The Impact of Variation in Stopover Habitat Quality on Migrant Rufous Hummingbirds

We examined the impact of variation in habitat quality on migrating Rufous Hummingbirds ( Selasphorus rufus ) in the California Sierra Nevada. As do other migratory species, these birds depend on "stopover" habitats en route for feeding and replenishing depleted energy stores. During seven years of study, the quality of the stopover habitat (assessed in terms of the density of nectar food resources) varied widely due to natural variation in flowering. In years when stopover habitat quality was poor, incoming body masses were low and stopover durations were long. Population densities of migrant hummingbirds at the study site were coupled to habitat quality both within and among years. These observations demonstrate important effects of stopover habitat variation on the physiological, behavioral, and population ecology of migrating hummingbirds. High-quality stopover habitats are critical links between breeding and wintering areas for many species, and their preservation should be considered an essential component of strategies aiming to conserve migratory bird populations.     

Are Declines in North American Insectivorous Songbirds Due to Causes on the Breeding Range?

Previous studies have reported a recent decline in breeding populations of migratory songbirds in eastern and central North America. Several explanations have been suggested: deforestation on the wintering grounds in the tropics and habitat loss, increased predation pressure, and increased cowbirds parasitism on the breeding range. We used these factors to assign 47 species of insectivorous passerines to groups with contrasting vulnerability, and then used the North America Breeding Bird Survey to analyze population trends in these groups on a large continental scale. Variables indexing susceptibility to predation on the breeding ground were most strongly correlated with population trends form 1968 to 1987. During the period from 1978 to 1987, migratory status was also significantly associated with population trends long-distance migrants to the neotropics exhibited a small, nonsignificant decreasing trend, whereas residents and short-distance migrants increased strongly. During the same time period, the group of species with low nest location, open nest, and high cowbird parasitism declined significantly. Although it is difficult to separate the effects of multiple factors, our analyses suggest that predation on the breeding ground in North America has played a larger role in the decline of migratory songbirds than deforestation on the wintering grounds in the tropics.     

Song overproduction and selective attrition lead to song sharing in the field sparrow (Spizella pusilla)

Summary Male field sparrows settling on particular territories for the first time often sing two or more song types. Vocal experience with neighboring males then leads in most cases to the deletion from the male's repertoires of all but one song type. In 2 years, settling males retained the song type that most closely resembled that of a neighbor. Focal observations in 1 year revealed that the most actively singing neighbor was the one the new birds resembled. Songs were not selected on the basis of their absolute acoustic characteristics, but rather by their resemblance to neighbors' songs. After the attrition process is complete, males retain their song for the rest of their lives. Evidence supports the hypothesis that the actual acquisition of a song need not take place at the time and place as males occupy territories. Rather, males may acquire an abundance of song models earlier in life and then select songs from this repertoire that most closely resemble those of their neighbors. The development of mature repertoires and of local dialects is the outcome of one process in this species.     

Morphogenesis of opal teeth in calanoid copepods

Opal teeth of calanoid copepods develop early in the premolt phase of the molt cycle. They form in the apolysis space beneath the old tooth row on the mandibular gnathobase. We examined stages of tooth formation inNeocalanus spp. andCalanus pacificus. Apolysis occurs early in the distal gnathobase, then several epidermal cell types participate sequentially in formation of new teeth. Fibrous molds in the shapes of the new teeth are extruded onto the epidermal surface, then additional materials, probably proteinaceous, are secreted into them. Tooth molds next are linked to a gland in the proximal part of the gnathobase by ducts of an unusual type, lamellar-walled ducts. Silicification follows, apparently using highly osmiophilic material supplied by the proximal gland. Opal is laid down at the outer periphery of the mold then thickens toward the attachment of the mold to newly formed chitin at its base. During apolysis the epidermal cells move proximally without breaking ducts that connect small dermal glands with pores in the sides of the opal teeth. The molds for the new teeth form surrounding these ducts, and new pores result. The glands are like the ciliary exocrine glands seen in other Crustacea, with the duct deriving from fusion of the axonemes of a cilium. Presumably the glands secrete a substance into food newly broken by the teeth. This could be a toxin or a digestive enzyme.     

The toxicity of heavy metals to embryos of the American oyster Crassostrea virginica

The acute toxicity of 11 heavy metals to embryos of the American oyster Crassostrea virginica was studied and the concentrations at which 50% of the embryos did not develop were determined. The most toxic metals and their LC₅₀ values were mercury (0.0056 ppm), silver (0.0058 ppm), copper (0.103 ppm) and zinc (0.31 ppm). Those metals that were not as toxic and their LC₅₀ values were nickel (1.18 ppm), lead (2.45 ppm) and cadmium (3.80 ppm). Those metals that were relatively non-toxic and their LC₅₀ values were arsenic (7.5 ppm), chromium (10.3 ppm) and manganese (16.0 ppm). Aluminum was non-toxic at 7.5 ppm, the highest concentration tested.     

