Which of the following can be signs of pain in birds?

All of the listed signs can be indicators of pain in birds, making the selection comprehensive and accurate.

Vocalization can often change in an injured or stressed bird, as they may express discomfort or pain through specific calls or changes in their usual vocal patterns. This behavioral change alerts caretakers to possible underlying issues that require attention.

Sudden tensing of muscles, often observed as a stiffening posture or a refusal to move, is a physiological response to pain. Birds may instinctively react to pain by tensing their muscles as part of their fight-or-flight response, which can also manifest in their overall demeanor and behavior.

Tachypnea, or an increased respiratory rate, can indicate stress or pain in birds. When a bird is in pain, it may have difficulty breathing due to discomfort or anxiety, leading to a rapid breathing rate. This change in respiratory behavior is often accompanied by other signs that warrant further assessment by a veterinarian.

Considering these factors, all the provided signs collectively indicate that a bird may be experiencing pain, making the inclusion of all options in the correct answer appropriate.