THE HABITS OF FIDDLER-CEABS. 



115 



good-sized snake was just entering a burrow about 1 meter away. 

 The lack of fiddlers on this occasion was probably not due to 

 the inclement weather for these animals often fed serenely in 

 great numbers during the day in the midst of violent rainstorms. 

 Furthermore, as fiddlers are often active on moonlight nights, 

 the conclusion seems to be warranted that a certain amount of 

 light is necessary to bring them from their burrows. The 

 observations of Holmes ('08) support this view since he found 

 that Uca pugnax was strongly positively phototropic when tested 

 under laboratory conditions. 



At Manila the burrows of the genus Uca are found for the 

 most part between low- and high-tide marks on the mud flats. 

 Many of them are so high that they are covered only at the time 

 of very high tides, and their openings therefore may not be 

 inundated for a number of days at a time. It would seem, then, 

 that the location selected for a burrow is apparently not a matter 

 of chance. The different species show a preference for certain 

 levels, and this results in more or less clearly-marked zones on 

 the shore of an estero: (1) High along the edge of the shore 

 Uca forcipata is found, (2) this zone grades into the one of 

 U. rathbunse just below, while (3) U. marionis and U. marionis 

 nitida are found in the softer mud of the deeper parts of the 

 estero. The less abundant U. annulipes and U. gimardi were 

 usually found in the second and third zones respectively. This 

 stratification in habitats is very clearly shown (Table I) as the 

 crabs emerge from their holes when the tide is falling. 



Table I. — Giving the number of each species of fiddler-crab observed in a 

 certain area as the tide was receding. 



Date. 



Time. 



U. f orci- 

 pata. 



U. rath- 

 bunse. 



U. mario- 

 nis and 

 U. mario- 

 nis nitida 



U. annu- 

 lipes. 





p. m. 













2. BO 





















3.00 



2 















June 16 __ 



3.13 

 3.35 



8 

 22 





 8 





 





 







3.46 



27 



4 













4.05 



31 



10 













4.32 



82 



12 



2 



1 





2.00 





















3.15 



2 















June 18 



,8.35 

 ,3.51 



B 

 11 







1 





 





 







4.14 



16 



6 













6.12 



70 



14 



1 



1 



