you seem to be fixated on the notion of consciousness as being "consciousness sufficiently similar to a human that I would interact with it as if it was a human". maybe some domesticated animals and particularly precocious apes and cetaceans meet those criteria.

In many religious and philosophical traditions though the principle of Panpsychism is the guideline. It means, approximately, that consciousness is an inherent building block of reality and some form of consciousness is an emergent phenomena of just about any sufficiently complex system. This posits the existence of many forms of consciousness that are utterly alien to human consciousness and that we could not readily interact with.

Not great, but the best we have at the moment: https://en.wikipedia.org/wiki/Mirror_test

I don't understand how my cat reacts to a mirror. He notices me in a mirror, but how come he doesn't react to seeing himself, either "hey that's me" or "what's that other cat doing here!?!"

You don't need an objective measure. An approximate one is already better than just "optimising for human happiness".

And I guess you do what I proposed already anyways: The suffering of a dog or a horse is probably also - to some extent - your concern. The suffering of a piece of rock probably less so. Should we learn that rocks can feel pain, too (granted this is unlikely), we should update our morality. It's also part of most countries' laws to prevent unnecessary suffering of animals. And this is all based on the assumed degree to which they are able to suffer. You will get fined for torturing a dog; you won't for torturing a mosquito.

Careful - fancy thoughts: I could imagine that we will update our morality regarding plants one day (given that we see more and more evidence that they communicate with each other, send stress signals etc.).

Sometimes you have to act before all possible information and understanding is in.

The odds are overwhelming at this point that many, many non-human animals have consciousness very much like our own.

That's a very nice sentiment, but aside from the obvious (dolphins, a few whales, some primates, and elephants) do you have any sort of proof or justification for this statement? "Many many" is a very strong claim.

The two "many"s was a typo.

You just named "many", as far as I'm concerned. How many proven examples do we need before we start to think that the only reason we don't know of 1000s more is because of lack of research?

You also forget cephalopods. Oh, and Magpies and some other birds.

Do you have an objective measure of human consciousness?

Having a discussion about what constitutes consciousness likely meets whatever criteria you can come up with handily.

Having a theory of mind is another one of those big ones. The problem is differentiating true awareness of the concepts of 'self' and 'other' from rote instinct - is a leopard stalking a gazelle aware of the gazelle as an entity and takes actions accordingly, or is it merely reacting to known sets of stimuli?

Exactly. Being able to discuss what constitutes consciousness meets criteria handily because having a clear concept of self and other as well as being able to reason about that are both prerequisites.

It's sort of like the old question of what constitutes pornography? The border is fuzzy and unknown (in this case because people have different standards), but it's fairly easy to construct a case where the vast majority agree it's on one side or the other.

Optimising for human happiness includes not decimating ecosystems that we depend on to survive.