Foraging behaviour of Terek SandpipersXenus cinereus feeding on Sand-Bubbling CrabsScopimera globosa

Summary On the intertidal flats of the Nakdong Estuary in South Korea Terek Sandpipers foraged solitarily, and made 0.5–6 m long runs which ended with pecks on or into the sediment to capture Sand-bubbling Crabs. The birds foraged during low tide and spent about 80 % of their time foraging; the rest preening and resting. More than half of the recorded prey and over 80 % of the average energetic intake consisted of Sand-bubbling Crabs. As the size of captured crabs increased, a greater proportion was washed before ingestion. Small crabs were always swallowed, but of the larger crabs an increasing portion was eventually rejected after capture. When deep down in their burrows, only the smallest crabs were within the reach of the sandpipers' bills. Henceforth, the crabs were only available when outside their burrows, on the surface. This happened for only three hrs (or one third) of each diurnal low tide period. Early in the tidal cycle after the crabs came to the surface, Terek Sandpipers made many runs and pecks per unit time to capture them. When crabs were most abundant and easy to catch, the birds were apparently more selective in their prey choice: more captured crabs were washed before being eaten and more were eventually rejected. Suggestions are made to explain the behaviour of both the predator and the prey.

---

Verhalten von Terekwasserläufern(Xenus cinereus) beim Erbeuten von Winkerkrabben(Scopimera globosa)

Zusammenfassung Im Watt der Nakdong-Mündung in Südkorea gingen Terekwasserläufer einzeln der Nahrungssuche nach; ihre Beute waren hauptsächlich Winkerkrabben. Nach einer Laufstrecke von 0.5–6 m pickten sie nach der Beute auf oder im Sediment. Die Vögel suchten während des Niedrigwassers nach Nahrung und verwendeten dafür etwa 80 % ihrer Zeit; den Rest verbrachten sie mit Putzen und Rasten. Mehr als die Hälfte der festgestellten Beute und über 80 % der mittleren Energieaufnahme bestand ausScopimera globosa. Mit steigender Beutegröße wurde ein größerer Anteil der Beute vor dem Verschlucken gewaschen. Kleine Krabben wurden immer verschluckt, während von den größeren ein zunehmender Anteil schließlich verworfen wurde. Wenn die Krabben tief unten in ihren Höhlen saßen, befanden sich nur die kleinsten in der Reichweite der Schnäbel. Daher waren die meisten Krabben nur außerhalb ihrer Höhlen an der Oberfläche erreichbar, und zwar lediglich während drei Stunden (oder einem Drittel) der täglichen Niedrigwasserperiode. Früh in der Tidenperiode, wenn die Krabben an die Erdoberfläche gekommen waren, liefen und pickten die Terekwasserläufer pro Zeiteinheit oft, um die Krabben zu fangen. Wenn die Krabben am häufigsten waren und sich am leichtesten fangen ließen, waren die Vögel anscheinend selektiver in ihrer Beuteauswahl: Mehr Krabben wurden vor dem Verzehr gewaschen und mehr wurden schließlich verworfen. Zur Erklärung des Verhaltens sowohl des Räubers als auch der Beute werden Hypothesen angeboten.

     

Phenotypic compromise in the face of conflicting ecological demands: an example in red knots Calidris canutus

Phenotypic flexibility is a phenomenon where physiological functions in animals are reversibly adjusted in response to ecological constraints. Research usually focuses on effects of single constraints, but under natural conditions animals face a multitude of restrictions acting simultaneously, and potentially generating conflicting demands on the phenotype. We investigated the conflicting demands of low temperatures and a low quality diet on the phenotype of a shorebird, the red knot Calidris canutus . We tested the effects of switching diet from a high quality trout food to low quality hard-shelled bivalves in captive birds acclimated to temperatures reflecting natural winter conditions. Feeding on bivalves generated a digestive constraint forcing the birds to increase the height and width of their gizzard by 66% and 71%, respectively, over 30 days. The change in gizzard size was associated with an initial 15% loss of body mass and a reduction in size of the pectoral muscles by 11%. Because pectoral muscle size determines summit metabolic rate (M_sum, an indicator of cold endurance), measured M_sum declined by 9%. Therefore, although the birds were acclimated to cold, gizzard growth led to a loss of cold endurance. We propose that cold-acclimated knots facing a digestive constraint made a phenotypic compromise by giving-up cold hardiness for digestive capacity. Field studies suggest that phenotypic compromises occur in free-living red knots as well and help improve survival.     

