The widespread use of nest-boxes significantly improved our understanding of the ecology and behaviour of secondary cavity-nesting birds. Although former investigations showed that nest-box characteristics (e.g. physical dimensions, material) may determine where birds will roost or breed, biological consequences of the age of nest-boxes have been rarely investigated with field experiments. To test if age of cavities may influence roosting or breeding behaviour in cavity-nesting birds, we created a set-up of three experimental groups of wooden boxes with the same physical dimensions: old boxes that were occupied at least once for nesting during
years prior to this study, old boxes that were never accepted for breeding during years prior to this study, and new boxes. Half of the old boxes were relocated within the study plot and replaced by new ones. Box age did not have an impact on occupation rates during the winter period, and therefore did not seem to influence where the birds roosted. However, breeders occupied the old previously unoccupied boxes less frequently than the other boxes. Moreover, birds bred much earlier in new boxes than in the old boxes that were previously never exploited. We discuss when and how cavity age can influence roosting or breeding in nest-box exploiters. Our results
strongly suggest that maintenance procedures of plots where old boxes are replaced by new ones can influence how and where birds will breed.
The oviposition deterring effects of fresh larval tracks of Cheilomenes sexmaculata (F.), Ceratomegilla undecimnotata (Schneider), Cycloneda limbifer Casey, and Harmonia dimidiata (F.) on C. sexmaculata females were compared in standard laboratory choice tests. Moreover, the persistence of intraspecific effects of C. sexmaculata larval tracks were investigated. Fresh tracks of C. sexmaculata, C. limbifer and C. undecimnotata larvae effectively deterred C. sexmaculata females from ovipositing. The effect of fresh larval tracks of H. dimidiata was not statistically significant. The oviposition-deterring effects of 10 d-old conspecific larval tracks were considerably lower than those of fresh tracks, but remained significant. Clutch sizes were smaller in the blank test without larval tracks than in choice tests with fresh tracks of conspecific, C. limbifer, C. undecimnotata, H. dimidiata larvae and with 10 d-old tracks of conspecific larvae. The study indicates that semiochemicals in the tracks of conspecific and heterospecific coccinellid larvae can contribute considerably to the spacing of C. sexmaculata offspring among prey resources of differing quality and that conspecific as well as heterospecific larval tracks can influence clutch size.
Quantitative data are presented on the spatial distribution of metacercariae of the digenean trematode Diploslomum phoxini (Faust, 1918) in the brains of minnows, Phoxinus phoxinus (Linnaeus, 1758), from two Scottish populations. Sequential examination of serial histological sections revealed metacercariae to be unevenly distributed throughout the brain, aggregating in specific regions including the cerebellum, the medulla oblongata and the optic lobes. In addition, a number of metacercariae were found in the anterior part of the spinal cord. The inferior lobe of the cerebellum, pituitary, olfactory lobes and olfactory bulbs were largely free of metacercariae. Reasons for the uneven distribution of metacercariae within the brains of infected minnows are discussed, including the possibility that the parasite may have evolved to enhance its transmission to subsequent hosts by aggregating in regions known to be important in the control of the host’s antipredator responses.