NORTH AMERICAN BIRDS. 339 



notorious parasite, and does not build a nest, but like the European Cuckoo, lays 

 its eggs in the nests of other birds, usually in those of species smaller than- itself. 

 Generally a single egg is deposited, but as many as five have been found in a nest 

 The exact number the female lays is not known. Eggs of this bird are subject to 

 great variation in their size and markings, and when found in the nests of such birds 

 as the Cardinal Redbird, Towhee Bunting, Meadow Lark and Brown Thrasher,* it 

 is sometimes difficult to readily distinguish which is which." Yet it should not be 

 understood that the Cowbird's eggs look exactly like those of the species just men- 

 tioned, for they really have, on the whole, only a faint resemblance to them, and 

 when a large series of either species is brought together and compared with those 

 of the Cowbird the difference is at once apparent. Dr. Jones suggests that when 

 the egg of the Cowbird resembles so closely the eggs in the nest where it has been laid, 

 as to make identification uncertain, it is a good plan to blow all the eggs and notice 

 if the suspected egg has a yelk of different tint from the balance of the set. If it has, 

 it is strong evidence that it was laid by an intruder, for almost invariably eggs of the 

 same set have the same tinted yelks. The ground-color of the Cowbird's egg is white 

 or gray, sometimes obscured by the abundance of markings. Spots, specks and 

 blotches are generally pretty evenly distributed over the entire surface. The mark- 

 ings vary from a chocolate-brown to those of a reddish and yellowish-brown. The 

 whole surface of am egg is often quite densely marked with specks the size of a pin 

 point, while the shell of other specimens is sparsely spotted. Ten specimens selected 

 at random from a very large series exhibit the following sizes: .80x.62, .82x.66, .84x 

 .62, .881.66, .89X.63, .87X.65, .82x.60, .83x.64, .89x.64, .80x.62. A common size is 

 .88x.64. 



495a. DWARF COWBIRD. Molothrus ater obscurus (Gmel.) Geog. Dist. 

 Mexico, and southern border of the United States from Texas to Arizona and Lower 

 California. 



This is a smaller form, inhabiting the southern border of the United States 

 from Texas to Arizona and southward. Its habits are identical with the Cowbird of 

 the East, and the eggs are colored the same, but like the bird, average smaller. 

 Five specimens measure: .77x.60, ,80x.59, .75x.59, .70x.57, .72x.58. The average size 

 of ten specimens from Arizona is .74x.59. 



496. RED-EYED COWBIRD. Callothrus robustus (Cab.) Geog. Dist. East- 

 ern and Southern Mexico, Yucatan, and south to Panama; north to the lower Rio 

 Grande Valley in Texas. 



A bronze-colored Blackbird with blood-red iris. Common on the Lower Rio 

 Grande in Texas. Dr. Merrill took specimens at Hidalgo, but they were not so 

 abundant at this point as lower down the river, where they are common throughout 

 the year, a smaller proportion going south in winter. Those that remain gather in 



* Besides those above named the following are some of the nests In which the Cow- 

 bird's eggs have been found: Blue-gray Gnatcatcher, Black and White Warbler, Blue- 

 yellow-backed Warbler (Parula), Worm-eating Warbler. Prothonotary Warbler, Mary- 

 land Yellow-throat. Yellow Warbler, House Wren, Warbling, Yellow-throated and Red- 

 eyed Vireos, Indigo Bunting, Chipping Sparrow, American Goldfinch, Song Sparrow, 

 Swamp Sparrow, Slate-colored Junco, Oven Bird, Pewee, Acadian and Traill's Flycatchers, 

 Black-throated Bunting, European House Sparrow (Passer domesicus), Yellow-breasted 

 Chat, Bluebird, Orchard, Baltimore, Bullock's and Hooded Orioles, Scarlet Tanager, King- 

 bird, Towhee, Prairie Horned Lark (Octocoris alpestris practicola), Wilson's Thrush, 

 Wood Trush, Red-headed Woodpecker, Robin and Mourning Dove. 



