1. The change from the low intensity mobbing call 'duck' to the high intensity call 'tix' involves the addition of what is probably the first overtone and a slight rise in pitch of the fundamental tone. The first change has a lower threshold than the second. 2. Bouts of calls are usually associated with flights and commonly begin a little before take-off. 3. At or near take-off there is a change (the 'flight effect') which tends to initiate calling if it has not begun, and to accelerate it and/or cause the change from 'duck' to 'tix', if it has. 4. Experimental prolongation of flight prolongs calling and promotes the change to a 'tix' type of call. 5. Bouts of calls given when perched are accompanied by activity of the system controlling flight, which does not reach the threshold for take-off.
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| å ¨é¨æé´ | è¿å»ä¸å¹´ | è¿å»30天 | |
|---|---|---|---|
| æè¦æµè§æ¬¡æ° | 407 | 76 | 8 |
| å ¨ææµè§æ¬¡æ° | 91 | 0 | 0 |
| PDFä¸è½½æ¬¡æ° | 19 | 0 | 0 |
1. The change from the low intensity mobbing call 'duck' to the high intensity call 'tix' involves the addition of what is probably the first overtone and a slight rise in pitch of the fundamental tone. The first change has a lower threshold than the second. 2. Bouts of calls are usually associated with flights and commonly begin a little before take-off. 3. At or near take-off there is a change (the 'flight effect') which tends to initiate calling if it has not begun, and to accelerate it and/or cause the change from 'duck' to 'tix', if it has. 4. Experimental prolongation of flight prolongs calling and promotes the change to a 'tix' type of call. 5. Bouts of calls given when perched are accompanied by activity of the system controlling flight, which does not reach the threshold for take-off.
| å ¨é¨æé´ | è¿å»ä¸å¹´ | è¿å»30天 | |
|---|---|---|---|
| æè¦æµè§æ¬¡æ° | 407 | 76 | 8 |
| å ¨ææµè§æ¬¡æ° | 91 | 0 | 0 |
| PDFä¸è½½æ¬¡æ° | 19 | 0 | 0 |