Delay in arrival: lineage-specific influence of haemosporidians on autumn migration of European robins

Haemosporidian blood parasites are widely used in evolutionary ecological research when exploring the effects of parasites on different life-history traits of their bird hosts. However, their roles in bird migration are less studied. If these parasites deteriorate the body condition of the birds strongly, they might negatively affect the whole migration phenology and the survival of the birds as well. In our study, we tested the relationships between infection for parasite genera (Haemoproteus or Plasmodium), the three most frequent parasite lineages and body condition (body mass, fat deposit), and the timing of autumn migration in the European Robin (Erithacus rubecula). We found that mean body mass and fat scores did not differ between parasitized and non-parasitized individuals, but infected juveniles arrived later than their non-infected counterparts. The difference in the arrival time of parasitized and non-parasitized birds was greater in the case of Haemoproteus infections. However, when we analysed the effects of the distinct parasite lineages separately, we found that prevalence of parasite lineages correlated with the body mass, fat storage, and timing of autumn migration of the birds in a different direction. Our results therefore emphasize the importance of testing the impacts of the different parasites individually, because possible lineage-specific effects on bird condition during migration might exist.

Does offspring sex ratio differ between urban and forest populations of great tits (Parus major)?

Since male and female offspring may have different costs and benefits, parents may use sex ratio adjustment to increase their own fitness under different environmental conditions. Urban habitats provide poorer conditions for nestling development in many birds. Therefore, we investigated whether great tits (Parus major) produce different brood sex ratios in urban and natural habitats. We determined the sex of nestlings of 126 broods in two urban and two forest sites between 2012 and 2014 by molecular sexing. We found that brood sex ratio did not differ significantly between urban and forest habitats either at egg-laying or near fledging. Male offspring were larger than females in both habitats. This latter result suggests that male offspring may be more costly to raise than females, yet our findings suggest that urban great tits do not produce more daughters despite the unfavourable breeding conditions. This raises the possibility that other aspects of urban life, such as better post-fledging survival, might favour males and thereby compensate for the extra energetic costs of producing male offspring.

Haematospirillum and insect Wolbachia DNA in avian blood

In this study, blood samples of 259 Acrocephalus sp. warblers were molecularly analysed for Anaplasmataceae and Rhodospirillaceae based on PCR amplification of 16S rRNA gene fragments. One bird blood sample (from Reed Warbler, Acrocephalus scirpaceus) yielded a sequence with 99.8% identity to Haematospirillum jordaniae. This is the first molecular evidence for the occurrence of this species in the blood of any vertebrate other than human. Another bird blood sample (from Marsh Warbler: Acrocephalus palustris) yielded a Wolbachia sequence, closely related to a moth endosymbiont with 99.8% identity. A nematode origin of Wolbachia DNA detected here in avian blood can be excluded, because results of phylogenetic analysis showed its closest alignment with insect wolbachiae. This is the first finding of insect Wolbachia DNA in the circulatory system of birds, which can be explained either by the inoculation of wolbachiae by blood-sucking vectors, or passing of Wolbachia DNA from the gut into the blood of this insectivorous bird species.