Yes lard – a bad choice I have found. As you have noticed the birds come up covered in the stuff. I found the cheapest Tesco (or other brand) suet much better for the purpose. (IMO)
I used clean yogurt pots to form the shape. With pan on stove, melt suet but don’t get the fat too hot. Add your preferred feed to soak up the fat then transfer to the pots, put out to set and hey- presto, bird cakes.
It is even possible to add a string though the base so they can be taken out of the pots and hung up.
To make round balls like the one you can buy you could spoon some into quality plastic bags when it’s cooled down a little. You can mould them to shape before they set.
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