Host-Parasite Interactions in Avian Systems

Interactions between birds and their parasites span a spectrum of ecological, behavioural and evolutionary dynamics. Avian hosts contend with a diverse assemblage of parasites, including blood‐feeding ectoparasites (ticks, mites, flies), endoparasites (protozoans, helminths) and nest‐breeding dipterans. Parasites exploit avian resources to complete their life cycles, often reducing host fitness through blood loss, tissue damage, impaired growth or increased susceptibility to secondary infections. Hosts, in turn, deploy a suite of defences ranging from innate and acquired immune responses to anti‐parasite behaviours such as preening, nest sanitation and the use of botanical repellents. Coevolutionary pressures shape parasite virulence and host resistance or tolerance strategies, with outcomes influenced by host life history, environmental conditions and anthropogenic change. Understanding these interactions is crucial not only for avian conservation—especially on islands and in biodiversity hotspots—but also for broader epidemiological and ecosystem‐health perspectives, as birds can serve as reservoirs or vectors of zoonotic agents.

Research from Nature Portfolio

Experimental removal of seabird ticks in a colonial breeding albatross demonstrated for the first time a direct causal link between high tick loads and reduced chick growth, bill development and fledging survival. Chicks from which ticks were regularly removed exhibited greater body mass, accelerated growth rates and higher survival to fledging than control chicks, underscoring the sublethal accumulation of parasitic effects on fitness.

Behavioural innovation in Darwin’s finches reveals a chemical defence against ectoparasites: individuals rub endemic Psidium galapageium leaves on their feathers. Extracts from these leaves repel both mosquitoes and invasive nest flies and inhibit fly larval growth, illustrating an adaptive use of plant secondary compounds to reduce parasitic burdens in the wild.

Host-Parasite Interactions in Avian Systems publication trend

The graph below shows the total number of articles in host-parasite interactions in avian systems across all publications each year (not limited to Nature Index journals).

Technical terms

Ectoparasite: A parasite that lives on the external surface of the host, such as ticks, mites or lice.

Endoparasite: A parasite that lives inside the host’s body, including protozoans and helminths.

Resistance (host): Host defence strategy that reduces parasite fitness, often via immune responses or behavioural rejection.

Tolerance (host): Host defence strategy that mitigates the fitness consequences of parasitism without directly reducing parasite abundance.

Virulence: The degree to which a parasite harms its host, often measured as morbidity or mortality induced.

Founder effect: A genetic phenomenon in which a new population, derived from a small number of colonising individuals, shows reduced genetic diversity and may diverge rapidly under selection.

References

1. Experimental evidence of high tick infestation limiting chick growth and survival in a colonial seabird. Scientific Reports (2024).
2. Darwin’s finches treat their feathers with a natural repellent. Scientific Reports (2016).
3. Genomic Insights into the Successful Invasion of the Avian Vampire Fly (Philornis downsi ) in the Galápagos Islands. Molecular Biology and Evolution (2025).
4. Host tolerance and resistance to parasitic nest flies differs between two wild bird species. Ecology and Evolution (2019).