Geology topics

R.B. Hamilton

Publications and source records attributed to R.B. Hamilton.

5 recordsLinked to original sources

USGS2011

Search behavior of arboreal insectivorous migrants at gulf coast stopover sites in spring

Search behavior of arboreal insectivorous migrants was studied at three stopover sites along the northern coast of the Gulf of Mexico during spring migrations, 1993–1995. We examined if search behavior was affected by phylogeny, or by environmental factors. A sequence of search movements (hop, flutter, or flight) in a foraging bout was recorded for each migrant encountered. Search rate, frequency, and distance of movements were calculated for each species. Search rate was positively correlated with proportion of hop, but negatively correlated to flight distance. Hop distance was positively correlated to tarsus length, as was flight distance to wing length for the 31 species of migrants. Cluster analysis indicated closely related species generally have similar foraging modes, which range from “sit-and-wait” of flycatchers to “widely foraging” of warblers. Migrants tended to use more hops in dense vegetation, but more flights in areas with sparse vegetation. Migrants also used more flights when foraging in mixed-species flocks and during periods of high migrant density. Logistic models indicated warblers were more influenced by environmental factors than vireos, possibly because warblers are near-perch searchers and more affected by these factors.

Wilson Journal of Ornithology↗

USGS2005

Coastal forests of the Gulf of Mexico: A description and some thoughts on their conservation

Millions of Nearctic-Neotropical landbirds move through the coastal forests of the Gulf of Mexico each spring and autumn as they migrate across and around the gulf. Migration routes in the gulf region are not static—they shift year to year and season to season according to prevailing wind patterns. Given the dynamic nature of migration routes, coastal forests around the Gulf of Mexico potentially can provide important stopover habitat to en route migrants. The coastal forests from the Florida Keys to the Yucatan Peninsula include a wide range of habitat types that we have classified as 19 broad community types. From literature reviews, we determined that the majority of these coastal habitats have been lost or degraded due to the effects of development, agriculture, livestock grazing, timber industry activities, and the spread of exotic species. The continued loss and degradation of coastal forests pose a risk to migrating birds, and thus we need to develop a conservation strategy that maximizes the suitability of the remaining forested patches around the gulf. An effective conservation strategy will require considerations at the gulf-wide, regional, landscape and habitat levels. These considerations should include migrant movement and landfall patterns, migrant use of inland versus coastal fringe stopover sites, the creation of landscape mosaics that incorporate patch size and inter-patch distance, and the availability of within habitat resources.

