ABSTRACT. The Sierra Madre Occidental and neighboring Madrean Sky Islands span a large and biologically diverse region of northwest Mexico and portions of the southwestern United States. Little is known about the abundance and habitat use of breeding birds in this region of Mexico, but such information is important for guiding conservation and management. We assessed densities and habitat relationships of breeding birds across Sky Island mountain ranges in Mexico and adjacent portions of the Sierra Madre from 2009 to 2012. We estimated densities at multiple spatial scales, assessed variation in densities among all major montane vegetation communities, and identified and estimated the effects of important habitat attributes on local densities. Regional density estimates of 65% of 72 focal species varied significantly among eight montane vegetation communities that ranged from oak savannah and woodland at low elevations to pine and mixed-conifer forest at high elevations. Greater proportions of species occurred at peak densities or were relatively restricted to mixedconifer forest and montane riparian vegetation likely because of higher levels of structural or floristic diversity in those communities, but those species were typically rare or uncommon in the Sky Islands. Fewer species had peak densities in oak and pine-oak woodland, and species associated with those communities were often more abundant across the region. Habitat models often included the effects of broadleaf deciduous vegetation cover (30% of species), which, together with tree density and fire severity, had positive effects on densities and suggest ways for managers to augment and conserve populations. Such patterns combined with greater threats to highelevation conifer forest and riparian areas underscore their value for conservation. Significant populations of many breeding bird species, including some that are of concern or were not known to occur regionally or in mountain ranges we surveyed, highlight the importance of conservation efforts in this area of Mexico.RESUMEN. Abundancia y relaciones de h abitat de aves reproductivas en las Islas del Cielo y la contigua Sierra Madre Occidental del noroeste de M exico La Sierra Madre Occidental y las vecinas Islas del Cielo Madrenses abarcan una extensa y biol ogicamente diversa regi on del noroeste de M exico y porciones del sudoeste de Estados Unidos. Poco se sabe sobre la abundancia y el uso de h abitat de las aves que cr ıan en esta regi on de M exico, pero dicha informaci on es importante para guiar la conservaci on y el manejo de la zona. Evaluamos densidades y relaciones de h abitat de aves reproductoras a lo largo de las cadenas montañosas de las Islas del Cielo en M exico y puntos adyacentes de la Sierra Madre desde el 2009 al 2012. Estimamos densidad a m ultiples escalas, analizando la variaci on en la densidad entre las principales comunidades vegetales montanas, e identificamos y estimamos los efectos de importantes atributos de h abitat en las densidades locales. Estimaciones de densidad ...

Lignin/polypropylene composites were compounded by melt blending in a thermokinetic mixer and then ASTM specimens suitable for tensile testing were made by injection moulding. Two polypropylenes with different molecular weights were used as matrices. Lignin contents in the composites ranged from 10 to 55 wt.‐%. Tensile modulus, strength and elongation were determined for those composites. The experimental data thus obtained were thus mathematically fitted to several micromechanical models. Micromechanical models best suited for fitting experimental data were those of Halpin‐Tsai, Nielsen and Pukánszky. Fitting of predicted data to the experimental data was good in most cases, thus revealing the ability of those models for predicting the tensile properties of lignin/polypropylene composites and estimate the unknown modulus of elasticity of the lignin used as filler.

Treating extra heavy crude with a low catalytic activity solid in an FCC-like process yielded a superior liquid product without yield loss compared to thermal operation.

once widespread and apparently common in the mountains of mainland Mexico, to which it is endemic, the Cinereous owl (Strix sartorii) seems to have declined precipitously. in 2015, 2016, 2017, and 2019 we searched for the Cinereous owl in eight Mexican states where it had been reported previously. We detected it at only a single site, rancho la Noria on Cerro San Juan, Nayarit. our results suggest that the Cinereous owl may have disappeared from much of its former range, and that the Fulvous owl (Strix fulvescens) may now inhabit areas in oaxaca formerly occupied by the Cinereous owl, perhaps as a result of habitat alteration. The Cinereous owl may qualify for recognition as vulnerable or endangered. Comprehensive surveys are urgently needed to establish its current status and distribution. Such surveys should also be used to determine the current distribution of the Fulvous owl, and to investigate the reasons why it now occurs in areas formerly occupied by the Cinereous owl.

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