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In many countries around the world impacts of climate change are assessed and adaptation options identified. We describe an approach for a qualitative and quantitative assessment of adaptation options to respond to climate change in the Netherlands. The study introduces an inventory and ranking of adaptation options based on stakeholder analysis and expert judgement, and presents some estimates of incremental costs and benefits. The qualitative assessment focuses on ranking and prioritisation of adaptation options. Options are selected and identified and discussed by stakeholders on the basis of a sectoral approach, and assessed with respect to their importance, urgency and other characteristics by experts. The preliminary quantitative assessment identifies incremental costs and benefits of adaptation options. Priority ranking based on a weighted sum of criteria reveals that in the Netherlands integrated nature and water management and risk based policies rank high, followed by policies aiming at 'climate proof' housing and infrastructure.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The role of food in avian reproduction is generally studied from the perspective of the protein and energy demand of birds. This study provides the first experimental evidence that calcium availability may limit reproduction in wild birds as well. 2. Data are presented showing that a large proportion of great tits Parus major on calcium-poor soils in the Netherlands produce eggs with thin and porous shells and desert the clutch before hatching. About 10% of the females do not lay at all. 3. Free-living great tits were supplied with an additional calcium source, i.e. snail shells and chicken eggshells. This treatment reduced the number of females without eggs, the frequency of clutch desertion, the proportion of nests with defective eggshells and the proportion of non-hatched eggs in clutches that produced young. The calcium supplements did not affect clutch size or laying date. 4. We suggest that possible adaptations to a limited calcium supply are not yet evident because the low calcium availability is a recent phenomenon caused by acid deposition and because a large part of the breeding population consists of immigrants from calcium-rich areas. 5. We provide evidence that calcium limitation in avian reproduction may be widespread on calcium-poor soils. 6. The results imply that the costs of egg formation in calcium-poor areas can be much higher than is currently estimated and that food conditions during egg-laying have a greater impact on avian reproduction than is presently believed.

The calcium demand of egg-laying birds is much higher than in other vertebrates during reproduction. We showed elsewhere that a low level of calcium availability can greatly affect the eggshell quality and reproduction of free-living passerines. However, there are few data on calcium demand and calcium intake in relation to egg laying and behaviour and egg-laying performance under conditions of calcium shortage in nondomesticated birds. We examined these aspects in an experiment with captive great tits, Parus major, on a diet deficient in calcium, with or without snail shells as an additional calcium source. More than 90% of the calcium intake for egg production took place during the egg-laying period. Females ingested about 1.7 times as much calcium as they deposited in eggshells. Removing the snail shells after the first egg resulted in eggshell defects and interruptions of laying after 1-3 d. Females without snail shells doubled their searching effort and started to burrow in the soil and to eat sand, small stones, and their own eggs. Most calcium was consumed in the evening, probably to supplement the calcium available from the medullary bone with an additional calcium source in the gut during eggshell formation. The results demonstrated that eggshell formation requires accurate timing of the calcium intake and that obtaining sufficient calcium is time-consuming, even in calcium-rich environments. These factors pertaining to calcium intake greatly affect the ability of birds to collect sufficient calcium for eggshell formation in calcium-poor areas.