Assessing Population Trends of New-Hampshire Forest Birds: Local vs Regional Patterns

We examined the changes in abundance between 1969 and 1986 of 19 forest-dwelling, mostly migratory bird species breeding in New Hampshire at 2 different scales: one local (an intensively studied 10-ha plot in unfragmented forest) and the other regional (Breeding Bird Surveys statewide). Twelve of the 19 species exhibited similar trends at both scales. Eight neither increased nor decreased, and 4 (Least Flycatcher, Winter Wren, Wood Thrush, and Swainsoh\u27s Thrush) declined significantly. Others increased, decreased, or re-mained steady at one or the other scale. Overall, more species declined than increased both locally (8 vs. 1) and regionally (5 vs. 1). Comparisons of these patterns, combined with results of intensive studies at the local level, suggest that changes in food abundance and in vege-tation structure related to forest succession on the breeding grounds, along with other pro-cesses that influence bird reproductive success and survivorship, are the most plausible explanations for most of the observed trends. Winter mortality was also identified as affecting breeding abundances, but only in short-distance migrant and permanently resident species. We have no evidence to indicate that the numbers of long-distance migrants were affected by events in their Neotropical wintering areas, although this possibility is difficult to assess from breeding-ground data. We urge caution in attributing declines of breeding forest migrant birds to tropical deforestation or similar causes until we either can eliminate alternate explanations that involve breeding-season events or have available critically needed demo-graphic information on migrant populations in their wintering areas

Observations of Musk Oxen on Banks Island, Northwest Territories, Canada

Notes summer 1963 observations of Ovibos moschatus. On a reconnaissance flight over the northern third of the island on Aug. 2 nearly sixty were seen, indicating greater abundance than hitherto supposed. Only two were seen south of the reconnaissance area during a two-month period; apparently they concentrate in the northern part at least during the summer

Consequences of Dominance-Mediated Habitat Segregation in American Redstarts During the Nonbreeding Season

Several species of migratory songbirds exhibit a distinct form of habitat segregation while on their Neotropical wintering grounds in which males and females occupy different habitat types. In the American Redstart (Setophaga ruticilla), that sexual habitat segregation is a result of behavioral dominance of older males. In that study, we examined whether such dominance behavior and the resulting differential habitat segregation has consequences for the condition or survival of excluded individuals. We quantified the physical condition and survival of redstarts (both males and females) occupying two habitat types that differed in the proportion of males and females present in Jamaica. Both sexes of redstarts occupying female-biased habitat lost significantly more mass over-winter and had lower annual survival and longevity compared to individuals in male-biased habitat. These results suggest that nonbreeding habitats differed in suitability, with the least suitable habitat being occupied predominately by females. Because most female redstarts are forced to over-winter in these kinds of habitats, they may often be in poor physiological condition prior to departing on spring migration for the breeding grounds. This in turn may influence dynamics of the breeding period by determining their condition and perhaps reproductive success. Furthermore, because winter habitat segregation appears to lower female survivorship, it may also limit the number and availability of breeding females. These results implicate events that occur during the nonbreeding period as playing a critical role in the annual dynamics of this migratory species

Foraging Behavior of American Redstarts in Breeding and Wintering Habitats: Implications for Relative Food Availability

We investigated food availability for a long-distance migrant species, the American Redstart (Setophaga ruticilla), in both its summer breeding habitat in New Hampshire and in its winter habitat in Jamaica. We used four components of foraging behavior (prey attack rate, foraging speed, time spent foraging, and foraging maneuver use) as indicators of the relative availability of prey in the two seasons. Redstarts attacked prey at a significantly greater rate in summer than in winter, indicating that foraging birds encountered prey more frequently in summer. The winter prey-encounter rate was low even though redstarts moved almost twice as fast while foraging in winter as in summer. Male redstarts also spent more time foraging in winter (85%) than in summer (43-65%), possibly to balance the low rate at which they encountered prey. In winter, redstarts used more foraging maneuvers that were directed towards small flying prey, whereas in summer they used maneuvers that resulted in the capture of relatively large and presumably energy-rich prey such as lepidopteran larvae. That wintering redstarts foraged faster, attacked prey less often, and spent more time foraging than those in summer indicates that the winter is a period of relative food scarcity for this species, whereas the breeding season is a period of greater resource abundance

