There can be several reasons why an adult African grey parrot might suddenly stop talking after years of speaking normally. Some possible explanations include:
Health Issues: Parrots, like any other living beings, can experience health problems that affect their ability to vocalize. Respiratory infections, respiratory distress, or other medical conditions could impact their vocal abilities.
Stress or Anxiety: Changes in the environment or the parrot's routine may lead to stress or anxiety, which can manifest as a loss of vocalization. This could include changes in their living conditions, the presence of new people or pets, or disruptions in their daily interactions.
Trauma or Fear: Traumatic experiences, such as a fright or a negative encounter, could result in the bird becoming wary or fearful, leading them to reduce their vocalizations.
Lack of Stimulation: Parrots need mental and physical stimulation to maintain their talking abilities. A lack of mental enrichment or social interaction might cause them to lose interest in talking.
Hormonal Changes: Hormonal shifts in parrots, particularly during breeding season, can affect their behavior, including their vocalizations.
Aging: As parrots age, they might naturally experience changes in their vocal abilities, just as humans might notice changes in their voices over time.
Regarding your question about why they don't all start talking again, even though they are capable of doing so: Talking in parrots is a learned behavior. While some African grey parrots are known for their exceptional mimicry abilities, not all individuals will necessarily have the same inclination or interest in talking. Each parrot is unique, with its own personality and preferences.
The capacity to talk doesn't guarantee that every parrot will do so consistently or throughout their entire life. Talking requires regular practice, motivation, and reinforcement. If a parrot loses interest, faces stress, or simply isn't in an environment that encourages vocalization, they might stop talking.
In some cases, with patience, training, and a conducive environment, parrots may start talking again. But it's important to note that there are no guarantees, and individual variations play a significant role.
If a sudden loss of talking or any significant behavioral change occurs in a parrot, it is advisable to have them examined by a qualified avian veterinarian to rule out any underlying health issues. Additionally, providing mental stimulation, social interaction, and a nurturing environment can help encourage the parrot to engage in vocalizations and maintain their talking abilities.