55 



the eel-fishing industry. In 1916, at the suggestion of Mr. 

 William C. Adams, then chairman of the Massachusetts Com- 

 missioners on Fisheries and Game, I visited three large heron- 

 ries and collected and examined much partially digested ma- 

 terial. The food consisted largely of fishes not considered of 

 much value for human consumption, the principal species being 

 the alewife. At a heronry on Cape Cod most of the food con- 

 sisted of squids. The only valuable food fishes found were one 

 eel and one pickerel. 



Under the circumstances these herons could not be considered 

 as detrimental to the fisheries at that time. Whether or not 

 they were beneficial depends largely on the food habits of squids 

 at that place and season. Squids destroy quantities of her- 

 ring spawn. Probably all American herons and bitterns attack 

 grasshoppers and locusts, and such caterpillars as cutworms and 

 army worms, whenever these insects become numerous in or 

 near their haunts. The larger species destroy field mice also. 



The brown pelican on the Florida coast lives mainly on men- 

 haden, an inedible fish, and both the brown pelicans and white 

 pelicans on the western plains feed more or less on grasshoppers 

 and locusts when these destructive insects are abundant. The 

 notion that fish-eating birds are seriously destructive to food 

 fishes arises from the fact that birds are conspicuous when 

 fishing, while porpoises, predatory fishes and other creatures 

 that devour food fishes and their eggs and young work mainly 

 beneath the surface, out of sight. Probably most if not all 

 fish prey on other fish or their spawn, and if we were to at- 

 tempt to increase the supply of valuable fish by killing off their 

 enemies, we should have to destroy most of the denizens of the 

 ocean. 



As an example of the useful habits of fish-eating birds, we 

 may note those of the fish ducks, the sheldrakes or mergansers. 

 These birds at times feed more or less upon trout, but they also 

 destroy the enemies of trout. Minnows are eaten by mergan- 

 sers, and minnows are said by good authority to devour large 

 numbers of trout eggs. Trout fry, too, are destroyed by 

 mosquitoes, which pierce the brains of the little fry when the 

 latter come to the surface and leave them floating dead upon 

 the current; but quantities of mosquito larvse are destroyed by 



