Bird species densities were determined for summer and winter on 132 study plots grouped into 25 riparian habitats in or near the Huachuca Mountains of southeastern Arizona. The habitats were defined based on the dominant riparian tree species, the size of the riparian stand, and the type of adjacent upland vegetation. Vegetation characteristics and physical environmental data were collected at each plot. The type of dominant riparian tree species influenced bird species richness and total density during the breeding season. Cottonwood habitats had the greatest richness, and both cottonwood and sycamore habitats had high densities. Upland vegetation was an important factor related to winter species richness and abundance, with plots in open grassland areas having greater richness and density. Riparian stand size was a relatively poor predictor of avian density or richness in either season. Groups of bird species that shared similar density distributions in the summer were associated with specific riparian habitats. The winter pattern of species groups was not as clear, and groups could not he assigned to riparian habitats, but they were related to either wooded or open upland vegetation. Riparian habitats were also clustered based on similar densities of birds. In summer, high-elevation habitats were distinct from low-elevation and foothill habitats. In winter, riparian habitats separated into categories of wooded vs. open adjacent vegetation.

In a 6-yr study of 70 generally insectivorous bird species in Arizona riparian woodlands, abundances of cavity-nesting species increased on 50 experimental plots compared with 49 control plots, following addition of artificial nest boxes. Open-nesting birds increased in abundance on control plots during the study but avoided experimental plots relative to control plots after box addition. Multivariate analysis revealed that a negative response of open nesters to the experiment was widespread among a large and ecologically diverse group of species. Results of this field experiment suggest that communitywide (diffuse) competition was an important factor influencing the distribution and abundance of birds in these riparian ecosystems.

Tissues from the proximal, middle, and distal regions of the ceca of Gambel's quail and domestic fowl were examined by scanning and transmission electron microscopy. Cellular and subcellular structures, including epithelial cell height, mitochondrial volume fraction, microvillous surface area, proportion of goblet cells, and junctional complex characteristics, were quantified by a variety of stereologic procedures and other measurement techniques. The mucosal surface of quail cecum shows a much more highly developed pattern of villous ridges and flat areas than that of fowl cecum. The fowl has significantly greater cell heights than the quail in all cecal regions. The mitochondrial volume fraction does not differ significantly with species or region, but mitochondria are concentrated on the apical side of the nucleus. In both species, the proximal cecal region has the greatest microvillous surface area. All 3 components of junctional complexes, including zonula occludens, zonula adhaerens, and macula adhaerens, are quantified. When all factors are considered, the quail cecum appears to have morphological characteristics consistent with a greater potential capacity for absorption than the fowl cecum.

Tissues from the proximal, middle, and distal regions of the ceca of Gambel's quail and domestic fowl were examined by scanning and transmission electron microscopy for ultrastructural detail. Cellular aad subcellular structures, including epithelial cell height, mitochondrial volume fraction, microvillar surface area, and junctional complex characteristics, were quantified by stereologic procedures. The mucosal surface of the quail ceca shows a more highly developed pattern of ridges and flat areas than that of the fowl. The fowl has significantly greater cell heights than the quail in all cecal regions. The mitochondrial volume fraction does not differ significantly with species or region, but the mitochondria in all samples tend to be concentrated on the apical side of the nucleus. In both species, the proximal cecal region has the greatest microvillar surface area. In the fowl cecum, the zona occludens and macula adherans heights are significantly less in the proximal than in the middle or distal regions. In the quail cecum, the zona adherans height is least is the distal region. The zona occludens height in the fowl middle and distal regions is significantly greater than those for the quail. The middle region of the quail cecum has the lowest proportions of cell boundaries with zona adherans and macula adherans in the junctional complexes. When all factors are considered, the quail ceca appear to have morphological characteristics consistent with a greater potential capacity for absorption by passive diffusion than the fowl ceca.The gross anatomy, including form, function, and occurrence, of the avian cecum has been well covered by McLelland (this issue) and others in the older literature (Leopold, '53; Ziswiler and Farner, '72; Duke, '86). However, relatively little work has been done on the ultrastructure of avian ceca. Hodges ('74) described the various layers in the walls of the ceca of the domestic fowl (Gallus domesticus), including muscularis externa, submucosa, muscularis mucosae, and mucous membrane, and he discussed three distinct regions of the ceca. The proximal region had well developed villi, with lymphoid cells in the tunica propria and many goblet cells in the epithelium. In the middle region, cecal walls were thinner than in the proximal region, and well developed longitudinal folds were present in the mucous membrane. In the distal region, the folds were less developed, and the villi were short and blunt. The proportion of goblet cells decreased from the proximal to the distal region. Clarke ('78) examined the ileocecorectal junction in the domestic fowl and found a muscular ring of tissue projecting into the lumen of the intestine immediately anterior to the cecal openings. These openings were narrow and filled with villi. Clarke suggested 0 1989 ALAN R. LISS, INC.that this structure could be related to filtering of material during filling of the ceca. Hanssen ('79) qualitatively described the microanatomy of the ceca and small intestine of wild and captive willow grouse (Lagopus l...

To obtain minerals suitable for age-dating and other analyses, it is necessary to first reduce the mineral-bearing rock to a fine, sand-like consistency. Reducing whole rock requires crushing, grinding, and sieving. Ideally, the reduced material should range in size from 80-to 270-mesh (an opening between wires in a sieve). The openings in an 80-mesh sieve are equal to 0.007 inches, 0.177 millimeters, or 177 micrometers. This size range ensures that compound grains are mostly disaggregated and that grains, in general, are dimensionally similar. This range also improves the segregation rate of conspicuous to extremely small individual heavy mineral grains. Once the rock is reduced to grains, it is necessary to separate the grains into paramagnetic and nonparamagnetic and heavy and light mineral fractions. In separating grains by property, those minerals chemically suited for radiometric dating are abundantly concentrated. Grams of mineralogical material can then be analyzed and characterized by multiple methods including trace element chemistry, laser ablation, and in particular, ion geochronology.