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The benthic fauna of two areas in the western Dutch Wadden Sea, Posthuiswad and Staart van Schieringhals, was described in 1930-1960 and again between 1996 and 2005. Here, we document the changes. Whereas both areas formerly had high densities of species that biogenically structured the intertidal mudflats such as mussels Mytilus edulis and cockles Cerastoderma edule, by 1996 they had shown a tenfold decrease in the densities of molluscs, with no recovery till 2005. Although the number of species of polychaetes and crustaceans may not have changed much, their relative abundance did. Nowadays, more polychaete species are common than before. We briefly discuss whether the changes in benthic community composition could be due to industrial fishery practices or eutrophication effects. [ABSTRACT FROM AUTHOR]

This article discusses a study which examined the decline in the food stocks of Afro-Siberian Red Knots in the western Dutch Wadden Sea. Particular focus is given to the boundaries of the western Dutch Wadden Sea, which was surveyed from 1996-2005. Between July and early September, annual sampling of intertidal macrozoobenthic prey were performed. An optimal diet model was used in this study to predict the intake rate of Red Knots. Results of the study showed that there were changes in the extent of intertidal mudflats that fulfilled the minimum intake needs of Red Knots. From 1996-2005, the study found an 86% drop in suitable foraging area. It also found a decline in the proportion of Red Knots without primary moult.

The article focuses on a study which described the use of the behavioural anti-predation trait of the marine bivalve Macoma balthica as an indicator of population size change. The study utilized the burrowing depth character of Baltic tellin to forecast population change. It analyzed three components of population change, namely the decline in the risk of predation at a given depth, increased in the marginal value of energy, and the decline in Macoma balthica's expected future fitness. Study authors concluded that behavioural ecology can be used to predict the perception of animals about their environment.

We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus ) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2 H, 17 O, and 18 O. Thereafter, blood samples were taken and distilled. The resulting water samples were analysed using an isotope ratio mass spectrometry (for 2 H and 18 O only) and a stable isotope ratio infrared laser spectrometry ( 2 H, 17 O, and 18 O) to yield estimates of the amount of body water in the birds, which in turn could be correlated to the amount of body fat. Here, we validate laser spectrometry against mass spectrometry and show that all three isotopes may be used for body water determinations. This opens the way to the extension of the doubly labelled water method, used for the determination of energy expenditure, to a triply labelled water method, incorporating an evaporative water loss correction on a subject-by-subject basis or, alternatively, the reduction of the analytical errors by statistically combining the 17 O and 18 O measurements. [ABSTRACT FROM AUTHOR]

1. When prey occur at high densities, energy assimilation rates are generally constrained by rates of digestion rather than by rates of collection (i.e. search and handle). As predators usually select patches containing high prey densities, rates of digestion will play an important role in the foraging ecology of a species.2. The red knotCalidris canutusshows tremendous inter- and intra-individual variation in maximum rates of digestion due to variation in the size of the processing machinery (gizzard and intestine), which makes it a suitable species to study the effects of digestive processing rate on foraging decisions.3. Here we report on patch use, prey choice, and daily foraging times as a function of gizzard size in free-ranging, radio-marked, red knots. As knots crush their bulky bivalve prey in their gizzard, the size of this organ, which we measured using ultrasonography, determines digestive processing rate.4. Using the digestive rate model, we a priori modelled patch use, prey choice, and daily foraging times as a function of gizzard mass. Focusing on two contrasting patches, birds with small gizzards were expected to feed on high-quality (soft-bodied) prey found in low densities in the one patch, while birds with large gizzards were expected to feed on low-quality (hard-shelled) prey found in high densities in the other patch. Assuming that red knots aim to balance their energy budget on a daily basis, we expected daily foraging time to decline with gizzard mass.5. Observed patch and prey choices were in quantitative agreement with these theoretical predictions. Observed daily foraging times were only in qualitative agreement: they declined with gizzard mass but less steeply than predicted.6. We discuss that red knots might be aiming for a slightly positive energy budget in order to (i) refuel their stores depleted during migration, and (ii) to insure against unpredictability in supply and demand during winter. Red knots arriving from their breeding grounds with small gizzards are only able to realize this aim when densities of soft-bodied prey are high, which is the case in late July and early August. Rapidly declining soft-bodied prey densities throughout late summer pose a major penalty for individuals arriving late at their wintering grounds.7. The long daily foraging periods required by knots with small gizzards are only feasible through‘tide-extension’. In our study area, birds can and do raise the daily low tide period from 12 h to almost 17 h by moving along with the tide in an easterly direction, subsequently flying back to their starting point at the high tide roost.Journal of Animal Ecology(2005) doi: 10.1111/j.1365-2656.2004.00904.x [ABSTRACT FROM AUTHOR]

