Conservation biologist warns bird feeders are killing some birds as populations decline

A conservation biologist has warned that bird feeders are negatively affecting some wild birds. He describes them as giving a 'leg up' to some species, making it hard for others to compete.

Installing one of the best bird feeders in our gardens is a great way to attract wildlife, but Professor Alexander Lees highlights that as well as disrupting the natural order of things, some birds are catching a disease when visiting them. This is causing a sharp decline in a common species, he says.

'For some species which are declining, like the house sparrow, it could be really important for them in cities where there isn’t much food,' he tells Naga Munchetty and Charlie Stayt on BBC Breakfast. 'But for other species, like the greenfinch – they have undergone this catastrophic decline because of catching diseases at bird feeders.'

Professor Lees says that trichomonosis is the most common disease that can kill off birds when visiting bird feeders. This infection is spread through food and water that is contaminated with freshly regurgitated saliva, and the more birds at a feeder or birdbath there are, the more likely it is to spread.

It affects the digestive system and causes lesions in the throat that makes it hard for the infected bird to swallow food, according to the RSPB.

Professor Alexander Lees goes on to say that marsh tits will naturally compete with the blue tit. He believes that the marsh tit populations have crashed, along with willow tits, because we're giving a leg up to blue tits with our bird feeders.

'To understand where we should be feeding and how and why, we do need more science to underpin that,' he says. 'But, you know, the obvious thing to do to increase biodiversity in your garden isn’t just putting a feeder up.'

He argues that trying a range of wildlife garden ideas is paramount - adding that we need to improve our gardens for all sorts of species. Professor Alex Lees describes putting a bird feeder up as giving instant gratification, although this isn't often the case.

It's lovely to see different birds coming to your feeder, but from our experience, it can take several weeks for the birds to come. The best thing you can do is to look at ways to invite a vast array of creatures into your outdoor space, from planting bee-friendly plants to creating a garden pond or planting bushes.