Hello, thanks for your question today! I am Dr. Drew, and I am a licensed veterinarian. I'll be happy to help you in any way I can.
There may not necessarily be any reason for you to be in a state of panic.
There's nothing that is specifically harmful about having a bird in the mouth,
though of course if an entire bird were swallowed, it could lead to digestive upset.
It is an option to seek veterinary care, if you wish to have an x-ray to see if the bird is in the pup's stomach,
but if not, then you'll have to watch for signs of vomiting, loss of appetite, abdominal pain, and lethargy.
I would not typically suggest inducing vomiting unless you're sure that something was eaten which should not have been.
Since you stated that you are not sure, it may be reasonable to monitor him closely for the rest of the day.
From the time I saw what looked like it might have been a dead bird on the ground and then found a feather in the dog's mouth was just a split second. Could a dog swallow a bird that quickly? Also should I give him his regular dog food?