Parent-off spring associations in wintering brent geese: parental investment or mutual assistance?

The continued parent-offspring associations in the Eastern Canadian High Arctic light-bellied brent goose Branta bernicla hrota was examined to determine whether this is an example of continued parental investment or mutual assistance. Adults with juveniles spend more than twice as much time being vigilant and aggressive than do those without offspring. The loss of a partner, however, does not result in the remaining parent increasing parental care but does result in increased 'self-care' by the juveniles. Neither parents nor single-parent juveniles appear to pay an energetic cost relative to non-parental adults and two-parent juveniles, respectively. Differences in the feeding distribution of parents and non-parents and equivalent or better physical condition suggests that families are able to maintain access to a superior food supply over the winter. Passive 'assistance' by juveniles may assist in maintaining this position in favoured areas, and this is achieved with little overt aggression. The present study thus provides no data that show a net cost to parents by remaining with their juveniles over the winter period. Thus, mutual assistance might be a better explanation of the prolonged association rather than a period of parental investment with an overall cost.

Delamination Fracture Related to Tempering in a High-Strength Low-Alloy Steel

The delamination or splitting of mechanical test specimens of rolled steel plate is a phenomenon that has been studied for many years. In the present study, splitting during fracture of tensile and Charpy V-notch (CVN) test specimens is examined in a high-strength low-alloy plate steel. It is shown that delamination did not occur in test specimens from plate in the as-rolled condition, but was severe in material tempered in the temperature range 500 °C to 650 °C. Minor splitting was seen after heating to 200 °C, 400 °C, and 700 °C. Samples that had been triple quenched and tempered to produce a fine equiaxed grain size also did not exhibit splitting. Microstructural and preferred orientation studies are presented and are discussed as they relate to the splitting phenomenon. It is concluded that the elongated as-rolled grains and grain boundary embrittlement resulting from precipitates (carbides and nitrides) formed during reheating were responsible for the delamination.