Maternal instincts or hunger?

The neighbour's cat has had kittens agian, as she does every year, and has been keeping thme in a box in my workshop. A couple got extracted by an animal unknown but probably one of the neighbour's dogs a week or so ag. but two remain.
Ruadh has become obsessed by them, sitting by the box and staring at them. Tricia things it might be hunger but I prefer to think of Ruadh as having some form of maternal instinct. 
The cat does leave the kittens on their own when Ruadh is there so is clearly not too worried herself. Today they got an outing and spent the afternoon underneath the recliner. Ruadh as a consequence spent the afternoon there looking at them.