IRREGULAR MIGRATION 91 



Others of the larger herons seem to have similar 

 wandering habits, as they nest in retired colonies, 

 and after the breeding season the young in particu- 

 lar range far and wide wherever they find feeding 

 grounds. The yellow-crowned night heron, also a 

 form with southern breeding range, comes north 

 casually, while in the case of the black-crowned night 

 heron, northward wandering has been proved to be 

 the usual course from records obtained by marking 

 the young. Thus young birds marked by Dr. Paul 

 Bartsch near Washington, D. C, have been taken in 

 Maryland and New Jersey, while others banded by 

 different observers in the colony at Barnstable, 

 Massachusetts, have wandered north into southern 

 Maine. The distances covered in these instances 

 are not particularly great. 



It is probable that great blue herons also range 

 northward, since a specimen of the subspecies that 

 breeds in the Great Basin {Ardea herodias treganzai)^ 

 which I banded near the northern end of Great Salt 

 Lake, Utah, was killed subsequently near Billings, 

 Montana. From available evidence it appears that 

 the post-breeding movements of these herons is ex- 

 plosive, that is, the birds spread in all directions 

 from their breeding grounds, regardless of direction. 

 It may be considered as migration governed only by 

 the availability of food and safety from enemies, 

 which is counteracted in autumn by a directive 



