Shorebirds as integrators and indicators of mudflat ecology

Shorebirds are major, but thus far under-acknowledged, players in mudflatfood webs and associated physio-chemical processes. Mud is a critical habitat type for shorebirds, offering a multi-dimensional matrix of feeding opportunitiesthrough space and time. Shorebirds have evolved a spectrum of foraging modes withassociated morphologies, and sensory and physiological adaptations which exploitthese foraging opportunities. Although shorebirds are mud specialists and sentinelsof mudflat ecosystem functioning, they have not yet been well integrated into the“mud club”. In this chapter, we highlight the key roles shorebirds play in food webs,and in physical and chemical processes within mudflat ecosystems. We illustratehow shorebird distribution and behaviour provides a mirror of mudflat ecologybecause their foraging behaviour reflects the underlying ecological conditions,including temporal and spatial patterns in food/community structure in and acrossmud. In particular, shorebirds may be important indicators of essential fatty acidproduction by diatoms in epibenthic biofilm fields covering muddy intertidal flats,especially in estuaries. We conclude by highlighting the major challenges facingshorebirds today and call for a paradigm shift in shorebird conservation, based onrecreating and restoring intertidal mud ecosystems

Intertidal biofilm distribution underpins differential tide-following behavior of two sandpiper species (Calidris mauri and Calidris alpina) during northward migration

The discovery that some shorebird species graze heavily on biofilm adds importance to elucidating coastal processes controlling biofilm, as well as impetus to better understand patterns of shorebird use of intertidal flats. Western sandpipers (Calidris mauri) and dunlin (Calidris alpina) stopover in the hundreds of thousands on the Fraser River estuary, British Columbia, Canada, during northward migration to breeding areas. Western sandpipers show greater modification of tongue and bill morphology for biofilm feeding than dunlin, and their diet includes more biofilm. Therefore, we hypothesized that these congeners differentially use the intertidal area. A tide following index (TFI) was used to describe their distributions in the upper intertidal during ebbing tides. Also, we assessed sediment grain size, biofilm (= microphytobenthic or MPB) biomass and invertebrate abundance. Foraging dunlin closely followed the ebbing tide line, exploiting the upper intertidal only as the tide retreated through this area. In contrast, western sandpipers were less prone to follow the tide, and spent more time in the upper intertidal. Microphytobenthic biomass and sediment water content were highest in the upper intertidal, indicating greater biofilm availability for shorebirds in the first 350 m from shore. Invertebrate density did not differ between sections of the upper intertidal. Overall, western sandpiper behaviour and distribution more closely matched MPB biofilm availability than invertebrate availability. Conservation of sandpipers should consider physical processes, such as tides and currents, which maintain the availability of biofilm, a critical food source during global migration

Trace elements in pacific Dunlin (Calidris alpina pacifica): patterns of accumulation and concentrations in kidneys and feathers

Trace element concentrations were measured in Pacific Dunlin (Calidris alpina pacifica) to identify factors that influence accumulation and to assess toxicity risks. We report concentrations of cadmium, copper, and zinc in kidneys as well as copper, lead, mercury, selenium and zinc in feathers. Relationships between element concentrations and Dunlin age, sex, bill length, habitat preference, trophic level, and sample group were investigated with regression analyses. Stable isotope ratios of carbon and nitrogen in Dunlin muscle tissue were used to determine habitat preference and trophic level, respectively. Cadmium concentrations in kidneys were significantly related to habitat preference: [Cd] in estuarine foragers >[Cd] in terrestrial foragers. Cadmium accumulation was age-dependent as concentrations increased significantly within 10 months of hatch dates but not afterward. Concentrations of cadmium and zinc in kidneys as well as lead and mercury in feathers were below those known to cause deleterious effects in birds. In contrast, selenium concentrations in feathers (range: 2.1–14.0 µg/g) were often at levels associated with toxicity risks (>5 µg/g). Toxicity thresholds are not available for copper in kidneys or copper and zinc in feathers; however, measured concentrations of these elements were within documented ranges for sandpipers. Future studies should assess potential impacts of selenium on embryonic development in Dunlin and other sandpipers. Risk assessments would yield more conclusive results for all elements if impacts under ecologically relevant stresses (e.g. development in the wild, migration, predation) were better understood