TERNS AND SKIMMERS 261 



and wind which may blow the chicks about or bury them when they 

 are in a weak condition. Sudden violent thunderstorms with torrential 

 rain may kill many. In America snakes and owls prey upon chicks, 

 and elsewhere foxes and rats are predators. 



Under normal conditions, however, the chicks grow rapidly, and 

 begin to fly when they are about a month old. When they are undis- 

 turbed by trespassing man and mammals, the chicks remain close to 

 the nesting site. But if disturbed they are apt to gather into dense 

 flocks which wander or are driven about the ternery, causing great 

 anxiety to the crowd of adults flying above them. It is a matter of 

 wonder to the observer that the chicks ever sort themselves out and 

 are claimed again by their parents. It may well be that, as with the 

 penguin and the guillemot, the lost tern chick is able successfully to 

 beg food from other adults than its parents, but this has not been 

 actually proved. Most observers agree that there is voice recognition 

 between the adults and their own young at an early stage in the 

 rearing period. 



Incubation and Fledging Periods of Terns 



Black tern, Chlidonias nigra 

 Gull-billed, Gelochelidon nilotica 

 Caspian, Hydroprogne caspia 

 Sandwich, Thalasseus sandvicensis 

 Roseate, Sterna dougallii 

 Common, Sterna hirundo 

 Arctic, Sterna paradisaea 

 Little, Sterna albifrons 

 Sooty, Sterna fuscata 



(From the Handbook of British Birds , with corrections) 



The marsh-terns have not been so thoroughly studied. As far as 

 we know their breeding habits do not differ very substantially from 

 those of the sea-terns. The small marsh-terns (e.g. the black, white- 

 winged black and the whiskered terns) frequently build their nests on 

 floating heaps of water-weeds, but more often among rough herbage 

 in marshy ground. Apparently the incubation periods in the smaller 

 marsh-terns are shorter than in the sea-terns. 



In Britain the black tern has had an unfortunate history, for since 

 the year 1885 it has been probably quite extinct as a breeding species, 

 except for an interlude in 1941-42. It is an example of the effect man 

 can have on a species by altering its habitat. Formerly it nested mainly, 



