BROWN'S SONG SPARROW 1563 



MELOSPIZA MELODIA RIVULARIS Bryant 



Brown's Song Sparrow 

 Contributed by Val Nolan Jr. 



Habits 



This race inhabits "west-flowing stream courses" (Grinnell, 1928) 

 in a very limited region of central Baja California. Here, as Griffing 

 Bancroft (1930) writes, "there are several systems of dry river beds 

 which have an important influence on the biology of this region. 

 Even though the country be arid beyond anything known in the 

 United States there is still enough rainfall to provide some moisture. 

 This water, as well as a part of that from the cloud-bursts that come 

 once in a decade, finds its way to the sea by means of a subterranean 

 flow. * * * Occasionally the subterranean flow encounters bed rock 

 formations which force the water to the surface." 



G. Bancroft (1930) gives the following description of the breeding 

 biology of rivularis in this restricted range: 



This light-breasted type of Melospiza occurs wherever there are pools of water 

 with tule or willow. * * * It is by no means as abundant * * * as is, for instance, 

 M. m. coo-peri in the willow bottoms of southern California. Still it can hardly be 

 regarded as rare. 



The birds begin to lay the latter part of April and continue for at least six 

 weeks. Most of the nests are bulky affairs of tule, usually lined with palm fibre 

 or cow hair. They are normally placed in tule about four feet above the water. 

 * * * [Some were] surrounded by loose and fairly long dead tule leaves. These 

 more than equaled the bulk of the nest * * * . Some of the nests found were 

 in willow trees and one was in a thick weed clinging to a rock and overhanging 

 a pool. In general, excepting the unusual size of their nests, the habits of the 

 Brown Song Sparrow were much like those of the San Diegan form [coo-peri]. 

 They lay either two or three eggs, with four the record. 



The eggs themselves are unlike those of any other Song Sparrow I have exam- 

 ined. They are more brilliant than those of the northern birds, a brighter blue, 

 and altogether lacking in the common tan type, in which the spots are so close 

 together as to give the appearance of a reddish egg. 



G. Bancroft's measurements of 35 eggs from San Ignacio yielded an 

 average size of 21.2 x 15.9 mm., and of 250 eggs from El Rosario an 

 average size of 20.1 x 15.2 mm. 



Ridgway (1901) describes rivularis as being similar to fallax "but 

 larger, with longer, more slender, and more compressed bill, still less 

 strongly contrasted markings, and duller, less rufescent colors." 



Distribution 



Range. — The Brown's song sparrow is resident in south-central Baja 

 California (Santa Agueda Canyon and San Ignacio south to Comondu). 



