Q: can a citizen take posession of a un attended dog in public? to me this seems seizure without due process.

A: It somewhat depends upon the circumstances. Most communities have leash laws and in most places, unattended dogs wandering anywhere/everywhere on their own are prohibited. Packs of wild dogs are not good for society and how is one to know, looking at this particular dog, if it is wild or a runaway or someone's missing pet? I would think that most anyone is free to take control of an apparently abandoned animal though normally they should turn it in to the local County Animal Control or Humane Society and notify the police of the find. What should be clear is that anyone finding such an apparently abandoned dog is NOT free to just keep it and decide they now own it. If they find the true owner, they are obligated to return the pet to them. If they believe there are circumstances that should prevent the dog going back to the original owner, then they need to take that up with the local police. As for alleged Constitutional violations, to begin with they only apply to the government or governmental entity. An individual person does not deprive you of any Constitutional rights. They conceptually could steal from you but not violate your Constitutional rights. Bottom line is that you are likely to face an unsympathetic audience unless someone else has your dog; you can prove that it is your dog; and they refuse to return it to you. There are limits as to how hard/far you can legitimately complain when the owner is fundamentally at fault. Dogs are not supposed to be unattended in public. Without any human accompanying them, the dog is free to jump on people; scratch them; bark/make noise in inappropriate places; go to the bathroom with no one cleaning up; and more. All this before even getting to whether they may pick fights with other animals or humans or cause destruction of property. Hence anyone intervening to try to correct or limit the damage the unattended dog is possibly doing is normally doing a public service and filling in, albeit with the owner's advanced permission, to perform the owner's duties and to help protect the public. Life is likely to go alot smoother if you focus on complying with your legal obligations and NOT having an unintended dog in public rather than sniping about those attempting to fulfill your duty. Plus, with enough leash law violations and/or problems arising, you COULD find your property (i.e. the dog) removed from your possession (without compensation because you were breaking the law) and you could be banned from owning other pets for 5 years.