Alabama, Florida, Louisiana, Mississippi, Texas↗

USGS2001

Nest survival of forest birds in the Mississippi Alluvial Valley

In the Mississippi Alluvial Valley, flood control has led to a drastic reduction in the area of forest habitat and altered the patchwork of forest cover types. Silvicultural management of the remaining fragmented forests has changed to reflect the altered hydrology of the forests, current economic conditions of the area, and demand for forest products. Because forest type and silvicultural management impact forest birds, differences in avian productivity within these forests directly impact bird conservation. To assist in conservation planning, we evaluated daily nest survival, nest predation rates, and brood parasitism rates of forest birds in relation to different forest cover types and silvicultural management strategies within this floodplain. Within bottomland hardwood forests, nest success of blue-gray gnatcatcher ( Polioptila caerulea , 13%), eastern towhee ( Pipilo erythrophthalmus , 28%), indigo bunting ( Passerina cyanea , 18%), northern cardinal ( Cardinalis cardinalis , 22%), and yellow-billed cuckoo ( Coccyzus americanus , 18%) did not differ from that within intensively managed cottonwood plantations. However, average daily survival of 542 open-cup nests of 19 bird species in bottomland hardwoods (0.9516 ± 0.0028, ∼27% nest success) was greater than that of 543 nests of 18 species in cottonwood plantations (0.9298 ± 0.0035, ∼15% nest success). Differences in daily nest survival rates likely resulted from a combination of differences in the predator community -- particularly fire ants ( Solenopsis invicta ) -- and a marked difference in species composition of birds breeding within these 2 forest types. At least 39% of nests in bottomland hardwood forests and 65% of nests in cottonwood plantations were depredated. Rates of parasitism by brown-headed cowbirds ( Molothrus ater ) were greater in managed cottonwoods (24%) than in bottomland hardwoods (9%). Nest success in planted cottonwood plantations for 18 species combined (∼14%), and for yellow-breasted chat ( Icteria virens , 7%), eastern towhee (14%), indigo bunting (14%), and northern cardinal (17%) did not differ from nest success in cottonwood plantations that were coppiced from root sprouts following pulpwood harvest. Within bottomland hardwood forests, uneven-aged group-selection timber harvest reduced the combined daily nest survival of all species from 0.958 to 0.938, which reduced nest success by about 14%. Specifically, timber harvest reduced nest success of species that nest in the forest midstory and canopy, such as Acadian flycatcher ( Empidonax virescens ), from 32% before harvest to 14% after harvest. Conversely, those species that nest primarily in the shrubby understory-such as northern cardinal-were not affected by timber harvest and maintained an overall nest success of about 33%. Thus, birds nesting in the understory of bottomland hardwood forests are not adversely impacted by selective timber harvest, but there is a short-term reduction in nest success for birds that nest in the canopy and midstory.

Louisiana, Mississippi↗

USGS1999

Impact of forest type and management strategy on avian densities in the Mississippi Alluvial Valley, USA

Avian territory densities were determined from 20 Breeding Bird Censuses in mature (>30 years) bottomland hardwood stand: and 18 Breeding Bird Censuses in young (6-9 years old) cottonwood (Populas deltoides) plantations in the Mississippi Alluvial Valley. Avian species richness, diversity, and territory density were greater (p < 0.01) in bottomland hardwood stands than in intensively-managed cottonwood stands but these parameters were not impacted by selective timber harvest within bottomland hardwood stands nor by method of regeneration within cottonwood plantations (p > 0.05). Even so, detrended correspondence analysis based on avian territory densities readily segregated forest types and silvicultural treatments. Timber harvest within bottomland hardwood stands resulted in a shift in bird communities toward those found in cottonwood stands by increasing the densities of early-successional species such as Indigo Bunting (Passerina cyanea), Yellow-breasted Chat (Icteria virens), and Common Yellowthroat (Geothlypis trichas). Conversely, regenerating cottonwood stands from root sprouts, rather than planting stem cuttings, resulted in a shift in bird communities toward those found in bottomland hardwood stands by increasing densities of species such as White-eyed Vireo (Vireo griseus) and Wood Thrush (Hylocichla mustelina). Tree species diversity, angular canopy cover, and midstory density were positively associated with bird species assemblages in bottomland hardwood stands, whereas vegetation density at ground level was positively associated with bird communities in cottonwood plantations. Conversion of agricultural fields to short-rotation cottonwood plantations results in increased breeding bird populations by adding up to 140 additional territories 40 ha-1. Even so, relative conservation values, derive, from indicator species analysis and Partners in Flight concern scores, suggest that mature bottomland hardwood forests are twice as 'valuable' for bird conservation as are cottonwood plantations.

Forest Ecology and Management↗

USGS1996

A land manager's guide to point counts of birds in the Southeast

Current widespread concern for the status of neotropical migratory birds has sparked interest in techniques for inventorying and monitoring populations of these and other birds in southeastern forest habitats. The present guide gives detailed instructions for conducting point counts of birds. It further presents a detailed methodology for the design and conduct of inventorial and monitoring surveys based on point counts, including discussion of sample size determination, distribution of counts among habitats, cooperation among neighboring land managers, vegetation sampling, standard data format, and other topics. Appendices provide additional information, making this guide a stand-alone text for managers interested in developing inventories of bird populations on their lands.

General Technical Report↗