NO. 7 



PROTECTIVE ADAPTATIONS — McATEE 



Classifying the 237,399 identifications of the animal food of 

 nearctic birds and calculating the percentage of the determinations, by 

 phyla, we reach the results shown in the next table, the percentage 

 of species in each phylum among the whole number of known species 

 being repeated for ease in comparison. 



Idcntificalions of Animal Food hv Phyla 



Percentage 

 of species 

 in this 

 phylum 

 * among tlie 



Percentage of whole 



identifications mnnber of 



among those animal 



Number of of all species 



Phylinn identifications animals known 



Protozoa 12 .0050 1.4272 



Porifera 2 .0008 .4460 



Coelenterata 122 -0514 .8028 



Nemathelminthes 24 .0101 .2676 



Molluscoida 134 .0564 .3032 



Echinodermata 125 .0526 7136 



Annulata 1,131 .4764 .7136 



Arthropoda 210,752 88.7751 74.6188 



MoUusca 11,771 4.9583 10.8828 



Cliordata 13,326 5.6133 8.8427 



Without going into details, it is apparent that the percentage of 

 identifications preserves very well a relative ratio to that of the num- 

 ber of species and presumably, therefore, to the abundance of indi- 

 viduals in the phyla. What variations there are seem obviously due 

 to differences in the availability to birds of the differing types of 

 animals. 



Taking up the phyla in order, we begin with the 



PROTOZOA (oNE-CELLED ANIIMAL.s) 



Protective adaptations. — Judging from what is asserted about other 

 phyla, phosphorescence and the possession of bright colors in some 

 groups and of silicious or calcareous, often tuberculate or spinose, 

 tests or shells or of exoskeletons formed of foreign bodies in others, 

 are characters that would be deemed of protective significance in 

 Protozoa. 



Bird enemies. — Protozoa are too small to engage the attention ot 

 birds, those found in stomachs being Foraminifera strained from 

 water or mud, or picked up as gravel by ducks. It is probable also 

 that protozoa are consumed, along with the stems and leaves of 

 aquatic plants upon which they often are abundant, by wild ducks 



