parakeet ?

He probably is still missing her and probably has not gotten used to the new female yet and likewise, the female is still getting used to her new cagemate too. They will eventually get used to each other but it may take a few weeks or more.

I once had a cockatiel who lost his mate to eggbinding. It was so very sad because I took her to the vet and unfortunately she had to be euthanized. Since they were so attached to each other, I asked the vet if I could bring her home in a box so that the male could see her and be aware that she died. When I brought her home in the shoebox I brought him out of the cage and allowed him to perch on the side of the open box. When he saw her he tried to preen her little crest and nudge her, trying to get a response. After about 5-10 minutes of allowing him to stand guard on the side of the box I took him back to the flight cage with the other birds. As I walked away from the room where the female had been in the box he kept calling to her trying to get a response - this brought me to tears.

After that he remained in the flight cage with all the other cockatiels (about 10 others, boys and girls) but he never interacted with any of them at all until a few years later, a friend of mine was looking for a mate for her new female cockatiel. I told her that I had a few single males she could consider buying so I brought him and the other males into the living room so her bird and the boys could interact and we would find out which one might work well with her bird. As soon as we let her bird out to interact with the boys, her bird went right up to the lonely male and started checking him out. He perked up right away and immediately started chirping, chattering and whistling in her face! It was as though he thought his old female had returned and he was so happy I was again brought to tears and told my friend that this had to be the boy she took home because I had not seen him have that much interest in any other bird in the past two years. Her bird did not look anything like his old mate but he sure was happy with her anyway . . . and they lived happily ever after!

He might still be getting used to the new female,

Don't drop her in the same cage with your male right away, put her in a small temperary cage beside your male budgie and let them see and get used to each others calls. After about a week or 2 then add the female in and see how they act towards each other. Budgies DO have a very good memory as for an exsample - My female budgie likes me better than my brother so she remembers what I look like and how my voice sounds. Birds are ALL very smart, some more than others lol.

No they have very short memories. Mine died and the female was very sad and wouldn't eat for a while but then got over it quickly don't worry about it just make sure to give your bird attention

I think in time he will forget. Try adding a new treat stick or millet spray, or something else new that's interesting to take his mind off things. Some birds love music, and leaving a radio on for them is common practice.

Probably a combination of sad and shy of the new girl.

he will forgot~