762 U.S. NATIONAL MUSEUM BULLETIN 23 7 part 2 



Among the mammals, the larger animals such as horses and cattle 

 occasionally trample a nest, but losses from this are negligible. The 

 smaller animals are the most deadly, and Stuart Griddle writes me 

 that "The mammals known to prey on our ground-dwelling birds can 

 be placed in the following order, the smallest first-named: Baird's 

 white-footed mouse {PeTomyscus manicuLatus bairdii), Drummond's 

 vole {Microtus pennsylvanicus drummondii) , thirteen-lined ground 

 squirrel {Citellus t. tridecemlineatus) , short- tailed ermine (Mustela 

 erminea bangsi), prairie long-tailed weasel (Mustela jrenata longi- 

 cauda), least weasel (Mustela r. rixosa), northern plains skunk (Me- 

 phitis mephitis hudsonica), plains coyote (Canis I. latrans)." 



Of the above list, the three rodents are frequent raiders of grass- 

 land nests, but are often content with just one or two of a brood. 

 However, when raiding nests in tufts of grass above ground level, both 

 voles and white-footed mice often drill holes in the bottom of the 

 nest that allow all the contents to tumble through to their doom. 

 The weasels and largers predators are never satisfied with less than 

 the entire contents of the nest. 



Concerning the effect of raptors on the ground birds, Stuart Grid- 

 dle's letter continues: "While most of our hawks in Manitoba take 

 a few prairie birds, the marsh hawk is the most persistent hunter 

 and captures more young sparrows and other small birds than all the 

 other hawks together. I have often watched a harrier chase a spar- 

 row, knock it down with a sharp blow of a wing, then turn like a 

 flash and pounce on the half-stunned bird before it could recover and 

 fly again." 



James A Munro (1929), reporting on the nest of a marsh hawk, 

 writes: "A beheaded juvenile Baird's sparrow in nestling plumage was 

 the only food at her nest." Glen A. Fox writes from Saskatchewan 

 that: "I checked an active nest of Richardson's merlin, July 9, 

 1961. Thirteen tarsi were removed from the nest, and Donald R. 

 Baldwin of the Royal Ontario Museum of Zoology identified one as 

 that of an immature Baird's sparrow." 



A. hairdii is fortunate in one respect: nesting as it does in wide, 

 open grasslands, it shares with several neighboring species almost 

 complete immunity from the visits of that parasite, the brown- 

 headed cowbird. This bird prefers to lay in nests located in brush 

 or tree growth, and I have never found the nest of a prairie horned 

 lark, a Sprague's pipit, or a chestnut-collared longspur victimized by 

 it. The western meadowlark is usually exempt also, and not until 

 1962 did I find a nest of this species that had been visited by Molo- 

 thrus ater, two of the six eggs being strangers. This nest was within a 

 few feet of fairly heavy bush growth, which probably afforded the 



