How grey squirrels fatten themselves on tons of seed at the expense of birds

If birds in Britain are feeling at all peckish these days, don't blame it on the stinginess of humans. Blame the thieving grey squirrel.

Almost half of all households in the U.K. stock feeders full of nuts and seeds, to help birds make it through the harsh winter months.

But according to a new study published in the journal Landscape and Urban Planning, grey squirrels have been stealing millions of pounds of bird seed from feeders every year. And that's bad news for the bird population.

Mark Fellowes was a senior researcher on the study. He's a professor of ecology at the University of Reading. He spoke with As it Happens host Carol Off from Reading, England. Here is some of their conversation. 

Professor Fellowes, a lot of people think grey squirrels are cute. Are they wrong? 

I think grey squirrels are cute. There's a definite charm to them. They're comfortable around people. And they've become part of English society and culture, I suppose, in southern parts — where people are so used to seeing them that it's part of their lives. 

So how did you do your study of their behaviour, especially with bird feeders?

It was exceptionally simple. Here, if anybody looks out the window, they'll regularly see squirrels going on to their feeders. So it was just a simple question of how much food are squirrels taking, are they having an effect on the birds, and how much resource — how much money — are people spending on supporting squirrels?

So we simply put feeders out in gardens. We put automated camera traps up to record all the visitors to the feeders. And we just let those run for weeks and weeks, so we captured years worth of data. 

So what effect do grey squirrels have on the bird feeding?

Well there are two sides to this. There's the direct effect, and that is if a squirrel is on a feeder, no birds will visit it. Squirrels, compared to the birds most people have in their gardens around here, are pretty big and relatively feisty animals. 

The second bit is that people are spending — here — hundreds of millions of pounds on bird food. What we're seeing is a very large proportion of that is going to squirrels. Squirrels are dominating the feeders in our study almost half the time. 

So if people are spending a lot of money on that, they're essentially helping make baby squirrels. 

• AS IT HAPPENS: Squirrel blamed for car engine stuffed with nuts
• AS IT HAPPENS: New website claims squirrels are the real cyber threat

And what's wrong with that? If people are spending hundreds of dollars on bird feed, they also like watching the squirrels come and go from the feeders.

That's very true. And there are many people who will deliberately feed squirrels. The difficulty we have here is the grey squirrel was introduced from North America 150 years ago or so, by a rather wealthy landowner who thought it would make his park look pretty. 

They've spread throughout the country. They have essentially pushed out our native red squirrels, [who've] been completely wiped out from most of England — because they transmit something called squirrel pox, which they're immune to but our squirrels aren't. 

And the second thing is that the squirrels will raid birds' nests and eggs. 

So if you're trying to help birds when you're putting out food — if you don't protect your feeders to stop squirrels getting access — what you're doing is providing a great resource for a species that then may go to predate nests and eggs of birds you're actually trying to help.

So what's the solution? You're not telling people to stop feeding the birds?

No, not at all. And I would never for a moment suggest that. Many children growing up in towns and cities — their contact with wildlife is what's in their backyard. And it's hugely important that people maintain that contact.

It's more about developing the right techniques. It's really simple: just use feeders that have cages, or baffles, or barriers — or you can buy these slightly more-expensive spring-loaded ones where an animal over a certain weight sits on the feeder, it simply shuts off the food. And that's what I use in my garden.

Written by Donya Ziaee and Kevin Ball. Interview produced by Donya Ziaee. Q&A edited for length and clarity.