Geology topics

William D. Newmark

Publications and source records attributed to William D. Newmark.

3 recordsLinked to original sources

USGS2016

The influence of food abundance, food dispersion and habitat structure on territory selection and size of an Afrotropical terrestrial insectivore

Most tropical insectivorous birds, unlike their temperate counterparts, hold and defend a feeding and breeding territory year-around. However, our understanding of ecological factors influencing territory selection and size in tropical insectivores is limited. Here we examine three prominent hypotheses relating food abundance, food dispersion (spatial arrangement of food items), and habitat structure to territoriality in the Usambara Thrush Turdus roehli . We first compared leaf-litter macro-invertebrate abundance and dispersion, and habitat structure between territories and random sites. We then examined the relation between these same ecological factors and territory size. Invertebrate abundance and dispersion were sparsely and evenly distributed across our study system and did not vary between territories and random sites. In contrast, habitat structure did vary between territories and random sites indicating the Usambara Thrush selects territories with open understorey and closed overstorey habitat. Invertebrate abundance and dispersion within territories of the Usambara Thrush were not associated with habitat structure. We believe the most likely explanation for the Usambara Thrush’s preference for open understorey and closed overstorey habitat relates to foraging behavior. Using information-theoretic model selection we found that invertebrate abundance was the highest-ranked predictor of territory size and was inversely related, consistent with food value theory of territoriality.

Ostrich↗

USGS2016

Tarangire revisited: Consequences of declining connectivity in a tropical ungulate population

The hyper-abundance of migratory wildlife in many ecosystems depends on maintaining access to seasonally available resources. In Eastern and Southern Africa, land-use change and a loss of connectivity have coincided with widespread declines in the abundance and geographic range of ungulate populations. Using photographic capture-mark-recapture, we examine the historical pattern of loss of connectivity and its impact on population trends in a partially migratory wildebeest population in northern Tanzania. To estimate abundance, we use a novel modeling approach that overcomes bias associated with photo misidentifications. Our data indicate (1) diminished connectivity within and between seasonal areas as a result of human activities, (2) a reduction in the overall population size compared to historical numbers, with high variability over time, (3) the continued use of highly constrained movement corridors between the three main seasonal ranges, (4) higher recruitment in the non-migratory subpopulation (Lake Manyara National Park) than in other areas of the ecosystem, and (5) an increase in the relative abundance of resident to migrant wildebeest. Recent conservation efforts to protect seasonal habitat and to enforce anti-poaching policies outside protected areas have likely helped stabilize the population, at least temporarily, but we caution that several key vulnerabilities remain.

Tarangire-Manyara Ecosystem↗

USGS2013

Breeding biology of an afrotropical forest understory bird community in northeastern Tanzania

Many aspects of the breeding biology of Afrotropical forest birds are poorly known. Here we provide a description based on the monitoring of 1461 active nests over eight breeding seasons about one or more aspects of the breeding biology for 28 coexisting understory bird species on the Amani Plateau in the East Usambara Mountains, Tanzania. Mean nest height and mean distance of nest from forest edge varied widely among species with most species constructing nests across a broad vertical and forest edge to interior gradient. However, there were important exceptions with all sunbird species and several dove and waxbill species constructing nests in close proximity to the forest edge. For 17 common species for which we recorded two or more active nests, mean clutch size across species was 1.9 eggs per clutch, the lowest site-specific mean clutch size yet reported for a tropical forest bird community. For nine bird species, a subset of the 17 common species, length of breeding season, defined as the difference between the earliest and latest recorded incubation onset date, ranged from 88–139 days. Most of these nine species displayed a unimodal distribution in incubation onset dates across a breeding season which extended from the end of August through middle January. In summary, a wide variation exists in most aspects of the breeding biology within an understory forest bird community in the East Usambara Mountains.

Wilson Journal of Ornithology↗