Intelligence in Nature - Jeremy Narby [63]
a second, so even a slight hesitation by other birds increases the likelihood that the sentinel will reach the arthropod first. Using the following criteria, I classified 106 of 718 alarm calls as true or false: true if simultaneously I saw a hawk-like object fly by or if flock species subsequently alarmed and froze for several minutes, and false if the sentinel flew into the open after a falling arthropod while I simultaneously had a clear view of the entire region within 20 m of the bird and could thus eliminate the possibility of a passing hawk. Sentinels remained motionless on partially concealed perches when giving true alarms, whereas when giving false alarms, they flew with other birds into the open in pursuit of flushed arthropodsâ (p. 144). Dugatkin (1999) comments on Munnâs observations: âRemarkable as this story is, deceptive alarm callers are not all that smart. When giving a genuine alarm call, sentinels typically remain motionless on partly hidden perches. But, when emitting false alarm calls, alarmist birds fly out in the openâa very dangerous thing to do, if a predator is truly in the area. Despite being intelligent enough to deceive others, they havenât really mastered the art of chicanery, for if they had, theyâd not only voice a call but act the way scared birds act when danger is about. Of course, it is possible that natural selection has not favored such acting skills, since merely giving the call works so well. Yet that in many ways begs another question about cognitive complexity: why havenât the birds that keep getting bamboozled figured out that if an alarm caller doesnât head for the hills himself, then he is probably faking it? We simply donât know, nor has anybody even addressed the problemâ (p. 124). Munn (1986a) writes: âWhile knowledge of the development of the use of alarm calls by the sentinel species might assist in clarifying the type of thinking, if any, which is employed by the bird when making the call, certain facts suggest that some amount of thinking is involved in sending and receiving the alarm call. That the sender thinks about what its call implies is suggested by one occasion in which a Thamnomanes schistogynus began to give the false alarm as it flew out after a falling insect that was being chased by another bird, but once it became clear that the other bird had captured the insect, the calling antshrike immediately graded its call into a wider-frequency nonalarm rattle call, which functions like a rallying call for other birds. The bird apparently realized that the alarm call was no longer appropriate and switched to the nonalarm call in mid-vocalization. Additionally, the fact that both sentinel species use the false alarm calls more frequently when feeding fledglings might suggest that they are âsavingâ this trick for a situation in which they are genuinely desperate for extra food. The behavior of receivers suggests that they recognize that one potential meaning of the alarm calls is the approach of a predator. These birds are not simply startled by an alarm callârather, often they look in the direction of the call. This reaction is especially obvious when birds already in thick cover jerk their heads quickly and look in the direction of an alarm. This looking implies that alarm calls are interpreted as meaning something more like âhawk!â than like âjumpââ (p. 174).
Â
P. 15: CROW INTELLIGENCE
Savage (1995) writes: âBut can a mere bird brain really cope with this intellectual challenge? How can birds learn and remember without an elaborate cerebral cortex? By the 1960s, neurologist Stanley Cobb had the answer. The avian brain, he discovered, is built on its own unique plan. Instead of relying on the cortex, birds have developed another part of the forebrain, the hyperstriatum (which mammals lack), as their chief organ of intelligence. The larger the hyperstriatum, the better birds fare on intelligence tests. Crows, ravens and magpies are all at the high end of both scales. And, as other investigators have since determined, corvids are also tops among birds for overall