions, affecting aquatic invertebrate communities. The three stressors had significant individual and interactive effects on pond ecosystems. The insecticide neutralized the positive effects of nutrient additions on benthic invertebrate richness and mitigated the negative effects of sediment on zooplankton communities (antagonistic interactions). Moreover, we observed compensatory responses of tolerant benthic invertebrates, which resulted in reversal interactions between sediment and imidacloprid. Furthermore, our observations suggest that imidacloprid has the potential to increase net ecosystem production at environmentally relevant concentrations. Our findings support the hypothesis that the impacts of imidacloprid may be modified by other agricultural stressors. This has important implications on a global scale, given the widespread use of these pesticides in intensive agricultural landscapes and the growing body of literature suggesting that traditional pesticide assessment frameworks, based on laboratory toxicity tests alone, may be insufficient to adequately predict effects to complex freshwater ecosystems.

A neonicotinoid insecticide reduces fueling and delays migration in songbirds.

Neonicotinoids are neurotoxic insecticides widely used as seed treatments, but little is known of their effects on migrating birds that forage in agricultural areas. We tracked the migratory movements of imidacloprid-exposed songbirds at a landscape scale using a combination of experimental dosing and automated radio telemetry. Ingestion of field-realistic quantities of imidacloprid (1.2 or 3.9 milligrams per kilogram body mass) by white-crowned sparrows (Zonotrichia leucophrys) during migratory stopover caused a rapid reduction in food consumption, mass, and fat and significantly affected their probability of departure. Birds in the high-dose treatment stayed a median of 3.5 days longer at the site of capture after exposure as compared with controls, likely to regain fuel stores or recover from intoxication. Migration delays can carry over to affect survival and reproduction; thus, these results confirm a link between sublethal pesticide exposure and adverse outcomes for migratory bird populations.

Detecting Amphibians in Agricultural Landscapes Using Environmental DNA Reveals the Importance of Wetland Condition.

Amphibians are declining worldwide, in part because of large-scale degradation of habitat from agriculture and pervasive pathogens. Yet a common North American amphibian, the wood frog (Lithobates sylvaticus), ranges widely and persists in agricultural landscapes. Conventional survey techniques rely on visual encounters and dip-netting efforts, but detectability limits the ability to test for the effects of environmental variables on amphibian habitat suitability. We used environmental DNA to determine the presence of wood frogs and an amphibian pathogen (ranavirus) in Prairie Pothole wetlands and investigated the effects of 32 water quality, wetland habitat, and landscape-level variables on frog presence at sites representing different degrees of agricultural intensity. Several wetland variables influenced wood frog presence, the most influential being those associated with wetland productivity (i.e., nutrients), vegetation buffer width, and proportion of the surrounding landscape that is comprised of other water bodies. Wood frog presence was positively associated with higher dissolved phosphorus (>0.4 mg/L), moderate dissolved nitrogen (0.1-0.2 mg/L), lower chlorophyll a (≤15 µg/L), wider vegetation buffers (≥10 m), and more water on the landscape (≥0.25). These results highlight the effects of environmental factors at multiple scales on the presence of amphibians in this highly modified landscape-namely the importance of maintaining wetland water quality, vegetation buffers, and surrounding habitat heterogeneity. Environ Toxicol Chem 2019;38:2750-2763. © 2019 SETAC.

Long-distance migratory shorebirds travel faster towards their breeding grounds, but fly faster post-breeding.

Long-distance migrants are assumed to be more time-limited during the pre-breeding season compared to the post-breeding season. Although breeding-related time constraints may be absent post-breeding, additional factors such as predation risk could lead to time constraints that were previously underestimated. By using an automated radio telemetry system, we compared pre- and post-breeding movements of long-distance migrant shorebirds on a continent-wide scale. From 2014 to 2016, we deployed radio transmitters on 1,937 individuals of 4 shorebird species at 13 sites distributed across North America. Following theoretical predictions, all species migrated faster during the pre-breeding season, compared to the post-breeding season. These differences in migration speed between seasons were attributable primarily to longer stopover durations in the post-breeding season. In contrast, and counter to our expectations, all species had higher airspeeds during the post-breeding season, even after accounting for seasonal differences in wind. Arriving at the breeding grounds in good body condition is beneficial for survival and reproductive success and this energetic constraint might explain why airspeeds are not maximised in the pre-breeding season. We show that the higher airspeeds in the post-breeding season precede a wave of avian predators, which could suggest that migrant shorebirds show predation-minimizing behaviour during the post-breeding season. Our results reaffirm the important role of time constraints during northward migration and suggest that both energy and predation-risk constrain migratory behaviour during the post-breeding season.

