like the human voice, bird song typically contains sufficient individual variability to allow discrimination of individual vocal patterns by conspecifics. such discrimination is important to mate recognition of many monogamous species. seabirds, for example, often use vocalization patterns to recognize their mate upon reunion during the breeding season. in many colonial nesting birds, parent-offspring recognition is critical to allow parents to locate their own offspring upon return to nesting sites. cliff swallows ("petrochelidon pyrrhonota") have been demonstrated to preferentially respond to parental songs at a young age, providing a means of vocalization-based offspring recognition.