Family STERNIDAE. 



Sterna fluviatilis Naumann — Common Tern. 



(Plates 174—176, fig, a-1). 

 (Snoiickaert : Avifauna Ncerlandica, p. 115, No. 274). 



Colour of surface of shell : 



Colour of spots: 



Average dimensions: 

 Average weight of shell : 

 Texture of shell: 

 Shape: 



Nest and its site: 



Number of eggs : 

 Breeding season: 

 Duration of incubation : 

 * Remark: 



ranges from pale green or bluish white, and 

 greyish or greenish to umber yellow, in 

 various shades. * 



brown, in various tints ; underlying spots show 

 through purplish or grey. 



41 X 30 millimetres. 



about 1 gram. 



granulated very finely, evenly and smoothly. 



varies from broad blunt oval to pointed 

 oval; sometimes pyriform. 



on the ground, in a little hollow which is 

 sometimes lined with dry vegetable mate- 

 rial. (Breeds in colonies). 



generally 3. 



May— June. 



about 18 days. 



Mr. J AC. F^. TuYSSfi ') found in most of the 

 clutches in separate nests the mutual dif- 

 ference between the eggs of one clutch 

 to be much less than in those in colonics. 



') See: Jac. P. Thysse and R. Tepe, „Het intieme leven der Vogcls" 

 (Haarlem, 1906) p. 9. 