Filtration and transport of Bacillus subtilis spores and the F-RNA phage MS2 in a coarse alluvial gravel aquifer: implications in the estimation of setback distances

Filtration of Bacillus subtilis spores and the F-RNA phage MS2 (MS2) on a field scale in a coarse alluvial gravel aquifer was evaluated from the authors' previously published data. An advection-dispersion model that is coupled with first-order attachment kinetics was used in this study to interpret microbial concentration vs. time breakthrough curves (BTC) at sampling wells. Based on attachment rates (katt) that were determined by applying the model to the breakthrough data, filter factors (f) were calculated and compared with f values estimated from the slopes of log (cmax/co) vs. distance plots. These two independent approaches resulted in nearly identical filter factors, suggesting that both approaches are useful in determining reductions in microbial concentrations over transport distance. Applying the graphic approach to analyse spatial data, we have also estimated the f values for different aquifers using information provided by some other published field studies. The results show that values of f, in units of log (cmax/co) m(-1), are consistently in the order of 10(-2) for clean coarse gravel aquifers, 10(-3) for contaminated coarse gravel aquifers, and generally 10(-1) for sandy fine gravel aquifers and river and coastal sand aquifers. For each aquifer category, the f values for bacteriophages and bacteria are in the same order-of-magnitude. The f values estimated in this study indicate that for every one-log reduction in microbial concentration in groundwater, it requires a few tens of meters of travel in clean coarse gravel aquifers, but a few hundreds of meters in contaminated coarse gravel aquifers. In contrast, a one-log reduction generally only requires a few meters of travel in sandy fine gravel aquifers and sand aquifers. Considering the highest concentration in human effluent is in the order of 10(4) pfu/l for enteroviruses and 10(6) cfu/100 ml for faecal coliform bacteria, a 7-log reduction in microbial concentration would comply with the drinking water standards for the downgradient wells under natural gradient conditions. Based on the results of this study, a 7-log reduction would require 125-280 m travel in clean coarse gravel aquifers, 1.7-3.9 km travel in contaminated coarse gravel aquifers, 33-61 m travel in clean sandy fine gravel aquifers, 33-129 m travel in contaminated sandy fine gravel aquifers, and 37-44 m travel in contaminated river and coastal sand aquifers. These recommended setback distances are for a worst-case scenario, assuming direct discharge of raw effluent into the saturated zone of an aquifer. Filtration theory was applied to calculate collision efficiency (alpha) from model-derived attachment rates (katt), and the results are compared with those reported in the literature. The calculated alpha values vary by two orders-of-magnitude, depending on whether collision efficiency is estimated from the effective particle size (d10) or the mean particle size (d50). Collision efficiency values for MS-2 are similar to those previously reported in the literature (e.g. ) [DeBorde, D.C., Woessner, W.W., Kiley, QT., Ball, P., 1999. Rapid transport of viruses in a floodplain aquifer. Water Res. 33 (10), 2229-2238]. However, the collision efficiency values calculated for Bacillus subtilis spores were unrealistic, suggesting that filtration theory is not appropriate for theoretically estimating filtration capacity for poorly sorted coarse gravel aquifer media. This is not surprising, as filtration theory was developed for uniform sand filters and does not consider particle size distribution. Thus, we do not recommend the use of filtration theory to estimate the filter factor or setback distances. Either of the methods applied in this work (BTC or concentration vs. distance analyses), which takes into account aquifer heterogeneities and site-specific conditions, appear to be most useful in determining filter factors and setback distances.     

Meeting Concentration Targets in the Post-Kyoto World: Does Kyoto Further a Least Cost Strategy?

Preliminary analysis based on an aggregate model of global carbon emissions suggests that constraining emissions to the levels that would be imposed by compliance with the results of the Kyoto negotiations can increase the discounted cost of ultimately limiting atmospheric concentrations. Kyoto targets can be either too restrictive or too permissive depending upon the (currently unknown) trajectory of carbon emissions over the near- to medium-term and the (as yet unspecified) concentration target that frames long-term policy. The discounted cost of meeting low concentration targets like 450 ppmv. is diminished by allowing large sinks and/or by imposing more restrictive near-term emissions benchmarks (even if only Annex B countries are bound by the Kyoto accord). Conversely, the cost of achieving high concentration targets like 650 ppmv. is diminished by disallowing sinks and/or by imposing less restrictive emissions benchmarks. Intermediate concentration targets like 550 ppmv. look like high concentration targets (favoring no sinks and expanded near-term emissions) along low emissions paths; but they look like low concentration targets (favoring the opposite) along high emissions paths. Emissions trajectories that lie above the median, but not excessively so, represent cases for which adjustments in the Kyoto emissions benchmarks and/or negotiated allowances for sinks have the smallest effect on the cost of mitigation.