ON THE FEEDING-HABITS OF FISH AND BIRDS. 47 



Some Observations on the Feeding-habits of Fisli and Birds, with special 

 reference to Warning Coloration and Mimicry. By J. C. Mottram, 

 M.B. (Lond.). (Communicated by Prof. E. B. Poulton, F.R.S., 

 F.L.S.) 



(Plate 5.) 



[Read 1st March, 1917.] 



Material for this paper has been extracted from a journal, wherein are 

 recorded observations of the riverside habits, and especially the feeding- 

 habits, of fish and birds during the years 1909 to 1915 inclusive ; they 

 were not collected with any special object in view, and were made in the 

 British Isles and during one season in New Zealand. 



The paper is divided into two parts: the first deals with observations 

 which have a bearing on the hypothesis of Warning Coloration ; the second 

 with those which appear to throw fresh light on certain aspects of Mimicry. 



PART 1. 



Feeding-Habits o/Salmo fario, Linn, (the Brook Trout). 



The fish is strictly carnivorous. Its food consists of small fish, crustaceans, 

 molluscs, annelids, aquatic and floating insects. Vegetable matter was found 

 on only very few occasions out of five to six hundred autopsies. In New 

 Zealand, on one occasion, the stomach of a fish was filled with Spirogyra, 

 Link ; subsequently it was proved that the fish took the weed in order at the 

 same time to capture a small Trichopterous larva. The yellow bloom of the 

 furze, Ulex europceus, Linn., was also taken on account of a small orub 

 probably Tineina. In this country pieces of Ribbon-weed, Potamogeton, 

 Tourn., are taken in order to obtain Simulium, Latr., colonies, either larva or 

 pupa. Sometimes small pieces of wood, of grass stems, and grass and other 

 seeds are found in the alimentary canal ; these will be accounted for 

 subsequently. 



When the fish' are feeding on floating insects conditions are particularly 

 favourable for detailed observation : the insect can be clearlv seen and cannot 

 be taken by the fish without a marked disturbance of the surface. The 

 under-water feeding is less easily observed, but examination of stomach and 

 intestinal contents gives reliable information. 



The feeding-habits depend to a large extent on the quantity of the food- 

 supply. In waters where food of all kinds is abundant, as in many chalk- 

 streams, the fish, although they have the choice of many kinds of food 



