Origin and Detection of Microstructural Clustering in Fluids with Spatial-Range Competitive Interactions

Fluids with competing short-range attractions and long-range repulsions mimic dispersions of charge-stabilized colloids that can display equilibrium structures with intermediate range order (IRO), including particle clusters. Using simulations and analytical theory, we demonstrate how to detect cluster formation in such systems from the static structure factor and elucidate links to macrophase separation in purely attractive reference fluids. We find that clusters emerge when the thermal correlation length encoded in the IRO peak of the structure factor exceeds the characteristic lengthscale of interparticle repulsions. We also identify qualitative differences between the dynamics of systems that form amorphous versus micro-crystalline clusters.Comment: 6 pages, 5 figure

The Effects of Site Quality on Breeding-Site Fidelity in Bobolinks

We compared breeding-site fidelity of Bobolinks (Dolichonyx oryzivorus) at two low-quality sites (Bald Hill and Shackelton Point, BH +SP) with that at one high-quality site (Moore Road, MR) in central New York. Yearly density of fledglings at Moore Road was more than six times the density at Bald Hill and Shackelton Point. Furthermore, individual residents fledged 50-70% more young at the high-quality site. At Moore Road, 70% of the males and 49% of the females returned one or more times, compared with 44% of the males and 25% of the females at the low-quality sites. Successful residents (i.e. those fledging one or more young the previous year) were equally likely to return at all sites. However, the return rates of unsuccessful residents were more than three times higher at the high-quality site. Neither overall return rates nor intrasite dispersal of returning residents differed between individuals that had been successful or unsuccessful the previous year at the high-quality site. At the low-quality sites, individuals unsuccessful the previous year were much less likely to return than were successful individuals (55% vs. 19% for males, 41% vs. 9% for females). Those unsuccessful individuals that did return tended to move farther between nest sites than successful individuals. Overall, site productivity was the best predictor of yearly, site-specific return rates. For females (but not for males), individuals that were resident in one or more years previous were more likely to return than were novice residents (47% vs. 20%). Individuals that had nests experimentally destroyed by hay-cropping returned at similar rates to those of naturally unsuccessful residents. We believe that the patterns of breeding-site fidelity in Bobolinks are primarily the result of experience-based choices by the birds and do not simply reflect patterns of mortality. Bobolinks appear to use both their own reproductive success and that of others at their site to influence their decision to return to a breeding site

Multiple Paternity in a Territorial Passerine: The Bobolink

Electrophoretic and behavioral evidence corroborate the conclusion that Bobolink (Dolichonyx oryzivorus) females occasionally copulate with more than one male, which results in the insemination of a single clutch of eggs by those males. In 2 of 12 families from which blood samples were obtained from the mother, the putative father, and the nestlings, at least 2 males were responsible for fertilization of the clutch. We believe this is only the second bird species in which multiple paternity has been documented conclusively in the wild. Our speculation that it may not be uncommon leads to a caution for evolutionary biologists who use apparent reproductive success in birds to address questions about fitness

Responses of Nesting Bobolinks (Dolichonyx oryzivorus) to Habitat Edges

ABSTRACT.-Avoidance of habitat edges may be contributing to reduced densities of grassland birds in small habitat patches. Nest densities for grassland-nesting Bobolinks (Dolichonyx oryzivorus) were much lower than expected within 25m of forest edges at three sites in New York, and that pattern ( edge avoidance ) extended to 100m at one site. Nests located within 50 m of forest or wooded hedgerow edges had lower daily survival rates, compared with nests \u3e100m from any habitat edge. Bobolinks tended to move away from forest edges when renesting after nest failure; that pattern was especially evident in females that placed their first nest within 50 m of a forest or wooded hedgerow edge. Second nests of all seven of those females were farther from that edge type than their first nests. However, nest placement in relation to wooded edges did not vary significantly between years for those philopatric females nesting at our study sites for more than one year. Bobolinks also avoided nesting near road edges, even though nest survival rates were not lower near that edge type. However, Bobolinks did not appear to avoid nesting near edges adjacent to old fields or pastures. Nest survival near those edge types was higher than near wooded edges and similar to or higher than survival of nests \u3e100m from any edge. Thus, responses of Bobolinks to habitat edges were inconsistent, and nest success was dependent on type of edge

Responses of Nesting Bobolinks (Dolichonyx oryzivorus) to Habitat Edges

ABSTRACT.-Avoidance of habitat edges may be contributing to reduced densities of grassland birds in small habitat patches. Nest densities for grassland-nesting Bobolinks (Dolichonyx oryzivorus) were much lower than expected within 25m of forest edges at three sites in New York, and that pattern ( edge avoidance ) extended to 100m at one site. Nests located within 50 m of forest or wooded hedgerow edges had lower daily survival rates, compared with nests \u3e100m from any habitat edge. Bobolinks tended to move away from forest edges when renesting after nest failure; that pattern was especially evident in females that placed their first nest within 50 m of a forest or wooded hedgerow edge. Second nests of all seven of those females were farther from that edge type than their first nests. However, nest placement in relation to wooded edges did not vary significantly between years for those philopatric females nesting at our study sites for more than one year. Bobolinks also avoided nesting near road edges, even though nest survival rates were not lower near that edge type. However, Bobolinks did not appear to avoid nesting near edges adjacent to old fields or pastures. Nest survival near those edge types was higher than near wooded edges and similar to or higher than survival of nests \u3e100m from any edge. Thus, responses of Bobolinks to habitat edges were inconsistent, and nest success was dependent on type of edge