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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.

De ongunstige ontwikkeling van de weidevogelstand in Nederland is al tientallen jaren een punt van aandacht voor rijk en provincies. Maar alle inspanningen tot dusver hebben niet voor een omkeer kunnen zorgen; op z’n best is de achteruitgang afgeremd. De laatste jaren wordt steeds vaker gesproken over gebieden waar de beschikbare middelen geconcentreerder worden ingezet en waar de weidevogelstand weer kan floreren. Weidevogelkerngebieden. Wat mag er van verwacht worden en wat zijn de implicaties als deze richting wordt ingeslagen?

De Kenniskring Weidevogellandschap heeft SOVON, Bureau Altenburg & Wymenga en Alterra gevraagd onderzoek te doen naar sturende factoren die de populatie van weidevogels kan beïnvloeden. Toegespitst op de aspecten: Trek van de Grutto naar Afrika (via satellietzenders, i.s.m. RU Groningen); Waterpeil (in relatie tot foerageren van Grutto's); en de vegetatiestructuur. Conclusies zijn o.a. dat de trekroutes veilig gesteld dienen te worden; in Nederland zal het waterbeheer dusdanig moeten zijn, dat het vochtgehalte van de bodem niet onder de 30% zal dalen, zodat de voedselbeschikbaarheid optimaal is.

Due to the 'double-clutch' mating system found in the arctic-breeding Little Stint Calidris minuta, each parent cafes for a clutch and brood alone. The resulting constraint on feeding time, combined with the cold climate and a small body size, may cause energetic bottlenecks. Based on the notion that mass stores in birds serve as an 'insurance' for transient periods of negative energy balance, but entail certain costs as well, body mass may vary in relation to climatic conditions and stage of the breeding cycle. We studied body mass in Little Stints in relation to breeding stage and geographical location, during 17 expeditions to 12 sites in the Eurasian Arctic, ranging from north Norway to north-east Taimyr. Body mass was higher during incubation than during chick-rearing. Structural size, as estimated by wing length, increased with latitude. This was probably caused by relatively more females (the larger sex) incubating further north, possibly after leaving a first clutch to be incubated by a male further south. Before and after correction for structural size, body mass was strongly related to latitude during both incubation and chick-rearing. In analogy to a similar geographical pattern in overwintering shorebirds, we interpret the large energy stores of breeding Little Stints as an insurance against periods of cold weather which are a regular feature of arctic summers. Climate data showed that the risk of encountering cold spells lasting several days increases with latitude over the species' breeding range, and is larger in June than in July. Maintaining these stores is therefore less necessary at southern sites and during the chick-rearing period than in the incubation period. When guarding chicks, feeding time is less constrained than during incubation, temperatures tend to be higher than in the incubation period, reducing energy expenditure, and the availability of insect prey reaches a seasonal maximum. However, the alternative interpretation that the chick-tending period is more energetically stressful than the incubation period, resulting in a negative energy balance for the parent, could not be rejected on the present evidence.

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.

We measured Basal Metabolic Rate (EMR) of 16 wader species (order Charadriiformes) on their wintering grounds in Africa. The allometric regression equation relating BMR to body mass: BMR (W) = 4.02 x M (kg)(0.724) runs parallel to that of waders in temperate areas, but at a 20% lower elevation. Since waders wintering in the tropics have a reduced body mass, the difference in BMR between members of the same species at tropical and temperate latitudes was even larger and amounted to 31%. BMR did nor differ between families nor did it differ between long-distance migrants that breed in the Arctic and species that spend their entire life in the tropics. As migrant waders have a higher BMR during autumn migration in the north, we suspect that they reduce BMR upon arrival in the tropics. We hypothesize that this reduction is due to somatic factors under control of hormonal factors, including a reduction of organ sizes and probably suppressed thyroid activity induced by the high ambient temperatures in the tropics. The involvement of thyroid hormones in the regulation of BMR would be consistent with the fact that waders in the tropics regulate their body mass at a lower level than birds in temperate areas and may explain why the rate of premigratory fattening is slower in the tropics than further north. The mechanism, a dual control system including somatic and hormonal factors acting in concert, rapidly adjusts BMR of migratory waders to the different ecological conditions encountered during their long journeys to and from the breeding grounds.