My cat Cassie takes on a different personality in the spring, hunting young birds which she persists in bringing back into the home with her. Is there anything that I can do to deter this behaviour, and what should I do with the birds I rescued? Last year, they both died.
Try fitting Cassie with an elasticated collar, complete with a bell which will give the birds some warning of her approach - at least for a time. But before long, she is likely to have modified her hunting technique so that she can move quietly without the bell sounding, until making her final dash at the bird, by which time it will be too late. Sadly, young fledglings are especially vulnerable because they are not usually able to fly very strongly, nor are they as alert to danger as older birds.

Scolding Cassie is unlikely to have much effect. She is returning with the birds for you in much the same way as a mother cat will obtain food cat on the prowlfor her offspring. What you can do, however, is to close off the cat flap for a time as a way of deterring her from bringing any birds indoors, at least until there is less likelihood that there will be young fledglings for her to catch easily.

Unfortunately, a cat's bite will lead to unpleasant bacteria being deposited in the bird's body, and even if the bird is not badly injured, these can set up a fatal infection. Stress can also be a major killer at first, so having rescued the bird, avoid handling it more than strictly necessary. If you need an emergency temporary home for a small injured bird, then you might be able to convert Cassie's basket, lining this with some sheets of newspaper and adding a low perch.

Birds don't have a sense of smell, and so won't be alarmed by the cat's scent here. In the case of any birds which you do retrieve and are still alive, contact either your vet or a local bird hospital who may be able to nurse them back to health successfully, and release them in the wild.