Brood parasitism represents a unique mode of avian reproduction that requires a number of adaptations. For example, to reduce chances of puncture ejection of their eggs by small hosts, brood parasites may have been selected for laying eggs of unusually great structural strength. However, great structural strength of eggshells should hinder hatching. The goals of our study were to establish if chicks of the Common Cuckoo Cuculus canorus have more difficulty with hatching out of their strong eggs than chicks of species with eggs of similar size, and whether they possess any mechanisms facilitating hatching. To achieve these goals, we compared hatching pattern and selected body characteristics of chicks of the Common Cuckoo with those of another altricial species with eggs of a similar size, the Great Reed Warbler Acrocephalus arundinaceus. Although the rate of pecking was similar in the two species, the Common Cuckoo chicks started pecking earlier in relation to their emergence and consequently required more time and a greater cumulative number of pecks for breaking open their eggs than did young Great Reed Warblers. The two species also differed with respect to the pattern of opening their shells; in contrast to the warbler chicks, which enlarged the original pip circularly, the cuckoo chicks opened the egg by systematically creating a long narrow slit until they emerged. Finally, our study of hatched young revealed several differences; the Cuckoo hatchlings were significantly heavier, had a longer forearm, and their egg tooth was located significantly farther from the tip of the beak. The edge used for cutting through the shell was also significantly longer than that of hatchling Great Reed Warblers. To conclude, our data suggest that hatching is more difficult for a Cuckoo than for a Great Reed Warbler and that Cuckoos possess several mechanisms to overcome the problems of hatching from a structurally strong egg.

The cephalic structures of the final instar larva of 278 species of 140 genera of Braconidae were examined. On the basis of these and biological data, modifications are proposed in the classification of the higher categories. Zele (Helconinae) and Eubadizon (Blacinae) are placed in the Macrocentrinae (endoparasites of larval Lepidoptera) and Meteoridea is moved from the Helconinae and ranked as an independent subfamily. The Blacinae is completely dismembered: Aliolus, Triaspis, Urosigalphus, Blacus, and Calyptus form a tribe of the Helconinae (endoparasites of larval Coleoptera); Microtypus, Orgilus, and Stantonia form a tribe of the Agathidinae (endoparasites of larval Lepidoptera); and Pygostolus, Centistes, and Syrrhizus a subfamily near Euphorinae with Cosmophorus (endoparasites of adult Coleoptera). Present genera of Microgasterinae are separated into two tribes with the addition of the Cardiochilini as a third tribe. The Dacnusinae is reduced to a tribe of the Alysiinae. The Rogadinae is reduced to one tribe, Rogadini, containing only Rogas and allied genera (endoparasites of larval Lepidoptera). Rhyssalus is transferred to the Hecabolini, and Exothecini, Pambolini, Hormiini, and ectoparasitic Rogadini to the Braconinae (ectoparasites of larval Coleoptera, Lepidoptera, etc.). The problematic genus Gnaptodon is also placed in the Braconinae.

Blackcaps Sylvia atricapilla reject artificial cuckoo eggs, and their eggs vary little in appearance within clutches, whereas among clutches eggs vary considerably. Low variation within clutches facilitates discrimination of parasitic eggs, whereas high variation among clutches makes it harder for the cuckoo to mimic the eggs of a certain host species. These traits have most probably evolved as counteradaptations against brood parasitism by the common cuckoo Cuculus canorus, even though blackcaps are not regularly parasitised today. In this study, we investigated how fine-tuned the rejection of parasitic eggs is in this species by introducing three types of eggs into their nests: a real non-mimetic egg the approximate size of a cuckoo egg, an artificial mimetic egg the size of a cuckoo egg and a real conspecific egg. As the rejection frequency of both mimetic and non-mimetic artificial cuckoo eggs has been shown to be high in previous studies, the variation in rejection behaviour between individuals is low, indicating that most individuals within the population are able to reject parasitic eggs. Thus, we predict that (1) the intraclutch variation in egg appearance should be generally low in all individuals, and that (2) regarding conspecific eggs, rejection decisions should be highly dependent on the degree of mimicry between parasitic and host eggs. We found support for these predictions, which indicates that due to their highly sophisticated countermeasures against brood parasitism, blackcaps can probably be regarded as current winners of the arms race with the common cuckoo. Furthermore, the high and consistent rejection frequency of cuckoo eggs found throughout Europe for this species supports the spatial habitat structure hypothesis, which claims that woodland-nesting species breeding near trees, like blackcaps, presumably experienced a high level of parasitism throughout their range in the past and, therefore, their rejection behaviour, once evolved, spread rapidly to all populations.

No abstract

The central European lineage of Usutu virus was isolated from a blackbird (Turdus merula), which was found dead in the city of Brno, Czech Republic, in 2011. The virus RNA was detected in two other dead blackbirds in Brno during 2012.