Chickadees lengthen the number of "dees" in their calls depending on the perceived threat of nearby predators based on size/speed:
Templeton and his colleagues tested the alarm call responses of a flock of six chickadees against the presence of 13 birds of prey predators, which ranged in size from the 40-centimetre wingspan pygmy owl to the 140-centimetre wingspan rough-tail hawk. They also tested responses against two mammals, a cat and a weasel. Each predator was inserted into the chickadees aviary and tethered to a perch.
After analysing 5000 recorded alarm calls, the team found that the number of “dees” in the bird’s trademark “chickadee-dee-dee-dee” call corresponded to the size of the poised predator. Smaller hunters – which pose the greatest risk – received the most vociferous response. The alert causes the flock to mob their sitting foe in an attempt to drive it away.
Templeton and his colleagues tested the alarm call responses of a flock of six chickadees against the presence of 13 birds of prey predators, which ranged in size from the 40-centimetre wingspan pygmy owl to the 140-centimetre wingspan rough-tail hawk. They also tested responses against two mammals, a cat and a weasel. Each predator was inserted into the chickadees aviary and tethered to a perch.
After analysing 5000 recorded alarm calls, the team found that the number of “dees” in the bird’s trademark “chickadee-dee-dee-dee” call corresponded to the size of the poised predator. Smaller hunters – which pose the greatest risk – received the most vociferous response. The alert causes the flock to mob their sitting foe in an attempt to drive it away.
https://www.newscientist.com/article/dn7570-chirpy-chickadee...