376 SAUKOPSIDA (BIKDS). 



erratic manner, the so-called " gipsy-migrants," which leave one 

 district for another owing to scarcity of food, but have no fixed 

 place of migration. This form of movement we see in Tits 

 {Paridii') and "Woodpeckers (PiriiJn;). 



Those birds, such as the blackbird and thrush, which are 

 with us throughout winter and summer, are called "residents." 



Fossil birds present many peculiarities. Some (OdontornWies) 

 have teeth; others of older date have distinct lizard -like 

 characters, such as the feather-tailed Archeojit^ryx. 



