Breeding density and breeding synchrony have been reported to influence the intensity of sperm competition although results obtained so far are not conclusive. In this study we examine the investment of male lesser grey shrike (Lanius minor) into paternity guards in relation to breeding synchrony and breeding density. Male shrikes perform a double strategy to ensure paternity. They copulate frequently, mainly after territorial intrusions by other males, and guard their mates throughout the whole fertile phase. Our results indicate that, the two socio- ecological factors investigated, indirectly affect extra-pair behaviour in LGS’s. Males seem to be constrained by the frequency of intrusions by neighbouring males and this risk is associated with laying synchrony. The risk of intrusions depends on the timing and overlap of breeding attempts and males adjust their investment to paternity assurance accordingly. Furthermore, females seem to alter their egg laying patterns to minimise synchrony in situations where they find themselves in dense breeding situations. This is indicated by the negative correlation between breeding density and breeding synchronization. Extra-pair paternity, however, was not detected in our population. Thus the rate of extra-pair paternity is not necessarily an adequate measure to identify the influence of socio-ecological factors on male and female mating strategies.
Seasonal cycles constitute a major challenge for organisms since they may influence the genetic composition of a population, the species structure of a community and the interactions between organisms. Diapause is frequently used by insects to synchronize their life cycle with seasonal changes and is regarded as a key factor in the coexistence of competing species. Here the occurrence, abundance and emergence patterns of three poorly-known species of carnid flies (Carnus hemapterus Nitzsch, 1818, Hemeromyia anthracina Collin, 1949 and Hemeromyia longirostris Carles-Tolrá, 1992), which overwintered in the nests of several bird species at two localities, are reported and evidence of possible interspecific competition sought. Larvae of all three species were found in association with carrion and detritus. Both Hemeromyia species co-occurred in around 50% of the nests and Carnus with each of the Hemeromyia species at a lower rate (30-40% of the nests). Coexistence of all three carnid species was rare. We did not find any evidence of interspecific competition in the larval stage. Coexistence did not reduce the number of flies that emerged of any of the three species and the abundance of some species was even positively related. Species-specific emergence patterns and different habitat selection criteria (Carnus hemapterus seemed to avoid nests lined with vegetable material), which diminished the overlap between species were found. Such spatial and temporal segregation could facilitate the coexistence of these closely related species, which have similar ecological requirements, and might influence the seasonal dynamics of this poorly-known assemblage of insects inhabiting the nests of birds.