Site-Dependent Regulation of Population Size: a New Synthesis

The nature and extent of population regulation remains a principal unanswered question for many types of organisms, despite extensive research. In this paper, we provide a new synthesis of theoretical and empirical evidence that elucidates and extends a mechanism of population regulation for species whose individuals preemptively use sites that differ in suitability. The sites may be territories, refuges from predation, oviposition sites, etc. The mechanism, which we call site dependence, is not an alternative to density dependence; rather, site dependence is one of several mechanisms that potentially generate the negative feedback required for regulation. Site dependence has two major features: (1) environmentally caused heterogeneity among sites in suitability for reproduction and/or survival; and (2) preemptive site occupancy, with the tendency for individuals to move to sites of higher quality as they become available. Simulation modeling shows that these two features, acting in concert, generate negative feedback when progressively less suitable sites are used as population size increases, reducing average demographic rates for the population as a whole. Further, when population size decreases, only sites of high suitability are occupied, resulting in higher average demographic rates and, thus, population growth. The modeling results demonstrate that this site‐dependent mechanism can generate negative feedback at all population sizes in the absence of local crowding effects, and that this feedback is capable of regulating population size tightly. Operation of site dependence does not rely on the particular type of environmental factor(s) ultimately limiting population size, e.g., food, nest sites, predators, parasites, abiotic factors, or a combination of these. Furthermore, site dependence operates in saturated or unsaturated habitats and over a broad range of spatial scales for species that disperse widely relative to site diameter. A review of relevant field studies assessing the assumptions of the mechanism and its regulatory potential suggests that site dependence may provide a general explanation for population regulation in a wide variety of species

Lidar Remote Sensing Variables Predict Breeding Habitat of a Neotropical Migrant Bird

A topic of recurring interest in ecological research is the degree to which vegetation structure influences the distribution and abundance of species. Here we test the applicability of remote sensing, particularly novel use of waveform lidar measurements, for quantifying the habitat heterogeneity of a contiguous northern hardwoods forest in the northeastern United States. We apply these results to predict the breeding habitat quality, an indicator of reproductive output of a well-studied Neotropical migrant songbird, the Black-throated Blue Warbler (Dendroica caerulescens). We found that using canopy vertical structure metrics provided unique information for models of habitat quality and spatial patterns of prevalence. An ensemble decision tree modeling approach (random forests) consistently identified lidar metrics describing the vertical distribution and complexity of canopy elements as important predictors of habitat use over multiple years. Although other aspects of habitat were important, including the seasonality of vegetation cover, the canopy structure variables provided unique and complementary information that systematically improved model predictions. We conclude that canopy structure metrics derived from waveform lidar, which will be available on future satellite missions, can advance multiple aspects of biodiversity research, and additional studies should be extended to other organisms and regions

What role should the commercial food system play in promoting health through better diet?

Martin White and coauthors consider that the commercial food system has the potential to show leadership and support for dietary public health, but systemic change is needed first and this is likely to require governmental actio

Selective sidewall wetting of polymer blocks in hydrogen silsesquioxane directed self-assembly of PS-b-PDMS

We show the importance of sidewall chemistry for the graphoepitaxial alignment of PS-b-PDMS using prepatterns fabricated by electron beam lithography of hydrogen silsesquioxane (HSQ) and by deep ultraviolet (DUV) lithography on SiO2 thin films. Density multiplication of polystyrene-block-polydimethylsiloxane (PS-b-PDMS) within both prepatterns was achieved by using a room temperature dynamic solvent annealing environment. Selective tuning of PS and PDMS wetting on the HSQ template sidewalls was also achieved through careful functionalization of the template and substrate surface using either brush or a self-assembled trimethylsilyl monolayer. PDMS selectively wets HSQ sidewalls treated with a brush layer of PDMS, whiereas PS is found to selectively wet HSQ sidewalls treated with hexamethyldisilazane (HMDS) to produce a trimethylsilyl-terminated surface. The etch resistance of the aligned polymer was also evaluated to understand the implications of using block copolymer patterns which have high etch resistance, self-forming (PDMS) wetting layers at both interfaces. The results outlined in this work may have direct applications in nanolithography for continued device scaling toward the end-of-roadmap era