Summary 1.The loss and human modification of wetlands world-wide underscores the importance of efficient management. For wetlands that provide habitats for non-breeding waterbirds, such management often aims to support a rich and abundant waterbird community. 2. Among the world's many seasonal, moist-soil managed wetlands, annual winter flooding is followed by spring drawdown to encourage germination of waterfowl food plants. Recommendations on how best to maintain flooded wetlands for multiple species are mostly theoretical, and drawdown management typically focuses on spring for migrating shorebirds. The benefits and drawbacks of shallow-water management in winter have not been examined, especially where sizeable populations of wintering shorebirds and waterfowl occur together. 3. We considered The Grasslands Ecological Area in California's Central Valley, USA, as a model wetland complex in which to assess optimal winter flood-depth for multispecies use. We also examined the relative benefits for each waterbird group (e.g. shorebirds and waterfowl) of drawdowns conducted in winter and spring. We experimentally dewatered wetlands of measured topography in the winter and spring of 1994-95, documenting changes in waterbird species richness and abundance associated with daily changes in habitat diversity and availability. 4. Results indicated limited regional availability of shallow-water habitat across the landscape in winter but not spring, as use by shorebirds and teal increased on drawndown wetlands in winter only. Use by deeper-water dabbling ducks and diving waterbirds declined during the later stages of drawdown in both seasons, but not until use by shorebirds and teal had peaked. The maximum diversity and abundance of waterbirds occurred at average depths of 10-20 cm on wetlands with topographic gradients of 30-40 cm. 5. This study has important implications for the winter management of seasonal wetland complexes, especially moist-soil systems where managers provide habitat for different waterbird groups (from shorebirds to diving waterbirds) simultaneously. In general, where topography is variable (e.g. a difference of 30-40 cm between the deepest and shallowest zones), wetlands flooded to average depths of 15-20 cm should accommodate the greatest richness and abundance of waterbirds.

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Precocial young often experience high mortality prior to achieving flight, especially in the first days after hatching. We quantified relationships between chick age, survival, behavior, and response to natural and anthropogenic danger for the threatened Western Snowy Plover (Charadrius alexandrinus nivosus) in coastal northern California, USA. Plover chicks were most likely to die in the first three days of their 28-day prefledging period, especially on sandy ocean beaches compared to coarser substrates of river habitats. Chick survival in both habitats increased across the ∼120-day chick-rearing period. Improved survival of older chicks coincided with an age-related reduction in brooding and increased distance from the tending parent, which was not related to season. Lower survival of younger chicks was correlated with a tendency to lie motionless when approached by humans; nearly all older chicks responded to human approach by running to evade danger. Chicks of all ages were more likely to lie motionless when potential avian predators flew nearby. Agedependent survival of Snowy Plover chicks paralleled a trend of increasing development, thermal independence from adults, and capability of evading predators. Abstract. Precocial young often experience high mortality prior to achieving flight, especially in the first days after hatching. We quantified relationships between chick age, survival, behavior, and response to natural and anthropogenic danger for the threatened Western Snowy Plover (Charadrius alexandrinus nivosus) in coastal northern California, USA. Plover chicks were most likely to die in the first three days of their 28-day prefledging period, especially on sandy ocean beaches compared to coarser substrates of river habitats. Chick survival in both habitats increased across the ,120-day chick-rearing period. Improved survival of older chicks coincided with an age-related reduction in brooding and increased distance from the tending parent, which was not related to season. Lower survival of younger chicks was correlated with a tendency to lie motionless when approached by humans; nearly all older chicks responded to human approach by running to evade danger. Chicks of all ages were more likely to lie motionless when potential avian predators flew nearby. Age-dependent survival of Snowy Plover chicks paralleled a trend of increasing development, thermal independence from adults, and capability of evading predators.Key words: antipredator behavior, Charadrius alexandrinus, chick survival, habitat quality, human disturbance, predation danger, Snowy Plover. Supervivencia Relativa a la Edad y Comportamiento de los Pichones deCharadrius alexandrinusResumen. Los pichones precociales usualmente experimentan una alta mortalidad antes de adquirir la capacidad del vuelo, especialmente en los primeros días luego de eclosionar. Cuantificamos la relació n entre la edad del pichó n, la supervivencia, el comportamiento y la respuesta a peligros naturales y antropogénicos para la especie amenazada Charadrius ...

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Predation is an important cause of nest failure for many birds and has shaped the life‐history characteristics of many species, especially ground‐nesting shorebirds. We examined nesting success, causes of clutch failure and nest survival in relation to variation in substrate characteristics in a colour‐marked population of Western Snowy Plovers Charadrius alexandrinus nivosus breeding on riverine gravel bars in coastal northern California. Plovers experienced higher nesting success on gravel bars than on nearby beaches, which were characterized by more homogeneous, sandy substrates. On gravel bars, Plovers nested in habitats characterized by large, heterogeneous substrates, with more egg‐sized stones, compared with random sites. Egg crypsis, as indexed by time required of a naïve observer to detect a nest, increased with number of egg‐sized substrates. Nest survival correlated negatively with heterogeneity of substrates and positively with the number of egg‐sized stones. Consistently high nesting success of Plovers on gravel bars indicates that this high‐quality habitat deserves special management considerations given the species’ threatened status.