what made the chicks flutter their wings and shriek loudly
Answers
Answer ...
Many birds produce tonal flight sounds that are attributed to air flowing over or through the wings or tail (Bahr 1907; Bostwick 2006; Clark & Feo 2008). Four complementary lines of evidence suggest that these sounds are not vocal: (i) production only during a particular mode of flight, (ii) experimental elimination of sound production in live birds (Miller & Inouye 1983), (iii) experimental reproduction of flight sounds using isolated feathers (Bahr 1907; Carr-Lewty 1943; Reddig 1978), and (iv) inference of feather function based on an unusual shape. For instance, male Red-billed Streamertails (Trochilus polytmus; hereafter, streamertails) have greatly elongated fourth tail feathers (hereafter, streamers) and make a distinctive ‘whirring’ sound during various modes of flight (hereafter, the flight sound). Females and subadult males lack streamers and do not make the flight sound, causing ornithologists to attribute the production of the flight sound to the male's streamers (Allen 1961; Bond 1961; Downer & Sutton 1990; Tyrrell & Tyrrell 1990; Evans et al. 1994; Schuchmann 1999; Raffaele et al. 2003). However, inferences based on feather shape alone can be misleading. Here, I show that the tail streamers do not produce the sound; it is actually produced by the primary feathers eight