Ficedula Flycatchers and Avian Malaria

Parasites are fascinating. They are a major force in all aspects of ecological and evolutionary biology that can influence survival, behaviour, fitness, community ecology and intra- and interspecific interactions. My particular parasite of preference are the various protists that are responsible for avian malaria. Malaria itself is not a disease that is confined to humans. Malaria parasites can actually be found in almost all vertebrate groups (there is even the possibility of malaria or malaria-like parasites in fish!). In birds, avian malaria parasites fall into three main genera: Haemoproteus, Leucocytozoon and Plasmodium.

In birds, malaria parasites have been found in almost every species screened to date. The exceptions are some wading birds and some seabirds like the Crested Auklet. As in human malaria, these parasites are transmitted by biting insects. However, it is not just mosquitoes that are the culprits. Black flies, midges and louse flies are all perfectly good vectors.

For my PhD studies, I mainly focused on these parasites and how they influenced the inter- and intraspecific interactions of Collared and Pied Flycatchers.

Ficedula flycatchers provide something of a model natural system with which to explore many questions in ecology and evolution. The two species breed across Europe, with Collareds generally having a more southerly and easterly distribution and Pieds having a more northerly distribution. The two species have a broad overlap zone in Central Europe and hybridisation does occur, although in most places the two species are isolated from one another due to habitat use. During the winter, their ranges are completely isolated, with Pieds travelling to West Africa and Collareds to South Central Africa.

A map of the breeding and wintering ranges of the two species. Collareds in light grey, Pieds in dark grey and the overlap zone in mid grey. The dots denote sampling locations for some of my PhD work.

Since 2002, Anna Qvarnström has been monitoring the breeding population of Collared and Pied Flycatchers on the Swedish island of Öland in the Baltic Sea. Pied Flycatchers have probably been present on Öland for hundreds, if not thousands of years. However, Collareds only colonised in the early 1960’s. Since then, the number of Pied Flycatchers has decreased while there has been a corresponding increase in the number of Collared Flycatchers. There are several reasons for this. Firstly, Collared Flycatchers are much more aggressive and under most circumstances have better breeding success than Pieds. However, there are some exceptions to this rule. If the summer temperatures are low and if there is high rainfall when the nestlings are still in the nest, then their fledging success crashes (some years, we can lose up to 50% of the nestlings). Additionally, Collareds only do well in the best quality, deciduous habitats; sites with plenty of highly productive oak trees. Pied Flycatchers on the other hand are much better parents in bad conditions and they are perfectly happy to breed in poorer quality habitats, even in food poor places like pine forest. This has allowed for some regional coexistence, with a few Pieds hanging on in the periphery.

Like other birds, Ficedula flycatchers are no strangers to malaria parasites. To date, 54 malarial lineages have been detected in the two species. On Öland, prevalence hovers at around 40% for Collareds and 60% for Pieds. What is surprising to many people is that malaria parasites are not necessarily being transmitted in Africa. In fact, for both species ~80% of infections are known to be transmitted in Europe. That being said, the diversity of malarial lineages in Flycatchers that are transmitted in Europe is very low. This means that while the majority of lineages are African, the bulk of infections are happening in Europe.

Figure taken from my thesis

However, when looking at other populations around Europe, we find that these numbers can vary massively. For instance, the poor Pied Flycatchers living in SW Finland experience an infection rate of over 90%! While the Pieds living in Wales have a 30% infection rate and the Collareds living in the Czech Republic sit on an infection rate of only 20%. It has been theorised that this disparity in the infection rates between the two species has facilitated the replacement of Pied Flycatchers with Collared Flycatchers on Öland.

Throughout the course of my PhD I studied also studied the effects of malaria on survival, nest defence behaviours and how the parasites are able to manipulate their hosts. I hope to be able to update this page in the near future when those results are published!

Illustrations by the wonderful Emma Wood