Wildlife

Trichomonosis: Are our bird feeders up to scratch?

Could our feeding of wild birds, be aiding the spread of trichomonosis which has caused rapid decline of the British Greenfinch population and poses a threat to other beloved garden birds?

Green Finch on feeder

Alarmingly, research increasingly seems to suggests that our current methods, devices and habits of bird feeding may be exacerbating the spread of the fatal disease, trichomonosis (see our full report). Undoubtedly, this will cause some debate as many of the current bird feeders on the market and in use, may be potentially increasing the risk of transmission.

Trichomonosis is caused by the protozoan parasite Trichomonas gallinae which causes pathologic lesions in the upper digestive tract of the birds, blocking the oesophageal lumen (Stabler 1954). This makes it difficult for them to breathe and swallow, causing the birds to regurgitate food and/or water. Birds suffer from lethargy, often seen with fluffed-up plumage, with some having wet plumage around the bill, from drooling saliva or regurgitating food that they cannot swallow. The disease may progress over several days or even weeks, killing the weakened bird from starvation or predation.

Finch trichomonosis occurs year round, but according to the Garden Wildlife Health Project (GWH), June to September have been observed to be the peak months for this condition – requiring extra care and vigilance at this time.

Research shows that risk of general pathogen transmission is caused from direct transmission – close contact with infected individuals or indirectly, through contaminated food or water, or via faecal-oral routes associated with environmental contamination around feeding sites (Murray et al., 2016; Becker et al., 2015; Bradley and Altizer, 2006). GWH confirmed that the transmission of the Trichomonas gallinae parasite is most likely by birds feeding one another with regurgitated food during the breeding season or through ingesting food or drinking water contaminated by an infected bird.

According to the Canadian Wildlife Health Cooperative (CWHC), bird feeders can act as a “fomite” for various pathogens, such as Trichomonas gallinae, and lead to transmission of disease from infected to uninfected individuals (Murray et al., 2016; Becker et al., 2015; Bradley and Altizer, 2006). In their report on bird feeder associated diseases and threats, they explain: “Trichomonas gallinae can survive and replicate in moist bird seed for up to 24 – 48 hours depending on seed type (McBurney et al., 2017). Bird feeders lead to increased congregations of birds which is associated with increased contact rates within and between species that can result in direct transmission of diseases between infected and uninfected individuals, exacerbating and prolonging disease outbreaks (Murray et al., 2016; Becker et al., 2015; Bradley and Altizer, 2006)”.

As the research suggests, transmission risk is elevated due to the increased contact between birds at feeders and contamination of the feed or feeders with infectious organisms. Discard/regurgitated bird seed from an infected bird can quickly infect healthy birds coming into contact/eating it – as long as the parasite can survive and/or replicate in the food or water. According to R.W. Gerhold, Jr., DVM, PhD, MSVet (MSD Manual), the parasite has been shown to survive at least 2 hours – potentially up to 24 hours in distilled water. That means that despite the fact that the parasite is unable to survive for long periods outside of its host, there is still a high probability and risk of pathogen transmission in both (wet) seed and water.

The bigger the congregation of birds for sustained periods increases the risk of parasite transmission. The more accessible the bird seed supply, the higher the risk of direct and/or indirect, pathogen transmission. This is particularly problematic as most feeders allow birds to have some, if not complete access to the supply and could therefore be exacerbating the spread of the disease, such as for example bird tables and tray feeders. Feeders such as these, also tend to leave the seed exposed to rain. According to the CWHC, wet seed is a more suitable environment for the potential survival of the parasite.

Tube feeders, designed to allow several birds to feed at different levels could also be problematic, not only as they allow for several birds to congregate in close proximity, but also as potential discard from an infectious bird can trickle down to the multiple feeding access points below. Similarly, discarded seed on the ground, or collected by the feeder via waste capture trays for others to consume, may increase the spread of the disease.