Permanent female mimics in a lekking shorebird

Female mimics are known from many species, but permanent, non-conditional, alternative mating strategies are only known from an isopod, a fish, a lizard and a bird. The single bird example refers to lek-breeding ruffs Philomachus pugnax, a shorebird for which two strategies (independent and satellite) have been known for over 50 years. Ruffs also provided the single case of an animal with two, rather than three, permanent alternative mating strategies. Here, we describe a rare female-like morph of ruffs: the 'missing' third alternative mating strategy, which we have called 'faeder'. Faeders are slightly larger than females and in late April have testes 2.5 time the size of testes of normal males. On leks in aviaries and in the wild they appear to combine feminine and masculine behaviours. Faeders may represent the ancestral, care-giving, male strategy, but their relatively large testes suggest that currently they behave as sneakers.     

Small home ranges and high site fidelity in red knots (Calidris c. canutus) wintering on the Banc d’Arguin, Mauritania

Using automated and manual radio-telemetry and resightings of individual colour-ringed birds, we assessed the daily use of space of red knots Calidris canutus canutus at a tropical wintering area along the Sahara coast, the Banc d’Arguin in Mauritania. Confirming earlier suggestions, we found that birds were very faithful to their roosts and that the daily foraging range was small; in the course of several winter months birds used an area of only 2–16 km² of intertidal area. We found no differences between their movements in daylight and at night. Additionally, individuals seem to return to exactly the same locations in subsequent winters. This pattern is very different from red knots wintering in the temperate Wadden Sea. Here, they readily change roost sites and easily cover areas of about 800 km² in the course of weeks but, just as in Mauritania, no differences between day and night are apparent. In northern Patagonia and north-western Australia, red knots have range sizes closer to those on the Banc d’Arguin, but here they do show differences in space use between day and night. Ecological explanations for these contrasting patterns require further comparative data based on in-depth studies on the predictability of the food base and the presence of diurnal and nocturnal predators.     

Two estimates of the metabolic costs of antibody production in migratory shorebirds: low costs, internal reallocation, or both?

We measured the costs of mounting a humoral immune response using two novel antigens (tetanus and diphtheria) in two shorebird species (Scolopacidae): Red Knot (Calidris canutus, measured in autumn) and Ruff (Philomachus pugnax, measured in spring). Metabolic rate was measured during the preinjection phase, at the building phase of the primary immune response, and at peak secondary immune response by determining the oxygen consumption of the postabsorptive birds at rest. Confirming earlier studies, Red Knots and Ruffs responded with lower antibody titers to the diphtheria than to the tetanus antigen. Although Red Knots and Ruffs produced the same amounts of antibodies, Red Knots showed a significant 13% increase in basal metabolic rate (BMR) during the secondary antibody response, whereas Ruffs showed a 15%, but only marginally significant, reduction in BMR. The results from this study suggest that the energetic costs of an immune response may be small, but the "negative cost" in Ruffs hints at the possibility of resource reallocation and the concomitant difficulty of measuring such costs during "basal" metabolic rate measurements.     

Experimental tests of a seasonally changing visual preference for habitat in a long-distance migratory shorebird

Migratory shorebirds show highly organized seasonal cycles in physiological and morphological traits (body mass and composition, plumage, hormone levels, etc.), which in captivity is accompanied by restless behaviour at times when free-living birds would start migration. We introduce the idea that seasonally changing preference for habitat could motivate migrants to embark on migration and that this cognitive process could also guide them to seasonally appropriate places. We explored this by testing whether red knots (Calidris canutus), which also in captivity maintain marked circannual phenotypic rhythms, show evidence of seasonal change in preference for pictures of seasonally appropriate habitats. We first developed a method to verify whether red knots are able to memorize and discriminate contrasting pictures projected by LCD projectors. This was followed by two different experiments in which we tested for a seasonally changing preference for breeding or non-breeding habitat. When carried out during the pre-breeding season, the red knots are expected to prefer pictures of mudflats, their non-breeding habitat. At the start of the breeding season, they should prefer pictures of the tundra breeding habitat. We established that knots are able to distinguish and memorize projected images. We failed to demonstrate the predicted change in vision-based habitat preference, but for reasons of test design we do not interpret this as a strong rejection of the hypothesis. Instead, we suggest that experiments with greater numbers of individuals tested once, perhaps in combination with the provision of additional cues such as smells and sounds, will help the development of these ideas further.     

