chasing birds

[hfojvt]

I notice that Jack, my older beagle, will chase birds out of the yard and continue to bark at them if they are close by.

Yet he seems to leave the robins alone. So apparently there is a certain type or species of bird that he does not like.

Anybody have any ideas what bird species that would be, and why he doesn't like them? Or maybe he does like them - with ketchup.

Probably I need to try to get a picture.