There has been a growing interest in whether established ecogeographical patterns, such as Bergmann's rule, explain changes in animal morphology related to climate change. Bergmann's rule has often been used to predict that body size will decrease as the climate warms, but the predictions about how body size will change are critically dependent on the mechanistic explanation behind the rule. To investigate change in avian body size in western North America, we used two long-term banding data sets from central California, USA; the data spanned 40 years at one site and 27 years ) at the other. We found that wing length of birds captured at both sites has been steadily increasing at a rate of 0.024-0.084% per year. Although changes in body mass were not always significant, when they were, the trend was positive and the magnitudes of significant trends were similar to those for wing length (0.040-0.112% per year). There was no clear difference between the rates of change of long-distance vs. short-distance migrants or between birds that bred locally compared to those that bred to the north of the sites. Previous studies from other regions of the world have documented decreases in avian body size and have used Bergmann's rule and increases in mean temperature to explain these shifts. Because our results do not support this pattern, we propose that rather than responding to increasing mean temperatures, avian body size in central California may be influenced by changing climatic variability or changes in primary productivity. More information on regional variation in the rates of avian body size change will be needed to test these hypotheses.

For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprodTo order this and other USGS information products, visit http://store.usgs.gov Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.Suggested citation: Ackerman, J.T., Eagles-Smith, C.A., Heinz, G.H., De La Cruz, S.E., Takekawa, J.Y., Miles, A.K., Adelsbach, T.L., Herzog, M.P., Bluso-Demers, J.D., Demers, S.A., Herring, G., Hoffman, D.J., Hartman, C.A., Willacker, J.J., Suchanek, T.H., Schwarzbach, S.E., and Maurer, T.C., 2014, Mercury in birds of San Francisco Bay-Delta, California-Trophic pathways, bioaccumulation, and ecotoxicological risk to avian reproduction: U.S. Geological Survey Open-File Report 2014-1251, 202 p., http://dx.doi.org/10.3133/ofr20141251. Relations between log whole blood total mercury (THg) concentrations (µg/g ww) and whole blood stable isotope ratios of carbon (δ 13 C), nitrogen (δ 15 N), and sulfur (δ 34 S) in pre-breeding (green symbols) and breeding ( Relations between log whole blood total mercury (THg) concentrations (µg/g ww) and whole blood table isotope ratios of carbon (δ 13 C), nitrogen Correlation between single-species in mean fish total mercury (THg) concentrations (µg/g dw; ± SE), and corresponding Forster's tern THg concentrations in pre-breeding blood (µg/g ww; ± SE), breeding blood (µg/g ww; ± SE), and eggs (µg/g fww; ± SE) sampled from the same wetland location where fish were sampled .. Leverage plots for the relationship between total mercury (THg) concentrations (mg/g dry weight) and a suite of biomarkers in brains of prebreeding Forster's tern and Caspian tern adults (closed circles and closed triangles, respectively), breeding adult Forster's terns (semi-closed circles), and Tables Table 1. Population range sizes and percentage use of habitat types within 50 and 95 percent utilization distributions (UD) of pre-breeding American avocets and black-necked stilts radio-marked at each site during spring 2005 and 2006 Table 9.Mean percent number ( Table 16. Esophageal contents expressed as aggregate percent dry mass for surf scoters collected during 2003-2004 (2004) and 2004-2005 (2005) Table 17. Sample size, geometric means (µg/g dw), ± standard error and 95 percent CI for hepatic selenium (Se) and total mercury (THg), and renal cadmium (Cd) in female surf scoters only collected during fall (F), winter (W), spring (S) 2003-04 (2004) and 2004-05 (2005) Executive SummarySan Francisco Bay Estuary in northern California has a legacy of mercury ...