According to Dick Woods, Founder of Finches Friend, it’s all about, “Food, Feet and Faeces”. Woods explains, “Disease transmission is to a great extent down to regurgitation, faeces and damp. Choose feeders that keep the food dry and limits access by birds to a perch. People simply do not understand that a single sick bird, through its saliva can create a chain reaction within their feeders, damp food becomes a host for the Trichomonsis parasite which can present at other ports on side port feeders as the food drops. Husks stick to sick birds beaks and are then left around ports or dropped to the ground, in both scenarios they are infectious.”

Discarded bird food, below the feeder, or collected via waste capture tray, habitually encouraged as a means ‘secondary feeding’ for ground feeders, is likely therefore to put birds, such as chaffinches at risk of the disease. Researchers found that declines in chaffinches were more marked in peridomestic habitats than in rural habitats, which researchers suggests may be due to food provision increasing parasite spread (GWH).

Bird feeders where birds are able to sit in, walk on the seeds, or allow access to pigeons or doves, adds to the risk of (faecal) contamination. Even though current transmission is thought to be mostly finch to finch, it is also presumed that the spread of the parasite between finches and pigeons or doves, may also still occur. Suggesting therefore, that we should avoid using any form of ‘tray’ feeders such as window feeders, ground feeding trays and/or bird tables.

Hygiene is obviously crucial. The GWH recommend to forgo feeders made from porous materials and to opt instead for those that are conducive to effective cleaning and disinfecting, such as plastic. Bird baths can quickly become contaminated and should be therefore be regularly emptied, disinfected, rinsed and refilled with fresh, clean water. Bird feeders, should be regularly emptied, cleaned and disinfected to prevent contamination of the food. When asked how often, Woods said: “Simply put, you can’t clean too often, anecdotally we believe cleaning on average takes place monthly at best. We push for weekly, and design to make that simple, not a chore.” The GWH concurred, recommending weekly cleaning of bird feeders, whilst circumstances may vary. Considering the damaging potential of trichomonosis, perhaps it’s time we take this even further, and start to apply the same hygiene standards to bird feeders as we do for our pet’s food, perhaps even our own.

On account of its antimicrobial properties, bird feeders made from copper are increasingly available on the market. The antimicrobial activity of copper and copper alloys is well established, and copper has recently been registered at the U.S. Environmental Protection Agency as the first solid antimicrobial material (G. Grass, C.Rensing, M. Solioz, Feb 2011). Bacteria, yeasts, and viruses have been shown to be killed on metallic copper surfaces, coined as ‘contact killing’, which may suggest that bird feeders made from copper could be a potential option to reduce transmission. However, the GWH were unable to confirm this, nor are they aware of any research done on this area. Similarly, Woods said that though copper may be useful against bacterial and viral agents, he was unsure if it was of use against a parasite.

Due to the nature of this parasite, the sad reality though is that even a squeaky clean, properly disinfected feeder can become infectious again, imminently, if an infected bird is able to regurgitate contaminated food/water into the supply.

Going forward, perhaps the best advice is to reduce the need for supplementary feeding by creating bird friendly gardens that provide a good, consistent levels of natural sources of food, water and shelter for birds. A bird friendly garden is one for example; where herbaceous borders are left uncut over winter to provide ample food sources; includes plants and trees with good sources of berries – which have been positively associated with native and migratory bird species richness and regularly incorporate generous levels of garden compost for optimum garden biodiversity, ensuring they are rich in soil micro-organisms, worms, woodlice, slugs and other invertebrates for birds to feed on.

Any supplementary wild bird feeding provided in addition to a bird friendly garden, must be:

  • maintained to the highest possible hygiene levels
  • limited to small feeders/volumes to discourage large crowds of birds
  • only allows birds limited access to the food supply – ideally from a perch
  • designed to ensure the seed is not exposed to rain
  • ideally not accessible by pigeons or doves
  • ideally, species/food type specific to avoid cross-species contamination
  • preferably not be available to birds during the peak observed months, from June to September.

Further information: