Okay, tricky situation.
I agree from the photo that it's probably a variety of goldfinch or sisken or something similar. Once your bird is mature, a photo will help us identify the species. It's really a process of looking at the birds in your area and performing a process of elimination (while understanding that males, females and juveniles all look different. And some look different at different points in the season too. So while ensuring Peep is mature, it eliminates juveniles from the equation and we can focus on just mature males and females.)
This is where working with a rehabber will be helpful. They've seen all sorts of local birds in all stages of development.
You must understand that "Finch" is a really broad category. It literally includes hundreds of different species from nearly every continent. Saying you have 2 finches is a bit like saying you have 2 dogs. They both have the same name and the same basic structure, but the social and care needs can vary dramatically. (And genetically speaking, I believe dogs are much, much closer genetically than finches from various parts of the world. So while dogs look more diverse visually, I
believe they're much more closely related on a genetic level than finches. I'm sure one of the science folks will chime in if I'm wrong. LOL)
So just keep that point in mind.
Dylan (@Sheather) touched upon the primarily dilemma of trying to blend Peep with a society finch.
They're from two different species families, who've evolved thousands of miles apart. In nature, they would never meet.
They don't speak the same language. I'm not positive on the species of Peep, but it's likely that he's of an entirely different family than the finches you would get in a pet store (which are from Asia, Africa or Australia.)
Birds in the same geographical region have learned to co-exist. Since these two would never see each other in nature, it's a total crapshoot. It's a bit like putting a raccoon and a wallaby in a room and hoping they'll get along. It's total chance.
I was a licensed rehabber for about 10 years in the Boston area. As such, I worked with many people in your exact situation.
I'm not going to tell you to give up your bird that you've raised and clearly care for a lot. I learned long ago that that's just counterproductive and not-so-realistic, especially because many rehabbers are constantly at capacity. There's no real funding for it. Most rehabbers are independent as I was and they pay for everything out of pocket and hope for an occasional grant or donation. The few actual centers that exist are non-profit and most are overwhelmed. I know this from experience. So most rehabbers are willing to work with individuals like you to help you give this bird the best possible life.
Realistically speaking, this bird's chances of being released are remote. As a rehabber, birds who are candidates for release get minimal human contact in favor of letting them interact with other birds. As soon as the bird could eat independently and was fully feathered, it would go outdoors into one of my habitats -- large pens for lack of a better word. One section was in the forest; one was a more field-ey prairie sort of set up. They were all heavily planted with local plants that would be a food source. I'd spend hours each week harvesting plants that would serve as other natural sources of food and re-planting the habitats seasonally to reflect different seasonal food sources for the residents of that habitat. They had a feeder station, as bird feeders do exist in suburbia, but the environment was such that they did a lot of foraging. There were no perches or bird houses, but sticks and branches and little natural alcoves and so forth where they could roost.
It was a habitat designed to get them self-sufficient and ready for nature.
Your bird hasn't encountered any of that and Peep probably hasn't done much foraging either. So release would be impossible currently. He would definitely come right back, as it would be overwhelming and frightening and unfamiliar. If he didn't return straight away, his chances of surviving would be remote. He would likely live off of bird feeders. It's a bit like taking an city kid and putting him in the wilds of Montana and hoping he'll survive. He might. If he's lucky.
Peep would have to live in a transitional habitat as I had, where he could learn to forage and live amongst other local species. But even so, it's a 50-50 chance as to whether he could successfully live in the wild. Some are just too tame. And the older he gets, the more unlikely successful release becomes. This is especially true of a single bird of a social species. Some are socially inept due to lack of social exposure and this makes it impossible for them to live within a flock, which dramatically reduces chances of survival.
So in terms of options for Peep...
- You could surrender him to a rehabber with a transitional habitat. He may be release-able someday. If not, he can live as part of the transitional habitat permanently. Resident birds are an important part of a transitional habitat as they help the habitat more closely mimic nature.
- You could keep him as a pet, with the understanding that he will always have special needs. Social needs will be the most challenging, as all finches are very social by nature.
I would forget about the society finch as a friend. Keep him if you enjoy him (though I'd get him at least 1-2 friends of his own kind because society finches are, as the name implies, extremely social.)
Keeping the society in an adjoining cage will be nice for Peep, as birds simply weren't created to live in a void. They're always around other birds, even if they don't get along in the same cage.
Once you identify Peep's species, you can identify some birds that may be a nice companion. Chances of finding the same species may be slim, but you may be able to find another rescued bird in a similar situation.
This is where a rehabber can help. I'd get calls from people in your situation All. The. Time. Many were looking for help/advice; others were seeking a permanent home for their bird.
While a licensed rehabber cannot give you one of their birds, they
can pass along contact info for another private citizen who has a native species that needs a home. Of course, this would require additional commitment. But it's generally worth it when the species are compatible, because they can form a bond and fulfill each other's social needs. And a rehabber can help you determine a few local species and any non-local species that would be compatible with him.
(That dovetails with the third option for Peep -- giving him to another private citizen who is committed, knowledgeable and willing to care for him. Someone with another bird of his species or another compatible species.)
If Peep enjoys interacting with you, I would keep up with this because it's likely that yours will be the only meaningful relationship he ever forms. Finches are extremely social and in many ways, you will become his world; his everything. You have to be prepared for that and all that this entails.
I would *definitely* revamp his cage to be more natural. I would get some live, potted plants (bird safe) from your local environment. I would get some sticks/branches in place of traditional perches.
I would offer a little shallow dish of water for bathing.
You could create foraging bins --- a large, shallow tupperware (the type used to store cupcakes) with some little stones, small sticks and timothy hay or natural grasses (harvested from an area without pesticides/chemicals). Then sprinkle seeds and other foods in there and he can forage for them.
I'd feed a VERY varied diet too, just as he'd have in wild.
Once you know his species, you can harvest local foods that he would eat naturally as a nice supplement.
Here's a good general list to get you started:
http://www.petfinchfacts.com/finch-diet ... for-birds/
If possible, I would allow him time to fly outside of his cage throughout the house (though you would need to ensure it's safe. No other pets. No small areas behind dressers/desks/furniture where he could fall and get stuck.
Keeping a local species is virtually always illegal, but generally, nobody is going to bother you. The key is finding a vet who is willing to work with you in the event he's sick.
It's also absolutely essential to find a local rehabber who can serve as a resource for you -- someone who's familiar with this specific type of bird in a captive environment.
They can also offer additional advice on replicating a natural environment for your bird, diet, etc.
I think once you adorn his cage with foliage and branches, he'll be much happier. Once you know the species, you can revamp his cage to mimic the exact environment where he would live (some live in prairies; others forests. It varies.)
A species ID will also enable you to give him some nesting materials. Some enjoy an open nest, others a hooded nest, others a nest box. Some use bits of paper and tissue and leaves; others feathers and grasses and coconut husk. The wrong type of material and the wrong type of nest could definitely lead to frustration. Living in a really barren cage as he does could do it too. I suspect he probably feels vulnerable, as it's very open (though a nice size.) So adorning the cage with natural items will go a long way toward improving his life.
I'm happy to help with any general rehabber-related advice, and of course there's the forum. But a local rehabber will be key for helping you to keep him happy and healthy.
Best of luck!
I'd love to see a photo of him all grown up! That will be helpful in identifying his/her species.