TERNS AND SKIMMERS 263 



silences" (e.g. black-headed, lesser black-backed and kittiwake gulls), 

 is expressed in what the Marples call "dreads" and "panics." These 

 are distinct from the ordinary alarm when the sitting bird leaves the 

 nest, flies into the air for a short time, calling loudly, and then returns 

 quickly to the nest. "Dreads" and "panics" are characterised in all 

 the sociable terns at their nesting grounds by a sudden rise in the normal 

 clamour of the breeding group. It is succeeded by the whole colony 

 rising and sweeping away in a compact flock in complete silence, 

 only to return in a short time and resume their normal behaviour. 

 The movement appears to be so regimented that the observer could 

 believe that a command had been simultaneously obeyed. Although 

 dreads and panics apparently occur as a result of the visit of a human 

 being to the ternery, they have frequently been witnessed from a 

 long-established hide; therefore they cannot be considered solely due 

 to human agency — often they appear to be caused by no external 

 disturbance whatsoever. 



Tinbergen attributes the dread to a temporary re-assertion of the 

 flocking instinct, as against the dominant reproductive instinct. 

 Sometimes a flock will rise and hover over the body of a dead or 

 wounded companion; and perhaps afterwards attack it for awhile. 

 Sometimes only part of the ternery is affected by a dread. Sometimes 

 it is a flock of one species only that rises from a large ternery, thus 

 revealing the position of that specific colony. It appears that there 

 may be one individual which constantly starts and leads a dread. 

 The panic is a variation of the dread, according to the Marples, who 

 give this name to the sudden dashing about in the air of a group of 

 terns which afterwards zig-zag rapidly to earth or water in complete 

 silence, immediately flying back to the colony as noisily as usual. 

 Of the sea-terns only the little tern appears to take no part in a dread; 

 this may be due to its less colonial nesting habit. 



The apparently co-ordinated mass flights of terns are never directed 

 to the expulsion of a common enemy, such as man or another creature 

 trespassing in the territory of a ternery. But like the skuas and some of 

 the larger gulls, the individual tern will attack any trespasser passing 

 its nest. The ensuing fight with another bird may embroil several 

 other neighbours. Also like the gull, but with much greater accuracy, 

 the individual tern will defaecate upon the visitor, fouling his clothes 

 or person; and some species are extremely bold, freely striking the 

 intruder on the head (arctic and common terns). The noddy attacks 

 human beings quite savagely; this and other species will knock a 



