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.     

Semi‐field experiments investigating facilitation: arrival order decides the interrelationship between two saproxylic beetle species

1. Acanthocinus aedilis (Linnaeus) and Rhagium inquisitor (Linnaeus) both colonise the cambial layer in newly dead Scots pine Pinus sylvestris L. and thus are potential competitors. 2. Species interactions and in particular priority effects were investigated in an experiment with a replacement series design. Four pairs of adult beetles were released on each of 91 caged pine bolts (0.35 m long, 13 replicates). To test for priority effects, a 2‐week interval was used to separate the species. 3. The interrelationship in simultaneous coexistence was positive for A. aedilis and negative for R. inquisitor (+,?). Acanthocinus aedilis produced 161% more offspring per female in coexistence than alone. Rhagium inquisitor had lower offspring quality in coexistence where its larvae weighed 39% less than in one‐species bolts. 4. The interrelationship depended on arrival order. When A. aedilis had priority the interaction was again advantageous to A. aedilis (+,?) but when R. inquisitor had priority no species interaction occurred (0,0). Both species therefore fared better when having priority. 5. Facilitation in cerambycids is novel and the facilitative effect on A. aedilis could be oviposition incitement or resource enhancement by R. inquisitor.