Family STERNIDAE. 

 Hydrochelidon nigra (L.) — Black Tern. 



(Plate 180, fig. a-f). 

 (Snouckaert: Avifauna Neerlandica, p 116, No. 277). 



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: 



from pale to brownish yellow, in various 

 shades; also tinged greenish sometimes. 



reddish and blackish brown; underlying 

 spots show through grey. 



34.5 X 25 millimetres. 



0.65 gram. 



like that of 5. fliiviatilis. 



varies lictween pointed oval and pyriform. 



consists of dry vegetable materials; mostly 

 on floating masses of dead blades of 

 waterplants; on broken-down stalks and 

 blades of previous seasons; on the ground, 

 in wet grassland. (Breeds in colonies). 



usually 3. 



end of May, June, July; in the beginning of 

 August eggs have sometimes still been 

 found. ') 



about 17 days. 



I) See: „De Lcvende Natuur", IX, p. 137. 



