Inorganic and organic contaminants in Alaskan shorebird eggs

Assessment of contaminants, health and survival of migratory shorebirds in natural versus artificial wetlands - The potential of wastewater treatment plants as alternative habitats

The rapid destruction of natural wetland habitats over past decades has been partially offset by an increase in artificial wetlands. However, these also include wastewater treatment plants, which may pose a pollution risk to the wildlife using them. We studied two long-distance Arctic-breeding migratory shorebird species, curlew sandpiper (Calidris ferruginea, n = 69) and red-necked stint (Calidris ruficollis, n = 103), while on their Australian non-breeding grounds using an artificial wetland at a wastewater treatment plant (WTP) and a natural coastal wetland. We compared pollutant exposure (elements and per- and poly-fluoroalkyl substances/PFASs), disease (avian influenza), physiological status (oxidative stress) of the birds at the two locations from 2011 to 2020, and population survival from 1978 to 2019. Our results indicated no significant differences in blood pellet pollutant concentrations between the habitats except mercury (WTP median: 224 ng/g, range: 19-873 ng/g; natural wetland: 160 ng/g, 22-998 ng/g) and PFASs (total PFASs WTP median: 85.1 ng/g, range: <0.01-836 ng/g; natural wetland: 8.02 ng/g, <0.01-85.3 ng/g) which were higher at the WTP, and selenium which was lower at the WTP (WTP median: 5000 ng/g, range: 1950-34,400 ng/g; natural wetland: 19,200 ng/g, 4130-65,200 ng/g). We also measured higher blood o,o'-dityrosine (an indicator of protein damage) at the WTP. No significant differences were found for adult survival, but survival of immature birds at the WTP appeared to be lower which could be due to higher dispersal to other wetlands. Interestingly, we found active avian influenza infections were higher in the natural habitat, while seropositivity was higher in the WTP, seemingly not directly related to pollutant exposure. Overall, we found limited differences in pollutant exposure, health and survival of the shorebirds in the two habitats. Our findings suggest that appropriately managed wastewater treatment wetlands could provide a suitable alternative habitat to these migratory species, which may aid in curbing the decline of shorebird populations from widespread habitat loss.

Factors influencing mercury exposure in Arctic-breeding shorebirds

Mercury (Hg) pollution remains a concern to Arctic ecosystems, due to long-range transport from southern industrial regions and melting permafrost and glaciers. The objective of this study was to identify intrinsic, extrinsic, and temporal factors influencing Hg concentrations in Arctic-breeding shorebirds and highlight regions and species at greatest risk of Hg exposure. We analyzed 1094 blood and 1384 feather samples from 12 shorebird species breeding at nine sites across the North American Arctic during 2012 and 2013. Blood Hg concentrations, which reflect Hg exposure in the local area in individual shorebirds: 1) ranged from 0.01-3.52 μg/g ww, with an overall mean of 0.30 ± 0.27 μg/g ww; 2) were influenced by species and study site, but not sampling year, with birds sampled near Utqiaġvik, AK, having the highest concentrations; and 3) were influenced by foraging habitat at some sites. Feather Hg concentrations, which reflected Hg exposure from the wintering grounds: 1) ranged from 0.07-12.14 μg/g fw in individuals, with an overall mean of 1.14 ± 1.18 μg/g fw; and 2) were influenced by species and year. Most Arctic-breeding shorebirds had blood and feather Hg concentrations at levels where no adverse effects of exposure were predicted, though some individuals sampled near Utqiaġvik had Hg levels that would be considered of concern. Overall, these data increase our understanding of how Hg is distributed in the various shorebird breeding areas of the Arctic, what factors predispose Arctic-breeding shorebirds to Hg exposure, and lay the foundation for future monitoring efforts.

