No evidence for acoustic mate-guarding in duetting buff-breasted wrens (Thryothorus leucotis)

There are few empirical tests of the acoustic mate-guarding hypothesis for the function of duetting in birds. This hypothesis states that when females are fertile, males initiate many songs or answer most of their mates solo songs to form duets and repel rival males seeking extra-pair copulations. We tested the hypothesis by comparing song initiation and answer rates of males and females in socially monogamous buff-breasted wrens (Throthorus leucotis) during pre-fertile and fertile periods. During pre-fertile periods, males often sang for short periods before being answered by their mates, yet first duets were formed earlier relative to dawn and more duets were given during the dawn chorus on pre-fertile than fertile mornings. Males initiated more songs during pre-fertile than fertile periods, whereas there was no difference between stages in female song initiation rates. The proportion of songs answered by individuals of both sexes did not differ between breeding stages. Other mate-guarding behaviours, such as frequent copulation and maintaining close proximity to mates when fertile, did not appear to be important in this species, as no copulations were observed and there was no difference in the time pairs spent in close proximity when females were fertile or not. Parentage analysis revealed that only 3% of 31 broods had young that were likely the result of extra-pair paternity. These findings do not support the acoustic mate-guarding hypothesis, and suggest that the low rate of extra-pair paternity in buff-breasted wrens was maintained without the use of acoustic or traditional paternity guards.Communicated by R. Gibson     

Condition-dependent control of paternity by female purple martins: implications for coloniality

Proposed causal links between extra-pair copulation (EPC) and colony formation in socially monogamous birds hinge on the question of which sex controls fertilizations. We examined in colonial purple martins Progne subis (1) whether EPCs were forced or accepted by females, and (2) the degree to which apparently receptive females were able to obtain EPCs against their mates’ paternity defenses. Paternity analyses of multilocus DNA fingerprinting confirmed previous findings of a marked relationship between age class and extra-pair fertilizations (EPFs), with young males losing paternity of 43% (n = 53) of their putative offspring compared to 4% (n = 85) by old males. All assignable extra-pair offspring were sired by old males, with one male obtaining most EPFs each year. Contrary to the hypothesis that EPCs are forced, EPF frequency within age class did not increase with seasonal increases in the number of males per fertile female. Whereas the male control hypothesis predicted that the male age class that mate-guarded more would be cuckolded less, the reverse was true: young males guarded significantly more intensely. The male age class difference in cuckoldry could not be explained by the possibility that young and inexperienced females (which are usually paired to young males) were more vulnerable to forced copulation because EPFs were unrelated to female age. These findings suggest that females (1) pair with old males and avoid EPCs, or (2) pursue a mixed mating strategy of pairing with young males and accepting EPCs from old males. The receptivity to EPCs by females paired to young males put them in conflict with their mates. Two factors determined the paternity achieved by young males: (1) the relative size of the male to the female, with young males achieving much higher paternity when they were larger than their mates, and (2) the intensity of mate-guarding. Both variables together explained 77% of the variance in paternity and are each aspects of male-female conflict. Given female receptivity to EPCs, mate-guarding can be viewed as male interference with female mating strategies. We conclude that EPCs are rarely or never forced, but the opportunity for females paired to young males to obtain EPCs is relative to the ability of their mates to prevent them from encountering other males. Evidence of mixed mating strategies by females, combined with other features of the martin mating system, is consistent with the female-driven “hidden lek hypothesis” of colony formation which predicts that males are drawn to colonies when females seek extra-pair copulations. Received: 23 March 1995/Accepted after revision: 14 January 1996     

Driver speed selection on high-speed two-lane highways: Comparing speed profiles between uniform and differential speed limits

Objective: Although a considerable amount of prior research has investigated the impacts of speed limits on traffic safety and operations, much of this research, and nearly all of the research related to differential speed limits, has been specific to limited access freeways. The unique safety and operational issues on highways without access control create difficulty relating the conclusions from prior freeway-related speed limit research to 2-lane highways, particularly research on differential limits due to passing limitations and subsequent queuing. Therefore, the objective of this study was to assess differences in driver speed selection with respect to the posted speed limit on rural 2-lane highways, with a particular emphasis on the differences between uniform and differential speed limits.

Methods: Data were collected from nearly 59,000 vehicles across 320 sites in Montana and 4 neighboring states. Differences in mean speeds, 85th percentile speeds, and the standard deviation in speeds for free-flowing vehicles were examined across these sites using ordinary least squares regression models.

Results: Ultimately, the results of the analysis show that the mean speed, 85th percentile speed, and variability in travel speeds for free-flowing vehicles on 2-lane highways are generally lower at locations with uniform 65 mph speed limits, compared to locations with differential limits of 70 mph for cars and 60 mph for trucks.

Conclusions: In addition to posted speed limits, several site characteristics were shown to influence speed selection including shoulder widths, frequency of horizontal curves, percentage of the segment that included no passing zones, and hourly volumes. Differences in vehicle speed characteristics were also observed between states, indicating that speed selection may also be influenced by local factors, such as driver population or enforcement.     

Interactions of Sulfur Dioxide with Insoluble Suspended Particulate Matter

A laboratory study was conducted of the heterogeneous catalysis of sulfur dioxide at ppm concentrations in air by insoluble particles of CaCO₂, V₂O₅, Fe₂0₃, flyash from a coal-burning power plant, MnCO₂, activated carbon, and suspended particulate matter from urban air. The investigalion was performed by utilizing a new technique for aerosol stabilization which consists of depositing the aerosol on Teflon beads in a fluidized bed. The Teflon beads with deposited aerosol particles were then packed into a flow reactor. Progress of the chemical reaction of SO₂ with deposited particles was continuously monitored by determining the SO₂ concentrations in the reactor effluent with a microcoulometer.

In this investigation, CaCOg, V₂O₅, and flyash were essentially inert to SO₂ at room temperature. Fe₂O₃, activated carbon, MnO₂, and suspended particulate matter from urban air sorbed SO₂ from air streams with up to 14.4 ppm SO₂ in air. Evidence is presented which suggests that a substantial part of the sorbed SO₂ was physically adsorbed.

Bioassay procedures which utilize pulmonary flow resistance changes in guinea pigs to monitor response to inhaled SO₂-aerosol mixtures in air have indicated the weak or non-potentiating capacity of insoluble aerosols as contrasted to soluble aerosols. Potentiating response of an aerosol appears to be strongly associated with reaction of SO₂ in a water droplet containing aerosol ions and not with physically adsorbed SO₂ on an insoluble aerosol.     

LCA comparison of windrow composting of yard wastes with use as alternative daily cover (ADC)

This study compared the environmental impacts of composting yard wastes in windrows with using them in place of soil as alternative daily cover (ADC) in landfills. The Life Cycle Assessment was made using the SimaPro LCA software and showed that the ADC scenario is more beneficial for the environment than windrow composting. ADC use is also a less costly means of disposal of yard wastes. This finding applies only in cases where there are sanitary landfills in the area that are equipped with gas collection systems and can use yard wastes as alternative daily cover. Otherwise, the environmentally preferable method for disposal of source-separated yard wastes is composting rather than landfilling.