Conservation of Neotropical migratory birds in tropical hardwood and oil palm plantations.

Tropical forests in the Americas are undergoing rapid conversion to commercial agriculture, and many migratory bird species that use these forests have experienced corresponding populations declines. Conservation research for migratory birds in the tropics has focused overwhelmingly on shade coffee plantations and adjacent forest, but both cover types are now in decline, creating an urgent need to evaluate conservation opportunities in other agricultural systems. Here we compare how a community of 42 Neotropical migratory bird species and a subset of five conservation-priority species differ in usage and habitat associations among a secondary forest baseline and four expanding commercial plantation systems in Guatemala: African oil palm, teak, rubber, and mixed-native hardwoods. We found that mixed-native hardwood plantations supported the highest richness and diversity of all migrants and that the three hardwood plantation types generally outperformed oil palm in richness and diversity metrics. Despite this, oil palm supported high abundance of several common and widespread species also experiencing range-wide population declines and may therefore play an important role in conserving common species. Mature secondary forest hosted low abundance and diversity of the full migratory community, but high abundance and richness of conservation priority migrants along with native hardwood and teak plantations. Likewise, the percentage of forest cover on the landscape was positively associated with priority migrant abundance and richness but negatively associated with the abundance of migrants in general, highlighting how individual species within the broad group of Neotropical migratory landbirds respond differently to anthropogenic changes in land use. Across all cover types, the retention of tall overstory trees increased the abundance, richness, and diversity of all migrants, which indicates that vertical structural diversity and remnant trees are important habitat features for birds in agricultural landscapes. Our findings show that conservation opportunities exist in hardwood and oil palm plantations, though the species likely to benefit from conservation action will vary among plantation types. For the subset of conservation priority migrants, our results suggest that conservation efforts should combine strategies that retain and restore secondary forest, promote the adoption of native hardwood and teak plantations, and promote the retention of tall, remnant trees in agricultural landscapes.

Characterization of aerosols containing Zn, Pb, and Cl from an industrial region of Mexico City.

Recent ice core measurements show lead concentrations increasing since 1970, suggesting new nonautomobile-related sources of Pb are becoming important worldwide (1). Developing a full understanding of the major sources of Pb and other metals is critical to controlling these emissions. During the March, 2006 MILAGRO campaign, single particle measurements in Mexico City revealed the frequent appearance of particles internally mixed with Zn, Pb, Cl, and P. Pb concentrations were as high as 1.14 microg/m3 in PM10 and 0.76 microg/m3 in PM2.5. Real time measurements were used to select time periods of interest to perform offline analysis to obtain detailed aerosol speciation. Many Zn-rich particles had needle-like structures and were found to be composed of ZnO and/or Zn(NO3)2 x 6H2O. The internally mixed Pb-Zn-Cl particles represented as much as 73% of the fine mode particles (by number) in the morning hours between 2-5 am. The Pb-Zn-Cl particles were primarily in the submicrometer size range and typically mixed with elemental carbon suggesting a combustion source. The unique single particle chemical associations measured in this study closely match signatures indicative of waste incineration. Our findings also show these industrial emissions play an important role in heterogeneous processing of NO(y) species. Primary emissions of metal and sodium chloride particles emitted by the same source underwent heterogeneous transformations into nitrate particles as soon as photochemical production of nitric acid began each day at approximately 7 am.