In a natural setting, male cockatoos establish and defend territories, attracting and competing for females. In captivity, without enough space or appropriate territories, the presence of multiple females can create a highly competitive and aggressive environment. The male may become overly possessive of one or both females, leading to constant chasing, fighting, and vocalizations, making the environment stressful and unpleasant for all the birds.
Additionally, there's a risk of unwanted breeding if the male mates with both females. Cockatoos can be quite prolific breeders, and producing multiple clutches can place undue stress on the female(s) and drain their physical resources. Over time, this can lead to health problems and a decrease in lifespan.
Therefore, to avoid potential conflicts, it's generally recommended to keep cockatoos in pairs, with one male and one female, to provide a stable and harmonious living situation.