Roles of woodland birds in the transmission of emerging tree diseases

Emerging tree diseases, such as Acute Oak Decline (AOD), Horse-Chestnut Bleeding Canker and Ash Dieback, have gained considerable attention in recent years. The scientific community is challenged to address the uncertainty regarding the ecological and economic impacts of such diseases on the British countryside.

Trees are foundation species in many habitats, providing overarching structure, important ecosystem services (e.g. carbon sequestration, water retention and soil stability) and conservation of biodiversity in both natural and man-made landscapes. Due to this critical role in shaping and maintaining the biological integrity of diverse habitats, emerging tree diseases have the potential to cause cascading effects through ecosystems and negatively impacting associated fauna. Woodland birds, in particular, are especially vulnerable due to their intimate association with trees as sites for forage, shelter and nesting.

Outbreaks of AOD are attributed to several members of the Gram-negative Enterobacteriaceae (e.g. Brenneria sp., Gibbsiella sp. and Rahnella sp.) yet still very little is known about the vectoring of these pathogens between sites and individual trees. Previous studies have speculated that insects, especially wood-boring beetles, may be transporting the pathogens between sites and delivering them directly into the living tissue of new tree hosts. Xylella fastidiosa, another bacterial pathogen, spread by insects from the Cicadellidae and Ceropidae families, has very recently been found to infect a wide range of host plants including English Oak.

The contributory role of woodland birds in controlling insects acting as vectors of disease in trees remains largely under-studied. Birds themselves, however, may be inadvertently acting as vectors of disease transmission and delivering the bacteria via the oral route to sites of infection through such activities as wood-boring and active foraging in cracks along the trunks. Survival of passage through the bird intestinal tract by said pathogens is feasible, opening further possibilities of spread via faeces. We propose to investigate the intricate associations between trees, their diseases, insect vectors and their bird predators.

Proposal outline:
1. Dietary analyses and feeding ecology of wild birds across sites featuring differential occurrence of tree disease. Many birds are generalist feeders and able to exploit a broad range of food resources. Specialist insectivores are known to preferentially forage in tree species with the greatest abundance of their prey. Assessment of feeding ecology, including abundance of disease vector insects, will be conducted using next generation high throughput DNA sequencing targeting animal mitochondrial genes (12S rRNA, 16SrRNA and COI).
2. Does tree disease (i.e. diseased or not) status impact insect communities and abundance? Abundance of insects on trees will be monitored using frass traps, to assess whether tree disease results in inflated or suppressed populations of these herbivores.
3. Are woodland birds vectors of disease? Presence of bacteria associated with tree diseases within birds will be assessed using a combination of classic microbiology and 16S rRNA microbial community analyses.