Vol. XlX"j Snovgrass, F'ood and Size 0/ Bill t'n Geos_piza. 3 67 



THE RELATION OF THE FOOD TO THE SIZE AND 



SHAPE OF THE BILL IN THE GALAPAGOS 



GENUS GEOSPIZA. 



BY ROBERT E. SNODGRASS. 



The Fringillid genus Geospiza ^ of the Galapagos Archipelago 

 contains about thirty-four species and varieties. Four subgenera 

 may be distinguished on a color basis, but the specific and vari- 

 etal character are almost entirely in the shape and size of the bill. 

 The bill being the feeding organ, it is most natural to look first 

 for the cause of its variation in a variation of the character of the 

 food. 



Geospiza heliobates feeds entirely on insects. But it inhabits 

 exclusively the 'mangrove swamps' where there is nothing but 

 insect food available. The other species are all seed-eaters, 

 although they occasionally pick up a few ants and other small 

 insects. The seeds that they eat are mostly small and they are 

 usually swallowed whole, being found in this condition in the crop. 

 Large seeds when eaten are broken into pieces by the beak before 

 being swallowed, generally only fragments of such are to be found 

 in the stomach. The birds feed a great deal upon the ground, 

 picking up seeds that have fallen from the bushes, and at the same 

 time taking in with the food a considerable amount of gravel. 



With a view of determining whether there is any corresponding 

 variation between the bills and the food, Mr. Edmund Heller and 

 the writer, during 1898 and 1899, preserved the stomachs of two 

 hundred and nine specimens of Geospiza. These represent G. 

 pachyrhyncha, G. shrnua, G. conirostris, G. fortis p'ortis, G. fortis 

 platyrhyiicha, G.fuliginosa, G. scajide?is, G. sca7idens fatigata., G. 



' The name Geospiza is here used in the same sense as used by Rothschild 

 and Hartert (Novit. Zool., "VI, 1899), /. <?., to include all of the related Gala- 

 pagos genera of other authors, such as Platyspiza, Carnarhynchns, Geospiza 

 and Cactornis. Such a group is certainly a natural one ; and in it lines of 

 division are difficult to draw. Ridgway recognizes three genera : Platyspiza, 

 Camarhynchus and Geospiza. The names of species are according to the 

 synonymy in a paper yet to be published by Mr. Edmund Heller and the writer. 



