N. lewisi Habitats and Behavior 97 



developed in a fashion similar to that previously described, and the 

 underside of the rock was devoid of encrustation. 



Retreat development in larvae was not evident, although individu- 

 als repeatedly used the same rocks. Retreat development was apparent 

 in juveniles of more than 47 mm total length. The post-hatchling larvae 

 abandoned their retreats if larger rocks were placed in the aquaria. 

 Adults, however, remained in their original retreats even when addi- 

 tional cover was provided. Exceptions to this behavior were seen only in 

 those adults that were originally provided with plastic plates alone. 

 They would move to rock cover within 24 hr after it was introduced. 



Feeding. — All captives were fed twice weekly and maintained on a 

 diet of earthworms, chopped chicken hearts, and live invertebrates, 

 along with occasional ranid tadpoles and minnows. 



Both juveniles and adults displayed two feeding techniques. Most 

 commonly, an animal would lie in wait with snout protruding at the 

 opening of the retreat. Any organism or small object moving with the 

 flowing water that crossed the shelf area stimulated an alert response 

 from the attending animal, which flared its gills and moved partly out of 

 the opening. The second feeding technique was to actively search the 

 bottom of the tank. This was done primarily at night but sometimes 

 during the day. Distinct color fading was observed in striped post- 

 hatchling larvae when they were actively feeding at night. This fading 

 was so acute that their dark sides completely faded to gray-brown and 

 were indistinguishable from the light brown dorsum. 



Both sight and olfaction apparently play an important role in locat- 

 ing food. Movement of prey could be discerned at least a meter away. 

 Movement of potential prey also stimulated, but was not necessary for, 

 an attack to be initiated. Feeding animals seemed to respond to very 

 slight movements when the prey was within 5 cm. 



Olfactory response to food was tested by dropping chopped earth- 

 worms and chicken hearts at varying distances downflow and out of the 

 field of sight of the test animal. In 10 tests, where food was 1 m from it, 

 the animal responded within 32 to 125 seconds (x=47 sec). Response was 

 marked when the animal raised its head approximately 45 degrees from 

 the surface. As it walked towards the food, the animal would stop and 

 repeatedly put its snout to the substrate until it reached the food. Other 

 foods dropped on the shelf about 10 cm beyond the waiting animal 

 stimulated a similar response. Juveniles and larvae did not respond to 

 nonliving food dropped away from the entrance to their retreat areas. 

 Their response seemed to be stimulated by sight. 



Active stalking of prey occurred at night. Prey included earth- 

 worms, Eurycea larvae, tadpoles, and the fishes Notropis, Etheostoma, 

 and Umbra. The mudpuppy would walk slowly in the direction of the 



