508 Herr E. Hartert on the 



three in number, but in East Prussia four are often found. 

 According to my observations the male assists the female in 

 incubation. 



Falco iESALON, Tunst. 



Not very rare during the migration-period, chiefly in Octo- 

 ber. I did not meet with it in the middle of the winter. 



Falco subbuteo, L. 



Rather scarce. Breeds very late, eggs not being found 

 before the middle of June. 



Cerchneistinnunculus (L.). 



Very common. Exceptionally a pair remains during the 

 winter, then frequenting old towers or castles. 



Cerchneis vespertina (L.). 



Generally a rare visitor during migration, but sometimes 

 occurring in quantities. In September 1887 great numbers 

 passed, through East Prussia. I saw at least a hundred 

 myself, and specimens were obtained in many parts of East 

 Prussia. All those that I observed were in young plu- 

 mage ; not a single old bird was obtained or seen, so far 

 as I could make out. In the following spring, on the 9th 

 and lOtli of May, I saw a troop of five old females and 

 one male, but they remained a few days only and did not 

 breed. In 1884 I saw a pair late in May and during the first 

 days of June, but they also did not breed there. Probably 

 this species passes through much more frequently than it is 

 supposed to do. 



Pandion haliaetus (L.). 



Not rare in many suitable localities, but not found every- 

 where. Eggs are laid in the second half of May. 



Pernis apivorus (L.). 



A somewhat rare bird in East Prussia, but breeds regu- 

 larly. 



MiLVUS MILVUS (L.). 



Not rare. Arrives in March and lays its eggs in April 

 and May. If possible it takes an old nest of another bird. 



