Thank you JayBay for this tidbit of knowledge that you shared with us...always very interesting
Hi Evelyn. :-) Well, it appears that little bird just tipped the scales for your dog and she's obsessed with finding him. Since she isn't hearing you when you call her, it's time to use the leash to redirect her brain. Put some small tasty treats in a pocked and take her out in the garden with the leash on. As soon as you notice her attention leaving you, correct her with a pop-release of the leash. Call her name, if she doesn't respond, correct with the leash and the nano-second that she looks at you, give her the treat.
It will probably also help a lot to take her on long walks away from the house. She's exhibiting frustrated and obsessive behavior, and a change of scenery can work wonders for that - particularly if you keep it up every day. General rule of thumb on a walk is that YOU run the program, not your dog. She doesn't get to run ahead of you on a 25 foot flex leash, keep her at your side or slightly behind. You can also occasionally do the name response exercise with treats to help keep her attention on you. If she walks nicely for a good 10 minutes or so, then she can go a bit ahead and have a sniff around. Good behavior gets rewarded. Ask her to sit every so often when you're walking. The second her rear end hits the ground, give her a treat and praise her. All these things will help her to refocus her attention where you want it - on you.
All dogs need a job of some sort, and some dogs need a job more than others. If they aren't challened physically and mentally, that's when you see these kinds of obsessive behaviors crop up. Sadly, it's the smaller dogs who get the most neurotic because most people assume they aren't capable of working and get treated like a piece of china on a shelf. They may be small, but they're still dogs and have the same needs as any other dog. Dogs need to travel. It's part of their genetic makeup. Working with their abilities by walking every day satisfies both mental and physical needs.
Another thing you can do with her in the back garden is help her to use her nose and her brain in a game of hide and seek. Take a hollow Kong toy and freeze peanut butter and cheese inside it. Start by playing fetch with it. She'll quickly learn to recognize what's coming up when she sees it. Have someone else hold her on the leash, and let her see you "hide" the toy. Release her and she'll go right to it instead running off to find the birdie. LOL! As she gets better at the game, you can make it more challenging by hiding it somewhere and not letting her see it. Trust me, her nose will lead the way. :-)