ML, good for you for fostering! I am fairly new to chihuahuas too, but just got my second one. They are really sweet and special - now I am one of those crazy small dog people lol!
I agree about the harnesses - collars are not a good choice for most chi’s - they are too strong on thier windpipe. With the harness, make sure it is adjustted snugly so they can’t slip out of it. Had that happen a few times with my first chi and it is scary because chi’s tend to get scared and won’t let you catch them in certain circumstances.
Most chi’s tend to shake from nerves and/or the cold. I keep poloar sleece blankets on a couple of chairs when I am not home so they can snuggle in. Mine wear sweaters or little sweatshirts when it is cold out.
They can be finicky, but tend to be chow hounds about treats and snacks so be careful about that - they get fat easily.
My two love to play and are real farm dogs. I have 3 big dogs and they all get along great. Do watch out for owls and other predators - I NEVER leave my chi’s out in the yard without me due to the birds.
My older chihuahua is great with other dogs, but not good when people come to the house. He barks and will try to circle around and nip their ankles. I usually leach him and he is fine once the person is actually in the house and the other dogs are done greeting them.
I bring mine out on the weekends to Petsmart to keep them socialized. If someone wants to pat them, I tell the person that they are shy and to let the dog come to them. I never force the dogs to be patted - I think that would scare them more. I do sometimes have the person offer a treat (I usually have small treats with me). Mine are fine with people out and about, but will never be the super friendly types that a lab puppy or some other breeds are…
Here are my 2:
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