Resumen. Se conoce relativamente poco a cerca de las aves durante el período posterior al emplumamiento, cuando los pichones con capacidad de volar han abandonado el nido y deben aprender a forrajear independientemente. Examinamos los movimientos posteriores al abandono del nido, la selección de hábitat y la presencia en las colonias de individuos de la especie Sterna forsteri marcados con transmisores de radio justo antes del emplumamiento en la bahía de San Francisco, California. La proporción del día que las aves jóvenes pasaron en su colonia natal disminuyó a medida que su edad aumentó, desde el 65% al momento del emplumamiento hasta menos del 5% a las dos semanas de haber emplumado. De modo concordante, la distancia a su colonia a la que las aves fueron localizadas aumentó con su edad, de menos de 500 m durante la primera semana después de abandonar el nido a más de 5000 m para la quinta semana. La hora del día también influenció la presencia en la colonia: las aves de mayor edad pasaron más tiempo en la colonia durante las horas de la noche (20:00 a 05:00) que durante el día (06:00 a 19:00), cuando presumiblemente estaban forrajeando. Los ámbitos hogareños y las áreas núcleo de uso promediaron 12.14 km 2 y 2.23 km 2 , respectivamente. A cada una de cuatro escalas espaciales de análisis, las aves mostraron una preferencia marcada por los ambientes de estanques salinos. Los otros ambientes no fueron seleccionados a ninguna escala, pero las aves consistentemente evitaron las planicies mareales y las tierras altas. Éstas también evitaron los ambientes de bahías abiertas a las dos escalas espaciales más grandes, los pantanos mareales a las dos escalas más pequeñas y los barrizales y pantanos manejados a varias escalas. Dentro de los estanques salinos, las aves se econtraron más cerca de los diques (58 m) que lo que se esperaba (107 m). Nuestros resultados indican que los pichones de S. forsteri se dispersan desde su colonia natal antes de unas pocas semanas después de abandonar el nido, que los pichones de mayor edad usan su colonia natal principalmente para descansar durante la noche y que después del emplumamiento estas aves son altamente dependientes de los estanques salinos. POSTFLEDgINg FORSTER'S TERN MOVEMENTS, HAbITAT SELECTION, AND COLONy ATTENDANCE IN SAN FRANCISCO bAy Movimientos, Selección de Hábitat y Presencia en las Colonias de Sterna forsteri Después del EmplumamientoAbstract. Relatively little is known about birds during the postfledging period when flighted chicks have left the nest and must learn to forage independently. We examined postfledging movements, habitat selection, and colony attendance of Forster's Terns (Sterna forsteri) radio-marked just before they fledged in San Francisco bay, California. The proportion of the day spent at their natal colony declined as juveniles aged, from 65% at the time of fledging to <5% within two weeks of fledging. Accordingly, the distance postfledging terns were located from their colony increased as they aged, from <500 m within the first week of fledgin...

The breeding population of California Gulls (Larus californicus) in the San Francisco Bay estuary increased from 24 individuals in 1980 to a peak of over 53,000 in 2014, then declined to 38,040 in 2016. The expansion of the breeding population may be related to the availability of suitable nesting sites in close proximity to anthropogenic food subsidies at landfills. Telemetry data indicate that California Gull movements are largely dictated by the two primary landfills in South San Francisco Bay. The large population of California Gulls has had negative effects on locally breeding shorebirds and terns, especially the Forster’s Tern (Sterna forsteri), American Avocet (Recurvirostra americana), and Western Snowy Plover (Charadrius nivosus nivosus). In South San Francisco Bay, California Gulls were responsible for 13% and 38% of egg predation events at nests of American Avocets and Snowy Plovers, respectively, and 55% and 54% of chick predation events of American Avocets and Forster’s Terns, respectively. The forced relocation of the largest gull colony (~24,000) at Pond A6 in 2010 resulted in increased survival of Forster’s Tern chicks at the adjacent colony at Pond A7 in 2011. The California Gull population and its effects on locally breeding shorebirds and terns are among the most pressing concerns for wetland managers within the San Francisco Bay estuary, especially for the South Bay Salt Pond Restoration Project. Further research is needed to evaluate the gull’s reproductive rates, habitat use, and annual movements and so to clarify its demographics and to quantify its effects on other breeding birds.