The Bushpea Gallery currently holds 198 photos of 66 Australian mammal species.
Go out looking for birds and you'll almost certainly find a mammal or two running, bouncing, swimming, flying, hugging trees, standing, sleeping or even, very occasionally, charging you.
Being hairy, they generally look cuddlier and more attractive than reptiles and invertebrates but there are exceptions. I've been told for example, that I'm one.
Attractive or not, (the mammals we come across that is), we photograph them, sometimes because the birds in the area have been disturbed by those mammals, sometimes because we haven't found any birds, and sometimes, just because we're fascinated by hairy things. There's not much else to do until we find some more birds anyway, so why not?