It is often assumed that strong selection pressures give rise to trade-offs between body condition and time in long-distance migrating birds. Birds that are‘behind schedule’ in fuel deposition or moult should delay departure, and this should result in a negative correlation between initial condition and departure date. We tested this hypothesis in the Great KnotCalidris tenuirostrismigrating from north-west Australia to eastern Asia en route to Siberia. Great Knot gain mass and moult into breeding plumage before leaving northern Australia in late March and early April, and fly 5400–6000 km to eastern China and Korea. We radiotracked 27 individuals (17 males and ten females) to determine departure dates; 23 migrated and four remained in Australia. We characterized body condition at capture using body mass, predicted pectoral muscle mass (based on ultrasound estimates of the size of the pectoral muscles) and breeding plumage scores. Residual condition indices were uncorrelated, indicating that at the individual level, variation in one fuelling component was not strongly associated with variation in the other components. Birds that did not depart had lower residual body mass and breeding plumage indices than those that did migrate; these four birds may have been subadults. Neither sex, size nor the condition indices explained variation in departure date of migrants. Reasons for this are explored. Departure dates for northward migrating waders indicate that the migration window (span over which birds depart) decreases with proximity to the northern breeding grounds. We suggest that migration schedules become tighter as birds get nearer to the breeding grounds. Thus the lack of a relationship between condition and departure date in Great Knots may reflect the fact that the departure episode under study is the first one in sequence and is still 4–8 weeks before breeding. [ABSTRACT FROM AUTHOR]

[This corrects the article DOI: 10.1186/s40462-018-0142-4.].

When a diet switch results in a change in dietary isotopic values, isotope ratios of the consumer's tissues will change until a new equilibrium is reached. This change is generally best described by an exponential decay curve. Indeed, after a diet switch in captive red knot shorebirds (Calidris canutus islandica), the depletion of (13)C in both blood cells and plasma followed an exponential decay curve. Surprisingly, the diet switch with a dietary (15)N/(14)N ratio (δ(15)N) change from 11.4 to 8.8 ‰ had little effect on δ(15)N in the same tissues. The diet-plasma and diet-cellular discrimination factors of (15)N with the initial diet were very low (0.5 and 0.2 ‰, respectively). δ(15)N in blood cells and plasma decreased linearly with increasing body mass, explaining about 40 % of the variation in δ(15)N. δ(15)N in plasma also decreased with increasing body-mass change (r (2)=.07). This suggests that the unusual variation in δ(15)N with time after the diet switch was due to interferences with simultaneous changes in body-protein turnover.

Timing "in the real world" must cope with the temporal complexity of natural environments. Extreme examples for the resultant "multitasking" are migratory birds, which precisely time movements to remote areas. New field technologies highlight temporal accuracy, while captivity studies emphasize underlying programs and plasticity of schedules. After reviewing these findings, we focus on waders, which undertake spectacular long-distance migrations, have robust circannual clocks, and cope with diel, tidal, and polar environments. To explore features that may facilitate such multitasking, we speculated that melatonin amplitudes are low and damped during seasons when entrainment to subtle Zeitgebers occurs. We measured melatonin profiles under European daylength in two species with different ecologies and found low-amplitude melatonin cycles that changed over the year. Annual patterns neither fully supported our hypothesis, nor simply reflected daylight availability. While migratory birds are inspiring models for chronobiology, mechanistic understanding of their multitasking is still poor., (Copyright © 2012 Elsevier B.V. All rights reserved.)

We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2H, (17)O, and (18)O. Thereafter, blood samples were taken and distilled. The resulting water samples were analysed using an isotope ratio mass spectrometry (for 2H and (18)O only) and a stable isotope ratio infrared laser spectrometry (2H, (17)O, and (18)O) to yield estimates of the amount of body water in the birds, which in turn could be correlated to the amount of body fat. Here, we validate laser spectrometry against mass spectrometry and show that all three isotopes may be used for body water determinations. This opens the way to the extension of the doubly labelled water method, used for the determination of energy expenditure, to a triply labelled water method, incorporating an evaporative water loss correction on a subject-by-subject basis or, alternatively, the reduction of the analytical errors by statistically combining the (17)O and (18)O measurements.