Low costs of terrestrial locomotion in waders

Energy expenditure of terrestrial locomotion on a linear treadmill was measured in five wader species: Turnstone Arenaria interpres, Knot Calidris canutus, Grey Plover Pluvialis squatarola, Oystercatcher Haematopus ostralegus and Bar-tailed Godwit Limosa lapponica. Additional data on Redshank Tringa totanus were taken from the literature. The cost of running in these waders, measured as the slope of the regression line of energy expenditure against speed of locomotion, is significantly less than an allometrically calculated slope for all bird species (Taylor et al. 1982). It is also less than in grouse species which, like waders, must walk to gather their food. Cost of running for a 100 g wader is 22% below the cost of a grouse, and 68% below the cost of a hypothetical penguin of similar mass. Intraindividual cost of running in relation to body mass of a Turnstone and interindividual cost of running in Knots reveal much stronger increases of running costs with increasing body mass than interspecific allometric relations would predict, and this elevated activity cost probably importantly influences the set point for body mass regulation in birds

Experimental evidence for a causal effect of pair-bond duration on reproductive performance in oystercatchers (Haematopus ostralegus)

Many studies have suggested that reproductive performance improves during the pair-bond, which might explain why individuals remate with the same partner in many species. However, discussion exists about whether the association between reproductive performance and pair-bond duration that is reported in these studies reflects a causal relationship. Usually it is unclear whether a positive association is caused by pairs improving during their pair-bond or by high-quality pairs staying together for longer. Furthermore, reproductive performance often also depends on the age or breeding experience of parents, which all covary with pair-bond duration. A much needed experimental approach is lacking so far. We investigated the effect of pair-bond duration on reproductive performance in a long-lived monogamous bird species based on natural as well as experimental variation. The duration of oystercatcher (Haematopus ostralegus) pair-bonds, which were followed for 21 years, strongly affected reproductive output, even after controlling for effects of age and breeding experience. Pairs improved during their pair-bond, and there were no indications of selective disappearance of low-quality pairs; however, pairs that stayed together for very long performed badly. Experimental removal of one partner showed that the reproductive cost of divorce depended on the pair-bond duration with the old partner. In addition, after remating, the newly formed pairs strongly improved again, independent of the age and breeding experience of the remated pair members. As such, this study provides the first experimental evidence of a causal effect of pair-bond duration on reproductive performanc

Competitive abilities of oystercatchers (Haematopus ostralegus) occupying territories of different quality

Abstract In territorial species, habitat heterogeneity results in some individuals occupying poor quality sites while others occupy high quality sites. Floaters (mature nonbreeders) may accept a low quality territory, because it is the best they can get and defend ('inferior phenotype hypothesis'), or because it is a strategic alternative for a high quality territory in the long run ('queue hypothesis'). Oystercatcher Haematopus ostralegus territories differ consistently in the amount of offspring produced each year and this is related to the distance between the nesting and feeding territories. The inferior phenotype hypothesis was previously rejected on the basis of the absence of morphometric differences (assumed to indicate competitive abilities) among breeders. We investigated social dominance, in the field and in captivity, in relation to the quality of the breeding territory. In the field, birds with high-quality territories won more often compared to those occupying low-quality territories. However, this difference was not apparent in a small dataset of captive birds. These results are discussed in the framework of the long-term fitness prospects of settling in a high or low quality territory

Op naar kerngebieden voor weidevogels in Nederland : werkdocument met randvoorwaarden en handreiking

Een methode is uitgewerkt om kerngebieden te identificeren voor weidevogels. Als gidssoort is de grutto gebruikt, implicaties voor de andere weidevogelsoorten zijn aangeduid. Als zoekgebied voor kerngebieden zijn aangeduid gebieden die voldoen aan minumumdichtheden (15 dan wel 30 bp/100 ha). Aan de hand van trendgegevens is geanalyseerd welke factoren bepalend zijn voor de aantalsontwikkeling. De resultaten hiervan zijn als randvoorwaarden gehanteerd voor de nadere invulling van de kerngebieden. Met een metapopulatiemodel is verkend aan welke ruimtelijke voorwaarden kerngebieden moeten voldoen: o.a. omvang en onderlinge afstanden, in relatie tot de ruimtelijke kwaliteit. Scenarioberekeningen zijn uitgevoerd naar verschillende ruimtelijke invullingen. Er is een handreiking opgesteld als voorbeeld hoe kerngebieden in de praktijk geidentificeerd en uitgewerkt zouden kunnen worden

Habitat preference of geese is affected by livestock grazing:Seasonal variation in an experimental field evaluation

