No abstract

Wetland loss and degradation have been extensive across the world, especially in California’s Central Valley where over 90% of the natural wetlands have been converted to agricultural and urban uses. In the Central Valley today, a much smaller network of managed wetlands and flooded agricultural fields supports almost five million waterfowl and half a million shorebirds. Over 50% of waterbird habitat in the Central Valley is provided by flooded agricultural land, primarily rice (Oryza sativa). Each year non-breeding waterbird habitat decreases in the late winter as flooded agricultural fields are drained after waterfowl hunting season in late-January to prepare for the next crop. This study evaluated a practice called ‘variable drawdown’ that involves delaying the removal of water from rice fields by 1, 2, and 3 weeks to extend the availability of flooded habitat later into February and March. We studied waterbird response to variable drawdown in 2012 and 2013 at twenty rice farms throughout the northern half of the Central Valley. The staggered drawdown created a mosaic of water depths throughout the six-week study period. The 3-week delay in drawdown supported more dabbling ducks than earlier drawdowns in the first half of the study and more shorebirds and long-legged wading birds during the second half of the study. The timing of highest use of each drawdown treatment differed for each waterbird guild; dabbling ducks, geese and swans benefited at the beginning, then long-legged wading birds, followed by shorebirds. Despite the presence of appropriate water depths for shorebirds across the treatments during the entire study period, shorebird densities were highest near the end of the study when the 3-week-delayed drawdown was providing the majority of the habitat on the landscape. This suggests that shorebirds may have concentrated in our study fields due to decreasing availability of shallow water habitat elsewhere. The practice of variable drawdown successfully extended the availability of waterbird habitat provided by post-harvest flooded rice fields later into winter.

. 2012. Use of occupancy models to evaluate expert knowledge-based species-habitat relationships. Avian Conservation and Ecology 7(2): 5. http://dx.doi. org/10.5751/ACE-00551-070205 ABSTRACT. Expert knowledge-based species-habitat relationships are used extensively to guide conservation planning, particularly when data are scarce. Purported relationships describe the initial state of knowledge, but are rarely tested. We assessed support in the data for suitability rankings of vegetation types based on expert knowledge for three terrestrial avian species in the South Atlantic Coastal Plain of the United States. Experts used published studies, natural history, survey data, and field experience to rank vegetation types as optimal, suitable, and marginal. We used single-season occupancy models, coupled with land cover and Breeding Bird Survey data, to examine the hypothesis that patterns of occupancy conformed to species-habitat suitability rankings purported by experts. Purported habitat suitability was validated for two of three species. Research Papers Use of Occupancy Models to Evaluate ExpertAs predicted for the Eastern Wood-Pewee (Contopus virens) and Brown-headed Nuthatch (Sitta pusilla), occupancy was strongly influenced by vegetation types classified as "optimal habitat" by the species suitability rankings for nuthatches and wood-pewees. Contrary to predictions, Red-headed Woodpecker (Melanerpes erythrocephalus) models that included vegetation types as covariates received similar support by the data as models without vegetation types. For all three species, occupancy was also related to sampling latitude. Our results suggest that covariates representing other habitat requirements might be necessary to model occurrence of generalist species like the woodpecker. The modeling approach described herein provides a means to test expert knowledge-based species-habitat relationships, and hence, help guide conservation planning.RÉSUMÉ. Les relations espèces-habitat établies à partir des connaissances d'experts sont largement utilisées pour orienter la planification de la conservation, surtout lorsque les données sont rares. Ces relations présumées représentent les rudiments de la connaissance, mais sont rarement testées. L'adéquation du classement de milieux établi par des experts a été évaluée pour trois espèces de passereaux de la Plaine côtière de l'Atlantique Sud, aux États-Unis. Les experts ont utilisé des données publiées (recherches, histoire naturelle, relevés) et leur expérience sur le terrain afin de classer les milieux selon trois catégories, soit optimaux, adéquats ou marginaux. Nous avons appliqué des modèles de présence, fondés sur une seule saison, à des données d'occupation du sol et de relevés d'oiseaux nicheurs afin d'examiner l'hypothèse voulant que les profils de présence concordent avec le classement de la qualité des milieux présumé par les experts. La qualité présumée des milieux a été validée pour deux des trois espèces. Comme prédit pour le Pioui de l'Est (Contopus virens) et la Sittelle à t...

No abstract

No abstract