As for textbooks, the best thing to do would be to search online to see what can be ordered and shipped to your country.
Research on wild parrot flocks is definitely lacking. There are so many species and not enough funding or interested researchers. It is widely believed that captive raised parrots become sexually mature at a much younger age than wild parrots. This is based on observations of when wild parrots start breeding versus captive bred. However, we have learned that it is best to prevent young captive birds from breeding because there is still some physical development going on, and more importantly emotional development. Experienced Cockatiel breeders who breed their birds for show and quality will not even consider pairing their birds until they are a minimum of two years old. They have learned that younger birds have issues, as I have described before. Some breeders who breed for profit for the pet trade will let their birds breed as early and as often as possible. This is why the quality of birds like cockatiels, budgies, lovebirds & finches has gone down, and the lifespan of these birds is much shorter than it should be. Most likely the captive bred birds become mature at too young of an age due to what we feed them and the fact that they do not have the challenges that wild birds have or the changing seasons that wild birds experience. You have to also keep in mind that changing seasons means changing diets, so a wild parrot may eat entirely different foods throughout the year, depending on the season. We know the abundance of foods is one hormone trigger, and quite possibly the type of food in the wild contributes to hormones being active. In captivity, certain foods can definitely contribute to hormonal behavior and unwanted egg laying, as can offering an abundance of foods. In the wild, all aspects that make up the breeding season must be in place before the mature birds’ hormones are triggered and mating begins. Again, this is warmer weather, longer days, abundant food – most likely even certain types of food, and a safe place for nesting. Nature controls their hormones – as I said before, if wild cockatiels were hormonal year round, and were constantly trying to mate, the species wouldn’t survive. It’s all about high numbers and the best chance of survival when you have a prey species. There are other prey animals that follow similar schedules – most antelope species breed at the same time of year, and manage to give birth within days of each other. This means they have more safety in numbers. Half or more of the young may get taken by predators, but a few will survive. When one is born out of season, it is much less likely to survive when it’s the only baby in a herd of adults.
Your male is constantly hormonal because of the way he is living. You need to make the changes I recommended, and his hormones should settle back down so he can be a happy, normal cockatiel. Right now the poor bird is not in a natural hormonal state. He needs changes to turn off his hormones, just as wild cockatiels experience. He needs structure, a routine, less light, less freedom & roaming, no contact with the budgies or other birds right now, moving his cage to other places in the room weekly, rearranging toys in his cage. For captive birds, it is the owner’s responsibility to simulate seasonal changes when your bird gets stuck in a hormonal state. He needs to learn how to entertain himself in his cage – play with toys or forage. There are plenty of different foraging exercises you can offer him. In the wild, he would spend most of his day foraging for food. Go back and review the information I have given you. Understand that his experience with hormones is not what happens with wild birds. A wild cockatiel would have already mated and would be busy helping his mate with eggs or chicks. And then the season changes, breeding season ends, and the focus shifts back to his own survival and that of his mate and chicks. Hormones and the urge to breed will remain dormant until the next breeding season when all of the triggers come back into play.
As for training him not to chew on things you don’t want him to, all training needs to be done with positive reinforcement. When he chews on something he shouldn’t, give him something different to chew on. Keep different toys available and offer him a toy instead. If he chews on the toy, reward him with a treat. Repeat the process if he turns back to your clothes. This is where foraging training can be a good diversion. Here is a link to our foraging webinars and ideas: