Seasonal changes in a ultraviolet structural colour signal in blue tits, Parus caeruleus

Recent studies of blue tits, Parus caeruleus , have found sexual selection and a viability-indicating function of the structural ultraviolet and blue crown plumage, but the reasons for this signal variation are not understood. Furthermore, studies in England and Sweden have yielded somewhat different results (particularly with regard to the spectral position of the reflectance peak). Here we investigate whether the blue tit UV/blue ornament varies with time of year since such variation might be relevant to the signalling function as well as the apparent difference between populations. From 400 blue tits captured at two different localities in Sweden, we found that objective measures of 'hue' (spectral location), 'chroma' (spectral purity) and 'brightness' (spectral intensity), varied substantially with season. Just after moult (October), crown 'hue' is maximally UV-shifted (359 nm for males and 373 nm for females). Thereafter the peak drifts upwards and by the time of nestling feeding (June) male reflectance peaks at 404 nm and female at 413 nm. This change is probably due to feather wear as well as fat and dirt accumulation, which might constitute an additional male quality cue. Our results suggest that it is important to consider plumage age when exploring variation in structural plumage coloration, and that it can largely explain the difference between the British and Swedish studies. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 237–245.     

The Yellowing of Attached and Detached Cucumber Cotyledons

Measurements of various constituents and the activities of variousenzymes have been made in attached and detached cotyledons ofCucumis sativus. The complex changes observed suggest that thereis a reproducible pattern. Comparison of results for attachedand detached material shows that, although both become yellow,the other biochemical changes associated with yellowing arenot the same.     

Insect invasion sequences: systematic or stochastic?

Abstract. 1. This study examined the invasion sequence of Drosophila species arriving at decomposing strawberries.
2. It was found that the age of fruit affected the likelihood of Drosophila arrival, flies preferring relatively fresh fruit. However, there were no repeatable trends in invasion sequence of Drosophila species, different species responding in a similar manner to changes in fruit age.
3. Although no systematic trends in invasion sequence were observed, species tended to be temporally separated due to stochastic differences in their arrival at the fruit.
4. It is suggested that stochastic, as well as repeatable, temporal separation of species can have an important influence on subsequent community development.     

Nettle-feeding nymphalid butterflies: temperature, development and distribution

1. Four nymphalid butterflies, Aglais urticae L., Inachis io L., Polygonia c-album L. and Vanessa atalanta L., share the same primary host plant, Urtica dioica L., but have different margins to their U.K. and European ranges. Their developmental responses to a series of constant temperatures were measured.
2. Degree-day requirements were found broadly to explain the relative distributions and differences in voltinism of A. urticae , P. c-album and I. io . The migrant V. atalanta did not fit into the predicted pattern, and this species may be more limited by its ability to overwinter.
3. Although the most northerly distributed species, A. urticae , had the lowest degree-day requirement, it had the highest developmental threshold and performed best (for mortality, pupal weight and relative growth rate) at high experimental temperatures. It is suggested that this may be due to the gregarious nature of its larvae and their possible ability to thermoregulate.
4. At southern margins, different distributional limits may be explained partly by larval gregariousness (a more northern trait) and maximum temperatures at which development is possible.
5. Limits to the distributions of these mobile species are at least partially explicable by the interaction of climatic patterns and thermal biology. A rapid response to climate change is predicted, and has already been observed in two of the species.     

The influence of climate and topography in patterns of territory establishment in a range‐expanding bird

The Dartford Warbler Sylvia undata has recently expanded its range northwards and upwards in the UK, consistent with the hypothesis that this cold‐sensitive species has responded to a warming climate. We interrogated distribution data, collected during four national surveys of this species between 1974 and 2006, to assess whether this large‐scale range expansion has been accompanied by finer‐scale changes in topographic characteristics of breeding locations. Within sites occupied in successive surveys, there was some evidence of limited altitudinal expansion between surveys. Within wider landscapes occupied in successive surveys, the preceding winter climate tended to be harsher at newly colonized sites than at sites that had already been occupied in the previous survey, while territories in newly colonized sites also tended to be on steeper slopes, especially if at higher altitude, and (in 1994 only) to be more south‐facing. Territories in sites that had already been occupied in the previous survey tended to be lower altitude, less steep and more north‐facing than territories in newly colonized landscapes. In 2006 only, the winter climate was significantly milder in newly colonized landscapes than in already occupied sites. The combined effects of a changing climate and topography may have influenced the pattern of in‐filling in the existing range, while colonization of distant areas, especially more latterly, may have been facilitated by a combination of increased dispersal pressure from the existing range and warming of climate which made higher altitude habitat in the new areas more suitable for occupancy. Careful consideration needs to be given to the importance of fine‐scale topographical variation in determining species’ responses to climate change in order to underpin robust adaptation strategies.