Dynamic scaling of fronts in the quantum XX chain.

The dynamics of the transverse magnetization in the zero-temperature XX chain is studied with emphasis on fronts emerging from steplike initial magnetization profiles. The fronts move with fixed velocity and display a staircase like internal structure whose dynamic scaling is explored both analytically and numerically. The front region is found to spread with time subdiffusively with the height and the width of the staircase steps scaling as t(-1/3) and t(1/3), respectively. The areas under the steps are independent of time; thus the magnetization relaxes in quantized "steps" of spin flips.

How mixed-species foraging flocks develop in response to benefits from observational learning.

We created experimental situations where observers (great tit, Parus major and marsh tit, P. palustris) acquired one of five types of experience near conspecific and non-conspecific demonstrators: (1) neither demonstrator was feeding; (2) only the conspecific was feeding; (3) only the non-conspecific was feeding; (4) both were feeding and the observer received a reinforcement (food) near the conspecific; and (5) as (4), but the reinforcement was given near the non-conspecific. After each treatment, we recorded whether the observer approached a caged conspecific or a caged non-conspecific. There was a baseline preference for approaching conspecifics but this could be overcome by learnt associations so that the birds would then approach non-conspecifics. When there was an opportunity to distinguish between successful and unsuccessful foragers (demonstrators), and the successful forager was not conspecific, observers of the dominant species approached the successful subordinate non-conspecifics. Observers of the subordinate species approached the dominant species only if they had received a food reinforcement near them. Observers followed non-conspecific individuals more often at temperatures below than above 0 degreesC and chose a conspecific individual more often above than below 0 degreesC. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Density dependent effects between three competitive bird species.

Density and breeding success of the great tit Parus major, blue tit Parus caeruleus and collared flycatcher Ficedula albicollis were studied in nest box colony in oak forest over a period of 19 years.Intraspecific density dependent clutch size reduction was found with blue tit and great tit. In interspecific relation the high density of blue tits reduced the clutch size of great tits.In the hatching period neither intraspecific nor interspecific density dependence were showed between the tits when the third competitive species, collared flycatcher was present. The collared flycatcher significantly reduced the hatching success of both tit species and the number of fledglings of great tit.The effects of the great tits and combined density of the great and blue tits on the hatching failure and number of fledglings of collared flycatcher were found when the density of the tits was high. There were not significant relationships to the single density of blue tits.The temporal variability of the competition of the three bird species is discussed.

Keypeck conditioning with reinforcements in two different locations in thrush, tit and sparrow species.

Twenty-one individuals each of the species great tits (Parus major), blue tits (Parus caeruleus), marsh tits (Parus palustris), blackbirds (Turdus merula), songthrushes (Turdus philomelos), tree sparrows (Passer montanus) and house sparrows (Passer domesticus) were conditioned to a keypeck response by means of food reinforcement. The site where the reward was given was then changed. The number of reinforcements were then counted until the keypeck response followed immediately (within 10 seconds) on three successive occasions, and a comparison was made between species. Of the species studied the blackbird needed significantly fewer instances of reinforcement in order to re-establish an immediate keypeck response. A significant difference was also seen between the performance of the great tit and marsh tit, as well as between the blue tit and the marsh tit. No significant difference was found between the performance of the house sparrow and the tree sparrow.