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Conservation of migratory shorebirds and waterfowl presents unique challenges due to extensive historic loss of wetland habitats, and current reliance on managed landscapes for wintering and migratory passage. We developed a spatially-explicit approach to estimate potential shorebird and waterfowl densities in California by integrating mapped habitat layers and statewide bird survey data with expert-based habitat rankings. Using these density estimates as inputs, we used the Marxan site-selection program to identify priority shorebird and waterfowl areas at the ecoregional level. We identified 3.7 million ha of habitat for shorebirds and waterfowl, of which 1.4 million ha would be required to conserve 50% of wintering populations. To achieve a conservation goal of 75%, more than twice as much habitat (3.1 million ha) would be necessary. Agricultural habitats comprised a substantial portion of priority areas, especially at the 75% level, suggesting that under current management conditions, large areas of agricultural land, much of it formerly wetland, are needed to provide the habitat availability and landscape connectivity required by shorebird and waterfowl populations. These habitats were found to be largely lacking recognized conservation status in California (96% unconserved), with only slightly higher levels of conservation for priority shorebird and waterfowl areas. Freshwater habitats, including wetlands and ponds, were also found to have low levels of conservation (67% un-conserved), although priority shorebird and waterfowl areas had somewhat higher levels of conservation than the state as a whole. Conserving migratory waterfowl and shorebirds will require a diversity of conservation strategies executed at a variety of scales. Our modeled results are complementary with other approaches and can help prioritize areas for protection, restoration and other actions.

We examined nesting distribution and demography of the Pacific Coast population of Caspian Terns (Sterna caspia) using breeding records and band recoveries spanning two decades since the first population assessment. Since 1980, population size has more than doubled to about 12 900 pairs, yet the proportion of the population nesting at inland (18%) versus coastal sites (82%) has remained constant. Although the breeding range of the Pacific Coast population has expanded northward into Alaska and farther south in Mexico, there was no net latitudinal shift in the distribution of breeding pairs or new colonies. The distribution of breeding birds among areas changed dramatically, however, with 69% of breeding terns now nesting in Oregon (primarily in the Columbia River estuary) versus 4% during the late 1970s. During the past 20 years, there has continued to be a greater proportion of Caspian Terns breeding at anthropogenic sites compared to natural sites. Estimated annual survival rates for hatch-year and after-third-year birds during 1981– 1998 were greater than during 1955–1980, consistent with the higher rate of population increase in recent decades. Fecundity required to maintain a stable population (λ = 1) was estimated at 0.32–0.74 fledglings pair−1, depending on band recovery probabilities for subadults. Caspian Terns readily moved among breeding sites and rapidly colonized new areas; however, a greater concentration of breeding Caspian Terns among fewer colonies in response to anthropogenic factors is an important conservation concern for this species.Redistribución y Crecimiento de la Población de Sterna caspia en la Región de la Costa Pacífica de América del Norte entre 1981 y 2000Resumen. Se examinó la distribución de anidamientos y la demografía de la población de Sterna caspia en la costa del Pacífico usando registros reproductivos y anillos recobrados de aves marcadas durante dos décadas desde la primera evaluación poblacional. Desde 1980 el tamaño poblacional se duplicó a 12 900 parejas, aunque la proporción de la población anidando en la zona interior (18%) versus la zona costera (82%) permaneció constante. A pesar de que el rango reproductivo de la población costera del Pacífico se expandió hacia el norte llegando a Alaska y hacia el sur hasta México, no hubo un cambio latitudinal neto en la distribución de parejas reproductivas o de nuevas colonias. Sin embargo, la distribución de aves reproductivas entre las áreas cambió dramáticamente, con un 69% de los individuos reproductivos de Sterna caspia anidando ahora en Oregón (principalmente en el estuario del Río Columbia) comparado con un 4% a fines de la década del 70. Durante los últimos 20 años continuó habiendo una mayor proporción de individuos de Sterna caspia anidando en sitios con actividad antropogénica en comparación con áreas naturales. Las tasas de supervivencia anual para aves con menos de un año y aves con más de tres años fueron mayores durante 1981–1998 que durante 1955–1980, lo que es consistente con una mayor tasa de crecimiento poblacional en décadas recientes. La fecundidad requerida para mantener estable la población (λ = 1) se estimó en 0.32–0.74 volantones producidos por pareja, dependiendo de la probabilidad de recuperación de anillos en aves subadultas. Sterna caspia es capaz de moverse entre sitios reproductivos y coloniza nuevas áreas rápidamente. No obstante, una mayor concentración de individuos reproductivos de Sterna caspia en unas pocas colonias, como respuesta a factores antropogénicos, es una importante preocupación para la conservación de esta especie.

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