A dominant allele controls development into female mimic male and diminutive female ruffs

Maintaining polymorphisms for genes with effects of ecological significance may involve conflicting selection in males and females. We present data from a captive population of ruffs (Philomachus pugnax) showing that a dominant allele controls development into both small, ‘female mimic’ males (‘faeders’), and a previously undescribed class of small ‘female faeders’. Most male ruffs have elaborate breeding plumage and display behaviour, but 0.5–1.5% are faeders, which lack both. Females from a captive population previously lacking faeders were bred with two founder faeder males and their faeder sons. The faeders’ offspring had a quadrimodal size distribution comprising normal-sized males and females, faeders and atypically small females. By contrast, ornamented males fathered only normal-sized offspring. We conclude that both founding faeders were heterozygous for a faeder allele absent from the original population. This allele is dominant to previously described genes that determine development into independent versus satellite ornamented males. Unlike those genes, the faeder allele is clearly expressed in females. Small body size is a component of the male faeder mating strategy, but provides no obvious benefit to females. Bisexual expression of the gene provides the opportunity to quantify the strength of sexually antagonistic selection on a Mendelian trait.     

Efficacy and Safety of A Liposome-Based Vaccine against Protein Tau,Assessed in Tau.P301L Mice That Model Tauopathy

Progressive aggregation of protein Tau into oligomers and fibrils correlates with cognitive decline and synaptic dysfunction, leading to neurodegeneration in vulnerable brain regions in Alzheimer''s disease. The unmet need of effective therapy for Alzheimer''s disease, combined with problematic pharmacological approaches, led the field to explore immunotherapy, first against amyloid peptides and recently against protein Tau. Here we adapted the liposome-based amyloid vaccine that proved safe and efficacious, and incorporated a synthetic phosphorylated peptide to mimic the important phospho-epitope of protein Tau at residues pS396/pS404. We demonstrate that the liposome-based vaccine elicited, rapidly and robustly, specific antisera in wild-type mice and in Tau.P301L mice. Long-term vaccination proved to be safe, because it improved the clinical condition and reduced indices of tauopathy in the brain of the Tau.P301L mice, while no signs of neuro-inflammation or other adverse neurological effects were observed. The data corroborate the hypothesis that liposomes carrying phosphorylated peptides of protein Tau have considerable potential as safe and effective treatment against tauopathies, including Alzheimer''s disease.     

Intronic variation at the CHD1‐Z gene in Black‐tailed Godwits Limosa limosa limosa: correlations with fitness components revisited

Recently, Schroeder et al. (2010, Ibis 152: 368–377) suggested that intronic variation in the CHD1‐Z gene of Black‐tailed Godwits breeding in southwest Friesland, The Netherlands, correlated with fitness components. Here we re‐examine this surprising result using an expanded dataset (2088 birds sampled from 2004 to 2010 vs. 284 birds from 2004 to 2007). We find that the presence of the Z* allele (9% of the birds) is not associated with breeding habitat type, egg size, adult survival, adult body mass or adult body condition. The results presented here, when used in synergy with the previously reported results by Schroeder et al., suggest that there might be a tendency towards female adults with the Z* allele laying earlier clutches than adult females without the Z* allele. The occurrence of the Z* allele was also associated with a higher chick body mass and return rate. Chicks with the Z* allele that had hatched early in the breeding season were heavier at birth than chicks without the Z* allele and chicks with the Z* allele that had hatched late. Collectively, the results suggest that variation in the CHD1‐Z gene may indeed have arisen as a byproduct of selection acting on females during the egg fase and on chicks during the rearing stages of the reproductive cycle.     

Toxin constraint explains diet choice,survival and population dynamics in a molluscivore shorebird

Recent insights suggest that predators should include (mildly) toxic prey when non-toxic food is scarce. However, the assumption that toxic prey is energetically as profitable as non-toxic prey misses the possibility that non-toxic prey have other ways to avoid being eaten, such as the formation of an indigestible armature. In that case, predators face a trade-off between avoiding toxins and minimizing indigestible ballast intake. Here, we report on the trophic interactions between a shorebird (red knot, Calidris canutus canutus) and its two main bivalve prey, one being mildly toxic but easily digestible, and the other being non-toxic but harder to digest. A novel toxin-based optimal diet model is developed and tested against an existing one that ignores toxin constraints on the basis of data on prey abundance, diet choice, local survival and numbers of red knots at Banc d''Arguin (Mauritania) over 8 years. Observed diet and annual survival rates closely fit the predictions of the toxin-based model, with survival and population size being highest in years when the non-toxic prey is abundant. In the 6 of 8 years when the non-toxic prey is not abundant enough to satisfy the energy requirements, red knots must rely on the toxic alternative.