Assessment of Shorebird Migratory Fueling Physiology and Departure Timing in Relation to Polycyclic Aromatic Hydrocarbon Contamination in the Gulf of Mexico.

Shorebirds depend on staging sites in the Gulf of Mexico that are frequently subject to pollution by oil and its toxic constituents, polycyclic aromatic hydrocarbons (PAHs). It was hypothesized that PAH contamination lowers staging site quality for migratory shorebirds, with consequences for fueling and departure timing. Sediment total PAH concentrations were measured at six staging sites along the Texas and Louisiana Gulf Coast. Sites in Louisiana were expected to have higher total PAH concentrations as they were more heavily impacted by the Deepwater Horizon oil spill. From 2015 to 2017, 165 Sanderling ( Calidris alba) and 55 Red knots ( C. canutus) were captured at these same sites during their northward migration (late April to mid May). Mass, body morphometrics, and plasma metabolite measurements were taken to determine fuel loads and fueling rates, and a subset of birds (120 Sanderling and 39 Red knots) received a coded radio tag to determine departure dates using the Motus telemetry array. Compared to Texas sites, sediment in Louisiana had higher total PAH concentrations, dominated by heavier 6 ring indeno[1,2,3- cd]pyrene (48%). Plasma metabolite profiles suggested that fueling rates for Sanderling, but not Red knots, tended to be lower in Louisiana, and both species departed later than the study average from Louisiana. However, multiple factors, including migration patterns, food supply, and other contaminants, also likely influenced fueling and departures. PAH contamination in the Gulf of Mexico remains an ongoing issue that may be impacting the staging site quality and migration timing of long-distance migratory birds.

Polycyclic aromatic hydrocarbon exposure impairs pre-migratory fuelling in captively-dosed Sanderling (Calidris alba).

Efficient fuelling is essential for migratory birds because fuel loads and fuelling rates affect individual fitness and survival during migration. Many migrant shorebirds are exposed to oil pollution and its toxic constituents, polycyclic aromatic hydrocarbons (PAHs), at migratory staging sites, which has the potential to interfere with avian refuelling physiology. In this study, we orally dosed shorebirds with environmentally-relevant PAH mixtures to simulate dietary exposure during staging. Forty-nine wild-caught Sanderling (Calidris alba) were exposed to 0 (control), 12.6 (low), 126 (medium), or 1260 (high) µg total PAH/kg body weight/day. Birds were dosed during a 21-day period of autumn pre-migratory fuelling to mimic the typical staging duration of Sanderling. We measured daily changes in mass and fat loads, as well as ethoxyresorufin-O-deethylase (EROD) activity, serum biochemical profiles, and liver mass and lipid content following dosing. All dose groups gained fat and increased in mass (size-corrected) during the study period, with females having a higher average body mass than males. However, mass gain was 3.9, 5.4, and 3.8 times lower in the low, medium, and high dose groups, respectively, relative to controls, and body mass in the medium and high dose groups significantly declined near the end of the experiment. EROD activity showed a dose-dependent increase and was significantly elevated in the high dose group relative to controls. Higher individual EROD activity was associated with reduced serum bile acid and elevated serum creatine kinase concentrations in both sexes, and with elevated serum lipase concentrations in females. These results suggest that PAH exposure in Sanderling can interfere with mechanisms of lipid transport and metabolism, can cause muscle damage, and can lead to reduced overall fat loads that are critical to staging duration, departure decisions, migratory speed, and flight range. Given that many shorebirds migrate thousands of kilometers between the breeding and wintering grounds and frequently aggregate at key staging sites that are subject to contamination, PAH exposure likely represents a significant threat to shorebird migratory success.