The Paradox of Shorebird Diversity and Abundance in the West Coast and East Coast of India: A Comparative Analysis

Migratory shorebirds that move across continents along their flyways are undergoing a drastic decline globally. A greater proportion of them that regularly winter along the Indian coasts within the Central Asian Flyway (CAF) are also undergoing severe declines. However, the mechanisms underlying the population trends in these areas remain little understood. This study investigated the diversity, abundance, population dynamics and distribution patterns of shorebirds along the Indian coasts based on the available literature. The west coast of India is relatively less studied than the east coast in the CAF. Further, we observed that the diversity, abundance, population dynamics and distribution pattern of the shorebirds follow different trends on the west coast compared to the east coast. These variations are in accordance with the differences in topography and biotic and abiotic factors between the coasts. Anthropogenic activities have far-reaching effects on the survival and persistence of shorebirds along the coasts. The west coast is evidently more productive than the east coast at every trophic level and thus the west coast is expected to account for more abundance and diversity of shorebirds. Paradoxically, we found that the east coast supports a greater abundance and diversity of shorebirds than the west coast. The west coast, therefore, requires further investigations to obtain a better understanding of the causes of apparent differences in abundance and diversity as well as the observed declines in shorebirds, compared to the east coast of India.

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.

The influence of migration patterns on exposure to contaminants in Nearctic shorebirds: a historical study

Since the 1970s, many populations of shorebirds, including those breeding in the Arctic region, have been declining. One factor that may contribute to some of these declines is exposure to contaminants throughout the annual cycle. Here, we compared contaminant exposure (organochlorines, toxic trace elements) of four Arctic-breeding shorebirds (semipalmated plover Charadrius semipalmatus, semipalmated sandpiper Calidris pusilla, lesser yellowlegs Tringa flavipes, and short-billed dowitcher Limnodromus griseus), collected during breeding, migration, and wintering to examine how and when contaminants might pose a threat to these species. In general, plovers and dowitchers had higher levels of most organochlorine pesticides, and renal cadmium (Cd) and selenium (Se) than the other species. Although we found seasonal differences, no clear patterns in contaminant concentrations among sampling locations were detected but the concentrations found at the breeding grounds were always the highest for chlorinated pesticides and mercury (Hg). Our results suggest that birds migrating south are slowly depurating contaminant burdens, and that spring-migrating birds were exposed to primarily North American rather than Latin American contaminant sources at the time of sampling. We present these data collected in the 1990s to better interpret current-day trends, and potential contaminant exposure impacts on shorebird populations.

Metal Levels in Shorebird Feathers and Blood During Migration Through Delaware Bay

We investigated levels of arsenic mercury, lead, cadmium, and chromium in Red Knot (Calidris canutus), Semipalmated Sandpipers (Calidris pusilla), and Sanderling (Calidris alba) migrating through Delaware Bay, New Jersey to determine if contaminant levels are likely to be causing negative effects on the populations of these shorebirds, to compare among species, and to explore differences among individuals collected early and late during their migration stopover. We analyzed blood and feathers, both nonlethal ways of exploring contaminants in birds. Blood contaminant analysis provides a direct measure of recent dietary exposure, whereas feathers reflect body burden at the time of feather molt. We found some differences among species and between early and late samples. Levels of Hg and Pb were higher in Sanderling blood collected early (36.52 ± 8.45 and 145.00 ± 12.56 ng/g ww respectively) compared with later (16.21 ± 6.03 and 33.60 ± 4.05 ng/g ww respectively) during the migration stopover. Blood Pb levels of Sanderling in the early period were higher than those of the other two species (75.38 ± 15.52 ng/g ww in Red Knot and 42.39 ± 8.42 ng/g ww in Semipalmated Sandpipers). Semipalmated Sandpipers had lower blood As levels than the other two species (254.33 ± 40.15 and 512.00 ± 66.79 ng/g ww early and late respectively) but higher feather levels (914.01 ± 167.29 and 770.00 ± 116.21 ng/g dw early and late respectively), and their blood As was higher in the later sampling period compared with the early sampling period. Arsenic levels in shorebird tissues were relatively high and may reflect levels in horseshoe crab eggs, their primary diet item in Delaware Bay. In Red Knot, blood Cr levels were elevated in the later samples (572.17 ± 62.82 ng/g ww) compared to the early samples (382.81 ± 95.35 ng/g ww) and to the other species. The mean values of the metals analyzed were mostly below effect levels-the level that has a measurable negative impact-although relatively high As levels in Semipalmated Sandpiper feathers and some high levels of Pb need to be further explored.