- Nest-building behavior. Budgies will start collecting nesting materials, such as twigs, grasses, and even small pieces of paper, and carrying them to a potential nesting site. They may also start arranging and organizing these materials inside the nesting box or chosen nesting site.
- Courtship behavior. This includes the male budgie feeding the female, regurgitating food into her mouth. The male may also sing and display his feathers to the female in an attempt to win her over.
- Increased vocalizations. Both male and female budgies may start vocalizing more frequently and loudly as they approach the breeding season. This can range from soft chirps to more elaborate songs.
- Mating. If you observe the male mounting the female and successfully mating, it's a clear sign that the pair is breeding.
Remember, not all pairs of budgies will choose to breed, and breeding behavior can vary among individual birds. If you're considering allowing your budgies to breed, make sure you're well-prepared to provide them with proper care and housing, as well as to find responsible homes for any resulting chicks.