A bird’s eye view: using circuit theory to study urban landscape connectivity for birds

Context Connectivity is fundamental to understanding how landscape form influences ecological function. However, uncertainties persist due to the difficulty and expense of gathering empirical data to drive or to validate connectivity models, especially in urban areas, where relationships are multifaceted and the habitat matrix cannot be considered to be binary. Objectives This research used circuit theory to model urban bird flows (i.e. ‘current’), and compared results to observed abundance. The aims were to explore the ability of this approach to predict wildlife flows and to test relationships between modelled connectivity and variation in abundance. Methods Circuitscape was used to model functional connectivity in Bedford, Luton/Dunstable, and Milton Keynes, UK, for great tits (Parus major) and blue tits (Cyanistes caeruleus), drawing parameters from published studies of woodland bird flows in urban environments. Model performance was then tested against observed abundance data. Results Modelled current showed a weak yet positive agreement with combined abundance for P. major and C. caeruleus. Weaker correlations were found for other woodland species, suggesting the approach may be expandable if re-parameterised. Conclusions Trees provide suitable habitat for urban woodland bird species, but their location in large, contiguous patches and corridors along barriers also facilitates connectivity networks throughout the urban matrix. Urban connectivity studies are well-served by the advantages of circuit theory approaches, and benefit from the empirical study of wildlife flows in these landscapes to parameterise this type of modelling more explicitly. Such results can prove informative and beneficial in designing urban green space and new developments

Exploding electron bubbles.

Electron bubbles, used in laboratories throughout the world for probing the unusual properties of liquid helium, can be made to explode by the application of negative pressure, according to investigations by Classen et al. published last month

A new form of energy dissipation by a moving object in He II.

Despite the superfluid1 character of 4He below the lambda transition temperature, there are two distinct mechanisms by which an object moving through the liquid dissipates kinetic energy: (1) it can scatter the excitations (rotons, phonons, 3He isotopic impurities) that constitute the normal fluid component; and (2) for speeds in excess of the Landau critical velocity vL it can create rotons, apparently in pairs. The first process has been studied extensively, mostly by measurements of the zero-field mobilities of positive and negative ions. The second process, which is much rarer, has also been investigated in considerable detail by studies of the motion of negative ions in isotopically pure 4He at elevated pressures. Here, we report an attempt to extend the latter type of investigation to lower pressures. This yields unexpected results that can be accounted for satisfactorily only if we postulate the existence of a third dissipation mechanism