The number of staging geese in northwestern Europe has increased dramatically. Growing goose numbers put strong grazing pressure on agricultural pastures. Damage to agricultural land may be mitigated by managing nature reserves in order to optimally accommodate large numbers of grazing geese. Livestock grazing has been shown to facilitate foraging geese; we take the novel approach of determining the effects of four different livestock grazing treatments in a replicated experiment on the distribution of geese. We present experimental field evidence that livestock grazing of a salt marsh in summer affects the habitat preference of foraging geese during autumn and spring staging. In an experimental field set-up with four different livestock grazing treatments we assessed goose visitation through dropping counts, in both autumn and spring. Grazing treatments included 0.5 or 1 horse ha(-1) and 0.5 or 1 cattle ha(-1) during the summer season. The livestock grazing regime affected goose distribution in autumn, just after livestock had been removed from the salt marsh. In autumn, goose visitation was highest in the 1 head ha(-1) grazing treatments, where grazing intensity by livestock was also highest. In line with this result, goose visitation was lowest in the 0.5 head ha(-1) livestock grazing treatments, where the grazing intensity by livestock was lowest. The differences in goose visitation among the experimental treatments in autumn could not be explained by the canopy height. In spring we did not find any effect of livestock grazing treatment on goose visitation. Differences in the distribution of geese over the experiment between autumn and spring may be explained by changes in the availability of nutrient-rich vegetation. Livestock summer grazing with a high stocking density, especially with horses, can be used to attract geese to salt marshes in autumn and potentially reduces damage caused by geese to inland farmland. From a nature conservation interest point of view, however, variation in structure of the vegetation is a prerequisite for other groups of organisms. Hence, we recommend grazing of salt marshes with densities of 0.5 head ha(-1) of livestock when goose conservation is not the only management issue

Predation Danger Can Explain Changes in Timing of Migration: The Case of the Barnacle Goose

Understanding stopover decisions of long-distance migratory birds is crucial for conservation and management of these species along their migratory flyway. Recently, an increasing number of Barnacle geese breeding in the Russian Arctic have delayed their departure from their wintering site in the Netherlands by approximately one month and have reduced their staging duration at stopover sites in the Baltic accordingly. Consequently, this extended stay increases agricultural damage in the Netherlands. Using a dynamic state variable approach we explored three hypotheses about the underlying causes of these changes in migratory behavior, possibly related to changes in (i) onset of spring, (ii) potential intake rates and (iii) predation danger at wintering and stopover sites. Our simulations showed that the observed advance in onset of spring contradicts the observed delay of departure, whereas both increased predation danger and decreased intake rates in the Baltic can explain the delay. Decreased intake rates are expected as a result of increased competition for food in the growing Barnacle goose population. However, the effect of predation danger in the model was particularly strong, and we hypothesize that Barnacle geese avoid Baltic stopover sites as a response to the rapidly increasing number of avian predators in the area. Therefore, danger should be considered as an important factor influencing Barnacle goose migratory behavior, and receive more attention in empirical studies

Predicting impacts of food competition, climate, and disturbance on a long-distance migratory herbivore

Climate change is driving worldwide shifts in the distribution of biodiversity, and fundamental changes to global avian migrations. Some arctic-nesting species may shorten their migration distance as warmer temperatures allow them to winter closer to their high-latitude breeding grounds. However, such decisions are not without risks, since this intensifies pressure on resources when they are used for greater periods of time. In this study, we used an individual-based model to predict how future changes in food abundance, winter ice coverage, and human disturbance could impact an Arctic/sub-Arctic breeding goose species, black brant (Branta bernicla nigricans, Lawrence 1846), and their primary food source, common eelgrass (Zostera marina L.), at the Izembek Lagoon complex in southwest Alaska. Brant use the site during fall and spring migrations, and increasingly, for the duration of winter. The model was validated by comparing predictions to empirical observations of proportion of geese surviving, proportion of geese emigrating, mean duration of stay, mean rate of mass gain/loss, percentage of time spent feeding, number of bird days, peak population numbers, and distribution across the complex. The model predicted that reductions >50% of the current decadal (2007–2015) mean of eelgrass biomass, which have been observed in some years, or increases in the number of brant, could lead to a reduction in the proportion of birds that successfully migrate to their breeding grounds from the site. The model also predicted that access to eelgrass in lagoons other than Izembek was critical for overwinter survival and spring migration of brant, if overall eelgrass biomass was 50% of the decadal mean biomass. Geese were typically predicted to be more vulnerable to environmental change during winter and spring, when eelgrass biomass is lower, and thermoregulatory costs for the geese are higher than in fall. We discuss the consequences of these predictions for goose population trends in the face of natural and human drivers of change

Cost reduction in the cold: Heat generated by terrestrial locomotion partly substitutes for thermoregulation costs in Knot Calidris canutus

To test whether heat generated during locomotion substitutes for the thermoregulation cost, oxygen consumption of four post-absorptive temperate-wintering Knot Calidris canutus was measured at air temperatures of 25 degrees C (thermoneutral) and 10 degrees C (c. 10 degrees below the lower critical temperature) when the birds were at rest at night and during running on a treadmill, After allowing for body mass, the thermoregulation cost at 10 degrees C was significantly lower in active birds compared with birds at rest, At rest, the birds spent, on average, 0.50 watt (W; range, 0.47-0.57 W) on thermoregulation. During exercise, this cost factor averaged 0.33 W (range, 0.25-0.42 W), The average difference in thermoregulation cost was 35% (ranging from 26% to 49% between individuals) and provides an estimate of the amount of substituted heat, A review of nine studies, all restricted to small birds, showed that substitution is a widespread phenomenon, The consequences of such partial substitution for the annual energetics of Knot wintering in the temperate Wadden Sea v tropical west Africa are examined, Compared with a previous additive model, the model which includes substitution (i.e. the use of heat produced during activity) reduces the differences in maintenance metabolism between the two wintering strategies by 17%, from 1.19 W to 0.99 W