Ecology of the Nesting-Site 117 
served to fight or to drive away intruders as the Prairie Horned 
Lark did invariably. 
The breeding season and the song of both Larks and Bobolinks 
ended nearly at the same time but the similarity stopped there. 
The Lark, nearly resident, sang from late January to early July, 
bred from March to mid-July, whereas the Bobolinks, highly 
migratory, sang from mid-May to early July, bred from late 
May to mid-July. 
Located nests were in the densest, though not tallest, vegeta- 
tion. One was at the base of a clump of young evening prim- 
rose (Oenothera biennis), another in heavy plantain (Plantago 
major) blue grass (Poa pratensis) and wild strawberry (Frag- 
aria sp.). Thus the Bobolink is near one end of that series of 
ecological habitats of the open field determined by the density 
of vegetation—the Prairie Horned Lark at the other. 
Molothrus ater ater. Cowbird. Though the Cowbird arrived 
on April 16, in 1926, the first did not come onto the subdivision 
until April 30. Thereafter the bird was a frequent member of 
the fauna until June 27, when the last was noted. Females, 
apparently nest hunting, were flushed from the grass on May 
16 and May 26. In addition to the one case of parasitism of 
the Prairie Horned Lark (for which see back), there were also 
noted on the subdivisions one case of parasitism of a Vesper 
Sparrow (Sparrow was seen feeding young Cowbird) and an- 
other of a Song Sparrow (male was seen feeding the young 
Cowbird). 
Sturnella magna magna. Meadowlark. Next to the Bobo- 
links, the Meadowlarks claimed the eye and ear of the observer 
upon the subdivisions. In the fall of 1925 they were seen on 
October 4, 25 and 31. Those observed on October 4 had con- 
gregated in the marsh just south of the subdivision and were 
maintaining a remarkable jargon of experimental song—none 
full, but snatches of the real thing and all birds doing it at 
once. 
In 1926, the first returned March 19 and at the time of the 
great snows of late March many birds were on the barren sub- 
divisions. On April 1, I waded the more than a foot-deep snow 
to find that the Prairie Horned Larks were off their territories, 
off the subdivisions and along the roadside and the Meadowlarks 
