The BBC's Springwatch website recommended putting out grated cheese for birds.  However, cheese is made from milk.  As birds are not mammals, would they be able to digest cheese?

Hi Kate, good question. I personally wouldn't put milk-based products out for birds because I'm not sure that they could cope with the lactose, but that's a "better safe than sorry" approach since I really don't know the answer (there not being any hard research on lactose tolerance in birds).

Bluetits will take the cream from the tops of milkbottles by pecking through the foil lid, and this behaviour has been going on for 20 years or more and some bird breeders will give their birds milk, but I still expect that the lactose would cause mild digestive problems for many birds.

Last edited by Paolo Viscardi (20th Jun 2007 13:12:50)

Birds do indeed lack lactase (the enzyme that allows digestion of lactose), and a reasonable amount of this in their diet would theoretically give them digestive problems. However, cheese is really low in lactose - in fact the more familiar cheeses like Cheddar and so on virtually lack it entirely - and cheese doesn't (so far as we know) give birds any problems. In fact cheese is widely said to be good for both wild and captive birds, being a rich source of fat and calcium. Certainly wild birds (particularly thrushes) seem to prefer it over types of food, and it is also enjoyed by captive birds like parrots.

Some types of food are, apparently, toxic to birds, including caffeine, chocolate and avocados. Quite why anyone would be putting coffee out for the birds is a good question however.

Birds, and indeed people who can't digest unprocessed milk, can take advantage of other bacteria doing the work for them in the production of milk-based products such as yogurt and cheese. The various strains of bacteria used in the making of such products have already digested the lactose before the bird or person eats the cheese.

To find out more about this have a look at this page by a chemistry and biology professor in the US who makes lots of products at home. I've had a go at some of the projects with mixed success, but for any teachers on the site, these are fantasic 'edible science projects'

http://biology.clc.uc.edu/Fankhauser/Cheese/Cheese.html

"Hope is a duty from which palaeontologists are exempt."
David Quammen